An Innovative Solid-State Approach to Zinc Orthostannate: Remarkable Sintering Temperature Reduction via Lithium Doping and Mechanochemical Activation of Low-Melting Precursors

Abstract

Zinc orthostannate, often called zinc tin oxide (ZTO), possesses unique physical characteristics and is a promising wide band gap (3.6 eV) n-type semiconductor material for a broad range of applications. The standard solid-state fabrication of ZTO requires prolonged heat treatment of zinc oxide and stannic oxide powders at around 1000 °C. The biggest drawback of this process is the evaporation of zinc oxide during the synthesis. We report an innovative and efficient mechanochemically supported solid-state approach to Li-doped ZTO synthesis with the implementation of a low-melting lithium hydroxide sintering aid, which offers a significant lowering of the sintering temperature down to 850 °C and time to 90 min, maintaining the high quality of the resulting Li-doped ZTO materials. The effect of sintering temperatures in the range 850-900 °C on photoluminescence characteristics of the ZTO materials was studied, and the PL spectra well corroborate with the XPS data and the presence of O as well as Zn or Sn vacancies. The band gap value of the resulting ZTO materials oscillated around 3.6 eV. Moreover, a comprehensive spectroscopic and microscopic examination of the optimized Li-doped ZTO materials provided more profound insight into its vacancy-mediated formation via liquid-phase sintering and its gradual advancement in the low-temperature regime of 850-900 °C. Additionally, the surface analysis of the selected highest quality materials enabled the determination of the Zn diffusion from the Li-doped ZTO lattice to its surface, expanding the knowledge of the diffusion-evaporation process.