Phase structure and electrical properties of Sn and Zr modified BaTiO3 lead-free ceramics

In this study, a comprehensive analysis on the coupling role of co-doping Zr4+ and Sn4+ in BaTiO3 ceramics on the phase transition between rhombohedral (R), orthorhombic (O), tetragonal (T) and cubic (C) phases was performed on a simple composition Ba(Ti0.94Sn0.06-xZrx)O3 (0.00≤x≤0.06) (BTSZx). Optimizing the Zr content (x) and sintering temperature (Ts) enabled all samples, except for x=0.06, to exhibit the coexistence of O- and T-symmetries with different fractions (CO and CT) at room temperature. Enhanced piezoelectric properties with d33=402 pC/N and kp=39% were attained with x=0.01 at Ts=1550 °C because the CT/CO ratio was close to unity along with a proper average grain size, homogeneous grains and high relative density ρr. The degree of hybridization with O2− and different phase transition energies (ΔE) derived by adding Zr4+ and Sn4+ in B-sites essentially dominated the varying trend of the phase transition temperatures (TR-O, TO-T, TC). Larger ΔER-O, ΔEO-T and ΔEC-T in BaZrO3 than in BaSnO3 contributed to higher TR-O, TO-T and TC in BTZx than in BTSx when the same amount of Sn4+ or Zr4+ was added. Meanwhile, a faster TC decline in BTSx than in BTZx can be ascribed to a stronger hybridization between Zr4+ and O2− than between Sn4+ and O2−. Our result indicated that the forecast of phase diagrams for hybrid multi-component systems, such as BTSZ, via each end-member composition is a feasible and convenient strategy.