Enhanced structural and electrical properties of furnace-cooled SrZrO3-modified BFBT lead-free piezoceramics for high-temperature applications

Abstract

Abstract Lead-free SrZrO 3 (SZ)-modified BiFeO 3 –BaTiO 3 ceramics (BFBT–SZ x , x  = 0, 0.02, and 0.04 mol%) were synthesized via a conventional solid-state reaction route followed by furnace cooling. X-ray diffraction (XRD) confirmed a single-phase pseudocubic perovskite structure with no secondary phases, while energy-dispersive X-ray spectroscopy (EDS) verified the presence of all intended elements, including Sr and Zr. Field emission scanning electron microscopy (FESEM) revealed enhanced grain uniformity and densification, with average powder particle size decreasing from 1.68 μm to 0.98 μm. The bulk absolute density increased from 3.35 g/cm 3 (undoped) to 5.75 g/cm 3 (SZ–0.04), corresponding to a relative density increase from ~ 90% (undoped) to ~ 92.5% (SZ–0.02) and ~ 94% (SZ–0.04). Fourier transform infrared spectroscopy (FTIR) confirmed the formation of metal–oxygen bonds characteristic of the perovskite lattice. Dielectric measurements showed improved thermal stability and reduced loss upon doping. The dielectric constant ( ε r ) decreased with increasing SZ content from ~ 7200 ( x  = 0) to ~ 2550 ( x  = 0.04) at 1 MHz, while the temperature of the ε r peak shifted from ~ 350 ℃ (undoped) to > 400 ℃ (4% SZ) at 1 kHz. Doped samples maintained ε r variation within ± 5% over a broad 20–510 °C range, and the dielectric loss (tan δ) was significantly reduced with low dielectric loss values on the order of 10 –3 at 1 kHz, indicating diminished conduction losses. Increasing diffuseness parameter ( γ  = 1.69–1.89) confirmed relaxor behavior and enhanced polar disorder. Impedance spectroscopy revealed grain and grain boundary contributions in doped samples, while AC conductivity analysis indicated improved charge transport with temperature. Activation energy calculations showed a decrease from ~ 0.80 eV ( x  = 0) to ~ 0.20 eV ( x  = 0.04), confirming improved transport charge. The novelty of this work lies in demonstrating that low-level SZ doping simultaneously stabilizes the perovskite lattice, suppresses conduction loss, tunes relaxor-type response, and improves high-temperature dielectric reliability. These unique features make BFBT–SZ ceramics strong candidates not only for high-temperature dielectric and piezoelectric devices, as well as energy-related applications, including high-energy-density capacitors, energy storage systems, and thermally stable energy conversion modules.