UNIAXIAL-STRESS DEPENDENCE OF THE NUCLEAR-QUADRUPOLE RESONANCE FREQUENCY OF CL-35 IN NACLO3

Measurements of the NQR frequency of the Cl-35 nucleus in single crystals of sodium chlorate were made as a function of isothermal uniaxial stress along the (100), (110) and (111) crystalline directions, in the pressure range 0-4 MPa, at several temperatures around room temperature. A linear and directional behaviour is observed. A model is developed in order to obtain the linear terms of the static and dynamic contributions to the total variation in the electric field gradient (EFG) at the nucleus site. Also an averaged Gruneisen parameter of the rotational modes of CIO3- was estimated; this was found to have a negative value at room temperature. From the results it is inferred that the static and dynamic contributions have the same order of magnitude. The self-energy term due to anharmonicity of the rotational modes was obtained at room temperature. The result is a positive value of the same order of magnitude as the thermal strain contribution.