High-Pressure Synthesis, Magnetic and Electrical Properties of Perovskite-Type CeTaN₂O

Abstract

Recently, it has been discovered that the AB(N,O)₃-type perovskite oxynitrides exhibit excellent dielectric, ferroelectric, and photocatalytic properties, promising for application in the fields of optoelectronics, energy storage, and communication. Figure 1 illustrates the crystal structures of conventional ABO₃ (taking CaTiO₃ as an example) and AB(N,O)₃ (taking LaTiN₂O as an example) perovskites. Due to the differences in charge, ionic radius, and covalent bonding between N^3- and O^2- ions, the N substitution for O enhances the B(N,O)₆ octahedra tilting, giving rise to exotic properties and functionalities. However, the current fabrication process for this type of material is rather time-consuming, leading to products with appreciable amount of impurities. In this study, using oxide precursors and sodium amide as the nitrogen source, we successfully synthesized high-purity perovskite-type oxynitride CeTaN₂O bulk materials under high-temperature and high-pressure conditions provided by a cubic-anvil press. The synthesis time was reduced to 1 hour, achieving rapid production. The lattice structure and physical properties of the obtained samples were comprehensively investigated. X-ray powder diffraction experiments and subsequent Rietveld refinement indicated that the title material shows an orthorhombic crystal structure with the space group of Pnma. X-ray absorption spectroscopy confirmed the charge configuration and the anion composition as Ce³⁺Ta⁵⁺N₂O. Magnetization and specific heat measurements revealed that the exchange interactions are mostly antiferromagnetic with a potential magnetic transition below 2 K. The electrical transport data demonstrated typical semiconductor behavior, which can be further interpreted by a three-dimensional variable-range hopping model. Our study paves the way for the application of this exotic perovskite oxynitride.