RESUMO
1- x - y)BiFeO3-x(K0.5Bi0.5)TiO3-yPbTiO3 (BFKBT- PT) piezoelectric ceramics were investigated across the compositional space and contrasted against the xBiFeO3- (1-x)(K0.5Bi0.5)TiO3 (BF-KBT) system, whereby a range of relaxor-like/ferroelectric behavior was observed. Structural and piezoelectric properties were closely related to the PbTiO3 concentration; below a critical concentration, relaxor-like behavior was identified. The mechanisms governing the piezoelectric behavior were investigated with structural, electrical, and imaging techniques. X-ray diffraction established that longrange non-centrosymmetric crystallographic order was evident above a critical PbTiO3 concentration, y > 0.1125. Commensurate with the structural analysis, electric-field-induced strain responses showed electrostrictive behavior in the PbTiO3-reduced compositions, with increased piezoelectric switching in PbTiO3-rich compositions. Positive-up-negative-down (PUND) analysis was used to confirm electric-field-induced polarization measurements, elucidating that the addition of PbTiO3 increased the switchable polarization and ferroelectric ordering. Piezoresponse force microscopy (PFM) of the BF-KBT-PT system exhibited typical domain patterns above a critical PbTiO3 threshold, with no ferroelectric domains observed in the BF-KBT system in the pseudocubic region. Doping of BiFeO3-PbTiO3 has been unsuccessful in the search for hightemperature materials that offer satisfactory piezoelectric properties; however, this system demonstrates that the partial substitution of alternative end-members can be an effective method. The partial substitution of PbTiO3 into BF-KBT enables long-range non-centrosymmetric crystallographic order, resulting in increased polar order and TC, compared with the pseudocubic region. The search for novel high-temperature piezoelectric ceramics can therefore exploit the accommodating nature of the perovskite family, which allows significant variance in chemical and physical characters in the exploration of new solid-solutions.
RESUMO
Piezoelectric actuators and sensors are widely used for flow control valves, including diesel injectors, ultrasound generation, optical positioning, printing, pumps, and locks. Degradation and failure of material and electrical properties at high temperature typically limits these applications to operating temperatures below 200°C, based on the ubiquitous Pb(Zr,Ti)O3 ceramic. There are, however, many applications in sectors such as automotive, aerospace, energy and process control, and oil and gas, where the ability to operate at higher temperatures would open up new markets for piezoelectric actuation. Presented here is a review of recent progress and initial results toward a European effort to develop measurement techniques to characterize high-temperature materials. Full-field, multi-wavelength absolute length interferometry has, for the first time, been used to map the electric-field-induced piezoelectric strain across the surface of a PZT ceramic. The recorded variation as a function of temperature has been evaluated against a newly developed commercial single-beam system. Conventional interferometry allows measurement of the converse piezoelectric effect with high precision and resolution, but is often limited to a single point, average measurement and to limited sample environments because of optical aberrations in varying atmospheres. Here, the full-field technique allows the entire surface to be analyzed for strain and, in a bespoke sample chamber, for elevated temperatures.
