Sodium tantalates: monitoring crystallization via in situ total X-ray scattering

Abstract

Sodium tantalates, which have potential applications in photocatalysis, microelectronics and energy harvesting, are known to crystallize into several polymorphs on which the electrical and optical properties are dependent. As a photocatalyst, amorphous sodium tantalum oxide prepared by a sol–gel method has previously been shown to provide superior activity compared to crystalline counterparts. Intending to understand the structural basis of their activity in catalysis, this work provides insights into the crystallization behavior of sodium tantalates. The structural evolution of amorphous sodium tantalate was monitored during heat-induced crystallization. The local structure was investigated by pair distribution function analysis based on in situ total X-ray scattering experiments. Further information on the spatial arrangements was obtained from complementary scanning transmission electron microscopy and spectroscopy studies. It was found that a composite of natrotantite (RcH) and distorted perovskite (Cmcm or Pbnm) together with a considerable amount of amorphous solid is obtained during heating the amorphous starting material up to 700 °C. The findings of the present work are expected to shine further light on the alterations of the band gap energy and subsequent changes in the photocatalytic performance of this large band gap semiconductor material.