Special Issue "High-Pressure Studies of Crystalline Materials"

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystal Engineering".

Deadline for manuscript submissions: closed (20 March 2018)

Special Issue Editor

Guest Editor
Prof. Dr. Daniel Errandonea

Departamento de Física Aplicada-ICMUV, MALTA Consolider Team, Universidad de Valencia
Website | E-Mail
Phone: +34 963544475
Interests: high-pressure; phase trasitions; oxides; x-ray diffraction; novel technological materials

Special Issue Information

Dear Colleagues,

High-pressure research has seen a great progress during the last few decades as a consequence of the combined development of various experimental techniques and computer simulations. Recently, the number of studies of crystalline materials under high pressure has growth exponentially and the pressure range covered by them has been extremely extended reaching magnitudes of the order of Terapascals. Important discoveries have been achieved thanks to high-pressure studies. These breakthroughs concerns different research fields including solid-state physics, chemistry, and materials science among others. Metallization of hydrogen is the most recent of them. The impact of pressure on chemical and physical properties and some of the contemporary discoveries are the main reasons for producing the current Special Issue.

The Special Issue on “High-Pressure Studies of Crystalline Materials” pretends to give a forum aimed at describing and discussing recent results of high-pressure studies on structural, mechanical, vibrational, and electronic properties of crystalline materials. The intention is to give special emphasis to phase transitions and their effects on different properties, but other issues are not excluded. The Special Issue is open to both experimental and theoretical contributions. Researchers working in a wide range of disciplines are welcomed to contribute to it. The topics summarized under the keywords given below are just broadly examples of the greater number of topics in mind. The volume is especially open for any innovative contributions and also for brief reviews of current hot topics.

Prof. Dr. Daniel Errandonea
Guest Editor

Manuscript Submission Information

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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. Crystals 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 1200 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

  • High pressure research
  • Matter at extreme conditions
  • Structural properties
  • Vibrational and electronic properties
  • Equation of state
  • Phase transitions

Published Papers (12 papers)

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Research

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Open AccessArticle The Structure of Ferroselite, FeSe2, at Pressures up to 46 GPa and Temperatures down to 50 K: A Single-Crystal Micro-Diffraction Analysis
Crystals 2018, 8(7), 289; https://doi.org/10.3390/cryst8070289
Received: 11 June 2018 / Revised: 5 July 2018 / Accepted: 6 July 2018 / Published: 13 July 2018
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Abstract
We conducted an in situ crystal structure analysis of ferroselite at non-ambient conditions. The aim is to provide a solid ground to further the understanding of the properties of this material in a broad range of conditions. Ferroselite, marcasite-type FeSe2, was
[...] Read more.
We conducted an in situ crystal structure analysis of ferroselite at non-ambient conditions. The aim is to provide a solid ground to further the understanding of the properties of this material in a broad range of conditions. Ferroselite, marcasite-type FeSe2, was studied under high pressures up to 46 GPa and low temperatures, down to 50 K using single-crystal microdiffraction techniques. High pressures and low temperatures were generated using a diamond anvil cell and a cryostat respectively. We found no evidences of structural instability in the explored P-T space. The deformation of the orthorhombic lattice is slightly anisotropic. As expected, the compressibility of the Se-Se dumbbell, the longer bond in the structure, is larger than that of the Fe-Se bonds. There are two octahedral Fe-Se bonds, the short bond, with multiplicity two, is slightly more compressible than the long bond, with multiplicity four; as a consequence the octahedral tetragonal compression slightly increases under pressure. We also achieved a robust structural analysis of ferroselite at low temperature in the diamond anvil cell. Structural changes upon temperature decrease are small but qualitatively similar to those produced by pressure. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessArticle Evolution of Interatomic and Intermolecular Interactions and Polymorphism of Melamine at High Pressure
Crystals 2018, 8(7), 265; https://doi.org/10.3390/cryst8070265
Received: 1 June 2018 / Revised: 20 June 2018 / Accepted: 21 June 2018 / Published: 27 June 2018
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Abstract
Melamine (C3H6N6; 1,3,5-triazine-2,4,6-triamine) is an aromatic substituted s-triazine, with carbon and nitrogen atoms forming the ring body, and amino groups bonded to each carbon. Melamine is widely used to produce laminate products, adhesives, and flame retardants,
[...] Read more.
Melamine (C3H6N6; 1,3,5-triazine-2,4,6-triamine) is an aromatic substituted s-triazine, with carbon and nitrogen atoms forming the ring body, and amino groups bonded to each carbon. Melamine is widely used to produce laminate products, adhesives, and flame retardants, but is also similar chemically and structurally to many energetic materials, including TATB (2,4,6-triamino-1,3,5- trinitrobenzene) and RDX (1,3,5-trinitroperhydro-1,3,5-triazine). Additionally, melamine may be a precursor in the synthesis of superhard carbon-nitrides, such as β-C3N4. In the crystalline state melamine forms corrugated sheets of individual molecules, which are stacked on top of one another, and linked by intra- and inter-plane N-H hydrogen bonds. Several previous high-pressure X-ray diffraction and Raman spectroscopy studies have claimed that melamine undergoes two or more phase transformations below 25 GPa. Our results show no indication of previously reported low pressure polymorphism up to approximately 30 GPa. High-pressure crystal structure refinements demonstrate that the individual molecular units of melamine are remarkably rigid, and their geometry changes very little despite volume decrease by almost a factor of two at 30 GPa and major re-arrangements of the intermolecular interactions, as seen through the Hirshfeld surface analysis. A symmetry change from monoclinic to triclinic, indicated by both dramatic changes in diffraction pattern, as well as discontinuities in the vibration mode behavior, was observed above approximately 36 GPa in helium and 30 GPa in neon pressure media. Examination of the hydrogen bonding behavior in melamine’s structure will allow its improved utilization as a chemical feedstock and analog for related energetic compounds. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessArticle Systematics of the Third Row Transition Metal Melting: The HCP Metals Rhenium and Osmium
Crystals 2018, 8(6), 243; https://doi.org/10.3390/cryst8060243
Received: 6 April 2018 / Revised: 23 May 2018 / Accepted: 25 May 2018 / Published: 6 June 2018
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Abstract
The melting curves of rhenium and osmium to megabar pressures are obtained from an extensive suite of ab initio quantum molecular dynamics (QMD) simulations using the Z method. In addition, for Re, we combine QMD simulations with total free energy calculations to obtain
[...] Read more.
The melting curves of rhenium and osmium to megabar pressures are obtained from an extensive suite of ab initio quantum molecular dynamics (QMD) simulations using the Z method. In addition, for Re, we combine QMD simulations with total free energy calculations to obtain its phase diagram. Our results indicate that Re, which generally assumes a hexagonal close-packed (hcp) structure, melts from a face-centered cubic (fcc) structure in the pressure range 20–240 GPa. We conclude that the recent DAC data on Re to 50 GPa in fact encompass both the true melting curve and the low-slope hcp-fcc phase boundary above a triple point at (20 GPa, 4240 K). A linear fit to the Re diamond anvil cell (DAC) data then results in a slope that is 2.3 times smaller than that of the actual melting curve. The phase diagram of Re is topologically equivalent to that of Pt calculated by us earlier on. Regularities in the melting curves of Re, Os, and five other 3rd-row transition metals (Ta, W, Ir, Pt, Au) form the 3rd-row transition metal melting systematics. We demonstrate how this systematics can be used to estimate the currently unknown melting curve of the eighth 3rd-row transition metal Hf. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessArticle High-Pressure Elastic, Vibrational and Structural Study of Monazite-Type GdPO4 from Ab Initio Simulations
Crystals 2018, 8(5), 209; https://doi.org/10.3390/cryst8050209
Received: 19 April 2018 / Revised: 7 May 2018 / Accepted: 8 May 2018 / Published: 10 May 2018
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Abstract
The GdPO4 monazite-type has been studied under high pressure by first principles calculations in the framework of density functional theory. This study focuses on the structural, dynamical, and elastic properties of this material. Information about the structure and its evolution under pressure,
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The GdPO4 monazite-type has been studied under high pressure by first principles calculations in the framework of density functional theory. This study focuses on the structural, dynamical, and elastic properties of this material. Information about the structure and its evolution under pressure, the equation of state, and its compressibility are reported. The evolution of the Raman and Infrared frequencies, as well as their pressure coefficients are also presented. Finally, the study of the elastic constants provides information related with the elastic and mechanical properties of this compound. From our results, we conclude that monazite-type GdPO4 becomes mechanically unstable at 54 GPa; no evidence of soft phonons has been found up to this pressure at the zone center. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessArticle Structural Phase Transition and Compressibility of CaF2 Nanocrystals under High Pressure
Crystals 2018, 8(5), 199; https://doi.org/10.3390/cryst8050199
Received: 19 March 2018 / Revised: 26 April 2018 / Accepted: 26 April 2018 / Published: 3 May 2018
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Abstract
The structural phase transition and compressibility of CaF2 nanocrystals with size of 23 nm under high pressure were investigated by synchrotron X-ray diffraction measurement. A pressure-induced fluorite to α-PbCl2-type phase transition starts at 9.5 GPa and completes at 20.2 GPa.
[...] Read more.
The structural phase transition and compressibility of CaF2 nanocrystals with size of 23 nm under high pressure were investigated by synchrotron X-ray diffraction measurement. A pressure-induced fluorite to α-PbCl2-type phase transition starts at 9.5 GPa and completes at 20.2 GPa. The phase-transition pressure is lower than that of 8 nm CaF2 nanocrystals and closer to bulk CaF2. Upon decompression, the fluorite and α-PbCl2-type structure co-exist at the ambient pressure. The bulk modulus B0 of the 23 nm CaF2 nanocrystals for the fluorite and α-PbCl2-type phase are 103(2) and 78(2) GPa, which are both larger than those of the bulk CaF2. The CaF2 nanocrystals exhibit obviously higher incompressibility compare to bulk CaF2. Further analysis demonstrates that the defect effect in our CaF2 nanocrystals plays a dominant role in the structural stability. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessArticle The Jahn-Teller Distortion at High Pressure: The Case of Copper Difluoride
Crystals 2018, 8(3), 140; https://doi.org/10.3390/cryst8030140
Received: 14 February 2018 / Revised: 15 March 2018 / Accepted: 16 March 2018 / Published: 19 March 2018
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Abstract
The opposing effects of high pressure (in the GPa range) and the Jahn-Teller distortion led to many intriguing phenomena which are still not well understood. Here we report a combined experimental-theoretical study on the high-pressure behavior of an archetypical Jahn-Teller system, copper difluoride
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The opposing effects of high pressure (in the GPa range) and the Jahn-Teller distortion led to many intriguing phenomena which are still not well understood. Here we report a combined experimental-theoretical study on the high-pressure behavior of an archetypical Jahn-Teller system, copper difluoride (CuF2). At ambient conditions this compound adopts a distorted rutile structure of P21/c symmetry. Raman scattering measurements performed up to 29 GPa indicate that CuF2 undergoes a phase transition at 9 GPa. We assign the novel high-pressure phase to a distorted fluorite structure of Pbca symmetry, iso-structural with the ambient-pressure structure of AgF2. Density functional theory calculations indicate that the Pbca structure should transform to a non-centrosymmetric Pca21 polymorph above 30 GPa, which, in turn, should be replaced by a cotunnite phase (Pnma symmetry) at 72 GPa. The elongated octahedral coordination of the Cu2+ cation persists up to the Pca21Pnma transition upon which it is replaced by a capped trigonal prism geometry, still bearing signs of a Jahn-Teller distortion. The high-pressure phase transitions of CuF2 resembles those found for difluorides of transition metals of similar radius (MgF2, ZnF2, CoF2), although with a much wider stability range of the fluorite-type structures, and lower dimensionality of the high-pressure polymorphs. Our calculations indicate no region of stability of a nanotubular polymorph observed for the related AgF2 system. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessArticle The Electrical Properties of Tb-Doped CaF2 Nanoparticles under High Pressure
Crystals 2018, 8(2), 98; https://doi.org/10.3390/cryst8020098
Received: 9 January 2018 / Revised: 11 February 2018 / Accepted: 12 February 2018 / Published: 15 February 2018
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Abstract
The high-pressure transport behavior of CaF2 nanoparticles with 3 mol% Tb concentrations was studied by alternate-current impedance measurement. All of the electrical parameters vary abnormally at approximately 10.76 GPa, corresponding to the fluorite-cotunnite structural transition. The substitution of Ca2+ by Tb
[...] Read more.
The high-pressure transport behavior of CaF2 nanoparticles with 3 mol% Tb concentrations was studied by alternate-current impedance measurement. All of the electrical parameters vary abnormally at approximately 10.76 GPa, corresponding to the fluorite-cotunnite structural transition. The substitution of Ca2+ by Tb3+ leads to deformation in the lattice, and finally lowers the transition pressure. The F ions diffusion, electronic transport, and charge-discharge process become more difficult with the rising pressure. In the electronic transport process, defects at grains play a dominant role. The charge carriers include both F ions and electrons, and electrons are dominant in the transport process. The Tb doping improves the pressure effect on the transport behavior of CaF2 nanocrystals. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessArticle High-Pressure Synthesis, Structure, and Magnetic Properties of Ge-Substituted Filled Skutterudite Compounds; LnxCo4Sb12−yGey, Ln = La, Ce, Pr, and Nd
Crystals 2017, 7(12), 381; https://doi.org/10.3390/cryst7120381
Received: 18 October 2017 / Revised: 14 December 2017 / Accepted: 14 December 2017 / Published: 15 December 2017
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Abstract
A series of new Ge-substituted skutterudite compounds with the general composition of LnxCo4Sb12−yGey, where Ln = La, Ce, Pr, and Nd, is prepared by high-pressure and high-temperature reactions at 7 GPa and 800 °C.
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A series of new Ge-substituted skutterudite compounds with the general composition of LnxCo4Sb12−yGey, where Ln = La, Ce, Pr, and Nd, is prepared by high-pressure and high-temperature reactions at 7 GPa and 800 °C. They have a cubic unit cell and the lattice constant for each compound is 8.9504 (3), 8.94481 (6), 8.9458 (3), and 8.9509 (4) Å for the La, Ce, Pr, and Nd derivatives, respectively. Their chemical compositions, determined by electron prove microanalysis, are La0.57Co4Sb10.1Ge2.38, Ce0.99Co4Sb9.65Ge2.51, Pr0.97Co4Sb9.52Ge2.61, and Nd0.87Co4Sb9.94Ge2.28. Their structural parameters are refined by Rietveld analysis. The guest atom size does not affect the unit cell volume. The Co–Sb/Ge distance mainly determines the unit cell size as well as the size of guest atom site. The valence state of lanthanide ions is 3+. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Review

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Open AccessReview Copper Delafossites under High Pressure—A Brief Review of XRD and Raman Spectroscopic Studies
Crystals 2018, 8(6), 255; https://doi.org/10.3390/cryst8060255
Received: 10 May 2018 / Revised: 13 June 2018 / Accepted: 16 June 2018 / Published: 19 June 2018
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Abstract
Delafossites, with a unique combination of electrical conductivity and optical transparency constitute an important class of materials with their wide range of applications in different fields. In this article, we review the high pressure studies on copper based semiconducting delafossites with special emphasis
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Delafossites, with a unique combination of electrical conductivity and optical transparency constitute an important class of materials with their wide range of applications in different fields. In this article, we review the high pressure studies on copper based semiconducting delafossites with special emphasis on their structural and vibrational properties by synchrotron based powder X-ray diffraction and Raman spectroscopic measurements. Though all the investigated compounds undergo pressure induced structural phase transition, the structure of high pressure phase has been reported only for CuFeO2. Based on X-ray diffraction data, one of the common features observed in all the studied compounds is the anisotropic compression of cell parameters in ambient rhombohedral structure. Ambient pressure bulk modulus obtained by fitting the pressure volume data lies between 135 to 200 GPa. Two allowed Raman mode frequencies Eg and A1g are observed in all the compounds in ambient phase with splitting of Eg mode at the transition except for CuCrO2 where along with splitting of Eg mode, A1g mode disappears and a strong mode appears which softens with pressure. Observed transition pressure scales exponentially with radii of trivalent cation being lowest for CuLaO2 and highest for CuAlO2. The present review will help materials researchers to have an overview of the subject and reviewed results are relevant for fundamental science as well as possessing potential technological applications in synthesis of new materials with tailored physical properties. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessReview High-Pressure, High-Temperature Behavior of Silicon Carbide: A Review
Crystals 2018, 8(5), 217; https://doi.org/10.3390/cryst8050217
Received: 26 April 2018 / Revised: 10 May 2018 / Accepted: 11 May 2018 / Published: 16 May 2018
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Abstract
The high-pressure behavior of silicon carbide (SiC), a hard, semi-conducting material commonly known for its many polytypic structures and refractory nature, has increasingly become the subject of current research. Through work done both experimentally and computationally, many interesting aspects of high-pressure SiC have
[...] Read more.
The high-pressure behavior of silicon carbide (SiC), a hard, semi-conducting material commonly known for its many polytypic structures and refractory nature, has increasingly become the subject of current research. Through work done both experimentally and computationally, many interesting aspects of high-pressure SiC have been measured and explored. Considerable work has been done to measure the effect of pressure on the vibrational and material properties of SiC. Additionally, the transition from the low-pressure zinc-blende B3 structure to the high-pressure rocksalt B1 structure has been measured by several groups in both the diamond-anvil cell and shock communities and predicted in numerous computational studies. Finally, high-temperature studies have explored the thermal equation of state and thermal expansion of SiC, as well as the high-pressure and high-temperature melting behavior. From high-pressure phase transitions, phonon behavior, and melting characteristics, our increased knowledge of SiC is improving our understanding of its industrial uses, as well as opening up its application to other fields such as the Earth sciences. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessReview Layered Indium Selenide under High Pressure: A Review
Crystals 2018, 8(5), 206; https://doi.org/10.3390/cryst8050206
Received: 11 April 2018 / Revised: 2 May 2018 / Accepted: 7 May 2018 / Published: 9 May 2018
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Abstract
This paper intends a short review of the research work done on the structural and electronic properties of layered Indium Selenide (InSe) and related III–VI semiconductors under high pressure conditions. The paper will mainly focus on the crucial role played by high pressure
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This paper intends a short review of the research work done on the structural and electronic properties of layered Indium Selenide (InSe) and related III–VI semiconductors under high pressure conditions. The paper will mainly focus on the crucial role played by high pressure experimental and theoretical tools to investigate the electronic structure of InSe. This objective involves a previous revision of results on the pressure dependence of the InSe crystal structure and related topics such as the equation of state and the pressure-temperature crystal phase diagram. The main part of the paper will be devoted to reviewing the literature on the optical properties of InSe under high pressure, especially the absorption experiments that led to the identification of the main optical transitions, and their assignment to specific features of the electronic structure, with the help of modern first-principles band structure calculations. In connection with these achievements we will also review relevant results on the lattice dynamical, dielectric, and transport properties of InSe, as they provided very useful supplementary information on the electronic structure of the material. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessReview A Brief Review of the Effects of Pressure on Wolframite-Type Oxides
Crystals 2018, 8(2), 71; https://doi.org/10.3390/cryst8020071
Received: 8 January 2018 / Revised: 28 January 2018 / Accepted: 29 January 2018 / Published: 31 January 2018
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Abstract
In this article, we review the advances that have been made on the understanding of the high-pressure (HP) structural, vibrational, and electronic properties of wolframite-type oxides since the first works in the early 1990s. Mainly tungstates, which are the best known wolframites, but
[...] Read more.
In this article, we review the advances that have been made on the understanding of the high-pressure (HP) structural, vibrational, and electronic properties of wolframite-type oxides since the first works in the early 1990s. Mainly tungstates, which are the best known wolframites, but also tantalates and niobates, with an isomorphic ambient-pressure wolframite structure, have been included in this review. Apart from estimating the bulk moduli of all known wolframites, the cation–oxygen bond distances and their change with pressure have been correlated with their compressibility. The composition variations of all wolframites have been employed to understand their different structural phase transitions to post-wolframite structures as a response to high pressure. The number of Raman modes and the changes in the band-gap energy have also been analyzed in the basis of these compositional differences. The reviewed results are relevant for both fundamental science and for the development of wolframites as scintillating detectors. The possible next research avenues of wolframites under compression have also been evaluated. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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