Low-Temperature Synthesis of Tungsten Silicates with Pyrochlore and Tungsten Bronze Structure

Polyoxotungstosilicates with the general formulas Cat₄[SiW₁₂O₄₀] · mH₂O and Cat₆[SiW₁₁O₃₉Ni(H₂O)] · nH₂O were synthesized, where Cat = Rb⁺, Cs⁺, (CH₃)₄N⁺. By means of IR spectroscopy and x-ray diffraction analysis, it was shown that the compounds have the Keggin anion structure. The thermolysis of the obtained compounds within the temperature range of 600 – 800°C resulted in the formation of previously unknown pyrochlore-structure phases Rb_12/13Si_2/13W_22/13Ni_2/13O₆ and Cs_12/13Si_2/13W_22/13Ni_2/13O₆ with the with the unit cell parameters a of 10.284 and 10.309 Å, as well as phases with tungsten bronze structure Rb_12/20Si_3/20W_36/20O₆ and Si_3/38W_36/38O₃. The synthesis of tungsten silicates with pyrochlore and tungsten bronze structure through thermolysis of polyoxotungstosilicates reduces the temperature of their preparation to 600 – 650°C and heating time to 1 h, thus extending the ranges of chemical compositions and their morphological diversity.