Synthesis, structure and thermal stability of tellurium oxides and oxide sulfate formed from reactions in refluxing sulfuric acid

Abstract

Reactions between Te, TeO₂, TeCl₄, TeO₃ or H₆TeO₆ and 30–95 wt% H₂SO₄ were studied at temperatures up to the boiling point of the acid. Depending on the tellurium-containing reactant, H₂SO₄ concentration and synthesis temperature, Te₂O₃(SO₄), TeO₃ or TeO₃·xH₂O (x = 1.37–1.58) is obtained as the final product (alone or in admixture). The reaction products as well as thermally decomposed and/or crystallized/recrystallized products of these are characterized by powder X-ray diffraction and thermoanalytical techniques. The findings obtained by syntheses with, and thermal decompositions of, H₆TeO₆ concern three crystalline [TeO₃ (I), TeO₃ (II) and TeO₃ (III) in the present notations] and one amorphous modification of TeO₃, an amorphous modification of H₂TeO₄, one crystalline and one amorphous modification of TeO₃·xH₂O (x = 1.37–1.58) and two crystalline (one with somewhat more uncertain composition) and one amorphous modification of Te₂O₅. The crystal structures of TeO₃ (I) and Te₂O₃(SO₄) have been redetermined by Rietveld refinements of powder X-ray and neutron diffraction data, respectively.