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 (0), tetragonal (T) and cubic (C) phases was performed on a simple composition Ba(Ti0.94Sn0.06-xZrx)O-3 (0.00 <= x <= 0.06) (BTSZ(x)). 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 (C-O and G(T)) at room temperature. Enhanced piezoelectric properties with d(33)=402 pC/N and k(p)=39% were attained with x=0.01 at T-S=1550 C because the C-T/C-O ratio was close to unity along with a proper average grain size, homogeneous grains and high relative density rho. The degree of hybridization with O2- and different phase transition energies (Delta E) derived by adding Zr4+ and Sn4+ in B-sites essentially dominated the varying trend of the phase transition temperatures (TR-O, TO-T, T-C). Larger Delta ER-O, Delta EO-T and Delta EC-T in BaZrO3 than in BaSnO3 contributed to higher TR-O, TO-T and T-C in BTZ(x) than in BTSx when the same amount of Sn4+ or Zr4+ was added. Meanwhile, a faster T-C decline in BTSx than in BTZ 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.