Novel molten salt method for synthesizing high-quality La3Ni2O7 with enhanced crystallinity and layered structures

This study introduces a pioneering molten salt method that utilizes Bi₂O₃ as flux to successfully synthesize high-quality layered nickelates, exemplified by La₃Ni₂O₇. Compared to conventional solid-state reactions, this approach facilitates synthesis at a relatively low temperature of 1100°C, leading to significantly enhanced crystallinity and a well-ordered layered structure. X-ray Diffraction (XRD) analysis confirms the material possesses a bilayer perovskite structure with Amam space group symmetry, where the enhanced intensity of the (0010) peak indicates a substantial reduction in structural defects and stacking faults. Characterization by Scanning Electron Microscopy (SEM) and Energy-Dispersive x-ray Spectroscopy (EDS) reveals uniform grains exceeding 15 μm in size with a precise and homogeneous chemical stoichiometry. Moreover, electrical transport measurements show that the oxygen vacancy concentration is the key parameter for tailoring the physical properties of the material. Through high-pressure oxygen annealing, a characteristic charge or spin density wave transition can be clearly induced in the 150-200 K range. This method provides ideal samples for future studies and establishes a robust experimental platform for exploring the superconductivity in nickelate systems.