Effects of octahedral tilting on the piezoelectric properties of strontium/barium/niobium-doped soft lead zirconate titanate ceramics

Abstract

(Pb1-x-ySrxBay)(Zr0.976-zTi zNb0.024)O3 solid solutions have been investigated to understand the relationship between structural changes caused by isovalent strontium and barium substitution on the A-site and dielectric and piezoelectric properties. As strontium and barium were substituted for lead, the zirconium:titanium (Zr:Ti) ratio was modified so that all compositions had an optimized piezoelectric coefficient (d33). The value of d33 was at a maximum in the tetragonal phase near, but not at, the morphotropic-phase boundary (MPB). The real MPB was taken as the Zr:Ti ratio at which X-ray diffraction patterns appeared either pseudocubic or a mixture of rhombohedral and tetragonal. As strontium content increased, optimized d33 also increased from 410 pC/N (x = 0) to 640 pC/N (x = 0.12), commensurate with a decrease in the paraelectric-to-ferro-electric phase transition temperature (TC) from 350°C (x = 0) to 175°C (x = 0.12). However, for ceramics where x > 0.12, optimized d33 decreased even though the phase-transition temperature was ∼150°C. Low strontium concentration ceramics (x = 0-0.08) contained 80 nm ferrroelectric domains typical of PZT, but high strontium concentration ceramics (x = 0.12-0.16) contained fine-scale domains (20 nm) in some regions of the microstructure. In addition, [110] pseudocubic electron diffraction patterns revealed super-lattice reflections at 1/2{hkl} positions associated with rotations of the octahedra in antiphase. Co-doping ceramics with strontium (x = 0.06) and barium (y = 0.06) resulted in the disappearance of the 1/2{hkl} reflections, optimized d33 (∼520 pC/N, TC ≈ 205°C) for this composition was similar to that of ceramics where x = 0.08, y = 0, which had a TC of ∼250°C.