ZnSnO3 or Zn2SnO4/SnO2 Hierarchical Material? Insight into the Formation of ZnSn(OH)6 Derived Oxides

Piezoelectric materials are a class of compounds that is gaining increasing interest in various applications such as energy harvesting. During the last decade, lead-free ZnSnO3 perovskite ceramic has gained attention among the scientific community thanks to its unique symmetry-dependent and spontaneous polarization properties such as piezoelectricity and ferroelectricity. Nevertheless, only a few studies successfully prepared pure ZnSnO3, while most seem to mislead the product for its hydroxide precursor (ZnSn(OH)6) or a mixture of Zn2SnO4 and SnO2. In our work, we investigated the conversion of ZnSn(OH)6 at different temperatures (500, 600, 700, 750 and 800 °C) by X-ray powder diffraction analysis, and in-situ using synchrotron radiation up to 950 °C under ambient atmosphere and in a vacuum, to reproduce conventional reaction conditions. SEM and TEM have been used to understand the evolution of the particle shape and surface structure before and after the thermal treatments. Our results show the instability of the ZnSn(OH)6 phase, which converts into an amorphous structure at low temperature. Above 750 °C, the material segregates into Zn2SnO4 and SnO2, supporting the hypothesis that the thermal treatment of the hydroxide phase under typical conditions results in the formation of an oxide mixture rather than the phase pure ZnSnO3.