Electric-field-induced volume change and room temperature phase stability of (Bi1/2Na1/2)TiO3-x mol. % BaTiO3 piezoceramics

Phase stability of (1 - x) (Bi1/2Na1/2)TiO 3-x BaTiO3 (0 ??? x ??? 0.15) under electric field was investigated by measuring volume changes during a bipolar poling cycle. The unique nature of field-dependent phase stability with three distinctive regions is revealed by comparative studies using commercial soft PZT and relaxor PLZT. For x ??? 0.06 and x 0.13, similarly with PZT and PLZT, the axial strain expands with the contracting radial strain, but the former results in a remanent volume demonstrating an electric-field-induced phase transition. For 0.08 ??? x ??? 0.12, this field-induced phase transition is distinguished by negligible radial contractions implying polarization rotation. A "poling-induced" morphotropic phase boundary forms at x = 0.07.open433

Quenching-induced circumvention of integrated aging effect of relaxor lead lanthanum zirconate titanate and (Bi1/2Na1/2)TiO3-BaTiO3

The effect of quenching on the dielectric properties of ceramic Pb0.92La0.08(Zr0.65Ti0.35)(0.98)O-3 (PLZT 8/65/35) and (Bi1/2Na1/2)TiO3-6 mol. %BaTiO3 (BNT-6BT) was investigated after annealing at a wide range of temperatures. The dielectric permittivity showed that the magnitude and shape profile of the permittivity were significantly affected by the quenching process in comparison to furnace-cooled specimens. We propose that the changes originate from a circumvention of integrated aging that takes place during cooling process. A comparison between PLZT 8/65/35 and BNT-6BT allowed us to conclude that two different types of polar nanoregions exist in BNT-6BT and the transition between them peaks at around 300 degrees C.open3

Frequency and temperature dependence of actuating performance of Bi1/2Na1/2TiO3-BaTiO3 based relaxor/ferroelectric composites

Recently, composites of relaxors (matrix) and either ferroelectric or nonergodic relaxor (seed) were proposed as a solution to resolving one of the main drawbacks of incipient piezoceramics, namely the requirement for high driving electric fields. In this study, we investigate the temperature and frequency dependence of the actuating performance of Bi1/2Na1/2TiO3-BaTiO3-based composites. Apart from the reduction of driving field, the composite architecture offers an extra degree of freedom for tailoring the temperature stability for different operational conditions for actuators. High strain values appear to be sensitive especially to driving frequency. This is originated by the time-dependent process of the coalescence of polar nanoregions. In effect, proximity of driving field and poling field leads to high strain sensitivity. Hence, the driving electric field needs to be adjusted in order to meet the desired frequency specifications for given applications.open0

Evolving morphotropic phase boundary in lead-free (Bi1/2Na1/2)TiO3–BaTiO3 piezoceramics

The correlation between structure and electrical properties of lead-free (1-x)(Bi(1/2)Na(1/2))TiO(3)-xBaTiO(3) (BNT-100xBT) polycrystalline piezoceramics was investigated systematically by in situ synchrotron diffraction technique, combined with electrical property characterization. It was found that the morphotropic phase boundary (MPB) between a rhombohedral and a tetragonal phase evolved into a morphotropic phase region with electric field. In the unpoled material, the MPB was positioned at the transition from space group R3m to P4mm (BNT-11BT) with optimized permittivity throughout a broad single-phase R3m composition regime. Upon poling, a range of compositions from BNT-6BT to BNT-11BT became two-phase mixture, and maximum piezoelectric coefficient was observed in BNT-7BT. It was shown that optimized electrical properties are related primarily to the capacity for domain texturing and not to phase coexistence