Pressure Dependence Of Lattice Constants Research Articles

Influence of Temperature and Pressure on the Lattice Constant of SrTiO3 Perovskite by the Statistical Moment Method with Improved Interatomic Potential

Temperature and pressure dependence of lattice constants of a cubic Strontium Titanate (SrTiO3) has been investigated using the statistical moment method. The lattice constants at various temperatures is derived in closed analytic form by including the anharmonic effects of the lattice vibrations explicitly. The potential with the partial charge model and Morse function is used. The numerical lattice constants at high temperatures by the statistical moment method are in good and reasonable agreement with the other theories and the experimental data. Variations of the lattice parameter of SrTiO3 with the temperature are obtained at 1 atm, 8.2 GPa, and 15.2 GPa. Increasing of the lattice constants with increasing temperature is due to enhancing atomic anharmonic fluctuations in SrTiO3 lattice crystal at higher temperature. A decrease of the lattice constants with increasing pressure can be demonstrated by the reduction of atomic vibrations in SrTiO3 crystal lattice at higher pressures.

Crystal Growth and Investigation of High-Pressure Physical Properties of Fe2As

We reported the growth of Fe2As single crystals and the study of its physical properties via comprehensive measurements, such as transport properties under pressure and high-pressure synchrotron radiation X-ray diffraction. Fe2As is an antiferromagnetic metal with TN ~ 355 K. Within the pressure range of 100 GPa, no superconductivity was observed above 2 K. The abrupt drop in resistance from 21 to 31.7 GPa suggests a high-pressure phase transition happens. The high-pressure X-ray experiments indicate a new high-pressure phase appears, starting from 27.13 GPa. After the refinement of the high-pressure X-ray data, the pressure dependence of lattice constants of Fe2As (P4/nmm phase) was plotted and the bulk modulus B0 was obtained to be 168.6 GPa.

Pseudopotential study of wide band-gap GaN at high pressures

A pseudopotential approach is used to study the lattice and elastic properties of the wide band-gap GaN at zero and high pressures up to 120 kbar. When the pressure is 0 kbar, our findings are generally in agreement with the data reported in the literature. The pressure dependence of lattice constant, polarity, transverse effective charge, elastic constants and their related mechanical parameters, and microhardness has been examined and discussed. Our results show that all these features exhibit a monotonic behaviour against pressure. Upon compression up to 120 kbar, our results suggest that the material in question remains mechanically stable with higher stiffness, becomes more resistant to the deformations or deflections and its chemical bond and rigidity become stronger.

Anisotropic lattice compression of α- and β-CePdZn

The lattice constants of ZrNiAl type α-CePdZn and TiNiSi type β-CePdZn were measured at high pressure up to 14GPa at room temperature using X-ray diffraction (XRD) and a diamond anvil cell. The pressure dependence of lattice constants and volume of α-CePdZn were found to be smooth without any discontinuity, and having a bulk modulus, B0, and its pressure derivative, B0′, of 67GPa and 5.1, respectively. On the other hand, the a and b axes as well as volume of β-CePdZn were found to show anomalous pressure dependence at around 8GPa. B0 and B0′ of β-CePdZn were 90GPa and 2.1, respectively. These results suggest that a crossover in the electronic states is induced by applying pressure to β-CePdZn. The origins of these anomalous behaviors are discussed in connection with crossover and change in the topology of Fermi surface.

Sudden reversal in the pressure dependence ofTcin the iron-based superconductor CsFe2As2: A possible link between inelastic scattering and pairing symmetry

We report a sudden reversal in the pressure dependence of Tc in the iron-based superconductor CsFe2As2, similar to that discovered recently in KFe2As2 [Tafti et al., Nat. Phys. 9, 349 (2013)]. As in KFe2As2, we observe no change in the Hall coefficient at the zero temperature limit, again ruling out a Lifshitz transition across the critical pressure Pc. We interpret the Tc reversal in the two materials as a phase transition from one pairing state to another, tuned by pressure, and investigate what parameters control this transition. Comparing samples of different residual resistivity, we find that a 6-fold increase in impurity scattering does not shift Pc. From a study of X-ray diffraction on KFe2As2 under pressure, we report the pressure dependence of lattice constants and As-Fe-As bond angle. The pressure dependence of these lattice parameters suggests that Pc should be significantly higher in CsFe2As2 than in KFe2As2, but we find on the contrary that Pc is lower in CsFe2As2. Resistivity measurements under pressure reveal a change of regime across Pc, suggesting a possible link between inelastic scattering and pairing symmetry.

Investigation of the EXAFS Cumulants of Silicon and Germanium Semiconductors by Statistical Moment Method: Pressure Dependence

Pressure dependence of Extended X-ray Absorption Fine Structure (EXAFS) cumulants of silicon and germanium have been investigated using the statistical moment method (SMM). Analytical expressions of the first and second cumulants of silicon and germanium have been derived. The equations of states for silicon and germanium semiconductors have been also obtained using which the pressure dependence of lattice constants and volume of these semiconductors have been estimated. Numerical results using the developed theories for these semiconductors are found to be in good and reasonable agreement with those of the other theories and with experiment.

Theoretical Study of Structures of Solid Oxygen under High Pressure

The structure of solid oxygen under high pressure is studied up to 6 GPa with no empirical parameters. The potential of the crystal is described by superposition of O 2 pair potentials calculated by the ab initio method. Structural optimization is achieved with this potential energy surface. The monoclinic structure is stable up to 6 GPa and a monoclinic-orthorhombic structural transition is not found. The pressure dependence of lattice constants agrees with the result of recent X-ray diffraction experiments.

High-pressure study of antiferromagnetic order in CePd 2(Al,Ga) 3

The pressure effects on the antiferromagnetic order in CePd 2(Al 1- x Ga x ) 3 for x = 0.01 and 0.05 has been studied by specific heat measurements under pressure. It was found that antiferromagnetic order temperature T N increased initially with increasing pressure, then passed through a maximum and decreased at higher pressures. The pressure P max, which gives rise to the maximum T N, increased with the increase of Ga content. For x = 0.01, P max equals 1.0 GPa, while for x = 0.05, P max is 1.2 GPa. These results have been discussed in terms of the variation of the exchange coupling between the 4f and conduction electrons estimated from the pressure dependence of lattice constants. An interpretation has been given on the basis of Doniach phase diagram. This interpretation also indicates that the hybridization of the p electrons with 4f electrons played an important part in determining the antiferromagnetic order in the CePd 2Al 3 compound.

Pressure dependence of the lattice constant of diamond: Isotopic effects

The pressure dependence of lattice constants of 13C-enriched diamond and diamond of natural isotopic composition have been studied by using x-ray synchrotron radiation and the imaging plate technique. The compression curves reveal features which indicate an inversion of the isotope effect at high pressure.

Anomalous behavior of the pressure dependence of lattice constants in Tl 2Ba 2CuO 6+x

The crystal structure of Tl 2Ba 2CuO 6+ x has been investigated as a function of pressure and temperature under hydrostatic conditions using neutron powder diffraction. The crystal structure at 0.609 GPa and 60 K depends systematically on the path in pressure-temperature space by which these conditions are achieved. Applying pressure at room temperature and then cooling produces different changes in the structure than cooling first and then applying pressure. Our results support those of Sieburger and Schilling [1] who reported that the T c at high pressure for this compound depends markedly on whether the sample is pressurized at room temperature or low temperature. We speculate that this unusual behavior may be associated with differences in the mobility of interstitial oxygen defects between room temperature and 60 K and that applying pressure at room temperature changes the state of the sample through such processes as defect ordering, while changing the pressure at low temperature does not.

Effects of Initial Strains on the Pressure Dependence of Lattice Constants on Some Iron Group Metals and Alloys

The pressure dependence of the lattice constant was observed up to about 30 kbar with a solid pressure-medium using the powder X-ray diffraction method for some Ni- and Fe- based alloys. An anomalous behavior, a bulge, in the lattice constant versus pressure curve was observed in the low pressure region for every specimen with initial internal strains and the bulge vanished with annealing of the specimen. The bulge was observed when the specimen in the ferromagnetic state with nonzero magnetostriction constants had an initial strain before pressurization. A nonhydrostatic component of pressure inherent in the solid pressure medium also seems to play an important role in the appearance of the bulge.