Investigation of electric field-induced phase transitions in unfilled tungsten bronze relaxor ceramics designed by the high entropy concept

Electric field-induced phase transition behaviour, extensively studied in perovskite-structured ceramics, has not been previously reported in unfilled tetragonal tungsten bronze (TTB) structured ceramics. In this work, we present the first investigation of electric field-induced phase transitions in high entropy designed unfilled TTB structured Ca_0.25Sr_0.25Ba_0.25Pb_0.25Nb₂O₆ (CSBP) ceramics using dielectric and ferroelectric characterization techniques. The findings reveal that field-induced polarization in the CSBP ceramics evolve from irreversible to reversible with increasing temperature. Furthermore, relaxor ferroelectric behaviour was observed in the ceramics, attributed to the A-site cation disorders in the unfilled TTB structure, facilitated by the high entropy design. The absence of non-180° domain switching was indicated by microstructural observations and analysis of the strain-electric field (S-E) response. In-situ poling synchrotron studies and experimental S-E response measurements revealed an electrostrictive behaviour characterized by an electrostrain not originating from macroscopic structural transformations or long-range domain switching but more likely contributed by the reorientation of polar nanoregions. The results obtained provide a foundation for future studies investigating the electric field-induced phase transition and domain switching behaviour in the unfilled TTB structured ceramics.