M. T. Dova

Hyperfine interaction of ZrO2 — Tetragonal phase

The quadrupole hyperfine interaction of the tetragonal phase of the zirconium oxide has been measured at 1523 K using the time-differential perturbed angular correlation technique. The electric field gradient at zirconium sites was determined to beVzz=(17.5±0.4)·1017 Vcm−2 and axially symmetric.

TDPAC study on the thermal stability of zirconium tetrafluoride

The thermal evolution of the hyperfine interaction in α-ZrF4 is investigated between 293 K and 788 K. The first change, observed ay 534 K, is attributed to the appearance of the non-stoichiometric compound ZrO1.3F1.4. During the transformation, the relative fraction of the latter shows an Arrhenius behaviour with an activation energyEa=(22.6±5.5) kJ/mol. At approximately 700 K, ZrO1.3F1.4 gives rise to the monoclinic phase of ZrO2 and to β-ZrF4.

Quadrupole hyperfine interaction and thermal stability of ZrF4.3H2O

The quadrupole hyperfine interaction of ZrF4.3H2O is reported. This compound is observed to dehydrate to ZrF4 at 325 K. Spectra taken on cooling were observed to be time dependent, and the rehydration process involved was investigated at 293, 298 and 302 K. Contrary to what had previously been determined in HfF4.3H2O, no intermediate compound was observed to participate in the reaction investigated, thus confirming structural differences already reported to exist between these isoformulae compounds.

Hyperfine interactions in Li2ZrF6 and Li2HfF6

The quadrupole hyperfine interaction in Li2ZrF6 and Li2HfF6 has been studied as a function of temperature. Both lattices are characterized by very similar low and symmetric electric field gradients at probe sites and no phase transitions were observed up to 770 K. On heating, between 700 and 830 K, the Li2ZrF6 undergoes chemical reactions which give rise to ZrO2 and then to Li3ZrF7 (high temperature α-phase) and Li2ZrO3. On cooling, below 750 K, the α→β transition in Li3 ZrF7 already reported is found to take place. An analogous behaviour is determined for Li2HfF6. Accordingly, the same decomposition steps and exstence of high and low temperature phases for Li3HfF7 can be inferred.