Thermal expansion and anharmonicity of solid Kr studied by extended x-ray-absorption fine structure

Kr K-edge extended x-ray-absorption fine-structure spectra of solid Kr were measured over the temperature range of 24-43 K. The thermal expansion and Debye temperature were obtained by the analysis of the first-, third-, and fourth-nearest-neighbor (NN) Kr-Kr shells. For the third- and fourth-NN shells, the conventional Gaussian-distribution approximation was found to give the proper thermal expansion. On the other hand, for the first-NN shell, the cumulant-expansion analysis including the third-order asymmetry of the distribution function is necessary, although the higher-NN shells are more largely disordered in terms of the mean-square relative displacements. These results were confirmed by the classical Monte Carlo simulations. Effective cancellation of the asymmetric contribution was thus clarified for the higher-NN shells. The quantum-statistical calculations of the first-NN cumulants of Kr clusters were also carried out by varying the cluster size in order to examine the relationship between the pair potential and observed cumulants, and to justify the employed Kr-Kr pair potential.