Synthesis of Divalent Sn Compounds Under Microwave Non-Equilibrium Reaction Field

Chemical reaction between two or more components under microwave electromagnetic field is essentially "non-equilibrium reaction" because microwave absorbing behavior strongly depends on a nature of a material. Selective heating of a specific component plays a key role on the formation of non-equilibrium structure. The existence of stereoactive lone pair (5s²) is an issue of concern of Sn²⁺ compounds in a view point of ferroelectricity, however, it is difficult to synthesize Sn²⁺ compounds because SnO tends to decompose to metallic Sn and Sn⁴⁺O₂ at elevated temperature. Binary SnO-TiO₂ system is a typical selective heating system under microwave irradiation because SnO strongly absorbs microwaves, but TiO₂ is nearly transparent to microwaves. During microwave irradiation to the powder mixture of SnO and TiO₂, a drastic enhancement of reaction kinetics could be achieved under thermally non-equilibrium condition. This makes it possible to synthesize a non-equilibrium Sn²⁺ compound, Sn₂TiO₄, avoiding the disproportionation reaction of SnO. Optimal synthetic condition to obtain a single-phase Sn²TiO₄ and the comparison with the other external rapid heating system was studied.