Search results for "Pressure coefficient"
showing 5 items of 15 documents
High-pressure electronic structure and phase transitions in monoclinic InSe: X-ray diffraction, Raman spectroscopy, and density functional theory
2008
We have studied the crystal and electronic structure of monoclinic (MC) InSe under pressure finding a reversible phase transition to a ${\mathrm{Hg}}_{2}{\mathrm{Cl}}_{2}$-like tetragonal phase. The pressure evolution of the crystal structure was investigated by angle-dispersive x-ray diffraction and Raman spectroscopy in a diamond-anvil cell up to $30\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. From the diffraction experiments, we deduced that MC InSe becomes gradually more symmetric under pressure, transforming the crystal structure into a tetragonal one at $19.4\ifmmode\pm\else\textpm\fi{}0.5\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. This phase transition occurs without any volume change. Ra…
The effect of quantum size confinement on the optical properties of PbSe nanocrystals as a function of temperature and hydrostatic pressure
2013
A study based on photoluminescence and absorption measurements as a function of temperature and pressure for PbSe nanocrystals with sizes in the range 3–13 nm reveals the influence of size quantum confinement on the observed variation. In the case of the temperature variation, the effective bandgap changes from showing a positive rate of change to showing a negative one (for a quantum dot 3 nm in diameter), which can be accounted for by incorporating a linear variation of the carrier effective masses into a simple calculation of the exciton ground state in the quantum dot. In the case of the pressure variation, we observe a clear inverse correlation between the absolute value of the pressur…
Temperature and pressure dependence of the optical absorption in hexagonal MnTe
2000
The absorption edge of hexagonal (NiAs structure) antiferromagnetic MnTe has been measured by means of light transmission experiments carried out at different temperatures in the range 16--420 K $(P=1\mathrm{bar})$ and hydrostatic pressures up to 9 GPa $(T=295\mathrm{K}).$ An indirect band gap has been found, in agreement with previous band-structure calculations, with an energy of ${E}_{\mathrm{ig}}=1.272\ifmmode\pm\else\textpm\fi{}0.013\mathrm{eV}$ at room temperature and pressure. The temperature dependence of the absorption edge is linear above the N\'eel temperature ${T}_{N}=310\mathrm{K},$ with a temperature coefficient $dE/dT=\ensuremath{-}(3.5\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode…
Effects of pressure and temperature on the dielectric constant of GaS, GaSe, and InSe: Role of the electronic contribution
1999
In this work we report on direct measurements of the temperature and pressure dependences of the low-frequency dielectric constant along c axis $({\ensuremath{\varepsilon}}_{\ensuremath{\parallel}})$ of GaS, GaSe, and InSe. The temperature dependence of both the ordinary and extraordinary refractive indexes is also presented. A large increase of ${\ensuremath{\varepsilon}}_{\ensuremath{\parallel}}$ under pressure has been observed. In the framework of a rigid ion model, the lattice contribution to ${\ensuremath{\varepsilon}}_{\ensuremath{\parallel}}$ is shown to increase slightly under pressure, due to the change of the angle between the anion-cation bond and the layer plane. Consequently, …
New high-pressure phase and equation of state of Ce2Zr2O8
2012
In this paper we report a new high-pressure rhombohedral phase of Ce2Zr2O8 observed from high-pressure angle-dispersive x-ray diffraction and Raman spectroscopy studies up to nearly 12 GPa. The ambient-pressure cubic phase of Ce2Zr2O8 transforms to a rhombohedral structure beyond 5 GPa with a feeble distortion in the lattice. Pressure evolution of unit-cell volume showed a change in compressibility above 5 GPa. The unit-cell parameters of the high-pressure rhombohedral phase at 12.1 GPa are ah = 14.6791(3) {\AA}, ch = 17.9421(5) {\AA}, V = 3348.1(1) {\AA}3. The structure relation between the parent cubic (P2_13) and rhombohedral (P3_2) phases were obtained by group-subgroup relations. All t…