Composition driven (Ba,Ca)(Zr,Ti)O <sub>3</sub> lead‐free ceramics with large quality factor and energy harvesting characteristics
Vijay Bijalwan, Jiřı́ Erhart, Zdeněk Spotz, Dinara Sobola, Vladimír Prajzler, Pavel Tofel, Karel Maca
Abstract
Abstract A comprehensive study on energy harvesting characteristics as well as electro‐mechanical properties of lead‐free (1− x )(BaZr 0.2 Ti 0.8 )O 3 — x (Ba 0.7 Ca 0.3 Ti)O 3 ceramics were systematically carried out. Raman and Rietveld analyses show a formation of rhombohedral‐orthorhombic‐tetragonal (R‐O‐T) phase boundary region between 4/6 BZT/BCT and 6/4 BZT/BCT compositional range. Raman modes shift toward lower frequencies with increased Zr/Ca stoichiometric ratio attributed to asymmetric Ti‐O phonon vibrations, which caused local disorder, widening of energy band and reduced Curie temperature. The large mechanical quality factor Q m = 556 is related to the hardening effect and significantly high energy conversion efficiency η = 96% was discovered for 3/7 BZT/BCT composition. Largely, the noblest electro‐mechanical properties were retrieved for 5/5 BZT/BCT ceramics, in which d 33 = 500 pC/N (from quasi‐static d 33 meter), d 33 = 540 pm/V (from field‐dependent d 33 curves) indicating that the both methods are analogous with a deviation of 8%. The outstanding energy harvesting characteristics such as voltage constant g 33 = 27 × 10 −3 Vm/N, transduction coefficient d 33 × g 33 = 13 301 × 10 −15 m 2 /N, figure of merit under off‐resonance conditions FOM off = 12.1 × 10 −10 m 2 /N and fairly large η of 94% were attained again for 5/5 BZT/BCT ceramics. These outstanding characteristics were ascribed to the R‐O‐T phase boundary region that comprises a low energy barrier, consequently facilitated easy polarization rotation and triggered an increased electro‐mechanical conversion. These characteristics outperform other lead‐free and even most commercially available lead‐based ceramics, and thus suitable for sensors, actuators, resonators, and energy harvesting applications.