A Challenge To Prepare Perovskite Structure SnTiO₃

Most materials with large electric polarization are based on the perovskitestructure ABO₃, such as PbTiO₃. SnTiO₃with perovskite structure has been predictedas potential environmentally benign ferroelectric material calculated by first principleswithin density functional theory （DFT） in recent years. The ferroelectricity with apolarization in SnTiO₃is at least as high as in PbTiO₃. Full geometry optimizationprovides a stable tetragonal structure relative to cubic one reported by Matar. A largertetragonality leading to a higher polarization and a larger dielectric constant wereidentified. With respect to PZT, it has superior physical properties of the dielectric,ferroelectric, pyroelectric. Up to date, SnTiO₃has been focused on the piezoelectricmaterials as a new environmentally piezoelectric ceramic.Till to now, it is defeated to synthesize SnTiO₃using solid state reactions fromSnO and TiO₂. This is due to the disproportionation reaction of tin（II） oxide SnO totin（IV） oxide （SnO₂） and tin metal （Sn）. Complex oxides containing Sn²⁺have beenreported only for several compounds, for example SnWO₄, SnNb₂O₆and Sn₂TiO₄. So,SnTiO₃may be expected as a metastable phase with positive cohesive energies. It iswell known that the different raw materials can affect the reaction route and chemicalreaction barrier and even the ability to react. In this work, the synthesis explore of theSnTiO₃was carried out by high pressure and high temperature（HPHT）, sol-gel andconventional solid-state reaction with the tin source Sn, SnO, SnO₂, SnCl₂andtitanium source H₂TiO₃, TiO₂as the raw materials.The samples has been synthesized via TiO₂/H₂TiO₃, SnCl₂2H₂O, Sn after3hours sintered under the condition of the pressure of4.8GPa and1073K andcharacterized by XRD powder diffraction. The diffraction peaks of the phase weredifficultly matched to PDF card. And the peak position of a new phase were found at21.62°,29.01°,33.4°,34.8°,37.8°,49.09°,50.96°,59.8°. The new phase containingSn²⁺is weak acid and strong water absorption. This result may be useful to prepare SnTiO₃. Tin monoxide, SnO, is metastable at ambient conditions and it decomposesby a disproportionation reaction with a noticeable rate to Sn and SnO₂above600℃atHPHT. This result is consistent with the reported literature. So it is inappropriate tosynthesize SnTiO₃directly from SnO at HPHT.Monoclinic BiSbO₄is found to be an effective visible light responsivephotocatalyst in the degradation of the organic dye. BiSbO₄has been successfullyprepared by sol-gel method from Sb₂O₃and Bi（NO₃）35H₂O. The pure phase has beensuccessfully obtained above900℃. The grain size,800nm, was observed from thescanning electron microscopy （SEM）. The oxidizing reaction from Bi³⁺inBi（NO₃）35H₂O to Bi5+has been effectively restrained. This result may be helpful toprepare SnTiO₃from Sn²⁺by sol-gel method.The Crystal structure of the ternary oxide Sn₂TiO₄containing Sn²⁺, which isisostructural to Pb₃O₄, is built up by one-dimensional chains of edge-sharing metalcentered octahedra TiO₆along the c-axis and the chains are connected by Sn²⁺havingstereo active lone pair. In our work, we attempted to prepare Sn₂TiO₄by anion-exchanging reaction between potassium titanates synthesized via K₂CO₃and TO₂as starting materials and SnCl₂. The results confirmed that Sn₂TiO₄cannot besynthesized under the condition of low vacuum and the H₂O existed.