Editorial

197 KiB

Open AccessEditorial

by Winnie Wong-Ng and Claudia J. Rawn

Crystals 2017, 7(9), 279; https://doi.org/10.3390/cryst7090279 - 15 Sep 2017

Cited by 4 | Viewed by 3080

The goal of this special issue is to obtain new insights into the roles of crystallography in functional materials. This special issue consists of eight papers illustrating the structure and property relationships, as well as applications of selected classes of materials that deal [...] Read more.

The goal of this special issue is to obtain new insights into the roles of crystallography in functional materials. This special issue consists of eight papers illustrating the structure and property relationships, as well as applications of selected classes of materials that deal with various aspects of functional materials, ranging from battery, magnetic, photocatalysis, and waveguide materials, to luminescent metal-organic frameworks and borates, semiconductors, and inorganic electrides. This issue provides further evidence of the importance of crystallography in understanding and improving various properties of functional materials, whether they are single crystals, bulk polycrystalline materials, or thin films. Full article

(This article belongs to the Special Issue Crystallography of Functional Materials)

Research

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7155 KiB

Open AccessArticle

Extended Defect Propagation in Highly Tensile-Strained Ge Waveguides

by Meng Qi, William A. O’Brien, Chad A. Stephenson, Victor Patel, Ning Cao, Brian J. Thibeault, Marco Schowalter, Andreas Rosenauer, Vladimir Protasenko, Huili (Grace) Xing and Mark A. Wistey

Crystals 2017, 7(6), 157; https://doi.org/10.3390/cryst7060157 - 26 May 2017

Cited by 6 | Viewed by 5232

Abstract

Tensile-strained Ge is a possible laser material for Si integrated circuits, but reports of lasers using tensile Ge show high threshold current densities and short lifetimes. To study the origins of these shortcomings, Ge ridge waveguides with tensile strain in three dimensions were [...] Read more.

Tensile-strained Ge is a possible laser material for Si integrated circuits, but reports of lasers using tensile Ge show high threshold current densities and short lifetimes. To study the origins of these shortcomings, Ge ridge waveguides with tensile strain in three dimensions were fabricated using compressive silicon nitride (SiN_x) films with up to 2 GPa stress as stress liners. A Raman peak shift of up to 11 cm⁻¹ was observed, corresponding to 3.6% hydrostatic tensile strain for waveguides with a triangular cross-section. Real time degradation in tensile-strained Ge was observed and studied under transmission electron microscopy (TEM). A network of defects, resembling dark line defects, was observed to form and propagate with a speed and density strongly correlated with the local strain extracted from both modeled and measured strain profiles. This degradation suggests highly tensile-strained Ge lasers are likely to have significantly shorter lifetime than similar GaAs or InGaAs quantum well lasers. Full article

(This article belongs to the Special Issue Crystallography of Functional Materials)

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7796 KiB

Open AccessArticle

Crystallography and Growth of Epitaxial Oxide Films for Fundamental Studies of Cathode Materials Used in Advanced Li-Ion Batteries

by Leonid A. Bendersky, Haiyan Tan, Kamala Bharathi Karuppanan, Zhi-Peng Li and Aaron C. Johnston-Peck

Crystals 2017, 7(5), 127; https://doi.org/10.3390/cryst7050127 - 08 May 2017

Cited by 8 | Viewed by 8927

Abstract

Li-ion battery systems, synthesized as epitaxial thin films, can provide powerful insights into their electrochemical processes. Crystallographic analysis shows that many important cathode oxides have an underlying similarity: their structures can be considered as different ordering schemes of Li and transition metal ions [...] Read more.

Li-ion battery systems, synthesized as epitaxial thin films, can provide powerful insights into their electrochemical processes. Crystallographic analysis shows that many important cathode oxides have an underlying similarity: their structures can be considered as different ordering schemes of Li and transition metal ions within a pseudo-cubic sublattice of oxygen anions arranged in a face-center cubic (FCC) fashion. This oxygen sublattice is compatible with SrTiO₃ and similar perovskite oxides, thus perovskites can be used as supporting substrates for growing epitaxial cathode films. The predicted epitaxial growth and crystallographic relations were experimentally verified for different oxide films deposited by pulsed laser deposition (PLD) on SrTiO₃ or SrRuO₃/SrTiO₃ of different orientations. The results based on cross-sectional high-resolution TEM of the following films are presented in the paper: (a) trigonal LiCoO₂; (b) orthorhombic LiMnO₂; (c) monoclinic Li₂MnO₃; (d) compositionally-complex monoclinic Li_1.2Mn_0.55Ni_0.15Co_0.1O₂. All results demonstrated the feasibility of epitaxial growth for these materials, with the growth following the predicted cube-on-cube orientation relationship between the cubic and pseudo-cubic oxygen sublattices of a substrate and a film, respectively. Full article

(This article belongs to the Special Issue Crystallography of Functional Materials)

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3643 KiB

Open AccessArticle

Structure Determination and Luminescent Property Studies of the Single Crystal Na₃Sm(BO₃)₂

by Dan Zhao, Fa-Xue Ma, Cong-Kui Nie, Jian Wang, Lei Zhang and Yunchang Fan

Crystals 2017, 7(5), 129; https://doi.org/10.3390/cryst7050129 - 05 May 2017

Cited by 13 | Viewed by 4263

Abstract

Sodium samarium borate Na₃Sm(BO₃)₂, was prepared by a flux method and structurally characterized by single-crystal structure analysis for the first time. The results show that it crystallizes in the monoclinic system P2₁/n, [...] Read more.

Sodium samarium borate Na₃Sm(BO₃)₂, was prepared by a flux method and structurally characterized by single-crystal structure analysis for the first time. The results show that it crystallizes in the monoclinic system P2₁/n, with a = 6.5667(3) Å, b = 8.7675(4) Å, c = 10.1850(5), β = 90.86°, V = 586.32(5) Å³ and Z = 4. The structure contains NaO₇, NaO₆, NaO₅, SmO₈, and BO₃ units, which are interconnected via corner- or edge-sharing O atoms into a three-dimensional structure. The excitation spectra, emission spectra, decay time, and Commission International de l’Éclairage (CIE) chromaticity index of Na₃Sm(BO₃)₂ were studied. Under near light excitation (406 nm), the powdered Na₃Sm(BO₃)₂ shows the orange-red emission, which originates from the ⁴G_5/2→⁶H_9/2 and ⁴G_5/2→⁶H_7/2 transformation of Sm³⁺ ion. Full article

(This article belongs to the Special Issue Crystallography of Functional Materials)

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1009 KiB

Open AccessArticle

Crystal and Magnetic Structures in Layered, Transition Metal Dihalides and Trihalides

by Michael A. McGuire

Crystals 2017, 7(5), 121; https://doi.org/10.3390/cryst7050121 - 27 Apr 2017

Cited by 330 | Viewed by 24603

Abstract

Materials composed of two dimensional layers bonded to one another through weak van der Waals interactions often exhibit strongly anisotropic behaviors and can be cleaved into very thin specimens and sometimes into monolayer crystals. Interest in such materials is driven by the study [...] Read more.

Materials composed of two dimensional layers bonded to one another through weak van der Waals interactions often exhibit strongly anisotropic behaviors and can be cleaved into very thin specimens and sometimes into monolayer crystals. Interest in such materials is driven by the study of low dimensional physics and the design of functional heterostructures. Binary compounds with the compositions

M X_{2}

and

M X_{3}

where M is a metal cation and X is a halogen anion often form such structures. Magnetism can be incorporated by choosing a transition metal with a partially filled d-shell for M, enabling ferroic responses for enhanced functionality. Here a brief overview of binary transition metal dihalides and trihalides is given, summarizing their crystallographic properties and long-range-ordered magnetic structures, focusing on those materials with layered crystal structures and partially filled d-shells required for combining low dimensionality and cleavability with magnetism. Full article

(This article belongs to the Special Issue Crystallography of Functional Materials)

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3988 KiB

Open AccessArticle

Synthesis, Crystal Structure, and Luminescent Properties of New Zinc(II) and Cadmium(II) Metal-Organic Frameworks Based on Flexible Bis(imidazol-1-yl)alkane Ligands

by Marina Barsukova, Tatiana Goncharova, Denis Samsonenko, Danil Dybtsev and Andrei Potapov

Crystals 2016, 6(10), 132; https://doi.org/10.3390/cryst6100132 - 13 Oct 2016

Cited by 23 | Viewed by 5936

Abstract

New metal-organic frameworks (MOFs) based on zinc and cadmium ions, terephthalic acid, and flexible ligands 1,5-bis(imidazol-1-yl)pentane or 1,6-bis(imidazol-1-yl)hexane were prepared and characterized by X-ray diffraction, thermorgavimetric analysis and IR spectroscopy. The imidazolyl ligands were prepared by a new robust procedure involving the reaction [...] Read more.

New metal-organic frameworks (MOFs) based on zinc and cadmium ions, terephthalic acid, and flexible ligands 1,5-bis(imidazol-1-yl)pentane or 1,6-bis(imidazol-1-yl)hexane were prepared and characterized by X-ray diffraction, thermorgavimetric analysis and IR spectroscopy. The imidazolyl ligands were prepared by a new robust procedure involving the reaction between imidazole and 1,5-dibromopentane or 1,6-dibromohexane in a superbasic medium (KOH in DMSO). MOFs based on 1,5-bis(imidazol-1-yl)pentane had diamond topology (dia) and are triply interpenetrated. Ligands with longer spacer 1,6-bis(imidazol-1-yl)hexane, terephthalate ions and zinc(II) ions formed five-fold interpenetrated metal-organic framework also with dia topology, while cadmium(II) ions with the same ligands formed eight-connected uninodal net with a very rare self-penetrated topological type ilc and a point symbol 4²⁴.5.6³. The influence of the chemical composition of MOFs on their photoluminescent properties is investigated and discussed in detail. Full article

(This article belongs to the Special Issue Crystallography of Functional Materials)

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Review

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Open AccessReview

Structural Aspects of Porphyrins for Functional Materials Applications

by Lawrence P. Cook, Greg Brewer and Winnie Wong-Ng

Crystals 2017, 7(7), 223; https://doi.org/10.3390/cryst7070223 - 15 Jul 2017

Cited by 64 | Viewed by 9450

Abstract

Porphyrinic compounds comprise a diverse group of materials which have in common the presence of one or more cyclic tetrapyrroles known as porphyrins in their molecular structures. The resulting aromaticity gives rise to the semiconducting properties that make these compounds of interest for [...] Read more.

Porphyrinic compounds comprise a diverse group of materials which have in common the presence of one or more cyclic tetrapyrroles known as porphyrins in their molecular structures. The resulting aromaticity gives rise to the semiconducting properties that make these compounds of interest for a broad range of applications, including artificial photosynthesis, catalysis, molecular electronics, sensors, non-linear optics, and solar cells. In this brief review, the crystallographic attributes of porphyrins are emphasized. Examples are given showing how the structural orientations of the porphyrin macrocycle, and the inter-porphyrin covalent bonding present in multiporphyrins influence the semiconducting properties. Beginning with porphine, the simplest porphyrin, we discuss how the more complex structures that have been reported are described by adding peripheral substituents and internal metalation to the macrocycles. We illustrate how the conjugation of the π-bonding, and the presence of electron donor/acceptor pairs, which are the basis for the semiconducting properties, are affected by the crystallographic topology. Full article

(This article belongs to the Special Issue Crystallography of Functional Materials)

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6926 KiB

Open AccessReview

Polymorphism and Structural Distortions of Mixed-Metal Oxide Photocatalysts Constructed with α-U₃O₈ Types of Layers

by Nacole King, Jonathan Boltersdorf, Paul A. Maggard and Winnie Wong-Ng

Crystals 2017, 7(5), 145; https://doi.org/10.3390/cryst7050145 - 18 May 2017

Cited by 6 | Viewed by 6194

Abstract

A series of mixed-metal oxide structures based on the stacking of α-U₃O₈ type pentagonal bipyramid layers have been investigated for symmetry lowering distortions and photocatalytic activity. The family of structures contains the general composition A^m⁺_((n+1)/m) [...] Read more.

A series of mixed-metal oxide structures based on the stacking of α-U₃O₈ type pentagonal bipyramid layers have been investigated for symmetry lowering distortions and photocatalytic activity. The family of structures contains the general composition A^m⁺_((n+1)/m)B_(3n+1)O_(8n+3) (e.g., A = Ag, Bi, Ca, Cu, Ce, Dy, Eu, Gd K, La, Nd, Pb, Pr, Sr, Y; B = Nb, Ta; m = 1–3; n = 1, 1.5, 2), and the edge-shared BO₇ pentagonal pyramid single, double, and/or triple layers are differentiated by the average thickness, (i.e., 1 ≤ n ≤ 2), of the BO₇ layers and the local coordination environment of the “A” site cations. Temperature dependent polymorphism has been investigated for structures containing single layered (n = 1) monovalent (m = 1) “A” site cations (e.g., Ag₂Nb₄O₁₁, Na₂Nb₄O₁₁, and Cu₂Ta₄O₁₁). Furthermore, symmetry lowering distortions were observed for the Pb ion-exchange synthesis of Ag₂Ta₄O₁₁ to yield PbTa₄O₁₁. Several members within the subset of the family have been constructed with optical and electronic properties that are suitable for the conversion of solar energy to chemical fuels via water splitting. Full article

(This article belongs to the Special Issue Crystallography of Functional Materials)

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4717 KiB

Open AccessReview

Structure Property Relationships and Cationic Doping in [Ca₂₄Al₂₈O₆₄]⁴⁺ Framework: A Review

by John Robert Salasin and Claudia Rawn

Crystals 2017, 7(5), 143; https://doi.org/10.3390/cryst7050143 - 16 May 2017

Cited by 26 | Viewed by 6823

Abstract

Ca₁₂Al₁₄O₃₃ (C12A7, 12CaO·7Al₂O₃, or

{[{Ca}_{12} {Al}_{14} O_{32}]}^{2 +} : O^{2 -}

) is a material with a clathrate cage framework, positively charged and stabilized by anions occluded [...] Read more.

Ca₁₂Al₁₄O₃₃ (C12A7, 12CaO·7Al₂O₃, or

{[{Ca}_{12} {Al}_{14} O_{32}]}^{2 +} : O^{2 -}

) is a material with a clathrate cage framework, positively charged and stabilized by anions occluded within 17% of the cages. The occluded anion is modular and can be elemental, polyatomic, and electronic in nature. This review focuses on the electride C12A7 (

{[{Ca}_{24} {Al}_{28} O_{64}]}^{4 +} : (4 * \partial) e^{-} (2 - \partial) O^{2 -}

), where O₂₋ anions are replaced with electrons, and compliments previous structural and electronic property reviews to illuminate the structure–property relationships. Electride formation is updated with new findings in carbonaceous reduction methods. Most importantly, an extensive compilation of cationic doped C12A7 isostructural compounds is presented as motivation to study doped C12A7 electrides. Cationic dopants have profound impacts on the electronic properties due to changes in the density of states, localized electron behavior, and structural distortions. Full article

(This article belongs to the Special Issue Crystallography of Functional Materials)

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