Morphology control of high-quality hexagonal perovskite BaNiO3 by molten salt method

Abstract

BaNiO3 single crystals with a hexagonal perovskite structure are prized for their exceptional Ni oxidation state and face-sharing structure, which grants them a high-performance potential as electrocatalysts. Despite their potential, obtaining high-quality morphology of BaNiO3 single crystals remains a challenge, making their characterization difficult and limiting their efficiency. In this study, we present a method for synthesizing high-quality BaNiO3 single crystals by morphology control using a molten salt method, which involves modifying the concentration of KOH, reaction time, and cooling rate. The optimal conditions for synthesizing high-quality BaNiO3 single crystals were found to be a reactant-to-KOH ratio of 1:50 and a reaction time of more than 3 h, which resulted in hexagonal-prism-shaped single crystals. However, using different reactant-to-salt ratios and shorter reaction times led to the formation of polycrystalline or pine-needle-shaped BaNiO3 along with secondary phases of BaCO3 and NiO. A higher KOH concentration required a longer reaction time, as the precursor diffusion rate slowed down. The average size of BaNiO3 single crystals increased as the cooling rate decreased, reaching the average width of ∼90 μm and the length of over 1 mm at the cooling rate of 5 °C/h. Our findings present optimal conditions for synthesizing a high-quality single-crystalline BaNiO3 with a hexagonal perovskite structure and could contribute to the development of BaNiO3 crystals for applications in ferroelectrics, photovoltaics, and chemical catalysis.