High-performance ((Ba0.95Ca0.05)(1-x)Cux)(Sn0.08Ti0.92)O3 ceramics for solid-state cooling and energy harvesting applications

This study investigates the influence of A-site copper substitution (x = 0.015 and 0.020) on the microstructure, phase evolution, dielectric, ferroelectric, electrocaloric, and piezoelectric properties of lead-free (Ba 0.95 Ca 0.05 )(Sn 0.08 Ti 0.92 )O 3 (BCST) ceramics prepared using the conventional solid-state solution. Comprehensive characterization via scanning electron microscopy (SEM) revealed that Cu 2+ substitution at the A-site promotes liquid-phase sintering, enhancing grain uniformity and density in BCST-0.015Cu, while BCST-0.020Cu exhibited increased porosity due to incomplete grain boundary compaction. X-ray diffraction and Raman studies confirmed a coexisting orthorhombic-tetragonal phase structure at room temperature. BCST-0.015Cu demonstrated superior dielectric permittivity ( ε r ≈ 13,280), energy storage efficiency ( η = 60.86% at 343 K), and electrocaloric responsivity ( ΔT = 1.414 K, ζ = 0.292 K·mm/kV), attributed to its denser microstructure and relaxor-like behavior ( γ = 1.81). In contrast, BCST-0.020Cu showed slimmer polarization hysteresis and higher recoverable energy density ( W rec = 135.87 mJ/cm 3 at 353 K) but lower piezoelectric performance ( d 33 = 384 pC/N vs. 568 pC/N for BCST-0.015Cu). The interplay between Cu-induced microstructural refinement, phase coexistence, and functional properties highlights BCST-0.015Cu as a promising lead-free candidate for piezoelectric energy harvesting, energy storage and solid-state cooling applications.