Comparison of strain and ferroelectric properties of La,Nb and Li,Nb co-modified BNKT–ST ceramics

Abstract A comparison between the influence of concurrent A and B-site acceptor-donor (Li,Nb) and donor-donor (La,Nb) doping in Pb-free Bi 0.5 (Na 0.84 K 0.16 ) 0.5 TiO 3 –SrTiO 3 piezoelectrics on structure, ferroelectric and high voltage induced strain were made. In this work, Lithium was chosen as acceptor and Lanthanum was chosen as donor dopant on A-site and Nb 5+ as a B-site donor. Both modifier impurities promoted a phase evolution from the coexistent of two phase structures (rhombohedral-tetragonal) into a more symmetric single pseudocubic structure. Nonetheless, (La,Nb) donor-donor doping induced the phase transition at 1 mol%, while (Li,Nb) acceptor-donor doping at 2 mol%. Interestingly, acceptor-donor (Li,Nb) co-substitution results in the broadening of ergodic relaxor and ferroelectric (ER-FE) mixed phase boundary which is favourable for multidevice applications. This comparative study show that the A-site vacancies play a substantial role to induce the phase transformation from nonergodic-ergodic relaxor (NR-ER) and the improvement in their high voltage induced strain.