A convenient and quantitative route to Sn(iv)–M [M = Ti(iv), Nb(v), Ta(v)] heterobimetallic precursors for dense mixed-metal oxide ceramics

Abstract

The strategy of reacting SnCl₄ with M(OR)_x provided a convenient and quantitative approach to new heterobimetallics with a simple addition formula, [SnCl₄M(OR)_x(HOR)_y] (M = Ti, Nb, Ta; R = Et, Prⁱ, x = 4, 5; y = 0–2) or sometimes an oxo complex [SnCl₃(O)Ti₂(OPrⁱ)₇(HOPrⁱ)₂]. The alcoholysis reactions of these heterometallics afforded mixed alkoxo complexes [SnCl₄(μ-OEt)₂M(PrⁱO)_x(PrⁱOH)_y] [M = Ti (x = y = 2), Nb, Ta (x = 3, y = 1)] under mild conditions, or a planar rectangular oxo product [SnCl₃(μ-OEt)₂Nb(OEt)₂(EtOH)(μ-O)]₂ at refluxing/extended stirring time. DFT calculations shed light on the stability and reactivity of these complexes. The use of these thoroughly characterized heterometallics as sol–gel precursors suppresses the formation of the undesired SnO₂ grains, which are difficult to be sintered to a high density. The combined approach of using bottom-up synthesis of mixed Ti_0.5Sn_0.5O₂ nanoparticles and Spark Plasma Sintering allowed the successful densification of chloride-free mixed-metal oxide ceramics. The influence of thermal treatment before sintering on the density and spinodal decomposition of the TiO₂–SnO₂ pellets is reported.