Probing Molten Salt Flux Reactions Using Time-Resolved in Situ High-Temperature Powder X-ray Diffraction: A New Synthesis Route to the Mixed-Valence NaTi₂O₄

A new molten salt synthesis route to the mixed-valence sodium titanate NaTi 2 O 4 has been discovered. Reduction of Na 8 Ti 5 O 14 by Ti metal powder in a 3:1 molar mixture of NaCl:KCl at 770 °C produced crystals of NaTi 2 O 4 . Use of the molten salt flux lowered the synthesis temperature of this compound by over 400 °C. Time-resolved in situ high-temperature X-ray powder diffraction was used to probe the kinetics and mechanism of the reaction. Energy-dispersive X-ray diffraction (EDXRD) data revealed that the reaction is rapid; the phase begins to form in 30 min at 770 °C, and product formation is essentially complete within 2 h. Crystalline solids are present in the molten salt flux at all times during the course of the reaction, indicating that the mechanism most likely involves reactions occurring at the surfaces of the solid particles, mediated by the molten salt flux. Possible key intermediates identified through EDXRD and quenching studies are Ti 3 O, Na 2 Ti 6 O 13, and Na 0.54 TiO 2 . This new molten salt synthesis route offers a facile way to reproducibly prepare large samples of this mixed-valence compound for further study.