Next Issue
Volume 10, November
Previous Issue
Volume 10, September

Table of Contents

Crystals, Volume 10, Issue 10 (October 2020) – 104 articles

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
Cover Story (view full-size image) Nanolipoprotein particles (NLPs), also called “nanodiscs”, are discoidal lipid bilayer patches [...] Read more.
Order results
Result details
Select all
Export citation of selected articles as:
Open AccessArticle
Synthesis of Enaminones-Based Benzo[d]imidazole Scaffold: Characterization and Molecular Insight Structure
Crystals 2020, 10(10), 955; https://doi.org/10.3390/cryst10100955 - 21 Oct 2020
Viewed by 174
Abstract
(E)-1-(1H-Benzo[d]imidazol-2-yl)-3-(dimethylamino)prop-2-en-1-one 2 was synthesized by one-pot synthesis protocol of 2-acetyl benzo[d]imidazole with dimethylformamide dimethylacetal (DMF-DMA) in xylene at 140 °C for 8 h. Reaction of enaminone derivative 1 with acetylacetone in the presence of AcOH/NH [...] Read more.
(E)-1-(1H-Benzo[d]imidazol-2-yl)-3-(dimethylamino)prop-2-en-1-one 2 was synthesized by one-pot synthesis protocol of 2-acetyl benzo[d]imidazole with dimethylformamide dimethylacetal (DMF-DMA) in xylene at 140 °C for 8 h. Reaction of enaminone derivative 1 with acetylacetone in the presence of AcOH/NH4OAc under reflux afforded the cyclized pyridino-benzo[d]imidazole derivative 3. The latter compound was converted into the corresponding β-enaminone 4 with DMF-DMA. The single crystal X-ray diffraction technique eventually confirmed the assigned chemical structure of the N-alkyl-β-enaminone 2 and pyridino-benzo[d]imidazole derivative 3. N-alkyl-β-enaminone 2 crystallized in the monoclinic space group P21/n with unit cell parameters of a = 9.8953(3) Å, b = 5.7545(2) Å, c = 21.7891(7) Å, and β =100.627(2)°, and with one molecule per asymmetric unit. On the other hand, compound 3 crystallized in the orthorhombic crystal system and space group P212121 with unit cell parameters of a = 6.82950(10) Å, b = 8.00540(10) Å, c = 22.4779(2) Å, and also with one molecule per asymmetric unit. Based on Hirshfeld analysis, the H...H (51.3%), O...H (10.0%), N...H (10.3%), and C...H (27.6%) contacts in 2 and the H...H (46.8%), O...H (9.9%), N...H (13.0%), and C...H (21.6%) in addition to the C…C (6.7%) interactions in 3 are the most important towards crystal stability via molecular packing. The main difference is the presence of π–π interaction among the molecular units of 3 but not in 2. The calculated 1H and 13C NMR chemical shifts showed good agreements with experimental data. Electronic properties and reactivity parameters of both compounds are also calculated and compared. Full article
(This article belongs to the Section Organic Crystalline Materials)
Show Figures

Graphical abstract

Open AccessArticle
Exploring the Wet Mechanochemical Synthesis of Mg-Al, Ca-Al, Zn-Al and Cu-Al Layered Double Hydroxides from Oxides, Hydroxides and Basic Carbonates
Crystals 2020, 10(10), 954; https://doi.org/10.3390/cryst10100954 - 20 Oct 2020
Viewed by 230
Abstract
The synthesis of Mg-Al, Ca-Al, Zn-Al and Cu-Al layered double hydroxides (LDHs) was investigated with a one-step wet mechanochemical route. The research aims to expand on the mechanochemical synthesis of LDH using a mill designed for wet grinding application. A 10% slurry of [...] Read more.
The synthesis of Mg-Al, Ca-Al, Zn-Al and Cu-Al layered double hydroxides (LDHs) was investigated with a one-step wet mechanochemical route. The research aims to expand on the mechanochemical synthesis of LDH using a mill designed for wet grinding application. A 10% slurry of solids was added to a Netzsch LME 1 horizontal bead mill and milled for 1 h at 2000 rpm. Milling conditions were selected according to machine limitations and as an initial exploratory starting point. Precursor materials selected consisted of a mixture of oxides, hydroxides and basic carbonates. Samples obtained were divided such that half was filtered and dried at 60 °C for 12 h. The remaining half of the samples were further subjected to ageing at 80 °C for 24 h as a possible second step to the synthesis procedure. Synthesis conditions, such as selected precursor materials and the MII:MIII ratio, were adapted from existing mechanochemical methods. LDH synthesis prior to ageing was successful with precursor materials observably present within each sample. No Cu-Al LDH was clearly identifiable. Ageing of samples resulted in an increase in the conversion of raw materials to LDH product. The research offers a promising ‘green’ method for LDH synthesis without the production of environmentally harmful salt effluent. The synthesis technique warrants further exploration with potential for future commercial up-scaling. Full article
(This article belongs to the Special Issue Layered Double Hydroxides (LDHs))
Show Figures

Graphical abstract

Open AccessArticle
Calcium Phosphate Nanoparticle Precipitation by a Continuous Flow Process: A Design of an Experiment Approach
Crystals 2020, 10(10), 953; https://doi.org/10.3390/cryst10100953 - 19 Oct 2020
Viewed by 247
Abstract
Calcium phosphate nanoparticles (CaP NPs) are an efficient class of nanomaterials mainly used for biomedical applications but also very promising in other sectors such as cosmetics, catalysis, water remediation, and agriculture. Unfortunately, as in the case of other nanomaterials, their wide application is [...] Read more.
Calcium phosphate nanoparticles (CaP NPs) are an efficient class of nanomaterials mainly used for biomedical applications but also very promising in other sectors such as cosmetics, catalysis, water remediation, and agriculture. Unfortunately, as in the case of other nanomaterials, their wide application is hindered by the difficulty to control size, morphology, purity and degree of particle aggregation in the translation from laboratory to industrial scale production that is usually carried out in batch or semi-batch systems. In this regard, the use of continuous flow synthesis can help to solve this problem, providing more homogenous reaction conditions and highly reproducible synthesis. In this paper, we have studied with a design of experiment approach the precipitation of citrate functionalized CaP NPs aided by sonication using a continuous flow wet chemical precipitation, and the effect of some of the most relevant process factors (i.e., reactant flow rate, sonication amplitude, and maturation time) on the physico-chemical properties of the NPs were evaluated. From the statistical data analysis, we have found that CaP NP dimensions are influenced by the reactor flow rate, while the crystalline domain dimensions and product purity are influenced by the maturation process. This work provides a deeper understanding of the relationships between reaction process factors and CaP NP properties, and is a relevant contribution for the scale-up production of CaP NPs for nanomedical or other applications. Full article
Show Figures

Graphical abstract

Open AccessCommunication
Enhancement of Luminescence Dissymmetry Factor in Nano-Segregated Phase Generated by Phase Separation between Helical Nanofilaments and Liquid-Crystalline Smectic A Phase
Crystals 2020, 10(10), 952; https://doi.org/10.3390/cryst10100952 - 19 Oct 2020
Viewed by 221
Abstract
Although several methods exist for the synthesis of circularly polarized luminescent (CPL) materials, the methods are extremely complex and tedious. In recent years, the chiral host-achiral luminescent guest method and the achiral host-achiral luminescent guest method have been employed to fabricate CPL materials; [...] Read more.
Although several methods exist for the synthesis of circularly polarized luminescent (CPL) materials, the methods are extremely complex and tedious. In recent years, the chiral host-achiral luminescent guest method and the achiral host-achiral luminescent guest method have been employed to fabricate CPL materials; however, the main disadvantage of the latter is the small luminescence dissymmetry factor (glum) that limits the practical applications of the method. Therefore, this study reports on the enhancement of glum in a nano-segregated phase system, generated by the phase separation between helical nanofilaments (HNFs; originating from an achiral bent-core molecule) and a liquid-crystalline (LC) smectic A (SmA) phase (originating from an achiral rod-like mesogen). The observed glum value in the nano-segregated phase between the HNFs and LC SmA phase was larger than that in the nano-segregated phase between the HNFs and LC nematic (N) phase. The enhancement of the glum value was attributed to the order parameter (S) of the dye molecules in the SmA phase being larger than that in the N phase. Therefore, we concluded that the S value of the fluorescent dye molecules, doped into the embedded LC phase between the HNFs, strongly influenced the glum value. Full article
(This article belongs to the Special Issue Organic Optoelectronic Materials)
Show Figures

Graphical abstract

Open AccessArticle
Synthesis of Pure Phase NaP2 Zeolite from the Gel of NaY by Conventional and Microwave-Assisted Hydrothermal Methods
Crystals 2020, 10(10), 951; https://doi.org/10.3390/cryst10100951 - 19 Oct 2020
Viewed by 454
Abstract
The gel of zeolite NaY has potential as a precursor of other zeolites. The particular interest in this work is to convert the gel of NaY to NaP2. We found that the pure phase NaP2 can be produced simply by the conventional hydrothermal [...] Read more.
The gel of zeolite NaY has potential as a precursor of other zeolites. The particular interest in this work is to convert the gel of NaY to NaP2. We found that the pure phase NaP2 can be produced simply by the conventional hydrothermal (CH) method at 150 °C for 24 h. This NaP2 sample, named CH150, has an average particle size of 10.3 µm and an Si/Al ratio of 1.82. In the case of single crystallization via microwave-assisted hydrothermal (MH) method, various parameters were studied, including the crystallization temperature (90, 150, 175 °C) and time (15, 30, 45, 60 min). The samples were analyzed by X-ray diffraction and scanning electron microscopy. However, mixed phases of P1 and P2 or ANA were obtained from all samples. Another attempt was made by a double crystallization via MH method as followed: at 90 °C for 1 h, quickly cooled down to room temperature in the microwave chamber and aged for 23 h, and finally at 150 °C for 1 h. The sample, named MH90A150, has an average crystal size of 16.45 µm and an Si/Al ratio of 1.85. The high Al content of NaP2 in both samples (CH150 and MH90A150) could lead to interesting applications. Full article
(This article belongs to the Special Issue Zeolites)
Show Figures

Figure 1

Open AccessArticle
Magnetic Diagram of the High-Pressure Stabilized Multiferroic Perovskites of the BiFe1-yScyO3 Series
Crystals 2020, 10(10), 950; https://doi.org/10.3390/cryst10100950 - 17 Oct 2020
Viewed by 383
Abstract
Magnetic properties of the high-pressure stabilized perovskite BiFe1-yScyO3 phases (0.1 ≤ y ≤ 0.9) have been studied by means of magnetization measurements and neutron diffraction. The metastable perovskites of this series undergo irreversible polymorphic transformations upon annealing, [...] Read more.
Magnetic properties of the high-pressure stabilized perovskite BiFe1-yScyO3 phases (0.1 ≤ y ≤ 0.9) have been studied by means of magnetization measurements and neutron diffraction. The metastable perovskites of this series undergo irreversible polymorphic transformations upon annealing, the phenomenon referred to as conversion polymorphism. It has been found that the solid solutions with y ≥ 0.70 exhibit no long-range magnetic ordering regardless of their polymorph modification, while those with y ≤ 0.60 are all antiferromagnets. Depending on the scandium content, temperature and structural distortions, three types of the antiferromagnetic orderings, involving collinear, canted and cycloidal spin arrangements, have been revealed in the phases obtained via conversion polymorphism and the corresponding magnetic phase diagram has been suggested. Full article
(This article belongs to the Special Issue Magnetіc Structure Compounds)
Show Figures

Figure 1

Open AccessArticle
Formation Process of Columnar Grown (101)-Oriented Silicalite-1 Membrane and Its Separation Property for Xylene Isomer
Crystals 2020, 10(10), 949; https://doi.org/10.3390/cryst10100949 - 17 Oct 2020
Viewed by 270
Abstract
Silicalite-1 membrane was prepared on an outer surface of a tubular α-alumina support by a secondary growth method. Changes of defect amount and crystallinity during secondary growth were carefully observed. The defect-less well-crystallized silicalite-1 membrane was obtained after 7-days crystallization at 373 K. [...] Read more.
Silicalite-1 membrane was prepared on an outer surface of a tubular α-alumina support by a secondary growth method. Changes of defect amount and crystallinity during secondary growth were carefully observed. The defect-less well-crystallized silicalite-1 membrane was obtained after 7-days crystallization at 373 K. The silicalite-1 membrane became (h0l)-orientation with increasing membrane thickness, possibly because the orientation was attributable to “evolutionally selection”. The (h0l)-oriented silicalite-1 membrane showed high p-xylene separation performance for a xylene isomer mixture (o-/m-/p-xylene = 0.4/0.4/0.4 kPa). The p-xylene permeance through the membrane was 6.52 × 10−8 mol m−2 s−1 Pa−1 with separation factors αp/o, αp/m of more than 100 at 373 K. As a result of microscopic analysis, it was suggested that a very thin part in the vicinity of surface played as effective separation layer and could contribute to high permeation performance. Full article
(This article belongs to the Special Issue Zeolites)
Show Figures

Graphical abstract

Open AccessReview
Design Efficiency, Characteristics, and Utilization of Reinforced Foamed Concrete: A Review
Crystals 2020, 10(10), 948; https://doi.org/10.3390/cryst10100948 - 17 Oct 2020
Viewed by 227
Abstract
Foam concrete (FC) serves as an efficient construction material that combines well thermal insulation and structural properties. The studies of material characteristics, including the mechanical, physical, rheological, and functional properties of lightweight concrete, have been conducted rigorously. However, a lack of knowledge on [...] Read more.
Foam concrete (FC) serves as an efficient construction material that combines well thermal insulation and structural properties. The studies of material characteristics, including the mechanical, physical, rheological, and functional properties of lightweight concrete, have been conducted rigorously. However, a lack of knowledge on the design efficiency of reinforced FC (RFC) was found in current research trends, compared to reinforced lightweight aggregate concrete. Therefore, this paper presents a review of the performance and adaption in structures for RFC. According to the code specifications, the feasibility investigation was preliminarily determined in structural use through the summary for the mechanical properties of FC of FC’s mechanical properties. For reinforced concrete design, a direct method of reduction factors is introduced to design lightweight aggregate concrete, which is also suggested to be adapted into a lightweight FC design. It was found that flexural shear behavior is a more complex theoretical analysis than flexure. However, a reduction factor of 0.75 was recommended for shear, torsion, and compression; meanwhile, 0.6 for flexural members. Serviceability limit states design should be applied, as the crack was found predominant in RFC design. The deflection controls were recommended as 0.7 by previous research. Research on RFC’s compression members, such as a column or load load-bearing wall, were rarely found. Thus, further study for validating a safe design of RFC applications in construction industries today is highly imperative. Full article
(This article belongs to the Special Issue Hierarchical Composite Materials)
Show Figures

Figure 1

Open AccessArticle
Novel Sample-Stage for Combined Near Ambient Pressure X-ray Photoelectron Spectroscopy, Catalytic Characterization and Electrochemical Impedance Spectroscopy
Crystals 2020, 10(10), 947; https://doi.org/10.3390/cryst10100947 - 17 Oct 2020
Viewed by 247
Abstract
For an in-depth characterization of catalytic materials and their properties, spectroscopic in-situ (operando) investigations are indispensable. With the rapid development of advanced commercial spectroscopic equipment, it is possible to combine complementary methods in a single system. This allows for simultaneously gaining insights into [...] Read more.
For an in-depth characterization of catalytic materials and their properties, spectroscopic in-situ (operando) investigations are indispensable. With the rapid development of advanced commercial spectroscopic equipment, it is possible to combine complementary methods in a single system. This allows for simultaneously gaining insights into surface and bulk properties of functional oxides, such as defect chemistry, catalytic characteristics, electronic structure, etc., enabling a direct correlation of structure and reactivity of catalyst materials, thus facilitating effective catalyst development. Here, we present a novel sample-stage, which was specifically developed to pave the way to a lab–based combination of near ambient pressure X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy with simultaneous catalytic operando measurements. This setup is designed to probe different (model) systems under conditions close to real heterogeneous catalysis, with a focus on solid oxide electrochemical cells. In a proof of concept experiment using an electrochemical model cell with the doped perovskite Nd0.6Ca0.4Fe0.9Co0.1O3-δ as working electrode, the precise control of the surface chemistry that is possible with this setup is demonstrated. The exsolution behavior of the material was studied, showing that at a lower temperature (500 °C) with lower reducing potential of the gas phase, only cobalt was exsolved, forming metallic particles on the surface of the perovskite-type oxide. Only when the temperature was increased to 600 °C and a cathodic potential was applied (−250 mV) Fe also started to be released from the perovskite lattice. Full article
Show Figures

Graphical abstract

Open AccessArticle
Alkali-Activated Hybrid Concrete Based on Fly Ash and Its Application in the Production of High-Class Structural Blocks
Crystals 2020, 10(10), 946; https://doi.org/10.3390/cryst10100946 - 17 Oct 2020
Viewed by 247
Abstract
This article reports the production and characterization of a hybrid concrete based on the alkaline activation of a fly ash (FA) of Colombian origin, which was added with 10% Portland cement (OPC) in order to promote the compressive strength development at room temperature. [...] Read more.
This article reports the production and characterization of a hybrid concrete based on the alkaline activation of a fly ash (FA) of Colombian origin, which was added with 10% Portland cement (OPC) in order to promote the compressive strength development at room temperature. The alkali-activated hybrid cement FA/OPC 90/10 was classified as a low heat reaction cement (type LH), according to American Society of Testing Materials, ASTM C1157; the compressive strength was of 31.56 MPa and of 22.68 MPa (28 days) at the levels of paste and standard mortar, respectively, with an initial setting time of 93.3 min. From this binder, a hybrid concrete was produced and classified as a structural type, with a compressive strength of 23.16 MPa and a flexural modulus of rupture of 5.32 MPa, at 28 days of curing. The global warming potential index (GWP 100), based on life cycle analysis, was 35% lower than the reference concrete based on 100% OPC. Finally, its use was validated in the manufacture of a solid block-type construction element, which reached a compressive strength of 21.9 MPa at 28 days, exceeding by 40.6% the minimum strength value established by the Colombia Technical Standard, NTC 4026 (13 MPa) to be classified as high class structural blocks. Full article
(This article belongs to the Special Issue Recycling Silicate-Bearing Waste Materials)
Show Figures

Graphical abstract

Open AccessEditorial
Microstructural and Mechanical Characterization of Alloys
Crystals 2020, 10(10), 945; https://doi.org/10.3390/cryst10100945 - 17 Oct 2020
Viewed by 300
Abstract
This Special Issue on “Microstructural and Mechanical Characterization of Alloys” features eight papers that cover the recent developments in alloys (engineering materials), methods of improvement of strength and cyclic properties of alloys, the stability of microstructure, the possible application of new (or improved) [...] Read more.
This Special Issue on “Microstructural and Mechanical Characterization of Alloys” features eight papers that cover the recent developments in alloys (engineering materials), methods of improvement of strength and cyclic properties of alloys, the stability of microstructure, the possible application of new (or improved) alloys, and the use of treatment for alloy improvement. Full article
(This article belongs to the Special Issue Microstructural and Mechanical Characterization of Alloys)
Open AccessArticle
Effect of 3D Representative Volume Element (RVE) Thickness on Stress and Strain Partitioning in Crystal Plasticity Simulations of Multi-Phase Materials
Crystals 2020, 10(10), 944; https://doi.org/10.3390/cryst10100944 - 17 Oct 2020
Viewed by 373
Abstract
Crystal plasticity simulations help to understand the local deformation behavior of multi-phase materials based on the microstructural attributes. The results of such simulations are mainly dependent on the Representative Volume Element (RVE) size and composition. The effect of RVE thickness on the changing [...] Read more.
Crystal plasticity simulations help to understand the local deformation behavior of multi-phase materials based on the microstructural attributes. The results of such simulations are mainly dependent on the Representative Volume Element (RVE) size and composition. The effect of RVE thickness on the changing global and local stress and strain is analyzed in this work for a test case of dual-phase steels in order to identify the minimal RVE thickness for obtaining consistent results. 100×100×100 voxel representative volume elements are constructed by varying grain size and random orientation distribution in DREAM-3D. The constructed RVEs are sliced in depth up to 1, 5, 10, 15, 20, 25, 30, 40, and 50 layers to construct different geometries with increasing thickness. Crystal plasticity model parameters for ferrite and martensite are taken from already published data and assigned to respective phases. Although the global stress/strain behavior of different RVEs is similar (<5% divergence), the local stress/strain partitioning in RVEs with varying thickness and grain size shows a considerable variation when statistically compared. It is concluded that two-dimensional (2D) RVEs can be used for crystal plasticity simulations when global deformation behavior is of interest. Whereas, it is necessary to consider three-dimensional (3D) RVEs, which have a specific thickness and number of grains for determining stabilized and more accurate local deformation behavior. This estimation will help researchers in optimizing the computation time for accurate mesoscale simulations. Full article
(This article belongs to the Special Issue Crystal Plasticity)
Show Figures

Graphical abstract

Open AccessArticle
Crystallographic Orientation Dependence of Mechanical Responses of FeCrAl Micropillars
Crystals 2020, 10(10), 943; https://doi.org/10.3390/cryst10100943 - 16 Oct 2020
Viewed by 183
Abstract
Iron-chromium-aluminum (FeCrAl) alloys are used in automobile exhaust gas purifying systems and nuclear reactors due to its superior high-temperature oxidation and excellent corrosion resistance. Single-phase FeCrAl alloys with a body centered cubic structure plastically deform through dislocation slips at room temperature. Here, we [...] Read more.
Iron-chromium-aluminum (FeCrAl) alloys are used in automobile exhaust gas purifying systems and nuclear reactors due to its superior high-temperature oxidation and excellent corrosion resistance. Single-phase FeCrAl alloys with a body centered cubic structure plastically deform through dislocation slips at room temperature. Here, we investigated the orientation dependence of mechanical responses of FeCrAl alloy through testing single-crystal and bi-crystal micropillars in a scanning electron microscopy at room temperature. Single-crystal micropillars were fabricated with specific orientations which favor the activity of single slip system or two slip systems or multiple slip systems. The strain hardening rate and flow strength increase with increasing the number of activated slip system in micropillars. Bi-crystal micropillars with respect to the continuity of slip systems across grain boundary were fabricated to study the effect of grain boundary on slip transmission. The high geometrical compatibility factor corresponds to a high flow strength and strain hardening rate. Experimental results provide insight into understanding mechanical response of FeCrAl alloy and developing the mechanisms-based constitutive laws for FeCrAl polycrystalline aggregates. Full article
(This article belongs to the Special Issue Crystal Plasticity at Micro- and Nano-scale Dimensions)
Show Figures

Graphical abstract

Open AccessArticle
One-Dimensional Alternating Extended Hubbard Model at Quarter-Filling and Its Applications to Structural Instabilities of Organic Conductors
Crystals 2020, 10(10), 942; https://doi.org/10.3390/cryst10100942 - 16 Oct 2020
Viewed by 245
Abstract
The one-dimensional extended Hubbard model with lattice dimerization and alternated site potentials is analyzed using the renormalization group method. The coupling of electrons to structural degrees of freedom such as the anion lattice and acoustic phonons is investigated to obtain the possible instabilities [...] Read more.
The one-dimensional extended Hubbard model with lattice dimerization and alternated site potentials is analyzed using the renormalization group method. The coupling of electrons to structural degrees of freedom such as the anion lattice and acoustic phonons is investigated to obtain the possible instabilities against the formation of lattice superstructures. Applications of the theory to anionic and spin-Peierls instabilities in the Fabre and Bechgaard salts series of organic conductors and ordered alloys are presented and discussed. Full article
(This article belongs to the Special Issue Organic Conductors)
Show Figures

Figure 1

Open AccessArticle
The Detection of Monoclinic Zirconia and Non-Uniform 3D Crystallographic Strain in a Re-Oxidized Ni-YSZ Solid Oxide Fuel Cell Anode
Crystals 2020, 10(10), 941; https://doi.org/10.3390/cryst10100941 - 16 Oct 2020
Viewed by 312
Abstract
The solid oxide fuel cell (SOFC) anode is often composed of nickel (Ni) and yttria-stabilized zirconia (YSZ). The yttria is added in small quantities (e.g., 8 mol %) to maintain the crystallographic structure throughout the operating temperatures (e.g., room-temperature to >800 °C). The [...] Read more.
The solid oxide fuel cell (SOFC) anode is often composed of nickel (Ni) and yttria-stabilized zirconia (YSZ). The yttria is added in small quantities (e.g., 8 mol %) to maintain the crystallographic structure throughout the operating temperatures (e.g., room-temperature to >800 °C). The YSZ skeleton provides a constraining structural support that inhibits degradation mechanisms such as Ni agglomeration and thermal expansion miss-match between the anode and electrolyte layers. Within this structure, the Ni is deposited in the oxide form and then reduced during start-up; however, exposure to oxygen (e.g., during gasket failure) readily re-oxidizes the Ni back to NiO, impeding electrochemical performance and introducing complex structural stresses. In this work, we correlate lab-based X-ray computed tomography using zone plate focusing optics, with X-ray synchrotron diffraction computed tomography to explore the crystal structure of a partially re-oxidized Ni/NiO-YSZ electrode. These state-of-the-art techniques expose several novel findings: non-isotropic YSZ lattice distributions; the presence of monoclinic zirconia around the oxidation boundary; and metallic strain complications in the presence of variable yttria content. This work provides evidence that the reduction–oxidation processes may destabilize the YSZ structure, producing monoclinic zirconia and microscopic YSZ strain, which has implications upon the electrode’s mechanical integrity and thus lifetime of the SOFC. Full article
Show Figures

Graphical abstract

Open AccessArticle
Bismuth Polycations Revisited: Alternative Synthesis and Electronic Structure of Bi6Br7, and Bonding in Main-Group Polyatomic Ions from a Direct Space Perspective
Crystals 2020, 10(10), 940; https://doi.org/10.3390/cryst10100940 - 16 Oct 2020
Viewed by 295
Abstract
A bismuth subbromide, Bi6Br7, was synthesized in the form of single crystals using the reaction between Bi and Hg2Br2 in a gradient furnace. Its crystal structure was reinvestigated by low-temperature single-crystal X-ray diffraction (Pnnm, [...] Read more.
A bismuth subbromide, Bi6Br7, was synthesized in the form of single crystals using the reaction between Bi and Hg2Br2 in a gradient furnace. Its crystal structure was reinvestigated by low-temperature single-crystal X-ray diffraction (Pnnm, a = 15.4996(6) Å, b = 23.6435(7) Å, c = 9.0231(2) Å, Z = 8, R1 = 0.041, wRall = 0.087). Based on the diffraction data, the structure description was revised as containing Bi95+ cluster polycations and 1[Bi3Br145−] ladder-like anions. DFT calculations of band structure showed the compound to be a narrow-gap semiconductor with a band gap of ca. 1.3 eV, with the nature of the compound as ionic salt confirmed by charge density analysis. Direct-space bonding analysis based on the ELF topology and QTAIM partitioning, performed for all known homoatomic bismuth polycations, as well as isoelectronic main-group metal ions, shows patterns of localized pairwise and three-center bonding forming the frameworks of the clusters. In addition to obtaining new data, the use of highly augmented basis sets allowed us to revise and amend several previously made conclusions regarding bonding in such species. Full article
(This article belongs to the Special Issue Intermetallic)
Show Figures

Graphical abstract

Open AccessArticle
Characterization of Pure Face-Shear Strain in Piezoelectric α-Tellurium Dioxide (α-TeO2)
Crystals 2020, 10(10), 939; https://doi.org/10.3390/cryst10100939 - 15 Oct 2020
Viewed by 221
Abstract
Paratellurite, also known as α-tellurium dioxide, is a ceramic that is primarily employed for its interesting optical properties. However, this material’s crystal structure belongs to the 422 symmetry class that allows a unique piezoelectric behavior to manifest itself: deformation in pure face-shear. This [...] Read more.
Paratellurite, also known as α-tellurium dioxide, is a ceramic that is primarily employed for its interesting optical properties. However, this material’s crystal structure belongs to the 422 symmetry class that allows a unique piezoelectric behavior to manifest itself: deformation in pure face-shear. This means that crystal symmetry necessitates the piezoelectric tensor to have only a single non-zero coefficient, d123 = d14: such unique behavior has the potential to enable novel gyroscopic sensors and high-precision torsional microelectromechanical systems (MEMS) actuators, as pure face-shear can be used to induce pure torsion. Although α-TeO2 is one of the few known materials belonging to this symmetry class, considerable uncertainty in its single piezoelectric coefficient exists, with the few reported literature values ranging from 6.13 to 14.58 pC/N; this large uncertainty results from the difficulty in using conventional piezoelectric characterization techniques on paratellurite, limiting measurements to indirect methods. The novel applications that would be enabled by the adoption of this extraordinary material are frustrated by this lack of confidence in the literature. We therefore leverage, for the first time, a first-principles analytical physical model with electrochemical impedance spectroscopy (EIS) to determine, directly, the lone piezoelectric coefficient d123 = d14 = 7.92 pC/N. Full article
(This article belongs to the Special Issue Piezoelectric Materials and Technology)
Show Figures

Figure 1

Open AccessArticle
Designing Metasurfaces with Canonical Unit Cells
Crystals 2020, 10(10), 938; https://doi.org/10.3390/cryst10100938 - 15 Oct 2020
Viewed by 239
Abstract
Among different approaches to designing metasurfaces, surface sheet impedance is proving to be a straightforward path for many applications. Recent publications have proposed several methods for optimizing this design approach, enabling rapid metasurface development. Upon finding the requirements using the sheet impedance approach, [...] Read more.
Among different approaches to designing metasurfaces, surface sheet impedance is proving to be a straightforward path for many applications. Recent publications have proposed several methods for optimizing this design approach, enabling rapid metasurface development. Upon finding the requirements using the sheet impedance approach, design continues with the selection of unit cell geometry. This choice is usually based on approximate expressions that have been published throughout the years. We review the approximate expressions for metasurface unit cell design, with consideration of their applicability to certain applications, namely polarization-dependent beam-shaping metasurfaces. We evaluate the accuracy of the approximate expressions against simulation results from a full-wave electromagnetic solver, and propose an optimization approach to correct the proposed design for the observed error. The applicability of different unit cell types is discussed, especially considering the limitations of technological processes typically used in metasurface production. A prototype was developed to verify the validity of this design approach. Full article
(This article belongs to the Special Issue Polarization-Handling Metasurfaces)
Show Figures

Figure 1

Open AccessArticle
Investigation of Thermally Induced Deterioration Processes in Cold Worked SAF 2507 Type Duplex Stainless Steel by DTA
Crystals 2020, 10(10), 937; https://doi.org/10.3390/cryst10100937 - 14 Oct 2020
Viewed by 295
Abstract
Thermally induced deterioration processes were studied in cold worked (up to 60% deformation) SAF 2507 type super-duplex stainless steel (SDSS) by differential thermal analysis (DTA). DTA results revealed two transformations. Parent and inherited phases of these transformations were examined by other methods too, [...] Read more.
Thermally induced deterioration processes were studied in cold worked (up to 60% deformation) SAF 2507 type super-duplex stainless steel (SDSS) by differential thermal analysis (DTA). DTA results revealed two transformations. Parent and inherited phases of these transformations were examined by other methods too, such as micro-hardness tests, optical metallography and X-ray diffraction (XRD). Finally, these transformations were identified as the formation of α’- and σ-phases. Formation of strain-induced martensite (SIM) and recrystallization were not experienced until 1000 °C, despite high degree of cold working. Activation energies of the σ-phase precipitation and α’-phase formation were determined from the Kissinger plot, through DTA measurements—they are 275 and 220 kJ/mol, respectively—in good agreement with the values found in the literature. Full article
(This article belongs to the Special Issue Investigation of Duplex Stainless Steel)
Show Figures

Graphical abstract

Open AccessArticle
Control of Thermophysical Properties of Langasite-Type La3Ta0.5Ga5.5O14 Crystals for Pressure Sensors
Crystals 2020, 10(10), 936; https://doi.org/10.3390/cryst10100936 - 14 Oct 2020
Viewed by 266
Abstract
We present a possible method to reduce the anisotropy of the thermal stress generated on langasite-type La3Ta0.5Ga5.5O14 (LTG) piezoelectric crystals arising from the mismatch of the thermal expansion coefficients and Young’s moduli of the crystals and [...] Read more.
We present a possible method to reduce the anisotropy of the thermal stress generated on langasite-type La3Ta0.5Ga5.5O14 (LTG) piezoelectric crystals arising from the mismatch of the thermal expansion coefficients and Young’s moduli of the crystals and metals at high temperatures. To formulate this method, the thermal stresses of order-type langasite crystals, in which each cation site is occupied by one element only, were calculated and compared to each other. Our results suggest that the largest cation site affects the thermal stress. We attempted to replace La3+ in LTG by a larger ion and considered Sr2+. Single crystals of strontium-substituted LTG (Sr-LTG) were grown using the Czochralski method. The thermal stress along the crystallographic c-axis decreased but that perpendicular to the c-axis increased by strontium substitution into the LTG crystal. The anisotropic thermal stress was reduced effectively. The Sr-LTG single crystal is a superior candidate material for pressure sensors usable at high temperatures. Full article
Show Figures

Figure 1

Open AccessArticle
A Facile Fabrication Route of Poly(Ethylene Glycol Phenyl Ether Acrylate) Photopolymers with Efficient Optical Response for Holographic Storage
Crystals 2020, 10(10), 935; https://doi.org/10.3390/cryst10100935 - 14 Oct 2020
Viewed by 245
Abstract
A series of photopolymers based on ethylene glycol phenyl ethyl arylate (EGPEA) monomers and poly(methyl methacrylate) (PMMA) matrix with varying initiator concentrations and sample thicknesses have been synthesized and their optical performance characterized in this study. The advantages of lowering the initiator concentration, [...] Read more.
A series of photopolymers based on ethylene glycol phenyl ethyl arylate (EGPEA) monomers and poly(methyl methacrylate) (PMMA) matrix with varying initiator concentrations and sample thicknesses have been synthesized and their optical performance characterized in this study. The advantages of lowering the initiator concentration, including a rather short initiation time within a few seconds; a sharp rising optical response; and a stable saturated diffraction efficiency are demonstrated. The variation in the diffraction efficiency and response time with the exposure energy under various sample thickness and initiator concentrations is examined; a diffraction efficiency as high as 80% and a relatively short response time of 12–39 s are attainable. The dependence of the normalized optical parameter “sensitivity” on the exposure time is depicted, and the peak value of S ranges vastly from about 0.2 to 1.2 × 104 cm/J within a period of 15 s or so, with a maximum value of nearly 1.2 × 104. Favorable evidence of low initiator concentration can further be found when the dependence of the saturated diffraction efficiency with the exposure energy is examined. The data from this study using a low initiator concentration cover a range of exposure energy from 100 to 800 mJ/cm2 and a saturated diffraction efficiency from about 15% to 80%. The successful image reconstruction of 6-membered-ring metal nuts on a hologram based on this EGPEA/PMMA photopolymer system using a reflective holographic recording setup is demonstrated to verify its applicability to holographic storage. Full article
(This article belongs to the Special Issue Volume Holographic Optical Element (VHOE))
Show Figures

Figure 1

Open AccessEditorial
Characterisation and Study of Compounds by Single Crystal X-ray Diffraction
Crystals 2020, 10(10), 934; https://doi.org/10.3390/cryst10100934 - 14 Oct 2020
Viewed by 244
Abstract
A few years after the discovery in 1895 of X-rays by Röntgen, the first successful experiment single crystal X-ray diffraction (SCXRD) was reported by Laue, Friedrich, and Knipping [...] Full article
Open AccessArticle
Bridging the Gap between Bulk Compression and Indentation Test on Room-Temperature Plasticity in Oxides: Case Study on SrTiO3
Crystals 2020, 10(10), 933; https://doi.org/10.3390/cryst10100933 - 14 Oct 2020
Viewed by 256
Abstract
Dislocation-based functionalities in inorganic ceramics and semiconductors are drawing increasing attention, contrasting the conventional belief that the majority of ceramic materials are brittle at room temperature. Understanding the dislocation behavior in ceramics and advanced semiconducting materials is therefore critical for the mechanical reliability [...] Read more.
Dislocation-based functionalities in inorganic ceramics and semiconductors are drawing increasing attention, contrasting the conventional belief that the majority of ceramic materials are brittle at room temperature. Understanding the dislocation behavior in ceramics and advanced semiconducting materials is therefore critical for the mechanical reliability of such materials and devices designed for harvesting the dislocation-based functionalities. Here we compare the mechanical testing between indentation at nano-/microscale and bulk uniaxial deformation at macroscale and highlight the dislocation plasticity in single crystal SrTiO3, a model perovskite. The similarities and differences as well as the advantages and limitations of both testing protocols are discussed based on the experimental outcome of the crystal plasticity, with a focus on the pre-existing defect population being probed with different volumes across the length scales (“size effect”). We expect this work to pave the road for studying dislocation-based plasticity in various advanced functional ceramics and semiconductors. Full article
(This article belongs to the Special Issue Crystal Plasticity)
Show Figures

Graphical abstract

Open AccessEditorial
Special Issue Editorial: Eutectic Solvents
Crystals 2020, 10(10), 932; https://doi.org/10.3390/cryst10100932 - 13 Oct 2020
Viewed by 320
Abstract
Ionic liquids (ILs) is an umbrella term covering a variety of sub-definitions that focus on more specific subjects [...] Full article
(This article belongs to the Special Issue Eutectic Solvents)
Show Figures

Figure 1

Open AccessArticle
Synthesis, X-ray Structure, Hirshfeld Analysis of Biologically Active Mn(II) Pincer Complexes Based on s-Triazine Ligands
Crystals 2020, 10(10), 931; https://doi.org/10.3390/cryst10100931 - 13 Oct 2020
Viewed by 352
Abstract
Herein, the synthesis and antimicrobial activities of [Mn(MorphBPT)(H2O)2NO3]NO3; (1) and [Mn(PipBPT)(H2O)2NO3]NO3; (2) complexes of the pincer-type tridentate [...] Read more.
Herein, the synthesis and antimicrobial activities of [Mn(MorphBPT)(H2O)2NO3]NO3; (1) and [Mn(PipBPT)(H2O)2NO3]NO3; (2) complexes of the pincer-type tridentate ligands MorphBPT; 4-(4,6-di(1H-pyrazol-1-yl)-1,3,5-triazin-2-yl)morpholine and PipBPT; 2-(piperidin-1-yl)-4,6-di(1H-pyrazol-1-yl)-1,3,5-triazine are presented. Both complexes have slightly distorted octahedral coordination geometry. Their molecular packing depends on O–H···O, C–H···O hydrogen bonds and anion–π stacking contacts. Hirshfeld analysis was used to quantify the different contacts. Both complexes exhibited better anti-fungal activity than the standard Fluconazole and comparable antibacterial activity to Gentamycin against Staphylococcus aureus and Escherichia coli microbes. Moreover, complexes 1 and 2 are biologically more active than the free ligands against these microbes. Full article
Show Figures

Graphical abstract

Open AccessArticle
Structural Variations in Manganese Halide Chain Compounds Mediated by Methylimidazolium Isomers
Crystals 2020, 10(10), 930; https://doi.org/10.3390/cryst10100930 - 13 Oct 2020
Viewed by 320
Abstract
The structures of two new hybrid organic–inorganic manganese halide compounds [1MiH]MnCl3(H2O) and [4MiH]MnCl3(H2O) ([1MiH] = 1-methylimidazolium, [4MiH] = 4-methylimidazolium) have been determined by single crystal X-ray diffraction. Both are composed of one dimensional [MnCl3 [...] Read more.
The structures of two new hybrid organic–inorganic manganese halide compounds [1MiH]MnCl3(H2O) and [4MiH]MnCl3(H2O) ([1MiH] = 1-methylimidazolium, [4MiH] = 4-methylimidazolium) have been determined by single crystal X-ray diffraction. Both are composed of one dimensional [MnCl3(H2O)]n edge-sharing octahedral chains. The structures are compared to the previously reported isomeric analogue [2MiH]MnCl3(H2O) ([2MiH] = 2-methylimidazolium), and three closely related compounds. The variations in packing of the inorganic chains are shown to be influenced by hydrogen bonding abilities of the imidazolium or related moieties. Both new compounds show intense red luminescence at ambient temperature under UV irradiation. Full article
(This article belongs to the Special Issue Coordination Polymers: Structure, Bonding and Applications)
Show Figures

Figure 1

Open AccessArticle
High-Entropy FeCoNiB0.5Si0.5 Alloy Synthesized by Mechanical Alloying and Spark Plasma Sintering
Crystals 2020, 10(10), 929; https://doi.org/10.3390/cryst10100929 - 12 Oct 2020
Viewed by 269
Abstract
A FeCoNi(B0.5Si0.5) high-entropy alloy with the face-centered cubic (FCC) crystal structure was synthesized by mechanical alloying and spark plasma sintering (SPS). Phase evolution, microstructure, morphology and annealing behaviors were investigated. It was found that a single FCC solid solution [...] Read more.
A FeCoNi(B0.5Si0.5) high-entropy alloy with the face-centered cubic (FCC) crystal structure was synthesized by mechanical alloying and spark plasma sintering (SPS). Phase evolution, microstructure, morphology and annealing behaviors were investigated. It was found that a single FCC solid solution appears after 50 h of milling. The grain size was 10 nm after 150 h of milling. Microstructure parameters were calculated by the Rietveld fitting of the X-ray Diffraction patterns. Magnetic characterizations of milled and annealed powders at 650 °C for 1 h were investigated. The heat treatment improves the magnetic properties of the milled powders by enhancing the saturation magnetization value from 94.31 to 127.30 emu/g and decreasing the coercivity from 49.07 to 29.57 Oe. The cohabitation of the FCC phase with the equilibrium crystalline phases observed after annealing is responsible of this magnetic softening. The as-milled powder was also consolidated by spark plasma sintering at 750 and 1000 °C. The obtained specimen consolidated at 750 °C improved the coercivity to 25.06 Oe and exhibited a compressive strength of 1062 Mpa and Vickers hardness of 518 ± 14 HV, with a load of 2 kN. The nanoindentation technique with the Berkovich indentor gave hardness and indentation elastic modulus of 6.3 ± 0.3 Gpa (~640 HV) and 111 ± 4 Gpa for samples consolidated by SPS at 750 °C. Full article
Show Figures

Graphical abstract

Open AccessArticle
Numerical Analysis of a Novel Shaft Lining Structure in Coal Mines Consisting of Hybrid-Fiber-Reinforced Concrete
Crystals 2020, 10(10), 928; https://doi.org/10.3390/cryst10100928 - 12 Oct 2020
Viewed by 250
Abstract
To address the temperature cracking of concrete in frozen shaft linings in extra-thick alluvial layers in coal mines, a novel shaft lining structure of coal mines consisting of hybrid-fiber-reinforced concrete (HFRC) was developed. Using the Finite Element Method (FEM), a numerical simulation test [...] Read more.
To address the temperature cracking of concrete in frozen shaft linings in extra-thick alluvial layers in coal mines, a novel shaft lining structure of coal mines consisting of hybrid-fiber-reinforced concrete (HFRC) was developed. Using the Finite Element Method (FEM), a numerical simulation test of the HFRC shaft lining structure with four factors and three levels was carried out, and the mechanical characteristics of the shaft lining structure were obtained. The results show that under a uniform surface load, the maximum hoop stress position of the HFRC shaft lining presents a transition trend from the inside surface to the outside surface; the hoop strain of shaft lining concrete is always a compressive strain, and the inside surface is greater than the outside surface. The empirical formula for the ultimate capacity of this new type of shaft lining structure was obtained by fitting. Compared with the model test results, the maximum relative error of the calculated value is only 6.69%, which provides a certain reference value for designing this kind of shaft lining structure. Full article
(This article belongs to the Special Issue Numerical Study of Concrete)
Show Figures

Figure 1

Open AccessArticle
Influence of Alumina Air-Abrasion on Flexural and Shear Bond Strengths of CAD/CAM Composite
Crystals 2020, 10(10), 927; https://doi.org/10.3390/cryst10100927 - 12 Oct 2020
Viewed by 253
Abstract
The purpose of this study was to clarify the influence of alumina air-abrasion on flexural and bond strengths of CAD/CAM composites. The flexural strength (FS) of two brands of commercial CAD/CAM composites was investigated by the three-point bending test using two specimen designs: [...] Read more.
The purpose of this study was to clarify the influence of alumina air-abrasion on flexural and bond strengths of CAD/CAM composites. The flexural strength (FS) of two brands of commercial CAD/CAM composites was investigated by the three-point bending test using two specimen designs: the single-bar according to the ISO standard and the bonded-double-bar fabricated by bonding two bars with a resin cement. The bond strength between the composites and the resin cement was measured by a conventional shear bond strength (SBS) test. The FS of single-bar specimens was significantly decreased by the air-abrasion. For the FS of the bonded-double-bar specimen, on the other hand, there was no significant difference between the specimens with/without air-abrasion. The SBS for the composites was significantly increased by air-abrasion. The results suggest that alumina air-abrasion improves the SBS of the composites while weakening its FS. Contrarily, the FS of the air-abraded composite did not decrease when the composites were bonded with the resin cement. Full article
(This article belongs to the Special Issue Resin Ceramics Composite)
Show Figures

Figure 1

Open AccessArticle
Role of Strain Reversal in Microstructure and Texture of Pure Al during Non-Monotonic Simple Shear Straining
Crystals 2020, 10(10), 926; https://doi.org/10.3390/cryst10100926 - 12 Oct 2020
Viewed by 333
Abstract
The effect of reverse straining on the microstructure, texture, and hardness of the pure Al during the single cycle of the simple shear extrusion (SSE) process is investigated. Electron backscattering diffraction (EBSD), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM) are [...] Read more.
The effect of reverse straining on the microstructure, texture, and hardness of the pure Al during the single cycle of the simple shear extrusion (SSE) process is investigated. Electron backscattering diffraction (EBSD), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM) are used for microstructural evaluations. Due to the nature of the SSE process, the direction of the shear is reversed in the second half channel. As a result, the mean misorientation angle, dislocation density, and hardness decrease. The grain size increases to some extent in the exit of the channel compared with that in the middle. The structural evolution during the single pass of SSE is described in terms of the dislocation cancelling, “untangling” of the cell walls and disintegration of the “forward” cell structure due to the reverse straining in the second half channel. Some simple shear components replace the first texture component in the middle of the channel. At the exit of the channel, the primary texture components appear somewhat confirming the strain reversal effect in the second half channel. Full article
(This article belongs to the Special Issue Strain Reversal in Metals and Alloys: Origins and Consequences)
Show Figures

Graphical abstract

Previous Issue
Next Issue
Back to TopTop