Effects of preparation method on the microstructure and electrical properties of tungsten bronze structure Sr2NaNb5O15 ceramics

Herein, Sr2NaNb5O16 (SNN) ceramics with a filled tungsten bronze structure were synthesized by the various methods of conventional mixed-oxide (CMO), two-step sintering (TSS), reactive sintering (RS) and molten salt synthesis (MSS). It was found that varying the preparation method could result in significant differences in the ceramic morphology, relative density, and electrical properties. The TSS, RS and MSS methods all produced a pure tungsten bronze phase SNN ceramic, though the CMO method could not. Further characterization revealed a sharp drop in the Curie temperature and significant deterioration of the dielectric properties in the ceramics prepared by MSS compared to the other methods, likely owing to residual K+ from the molten salt. Systematic comparison of the electrical properties of the ceramics produced by the RS and TSS method found that the RS method was the most suitable preparation method for SNN ceramics. The superior ferroelectric and piezoelectric properties in the sample produced by the RS method were attributed to the highly distorted NbO6 octahedron, as suggested by Raman spectroscopy.