TDPAC characterization of Ni<SUB>2</SUB>HfF<SUB>8</SUB>·12H<SUB>2</SUB>O and its decomposition products

• Autores: Ceolín, Marcelo Raúl; Taylor, Marcela Andrea; Rivas, Patricia Claudia; Martínez, Jorge Alberto; Caracoche, María Cristina; Saitovitch, H.
• Año de publicación: 1990
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Física
• Institución: Universidad Nacional de La Plata

The hyperfine interaction in Ni2HfF8·12H2O has been determined between 77 K and 1100 K by means of the time-differential perturbed angular correlation technique. From 200 K on, the one-site phase existing at lower temperatures undergoes a gradual phase transition until, at room temperature, the populations of both phases attain a 2:1 ratio. While the quadrupole frequencies characterizing them exhibit aT; 3/2 thermal dependence, their population ratio seems to obey a Boltzmann distribution. At 350 K, when the η-value of the high temperature phase electric field gradient approaches its maximum value, the starting compound decomposes to NiHfF6·6H2O. A kinetics study of the Ni2HfF8·12H2O recovery at room temperature seems to indicate that a tri-dimensional diffusion mechanism is responsible for the corresponding reaction process. The first decomposition product of NiHfF6·6H2O left to atmospheric pressure is found to be NiHfF6·4H2O at 368 K and, between 414 K and 590 K, the high temperature cubic phase of NiHfF6 and Hf2OF6 can be simultaneously observed. Finally, monoclinic HfO2 appears from 1020 K on, having been preceded by an interaction which can be though of as depicting a preliminary stage in hafnia formation.
Facultad de Ciencias Exactas