STRUCTURAL PHASE-TRANSITION OF BARU2 3 M(1/3)O(3)(M=CA,CD, AND SR) STUDIED BY IN-117([-CD-117) TIME-DIFFERENTIAL PERTURBED-ANGULAR-CORRELATION/

Electric held gradients at In-117(<-- Cd-117) nuclei in BaRu2/3(M(0.97 ) Cd-116(0.03))(1/3) O-3 (M = Ca, Cd, and Sr) were measured in the tem perature range between 4 and 773 K by time-differential perturbed-angu lar-correlation of the 90-345 keV cascade gamma-rays. For each oxide, the quadrupole interaction frequency markedly increases below a specif ic temperature; the temperatures are between 4 and 77 K for M = Ca, an d about 300 and 600 K for M = Cd and Sr, respectively. Combined with t he results of the X-ray powder diffraction measurements, it is conclud ed that a hexagonal-monoclinic structural phase transition, associated with a deformation of MO(6) octahedra, takes place at the temperature .