Structural inheritance and change from ZnSn(OH)6 to ZnSnO3 compounds used for ethanol sensors: Effects of oxygen vacancies, temperature and UV on gas-sensing properties

Nano-sized ZnSn(OH)6 crystalline particles were synthesized by co-precipitation method at room temperature, in which NaOH as precipitant and oxalic acid as organic functional reagent were used. Scanning electron microscopy and X-ray diffraction analysis suggest that the morphology, size and growth rate of the ZnSn(OH)6 particles can be changed by oxalic acid, and those particles are polycrystalline based on selected area electron diffraction (SAED) and transmission electron microscope data. After dehydration of the ZnSn(OH)6 polycrystalline precursors at high temperature, their ZnSnO3 counterparts were formed, showing an amorphous structure according to SAED analysis. In this process, the morphology, size and oxygen vacancy defects of the former are inherited by the latter except for the crystalline structure. The structural change from polycrystalline to amorphous phase is caused by newly formed oxygen vacancies, which are proved by X-ray photoelectron spectroscopy data, and reflected by ultraviolet (UV) absorption red shift. When the concentration of oxalic acid is 0.059 M in the synthesizing system, the resulting ZnSn(OH)6 precursor has a biggest particle size and average crystalline size. Furthermore, its ZnSnO3 counterpart is most sensitive to ethanol gas, achieving a gas response as high as 147 at 500 ppm under the co-effect of temperature (220 °C) and UV.