Bond compressibility and bond Grüneisen parameters of CdTe

Abstract

Extended x-ray absorption fine structure (EXAFS) at the Cd K edge and diffraction patterns have been measured on CdTe as a function of pressure from 100 kPa (1 bar) to 5 GPa using a cell with nano-polycrystalline diamond anvils and an x-ray focussing scanning spectrometer. Three phases-zincblende (ZB), mixed cinnabar-ZB and rocksalt (RS)-are well distinguished in different pressure intervals. The bond compressibility measured by EXAFS in the ZB phase is slightly smaller than the one measured by diffraction and decreases significantly faster when the pressure increases; the difference is attributed to the effect of relative vibrations perpendicular to the Cd-Te bond. The parallel mean square relative displacement (MSRD) decreases, the perpendicular MSRD increases when the pressure increases, leading to an increasing anisotropy of relative atomic vibrations. A constant-temperature bond Grüneisen parameter (GP) has been evaluated for the ZB phase and compared with the constant-pressure bond GP measured in a previous experiment; an attempt is made to connect the bond GPs measured by EXAFS and the more familiar thermodynamic GP and mode GPs; the comparisons suggest the inadequacy of the quasi-harmonic approximation to deal with the local vibrational properties sampled by EXAFS.

Atomic Structure and Lattice Dynamics of CoSb3 Skutterudite-Based Thermoelectrics

“…Such a kind of phenomenon cannot be evaluated by long-range Bragg scattering-based techniques, as the case of X-ray and neutron diffraction. Instead, EXAFS can also probe structural and vibrational disorders of individual pair-bonds, being capable of distinguishing an anharmonic contribution as a function of pressure 30 and temperature. 31 Indeed, XAS was already used to characterize the local features of skutterudites, such as the case of RFe 4 Sb 12 (R = K, Na, Ca, Sr, and Ba), 32 LT 4 X 12 (L = Ce, Eu, Yb; T = Fe, Ru; X = P, Sb), 33 and Ba x In y Co 4 Sb 12 , 34 with success.…”

Metallic bonds and thermal vibration in brass

“…[1][2][3][4][5][6][7][8][9][10] Moreover, temperature dependent EXAFS analysis provides local thermodynamical information on the Debye-Waller factors (mean square relative displacements) and thermal expansion, and a lot of EXAFS works have been performed to develop the EXAFS methodology and clarify interesting structural and thermodynamical properties. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] For instance, in the study on the FeNi Invar alloy, 6 it was found that the interatomic distances and thermal expansion around Fe and Ni are meaningfully different from each other, although the X-ray diffraction looks as if the alloy formed perfect fcc lattice. On the other hand, from the theoretical point of view, the path-integral effective classical potential method (PIECP) [6][7][8][9][28][29][30][31][32][33] is regarded as one of the most appropriate methods to investigate the interatomic distance, the mean square relative displacements, and thermal expansion including the quantum fluctuation, which is essentially important to describe the harmonic and anharmonic thermal properties at low temperature.…”

Temperature-Dependent EXAFS Measurements of the Pb L3-Edge Allow Quantification of the Anharmonicity of the Lead–Halide Bond of Chlorine-Substituted Methylammonium (MA) Lead Triiodide

“…Although there are some publications dealing with the EXAFS edges of the anion, with the work being confined to bromine, we want to limit ourselves to the Pb L3-edge for better comparability. Besides the consideration of the temperature dependence of the EXAFS Debye–Waller factor, the framework of the temperature-dependent EXAFS cumulant analysis developed in the last decades − allows further statements about the properties of the investigated atomic pairs since statements about the anharmonicity can also be made …”