High-temperature heat treatment tailored crystals and microstructures of multicomponent rare-earth tantalates RETaO₄ nano powders

Tailoring crystals and microstructures of multicomponent rare-earth tantalate RETaO₄ nano powders can promote their application as thermal protective coating materials because their properties are dominated by the structures. In this work, multicomponent RETaO₄ nano powders are synthesized via the chemical coprecipitation method, and their structures are tailored by changing the annealing temperature. After annealed at 800–1500 °C, the multicomponent RETaO₄ nano powders can be crystallized into metastable tetragonal (t′), monoclinic-prime (m′), and monoclinic (m) phases, and their particle sizes (8–652 nm) gradually increase with increasing temperature. The optimal annealing temperature of RETaO₄ powders is determined to be 1000 °C based on the crystallinity degree and particle sizes, which are 11.3 nm and 89.5%, respectively. High-resolution transmission electron microscopy (HR-TEM) and corresponding energy dispersive X-ray spectroscopy (EDS) mapping have validated the compositional uniformity of each element at the nanoscale, and the interplanar spacing of different phases corresponds to the X-ray diffraction (XRD) Rietveld refinements. This work demonstrates that high-temperature heat treatment can act as an effective mean to tailor the particle sizes and crystal structures of RETaO₄ ceramic, which can be further applied to synthesize nano spherical powders and coatings in future studies.