Pyrochlores. VI. Preparative chemistry of sodium and silver antimonates and related compounds

Abstract

A number of pyrochlore-structure antimonates MSbyOz (M = Na, Ag, K) have been prepared by dry-firing methods. Each M forms a series of compounds which adopt the pyrochlore structure up to a maximum ratio of M:Sb; the ratio depends on M. Antimony in these compounds is usually present simultaneously in trivalent and pentavalent states.The preparation of the above antimonates by wet methods was also examined. The products obtained were found to depend on the pH of the solution. In acid solution a polyantimonate ion exists which on addition of M salts leads to compounds of formula MSb3Oz, while in alkaline solution the Sb(OH)6− ion exists and MSb(OH)6 antimonates are obtained.A previous literature claim that NaSbO3 occurs with the pyrochlore structure has been disproved. It has been shown that NaSbyOz pyrochlore phases exist only for Na:Sb less than 1:1.5.The preparation of antimonates in the presence of Cl− and from hydrated reactants was carried out. It was concluded that neither Cl− nor OH− or H2O play a significant part in causing an antimonate of Na, Ag, or K to adopt the pyrochlore structure.