Electric field gradients at the In-111 site in the ferroelectric and paraelectric phases of LiTaO3

The temperature dependence of the electric-field gradient of Cd-111 in sing le crystalline LiTaO3 was studied from room temperature to 1040 K in the fe rroelectric and paraelectric phases. The data taken at room temperature sho w unambiguously the presence of two quadrupole interaction frequencies, nu( Q1) =230 MHz and nu(Q2) =242 MHz, with nonzero asymmetry parameters, while above the Curie temperature (T-C = 878 K) the data are well described by a unique frequency. The electric field gradient shows a usual temperature dep endence, increasing approximately in a linear fashion until T-C and then de creasing faster. The initial increase is explained mostly by the lattice ex pansion, while above T-C it is necessary to consider Li and O displacements .