Search results for " GAP"
showing 10 items of 811 documents
Topological analysis of chemical bonding in the layered FePSe3 upon pressure-induced phase transitions
2020
The authors acknowledge the assistance of the University Computer Center of Saint-Petersburg State University in the accomplishment of high-performance computations. A.K. is grateful to the Latvian Council of Science project no. lzp-2018/2-0353 for financial support. Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2.
Investigation of conduction-band structure, electron-scattering mechanisms, and phase transitions in indium selenide by means of transport measuremen…
1996
In this work we report on Hall effect, resistivity and thermopower measurements in n-type indium selenide at room temperature under either hydrostatic and quasi-hydrostatic pressure. Up to 40 kbar (= 4 GPa), the decrease of carrier concentration as the pressure increases is explained through the existence of a subsidiary minimum in the conduction band. This minimum shifts towards lower energies under pressure, with a pressure coefficient of about -105 meV/GPa, and its related impurity level traps electrons as it reaches the band gap and approaches the Fermi level. The pressure value at which the electron trapping starts is shown to depend on the electron concentration at ambient pressure an…
Experimental and Theoretical Study of Bi2O2Se Under Compression
2018
[EN] We report a joint experimental and theoretical study of the structural, vibrational, elastic, optical, and electronic properties of the layered high-mobility semiconductor Bi2O2Se at high pressure. A good agreement between experiments and ab initio calculations is observed for the equation of state, the pressure coefficients of the Raman-active modes and the bandgap of the material. In particular, a detailed description of the vibrational properties is provided. Unlike other Sillen-type compounds which undergo a tetragonal to collapsed tetragonal pressure-induced phase transition at relatively low pressures, Bi2O2Se shows a remarkable structural stability up to 30 GPa; however, our res…
Phase transition of tetragonal copper sulfide Cu2S at low temperatures
2017
The low-temperature behavior of tetragonal copper sulfide, ${\mathrm{Cu}}_{2}\mathrm{S}$, was investigated by powder and single-crystal x-ray diffraction, calorimetry, electrical resistance measurements, and ambient temperature optical absorption spectroscopy. The experiments were complemented by density-functional-theory-based calculations. High-quality, polycrystalline samples and single crystals of tetragonal copper sulfide were synthesized at 5 GPa and 700 K in a large volume multianvil press. Tetragonal ${\mathrm{Cu}}_{2}\mathrm{S}$ undergoes a temperature-induced phase transition to an orthorhombic structure at around 202 K with a hysteresis of $\ifmmode\pm\else\textpm\fi{}21$ K, an e…
ScVO4 under non-hydrostatic compression:a new metastable polymorph
2016
Ustedes se ocupan e ver si se puede hacer de acceso público. Podria buscra el preprint al ser algo reciente. Se estudia el comportamiento bajo alta presión del vanadato de scandio, ScVO4, bajo compresión no hidrostática. El estudio se realiza mediante difracción de rayos X en polvo usando radiación sincrotrón. Se detecta una transición no reversible desde la fase zircon a la fase fergusonita alrededor de 6 GPa con una discontinuidad en el volumen de un 10%. La fase fergusonota se puede recuperar como metaestable confirmandose mediante XRD. Las simulaciones ab intio confirman los resultados experimentales. Las propiedades ópticas y la propiedades vibracionales de la fase fergusonita son disc…
Monazite-type SrCrO4 under compression
2016
We report a high-pressure study of monoclinic monazite-type SrCrO4 up to 26 GPa. Therein we combined x-ray diffraction, Raman and optical-absorption measurements with ab initio calculations, to find a pressure-induced structural phase transition of SrCrO4 near 8-9 GPa. Evidence of a second phase transition was observed at 10-13 GPa. The crystal structures of the high-pressure phases were assigned to the tetragonal scheelite-type and monoclinic AgMnO4-type structures. Both transitions produce drastic changes in the electronic band gap and phonon spectrum of SrCrO4. We determined the pressure evolution of the band gap for the low-pressure and high-pressure phases as well as the frequencies an…
Optical and structural study of the pressure-induced phase transition of CdWO$_4$
2017
Physical review / B 95(17), 174105 (2017). doi:10.1103/PhysRevB.95.174105
Putting the Squeeze on Lead Chromate Nanorods.
2019
We have studied by means of X-ray diffraction and Raman spectroscopy the high-pressure behavior of PbCrO4 nanorods. We have found that these nanorods follow a distinctive structural sequence that differs from that of bulk PbCrO4. In particular, a phase transition from a monoclinic monazite-type PbCrO4 to a novel monoclinic AgMnO4-type polymorph has been discovered at 8.5 GPa. The crystal structure, Raman-active phonons, and compressibility of this novel high-pressure phase are reported for the first time. The experimental findings are supported by ab initio calculations that provide information not only on structural and vibrational properties of AgMnO4-type PbCrO4 but also on the electroni…
High-pressure behavior ofCaMoO4
2017
We report a high-pressure study of tetragonal scheelite-type $\mathrm{CaMo}{\mathrm{O}}_{4}$ up to 29 GPa. In order to characterize its high-pressure behavior, we have combined Raman and optical-absorption measurements with density functional theory calculations. We have found evidence of a pressure-induced phase transition near 15 GPa. Experiments and calculations agree in assigning the high-pressure phase to a monoclinic fergusonite-type structure. The reported results are consistent with previous powder x-ray-diffraction experiments, but are in contradiction with the conclusions obtained from earlier Raman measurements, which support the existence of more than one phase transition in the…
Spectroscopic ellipsometry applied to phase transitions in solids: possibilities and limitations
2009
The possibilities of in situ spectroscopic ellipsometry applied to phase transitions investigation in oxide thin films and crystals are examined in this work, along with the use of various parameters calculated from ellipsometric data (band gap energy Eg, refractive index n and surface roughness) together with the directly measured main ellipsometric angles psi and Delta, for the detection of phase transitions. The efficiency of spectroscopic ellipsometry on "surface" phase transition and its sensitivity to surface defects are also demonstrated.