Low temperature acoustic characterization of PMN single crystal

This acoustic study of the relaxor single crystal PbMg1/3Nb2/3O3 is focused on the temperature evolution of longitudinal and shear ultrasonic wave velocities as well as on their attenuation within the temperature range of 4.2–300 K. Temperature dependences of all three independent elastic constants for the cubic structure (C11, C44, and C12) along with the bulk modulus B, the Cauchy ratio, and the degree of lattice anisotropy were derived from the velocity data set. Important parameters such as the Debye temperature, the Gruneisen parameter H, and the Poisson ratio were determined at cryogenic temperatures as well. Deep minima were found for C11 and C44 around the temperature Tm where the dielectric constant reaches a maximum, followed by a drastic increase of C11 and C44 at decreasing temperature and ultimately by a saturation at temperatures below 25 K. The behavior of these constants at T < Tm corresponds well to relations resulting from the Einstein-oscillator model. A changeover of C12(T) dependence ...