Articulo
TDPAC characterization of Ni<SUB>2</SUB>HfF<SUB>8</SUB>·12H<SUB>2</SUB>O and its decomposition products
Registro en:
issn:0304-3843
issn:1572-9540
Autor
Ceolín, Marcelo Raúl
Taylor, Marcela Andrea
Rivas, Patricia Claudia
Martínez, Jorge Alberto
Caracoche, María Cristina
Saitovitch, H.
Institución
Resumen
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