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.
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