Neutron diffraction study of asymmetric anharmonic vibration of the copper atom in cuprous chloride

Neutron diffraction measurements of CuCl with the zincblende structure were carried out at room temperature and the results examined on the basis of three possible structure models: (1) harmonic thermal vibration of atoms, (2) asymmetric anharmonic vibrations and (3) statistical disorder arrangement of the copper atom. It was found that the anharmonic model was the most plausible for the structure of CuCl. The final R value in the least-squares analysis was 0.037. The parameters in the effective one-atomic-potential fields for the zincblende structure V_j(r) = V_0j + ½α_j(u²₁ + u²₂ + u²₃) + β_ju₁u₂u₃ + ^{. . .} were obtained as α_Cu = 0.74 ± 0.01, α_C1 = 1.35 ± 0.02 × 10^-12erg Å^-2, and β_Cu = 1.15 ± 0.66, β_C1 = 0.0 ± 1.6 × 10^-12erg Å^-3. It is also shown that the temperature dependence of the Bragg reflexion observed from room temperature to 523°K can be explained very well with the use of the above parameters.