Evolution des tenseurs de dilatation thermique en fonction de la température. III. Etude expérimentale des oxydes PbO1,57, PbWO4, V2O5 et V2O3 et analyse des résultats

The evolution of thermal expansion tensor versus temperature has been measured by powder X-ray diffraction for PbO_1,57 (in the range 77–636°K), PbWO₄ (95–800°K), V₂O₅ (77–773°K) and V₂O₃ (77–600°K). Tensor anisotropy is explained considering structure and chemical bonds (V₂O₅, PbWO₄). We verified that the evolution of anisotropy (measured by aspherism index) is much different, according to whether the oxide presents a continuous phase transition (V₂O₃) or not (PbO_1,57, PbWO₄, V₂O₅).