ELASTIC STIFFNESS CONSTANTS OF COPPER INDIUM DISELENIDE DETERMINED BY NEUTRON-SCATTERING

From the acoustic-dispersion curves determined by inelastic neutron scattering, we obtain at room temperature the elastic stiffness constants of CuInSe2: at 10(10) Nm-1, c11 = 9.70, c12 = 5.97, c13 = 8.60, c33 = 10. 89, and c44 = 3.62. A theoretical calculation based upon the sphalerite approximation gives good agreement with the values of c11 and c44. Using the elastic constants, the isothermal compressibility is calculated along the c axis and the ab plane. Two low-energy optical modes were also observed at frequencies near 55 cm-1 at the Brillouin-zone center.