Studies of local structure at Zr sites in pressure amorphized zirconium tungstate.

Amorphous to crystalline transition in pressure quenched Zr(0.5)Hf(0.5)W(2)O(8) has been studied with respect to local structures of ZrO(6) using the perturbed angular correlation technique. In an untreated crystalline sample close to 0.7 fraction of the probe atoms occupy Zr sites of regular ZrO(6) while the remaining three fractions are understood to be associated with contracted and distorted octahedra. The existence of six distinct ZrO(6) could be deduced based on perturbed angular correlation studies in the pressure amorphized sample. In the amorphous sample these ZrO(6) are associated with appreciable octahedral distortions. Isochronal annealing measurements show that these octahedra remain structurally quite stable up to 800 K. Values of quadrupole frequencies tend to become close to those experienced by probe atoms in a crystalline sample for annealing at 870 K, implying that around this temperature there is an onset of amorphous to crystalline transition. Complete restoration of quadrupole parameters to those of the untreated crystalline sample is seen subsequent to annealing at 975 K.