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Special Issue "Inorganic Clathrate Materials"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (15 June 2016)

Special Issue Editors

Guest Editor
Prof. Matt Beekman

Department of Physics, California Polytechnic State University, San Luis Obispo, CA 93407 USA
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Interests: solid state physics; materials synthesis; materials chemistry; thermoelectric materials and technology
Guest Editor
Prof. Yuri Grin

Max-Planck-Institut für Chemische Physik fester Stoffe, Dresden, Germany
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Interests: preparation; crystal structure; chemical bonding; chemical and physical behavior of intermetallic compounds

Special Issue Information

Dear Colleagues,

In the past decade, inorganic clathrates have received rapidly increasing attention globally due to their unusual and potentially useful electronic, thermal, as well as chemical properties. The diverse behaviors they display are often directly related to the atomic interactions in these unique inclusion-type compounds, as well as their expanded framework structures. As prospects grow for utilizing these materials in energy harvesting, energy conversion, and energy storage applications, the compositional diversity they afford provides a broad materials space for further scientific and technological discovery.

This Special Issue aims to provide a forum for contributions focused on all aspects of inorganic clathrates, both scientific and technological, including new experimental and theoretical research that advances the understanding of the synthesis, structure, physical, and chemical properties, as well as applications of these materials.

Prof. Matt Beekman
Prof. Yuri Grin
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • clathrate
  • synthesis
  • structure
  • properties
  • thermoelectric
  • intermetallic
  • energy production, conversion, and storage

Published Papers (10 papers)

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Research

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Open AccessArticle Effects of the CO2 Guest Molecule on the sI Clathrate Hydrate Structure
Materials 2016, 9(9), 777; doi:10.3390/ma9090777
Received: 11 July 2016 / Revised: 15 August 2016 / Accepted: 8 September 2016 / Published: 15 September 2016
Cited by 1 | PDF Full-text (5104 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This paper analyzes the structural, energetic and mechanical properties of carbon dioxide hydrate clathrates calculated using finite cluster and periodic ab initio density-functional theory methodologies. Intermolecular interactions are described by the exchange-hole dipole moment method. The stability, gas saturation energetics, guest–host interactions, cage
[...] Read more.
This paper analyzes the structural, energetic and mechanical properties of carbon dioxide hydrate clathrates calculated using finite cluster and periodic ab initio density-functional theory methodologies. Intermolecular interactions are described by the exchange-hole dipole moment method. The stability, gas saturation energetics, guest–host interactions, cage deformations, vibrational frequencies, and equation of state parameters for the low-pressure sI cubic phase of the CO2@H2O clathrate hydrate are presented. Our results reveal that: (i) the gas saturation process energetically favors complete filling; (ii) carbon dioxide molecules prefer to occupy the larger of the two cages in the sI structure; (iii) blue shifts occur in both the symmetric and antisymmetric stretching frequencies of CO2 upon encapsulation; and (iv) free rotation of guest molecules is restricted to a plane parallel to the hexagonal faces of the large cages. In addition, we calculate the librational frequency of the hindered rotation of the guest molecule in the plane perpendicular to the hexagonal faces. Our calculated spectroscopic data can be used as signatures for the detection of clathrate hydrates in planetary environments. Full article
(This article belongs to the Special Issue Inorganic Clathrate Materials)
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Open AccessArticle Structure and Transport Properties of Dense Polycrystalline Clathrate-II (K,Ba)16(Ga,Sn)136 Synthesized by a New Approach Employing SPS
Materials 2016, 9(9), 732; doi:10.3390/ma9090732
Received: 11 July 2016 / Revised: 15 August 2016 / Accepted: 22 August 2016 / Published: 26 August 2016
Cited by 1 | PDF Full-text (2005 KB) | HTML Full-text | XML Full-text
Abstract
Tin clathrate-II framework-substituted compositions are of current interest as potential thermoelectric materials for medium-temperature applications. A review of the literature reveals different compositions reported with varying physical properties, which depend strongly on the exact composition as well as the processing conditions. We therefore
[...] Read more.
Tin clathrate-II framework-substituted compositions are of current interest as potential thermoelectric materials for medium-temperature applications. A review of the literature reveals different compositions reported with varying physical properties, which depend strongly on the exact composition as well as the processing conditions. We therefore initiated an approach whereby single crystals of two different (K,Ba)16(Ga,Sn)136 compositions were first obtained, followed by grinding of the crystals into fine powder for low temperature spark plasma sintering consolidation into dense polycrystalline solids and subsequent high temperature transport measurements. Powder X-ray refinement results indicate that the hexakaidecahedra are empty, K and Ba occupying only the decahedra. Their electrical properties depend on composition and have very low thermal conductivities. The structural and transport properties of these materials are compared to that of other Sn clathrate-II compositions. Full article
(This article belongs to the Special Issue Inorganic Clathrate Materials)
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Open AccessArticle High Pressure Properties of a Ba-Cu-Zn-P Clathrate-I
Materials 2016, 9(8), 692; doi:10.3390/ma9080692
Received: 1 June 2016 / Revised: 27 July 2016 / Accepted: 6 August 2016 / Published: 12 August 2016
Cited by 1 | PDF Full-text (2824 KB) | HTML Full-text | XML Full-text
Abstract
The high pressure properties of the novel tetrel-free clathrate, Ba8Cu13.1Zn3.3P29.6, were investigated using synchrotron powder X-ray diffraction. The pressure was applied using a diamond anvil cell. No structural transitions or decomposition were detected in the
[...] Read more.
The high pressure properties of the novel tetrel-free clathrate, Ba8Cu13.1Zn3.3P29.6, were investigated using synchrotron powder X-ray diffraction. The pressure was applied using a diamond anvil cell. No structural transitions or decomposition were detected in the studied pressure range of 0.1–7 GPa. The calculated bulk modulus for Ba8Cu13.1Zn3.3P29.6 using a third-order Birch-Murnaghan equation of state is 65(6) GPa at 300 K. This bulk modulus is comparable to the bulk moduli of Ge- and Sn-based clathrates, like A8Ga16Ge30 (A = Sr, Ba) and Sn19.3Cu4.7P22I8, but lower than those for the transition metal-containing silicon-based clathrates, Ba8TxSi46−x, T = Ni, Cu; 3 ≤ x ≤ 5. Full article
(This article belongs to the Special Issue Inorganic Clathrate Materials)
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Open AccessFeature PaperArticle Effect of Guest Atom Composition on the Structural and Vibrational Properties of the Type II Clathrate-Based Materials AxSi136, AxGe136 and AxSn136 (A = Na, K, Rb, Cs; 0 ≤ x ≤ 24)
Materials 2016, 9(8), 691; doi:10.3390/ma9080691
Received: 1 July 2016 / Revised: 3 August 2016 / Accepted: 5 August 2016 / Published: 11 August 2016
Cited by 1 | PDF Full-text (1463 KB) | HTML Full-text | XML Full-text
Abstract
Type II clathrates are interesting due to their potential thermoelectric applications. Powdered X-ray diffraction (XRD) data and density functional calculations for NaxSi136 found a lattice contraction as x increases for 0 < x < 8 and an expansion as x
[...] Read more.
Type II clathrates are interesting due to their potential thermoelectric applications. Powdered X-ray diffraction (XRD) data and density functional calculations for NaxSi136 found a lattice contraction as x increases for 0 < x < 8 and an expansion as x increases for x > 8. This is explained by XRD data that shows that as x increases, the Si28 cages are filled first for x < 8 and the Si20 cages are then filled for x > 8. Motivated by this work, here we report the results of first-principles calculations of the structural and vibrational properties of the Type II clathrate compounds AxSi136, AxGe136, and AxSn136. We present results for the variation of the lattice constants, bulk moduli, and other structural parameters with x. These are contrasted for the Si, Ge, and Sn compounds and for guests A = Na, K, Rb, and Cs. We also present calculated results of phonon dispersion relations for Na4Si136, Na4Ge136, and Na4Sn136 and we compare these for the three materials. Finally, we present calculated results for the elastic constants in NaxSi136, NaxGe136, and NaxSn136 for x = 4 and 8. These are compared for the three hosts, as well as for the two compositions. Full article
(This article belongs to the Special Issue Inorganic Clathrate Materials)
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Open AccessArticle Micro-Tomographic Investigation of Ice and Clathrate Formation and Decomposition under Thermodynamic Monitoring
Materials 2016, 9(8), 668; doi:10.3390/ma9080668
Received: 15 June 2016 / Revised: 18 July 2016 / Accepted: 27 July 2016 / Published: 8 August 2016
PDF Full-text (10608 KB) | HTML Full-text | XML Full-text
Abstract
Clathrate hydrates are inclusion compounds in which guest molecules are trapped in a host lattice formed by water molecules. They are considered an interesting option for future energy supply and storage technologies. In the current paper, time lapse 3D micro computed tomographic (µCT)
[...] Read more.
Clathrate hydrates are inclusion compounds in which guest molecules are trapped in a host lattice formed by water molecules. They are considered an interesting option for future energy supply and storage technologies. In the current paper, time lapse 3D micro computed tomographic (µCT) imaging with ice and tetrahydrofuran (THF) clathrate hydrate particles is carried out in conjunction with an accurate temperature control and pressure monitoring. µCT imaging reveals similar behavior of the ice and the THF clathrate hydrate at low temperatures while at higher temperatures (3 K below the melting point), significant differences can be observed. Strong indications for micropores are found in the ice as well as the THF clathrate hydrate. They are stable in the ice while unstable in the clathrate hydrate at temperatures slightly below the melting point. Significant transformations in surface and bulk structure can be observed within the full temperature range investigated in both the ice and the THF clathrate hydrate. Additionally, our results point towards an uptake of molecular nitrogen in the THF clathrate hydrate at ambient pressures and temperatures from 230 K to 271 K. Full article
(This article belongs to the Special Issue Inorganic Clathrate Materials)
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Open AccessArticle Lattice Dynamics Study of Phonon Instability and Thermal Properties of Type-I Clathrate K8Si46 under High Pressure
Materials 2016, 9(8), 616; doi:10.3390/ma9080616
Received: 15 June 2016 / Revised: 11 July 2016 / Accepted: 21 July 2016 / Published: 25 July 2016
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Abstract
For a further understanding of the phase transitions mechanism in type-I silicon clathrates K8Si46, ab initio self-consistent electronic calculations combined with linear-response method have been performed to investigate the vibrational properties of alkali metal K atoms encapsulated type-I silicon-clathrate
[...] Read more.
For a further understanding of the phase transitions mechanism in type-I silicon clathrates K8Si46, ab initio self-consistent electronic calculations combined with linear-response method have been performed to investigate the vibrational properties of alkali metal K atoms encapsulated type-I silicon-clathrate under pressure within the framework of density functional perturbation theory. Our lattice dynamics simulation results showed that the pressure induced phase transition of K8Si46 was believed to be driven by the phonon instability of the calthrate lattice. Analysis of the evolution of the partial phonon density of state with pressure, a legible dynamic picture for both guest K atoms and host lattice, was given. In addition, based on phonon calculations and combined with quasi-harmonic approximation, the specific heat of K8Si46 was derived, which agreed very well with experimental results. Also, other important thermal properties including the thermal expansion coefficients and Grüneisen parameters of K8Si46 under different temperature and pressure were also predicted. Full article
(This article belongs to the Special Issue Inorganic Clathrate Materials)
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Open AccessFeature PaperArticle Effect of Transition Metal Substitution on the Structure and Properties of a Clathrate-Like Compound Eu7Cu44As23
Materials 2016, 9(7), 587; doi:10.3390/ma9070587
Received: 9 June 2016 / Revised: 6 July 2016 / Accepted: 14 July 2016 / Published: 19 July 2016
PDF Full-text (4304 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A series of substitutional solid solutions—Eu7Cu44−xTxAs23 (T = Fe, Co, Ni)—based on a recently discovered clathrate-like compound (Eu7Cu44As23) were synthesized from the elements at 800 °C. Almost up to
[...] Read more.
A series of substitutional solid solutions—Eu7Cu44−xTxAs23 (T = Fe, Co, Ni)—based on a recently discovered clathrate-like compound (Eu7Cu44As23) were synthesized from the elements at 800 °C. Almost up to 50% of Cu can be substituted by Ni, resulting in a linear decrease of the cubic unit cell parameter from a = 16.6707(1) Å for the ternary compound to a = 16.3719(1) Å for the sample with the nominal composition Eu7Cu24Ni20As23. In contrast, Co and Fe can only substitute less than 20% of Cu. Crystal structures of six samples of different composition were refined from powder diffraction data. Despite very small differences in scattering powers of Cu, Ni, Co, and Fe, we were able to propose a reasonable model of dopant distribution over copper sites based on the trends in interatomic distances as well as on Mössbauer spectra for the iron-substituted compound Eu7Cu36Fe8As23. Ni doping increases the Curie temperature to 25 K with respect to the parent compound, which is ferromagnetically ordered below 17.5 K, whereas Fe doping suppresses the ferromagnetic ordering in the Eu sublattice. Full article
(This article belongs to the Special Issue Inorganic Clathrate Materials)
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Open AccessArticle Binary Alkali-Metal Silicon Clathrates by Spark Plasma Sintering: Preparation and Characterization
Materials 2016, 9(7), 593; doi:10.3390/ma9070593
Received: 13 June 2016 / Revised: 12 July 2016 / Accepted: 13 July 2016 / Published: 19 July 2016
PDF Full-text (3359 KB) | HTML Full-text | XML Full-text
Abstract
The binary intermetallic clathrates K8-xSi46 (x = 0.4; 1.2), Rb6.2Si46, Rb11.5Si136 and Cs7.8Si136 were prepared from M4Si4 (M = K, Rb, Cs) precursors by
[...] Read more.
The binary intermetallic clathrates K8-xSi46 (x = 0.4; 1.2), Rb6.2Si46, Rb11.5Si136 and Cs7.8Si136 were prepared from M4Si4 (M = K, Rb, Cs) precursors by spark-plasma route (SPS) and structurally characterized by Rietveld refinement of PXRD data. The clathrate-II phase Rb11.5Si136 was synthesized for the first time. Partial crystallographic site occupancy of the alkali metals, particularly for the smaller Si20 dodecahedra, was found in all compounds. SPS preparation of Na24Si136 with different SPS current polarities and tooling were performed in order to investigate the role of the electric field on clathrate formation. The electrical and thermal transport properties of K7.6Si46 and K6.8Si46 in the temperature range 4–700 K were investigated. Our findings demonstrate that SPS is a novel tool for the synthesis of intermetallic clathrate phases that are not easily accessible by conventional synthesis techniques. Full article
(This article belongs to the Special Issue Inorganic Clathrate Materials)
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Open AccessArticle Synthesis and Structural Characterization of the New Clathrates K8Cd4Ge42, Rb8Cd4Ge42, and Cs8Cd4Ge42
Materials 2016, 9(4), 236; doi:10.3390/ma9040236
Received: 3 March 2016 / Revised: 17 March 2016 / Accepted: 21 March 2016 / Published: 25 March 2016
PDF Full-text (1916 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
This paper presents results from our exploratory work in the systems K-Cd-Ge, Rb-Cd-Ge, and Cs-Cd-Ge, which yielded the novel type-I clathrates with refined compositions K8Cd3.77(7)Ge42.23, Rb8Cd3.65(7)Ge42.35, and Cs7.80(1)Cd3.65(6)
[...] Read more.
This paper presents results from our exploratory work in the systems K-Cd-Ge, Rb-Cd-Ge, and Cs-Cd-Ge, which yielded the novel type-I clathrates with refined compositions K8Cd3.77(7)Ge42.23, Rb8Cd3.65(7)Ge42.35, and Cs7.80(1)Cd3.65(6)Ge42.35. The three compounds represent rare examples of clathrates of germanium with the alkali metals, where a d10 element substitutes a group 14 element. The three structures, established by single-crystal X-ray diffraction, indicate that the framework-building Ge atoms are randomly substituted by Cd atoms on only one of the three possible crystallographic sites. This and several other details of the crystal chemistry are elaborated. Full article
(This article belongs to the Special Issue Inorganic Clathrate Materials)
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Review

Jump to: Research

Open AccessFeature PaperReview Earth Abundant Element Type I Clathrate Phases
Materials 2016, 9(9), 714; doi:10.3390/ma9090714
Received: 6 July 2016 / Revised: 8 August 2016 / Accepted: 15 August 2016 / Published: 23 August 2016
PDF Full-text (2260 KB) | HTML Full-text | XML Full-text
Abstract
Earth abundant element clathrate phases are of interest for a number of applications ranging from photovoltaics to thermoelectrics. Silicon-containing type I clathrate is a framework structure with the stoichiometry A8-xSi46 (A = guest atom such as alkali metal) that can
[...] Read more.
Earth abundant element clathrate phases are of interest for a number of applications ranging from photovoltaics to thermoelectrics. Silicon-containing type I clathrate is a framework structure with the stoichiometry A8-xSi46 (A = guest atom such as alkali metal) that can be tuned by alloying and doping with other elements. The type I clathrate framework can be described as being composed of two types of polyhedral cages made up of tetrahedrally coordinated Si: pentagonal dodecahedra with 20 atoms and tetrakaidecahedra with 24 atoms in the ratio of 2:6. The cation sites, A, are found in the center of each polyhedral cage. This review focuses on the newest discoveries in the group 13-silicon type I clathrate family: A8E8Si38 (A = alkali metal; E = Al, Ga) and their properties. Possible approaches to new phases based on earth abundant elements and their potential applications will be discussed. Full article
(This article belongs to the Special Issue Inorganic Clathrate Materials)
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