Electric-field gradients at 181Ta sites in HfOx

G. N. DARRIBA; A. M. RODRIGUEZ; H. SAITOVITCH; P. R. J. SILVA; A. F. PASQUEVICH

La Plata, Argentina

Workshop; International Workshop 35th Anniversary of Hiperfine Interactions at La Plata; 2005

In the present work we report preliminary results about characterization and properties of the order-disorder transition in HfOx solid solutions via the determination of the Electric Field Gradient (EFG) at 181Ta radioactive probes. Oxygen solution into the metal was achieved by arc melting stoichiometric amounts of metallic Hf and HfO2 in argon atmosphere. Samples of HfOx with x = 0.1 and x = 0.2 were prepared. Two types of samples were used for the Perturbed Angular Correlation (PAC) experiments by doping alternatively with 181Ta, by neutron irradiation, the metallic Hf or the hafnium oxide. The PAC results on both samples were identical, disappearing both the hyperfine signal of the metal and the oxide showing a complete diffusion of the probes independently of the way of doping. The PAC signal of the HfOx solid solution consisted in a wide distribution of EFG’s probably due to the oxygen disorder. This scheme held even after long thermal treatments at high temperature (several days at 1273K). Moderate temperature (600K) treatments cooling samples at a very low rate, were also made. The experimental results are confronted with those arising from simple computer simulations.