Elastic Constants and Thermal Expansion of Cation Disordered Perovskites

The elastic constants of the cation disordered perovskites Pb(Mg1/3Nb2/3)O3, Pb(Zn1/3Nb2/3)O3 and (K3/4Bi1/4)(Zn1/6Nb5/6)O3 have been measured by the ultrasonic pulse superposition method, and the thermal expansion of (K3/4Bi1/4)(Zn1/6Nb5/6)O3 has been determined from 300 K to 800 K by X-ray powder diffraction. Both the elastic stiffness and the thermal expansion coefficients of cation disordered perovskites are somewhat smaller than those of simple perovskites. Consistent with previously reported electrostrictive and dielectric properties, the results can be explained by an intuitive ion “rattling” space model.