Debye-Waller factors of KBr at 4.2 and 295 K

The Debye-Waller factors of KBr have been determined both by X-ray and by neutron diffraction methods. Previous experiments have been carried out at or above room temperature. No such measurements have been reported at 4.2 K. Neutron diffraction experiments on a KBr powder at 295 and 4.2 K are reported here. The experimental results obtained were B_K = 2.55 ± 0.07, B_Br = 2.20 ± 0.04 Ų at T = 295 K, and B_K = 0.43 ± 0.05, B_Br = 0.35 ± 0.02 Ų at 4.2 K. These values differ from the theoretical estimates of Reid & Smith [J. Phys. Chem. Solids (1970), 31, 2689-2697], based on a quasiharmonic approximation using the shell model. The discrepancy may be attributed to the partial neglect of anharmonicity in the theoretical estimates.