Sangwook Kim

Revealing the role of heat treatment in enhancement of electrical properties of lead-free piezoelectric ceramics

The structural and electrical properties of the virgin, annealed, and quenched samples of 0.80BiFeO3–0.20BaTiO3 lead-free ceramics were investigated. The crystal structures investigated with the structure refinement method exhibited a rhombohedral structure for all the samples. The significant enhancement of ferroelectric and piezoelectric properties is ascribed to the relaxation of the lattice strain induced in the samples after the heat treatment. The bond-length calculated from the final structure refinement results revealed the increment of the A-O bond-length after the heat treatment, while the B-O bond-length was maintained in all the virgin, annealed, and quenched samples suggesting the specific influence of the lattice strain at the A-site of the material system.

Structural and electrical characteristics of potential candidate lead-free BiFeO3-BaTiO3 piezoelectric ceramics

The crystal structures and electrical properties of lead-free BiFeO3-BaTiO3 [(1-x)BFxBT] piezoelectric system are investigated as a function of BaTiO3 concentration. The well-saturated P-E hysteresis loop was observed in the 0.80BiFeO3–0.20BaTiO3 composition system, while a less hysteretic strain-electric field curve was exhibited by the 0.70BiFeO3–0.30BaTiO3 with a strain hysteresis of 16%, the value comparable to PZT-based piezoelectric ceramics. The crystal structures investigated under the synchrotron radiation X-ray diffraction exhibited a rhombohedral structure for BFBT system with xu2009=u20090.10–0.25 and a pseudo-cubic structure for BFBT system with xu2009=u20090.30–0.40. The structural phase diagram for the BiFeO3-BaTiO3 system is suggested based on the results of temperature-dependent synchrotron radiation X-ray diffraction measurement and investigated electrical properties.

Fabrication of lead-free piezoelectric (Bi0.5Na0.5)TiO3–BaTiO3 ceramics using electrophoretic deposition

Electrophoretic deposition (EPD) process has certain advantages such as it can be applied for a mass production and also can be combined with magnetic crystal alignment technique. In this work, we prepared lead-free 85(Bi0.5Na0.5)TiO3–15BaTiO3 (85BNT–15BT) piezoelectric ceramics by conventional uniaxial pressing and EPD process. Various conditions were optimized such as suspension media, applied electrical field, and deposition time in order to yield dense green ceramics of 85BNT–15BT composition using EPD process. 85BNT–15BT ceramics prepared using EPD process revealed the Curie temperature of about 250xa0°C, coercive field of about 30xa0kV/cm, and piezoelectric constant (d33) of 75xa0pC/N. The EPD-processed samples exhibited structural and electrical properties similar to that of the conventionally processed one suggesting the successful fabrication of 85BNT–15BT piezoelectric ceramics by EPD method without composition deviation. This study lays a foundation on the fabrication of Bi-based lead-free piezoelectric ceramics by an alternative route other than the conventionally practiced solid-state reaction method maintaining the similar chemical composition, moreover, leaving a large space to explore more in the future.

Effect of thermal annealing on crystal structures and electrical properties in BaTiO3 ceramics

Mechanical damage and stress caused by polishing and cutting of ferroelectric materials could deteriorate their dielectric, ferroelectric, and piezoelectric properties. BaTiO3 piezoelectric ceramics were polished and cut, and thermally annealed at 600, 800, 1000, and 1200u2009°C for recovery. The electrical measurements revealed a reduction in the coercive field, elimination of imprint behavior, and an increase in saturation polarization in the thermally annealed ceramics. Furthermore, the electromechanical properties measured by the resonance method, prior to thermal annealing were d33 = 184 pC/N, k33 = 0.36, and s33E = 10.9 × 10−12 m2/N, while the values after 1200u2009°C-4 h thermal annealing were d33 = 287 pC/N, k33 = 0.54, and s33E = 12.1 × 10−12 m2/N. The in situ crystal structure evaluation and Williamson-Hall analysis suggested the decrement of microstrain from 6.38 × 10−4 to 5.20 × 10−4, indicating the retrieval of the residual stress imposed. The enhancement of piezoelectricity by 56% was ascribed to the effective annealing out of the surface mechanical damaged layers.Mechanical damage and stress caused by polishing and cutting of ferroelectric materials could deteriorate their dielectric, ferroelectric, and piezoelectric properties. BaTiO3 piezoelectric ceramics were polished and cut, and thermally annealed at 600, 800, 1000, and 1200u2009°C for recovery. The electrical measurements revealed a reduction in the coercive field, elimination of imprint behavior, and an increase in saturation polarization in the thermally annealed ceramics. Furthermore, the electromechanical properties measured by the resonance method, prior to thermal annealing were d33 = 184 pC/N, k33 = 0.36, and s33E = 10.9 × 10−12 m2/N, while the values after 1200u2009°C-4 h thermal annealing were d33 = 287 pC/N, k33 = 0.54, and s33E = 12.1 × 10−12 m2/N. The in situ crystal structure evaluation and Williamson-Hall analysis suggested the decrement of microstrain from 6.38 × 10−4 to 5.20 × 10−4, indicating the retrieval of the residual stress imposed. The enhancement of piezoelectricity by 56% was ascribed to th...