排序方式: 共有38条查询结果,搜索用时 15 毫秒
1.
S. Meenakshi B.K. Godwal I. Orgzall S. Tkachev 《Journal of Physics and Chemistry of Solids》2006,67(8):1660-1667
We report the results of an X-ray diffraction study of CdAl2Se4 and of Raman studies of HgAl2Se4 and ZnAl2Se4 at room temperature, and of CdAl2S4 and CdAl2Se4 at 80 K at high pressure. The ambient pressure phase of CdAl2Se4 is stable up to a pressure of 9.1 GPa above which a phase transition to a disordered rock salt phase is observed. A fit of the volume pressure data to a Birch-Murnaghan type equation of state yields a bulk modulus of 52.1 GPa. The relative volume change at the phase transition at ∼9 GPa is about 10%. The analysis of the Raman data of HgAl2Se4 and ZnAl2Se4 reveals a general trend observed for different defect chalcopyrite materials. The line widths of the Raman peaks change at intermediate pressures between 4 and 6 GPa as an indication of the pressure induced two stage order-disorder transition observed in these materials. In addition, we include results of a low temperature Raman study of CdAl2S4 and CdAl2Se4, which shows a very weak temperature dependence of the Raman-active phonon modes. 相似文献
2.
3.
B K Godwal 《Pramana》1982,19(3):225-229
The method of first principle pseudopotential is used to simulate the volume variation of nuclear Grüneisen parameter. The
elements Al and Be, for which Neal’s experimental data exist are investigated. The nuclear Grüneisen obtained from the details
of phonon frequencies are in better agreement with the experimental data as compared to those obtained from approximate Slater
and Dugdale-MacDonald methods, often used in shock wave studies. 相似文献
4.
5.
Results of ab initio electronic structure calculations on the compound MgB2 using the FPLAPW method employing GGA for the exchange-correlation energy are presented. Total energy minimization enables
us to estimate the equilibrium volume, c/a ratio and the bulk modulus, all of which are in excellent agreement with experiment. We obtain the mass enhancement parameter
by using our calculated D (E
F) and the experimental specific heat data. The T
c is found to be 24.7 K. 相似文献
6.
Saha’s ionization equation has been solved for highZ elements with the aim of providing input for opacity calculations. Results are presented for two elements, tungsten and uranium.
The ionization potentials have been evaluated using the simple Bohr’s formula with suitable effective charges for ions. The
reliability of the free electron density, ion concentrations, etc., obtained from the Saha’s equation solutions has been checked
by comparing theP
T andE
T computed from them with those given by the Thomas-Fermi-Dirac equation of state. The agreement between the two is good from
temperatures above 0.2 keV. 相似文献
7.
We report the results of electrical resistance measurements at high pressures on Cs2MoS4 and KTbP2Se6. The results of high pressure X-ray diffraction study of Cs2MoS4 are also presented. Interestingly, in the case of Cs2MoS4 the resistance vs. pressure follows the behavior of the absorption edge vs. pressure obtained from our optical measurements lending further support to a direct-indirect band crossing. In the case of KTbP2Se6,the phase transition at about 9.2 GPa is reflected in a sharp drop of the resistance. In addition we report the pressure dependence of the lattice constants as well as the equation of state of Cs2MoS4. 相似文献
8.
The ambient structural details and the results of room temperature high pressure angle dispersive X-ray diffraction and electrical resistance measurements on the quasi-one-dimensional sulfide, InV6S8, to a pressure of 25 GPa are reported. The material does not undergo a phase transition in this pressure range, though an anomaly in the c/a ratio has been observed around 10 Gpa. A fit of the Murnaghan equation of state to the V/V0 versus pressure data, with the value of the derivative of B0 with respect to pressure, B′0, fixed at 4 has yielded a value of the bulk modulus, B0, of 110 GPa. We also present data of the pressure dependence of the lattice constants, a and c, the ratio c/a, and the resistance at room temperature. 相似文献
9.
10.
Alka B. Garg A.K. Verma R.S. Rao B.K. Godwal 《Journal of Physics and Chemistry of Solids》2007,68(3):367-372
Results of X-ray diffraction, electrical resistance, thermoelectric power measurements and electronic band structure calculations on NiSi2 under high pressure are reported. The thermoelectric power (TEP) changes sign near 0.5 GPa (from +30 to −20 μV/K). As the pressure is increased, the value of TEP increases further in magnitude and near 7 GPa it becomes −50 μV/K. The pressure vs. resistance curve measured up to 30 GPa using diamond anvil (DAC)-based technique exhibits a broad hump near 12 GPa and exhibits hysteresis on pressure release. The ADXRD patterns up to 42 GPa show a gradual irreversible loss of long-range order in NiSi2 with the diffraction lines progressively broadening under pressure. The FWHM of the diffraction lines show a rapid increase in the half-widths close to 0.5 GPa and also near 12 GPa. The computed band structure at a compression (without any disorder) corresponding to 12 GPa, exhibits an electronic topological transition (ETT). The rapid increase in disorder above 12 GPa implies that the ETT may be facilitating the structural disorder. It is suggested that the pressure drives the material through a region of entropic and energetic barriers and induces disorder in the material. 相似文献