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

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. xH(2)O (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. xH(2)O (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.