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.Facultad de Ciencias Exactas