Structure type of hexagonal tantalum bronzes with variable composition K6Ta6+ZO15F6(F, O)y: Ta(5-δ) bronzes and Ta5+ compounds

The structure type of hexagonal compounds with the variable composition K6Ta6+zO15F6(F, O)(y), where Z less than or equal to 1 and y less than or equal to 3 (sp. or. P6/m, a similar to 13.12 Angstrom, c similar to 3.86 Angstrom) has been studied. Based on the structural data for a crystal of the Ta5+-containing compound and two crystals of Ta(5-delta)+-containing bronzes formed at the cathode during electrolysis of salt melts containing Ta+ cations, it was established that the bronze formation is associated with the interstitial defects of intercalated Ta cations. The scheme of reduction of Ta cations at the cathode is suggested, and the formulas of the compounds are obtained with due regard for partial Ta reduction to various intearal oxidation deorees. The crystals of the colorless transparent Ta 5+-containing compound of the composition K6Ta6.275+O15F7.4, brown semitransparent partly reduced Ta+-containing bronze of the composition K6Ta6.335+Ta0.55+O15F8.2, and dark gray metal-like completely reduced Ta+-containing bronze of the composition K6Ta65+Ta+O15F7 are studied experimentally. (C) 2004 MAIK "Nauka/Interperiodica".