T. R. Shrout

Classification and consequences of complex lead perovskite ferroelectrics with regard to B-site cation order

From a number of studies on ferroelectric and related materials based on complex lead perovskites [Pb(B x ′B 1− x ″)O 3 ], it is apparent that the B-site cation order influences the crystallography, phase transitions, and other physical properties. A classification of complex lead perovskites is presented based on the relative scale of long-range cation order. In particular, we discuss the implications of cation order in relation to relaxor and normal ferroelectric behavior.

Investigation of a high Tc piezoelectric system: (1−x)Bi(Mg1/2Ti1/2)O3–(x)PbTiO3

(1−x)Bi(Mg1/2Ti1/2)O3–xPbTiO3 polycrystalline ceramics were investigated for potential as high-temperature piezoelectric materials. A morphotropic phase boundary (MPB) between tetragonal (T) and rhombohedral (R) ferroelectric (FE) phases, which exhibited enhanced piezoelectric activity and a ferroelectric–paraelectric phase transition at 478 °C was observed at x≈0.37. Electron diffraction patterns (x⩽0.37) contained discrete superlattice reflections at 12{hkl} positions arising from antiphase rotations of the O octahedra, consistent with R3c space group symmetry. These reflections were diffuse at the MPB (x=0.38) and absent in the T phase (x=0.5). In the unpoled state, FE R (x=0.35) ceramics revealed a polar microdomain structure whereas the T phase (x=0.5) contained classic {110} twin domain boundaries. However, poled R samples underwent a field-induced transformation to an aligned domain structure with {110} twin boundaries similar to those in the T phase. Correlations are made between structure and pro...

Phase Diagram of the Perovskite System (1−x)BiScO3-xPbTiO3

The perovskite (1−x)BiScO3-xPbTiO3 (BS-PT) system exhibits a large piezoelectric coefficient (d33>460pC∕N in polycrystalline form) and a high Curie temperature TC=450°C in the vicinity of the morphotropic phase boundary (x=0.64mol fraction PbTiO3), which separates the rhombohedral and tetragonal phases. The present contribution reports on revisions to the BiScO3-PbTiO3 phase diagram specifically, (i) the compositional dependence of the octahedral tilt-transition temperature (x<0.62mol fraction PT), as determined using variable-temperature transmission electron microscopy, (ii) high-temperature curvature of the rhombohedral-tetragonal morphotropic phase boundary determined using dielectric measurements on single crystals, and (iii) Curie temperatures in the tetragonal phase field, which exceed that of the PbTiO3 end member.

Nonlinear contributions to the dielectric permittivity and converse piezoelectric coefficient in piezoelectric ceramics

A measurement and analysis technique has been developed to quantify the complex contributions to the nonlinear dielectric and converse piezoelectric response in ferroelectric ceramics. The electric field dependent response was quantified in two important bulk ceramic piezoelectric systems, Pb(Zr1−x,Tix)O3 and (1−x)BiScO3–xPbTiO3 (BS-PT), at low frequency and room temperature. The nonlinear response was shown to obey the Rayleigh law in the specific field and frequency ranges reported. Analysis of BS-PT perovskites with different crystal structures revealed a ferroelectric phase dependence on the magnitude of the nonlinear contribution to the dielectric and piezoelectric responses. The magnitudes of the nonlinear coefficients, which quantify the irreversible extrinsic response, were found to be smallest in the ferroelectric tetragonal phase, larger in the rhombohedral composition, and highest at the morphotropic phase boundary. Finally, this work provides strong evidence that the same loss mechanism domina...

Classification of transition temperature behavior in ferroelectric PbTiO3–Bi(Me′Me″)O3 solid solutions

The ferroelectric transition temperature (Tc) behavior of perovskite solid solutions based on PbTiO3–Bi(Me′Me″)O3 (Me′=Fe3+, Zn2+, Sc3+, In3+, Mg2+, Ni2+, etc., and Me″=Ti4+, Nb5+, W6+) was considered. Trends in the Tc compositional dependence near the PbTiO3 end member could be described with a geometrical polynomial expression. Three main cases were observed: Case 1, a continued increase in transition temperature above the end member PbTiO3 (495°C); case 2, an increase and then decrease of the transition temperature; and case 3, a continuous decrease in the transition temperature with Bi(Me′Me″)O3 additions. It was noted that for all case 2 examples the enhancement of ΔTc=Tc(max)−Tc(PT) increased as the distribution of B-site ionic radii increased. A correlation was therefore proposed between the maximum enhancement in transition temperature and the spread of tolerance factor (Δt) and∕or variance in B-site ionic radius (σ2). Finally, it was proposed that these observations are consistent with random-fie...

Piezoelectric 3–3 composites

Abstract Piezoelectric composites of PZT and polymers were prepared by mixing tiny plastic spheres with PZT powder in an organic binder and firing the mixture to give a ceramic skeleton. After cooling, the skeleton was back-filled with polymer and poled. Dielectric and piezoelectric properties were measured on samples ranging from 30 to 70 volume % PZT, and compared with a rectangular skeleton model for 3–3 composites. Composites containing 50% PZT-50% silicone rubber appear especially useful for hydrophone applications with dhgh products a hundred times larger than PZT.

X-ray diffraction and phenomenological studies of the engineered monoclinic crystal domains in single crystal relaxor ferroelectrics

We present x-ray diffraction data, which demonstrate that after high field poling, solid solutions of lead zinc niobate with 8% lead titanate (PZN–PT) consist of a mixture of a dominant monoclinic phase and a remnant tetragonal phase. To understand the origin of this engineered monoclinic phase we studied a Devonshire phenomenological model that predicts the field induced phase transitions in PZN–PT. Although previous attempts to use this model for these materials have matched the phase diagram and dielectric behavior, we show that the coefficients used in those models cannot be reconciled with recent data on electric field behavior. By modifying the coefficients we are able to explain the phase diagram, dielectric behavior, and high field phase transitions in compositions near the morphotropic phase boundary. Using these coefficients, we find no stable monoclinic phase present in the model. This contradiction is explained by noting that within the engineered domain state the tetragonal regions strain the...

Transmission electron microscopy investigation of the high temperature BiScO3-PbTiO3 piezoelectric ceramic system

Recently, a perovskite solid-solution ((1−x)BiScO3−(x)PbTiO3) with superior electromechanical properties than PbZrO3−PbTiO3 (PZT) ceramics has been discovered. The system has a morphotropic phase boundary (MPB) between ferroelectric rhombohedral (R) and tetragonal (T) symmetries similar to PZT but the underlying domain structures and some aspects of the crystal chemistry remain to be elucidated. Therefore, transmission electron microscopy has been used to study changes in domain structure and symmetry as a function of x. Domain structures in the R and T phases have been found which closely resemble those in PZT. In addition, 12{hkl} superlattice reflections were observed, particularly in the 〈110〉 zone axis diffraction patterns from grains of the R phase (e.g., x=0.5), which were consistent with rotations of the octahedra in antiphase and the space group R3c. These reflections were absent in the R phase close to the MPB (x=0.64) and in the T phase (x=0.75). From these results, the low temperature phase di...

High-temperature perovskite relaxor ferroelectrics: A comparative study

The recent discovery of high-temperature piezoelectric ceramics based on Bi(Me′Me″)O3-PbTiO3 solutions have also permitted the development of high-temperature relaxor ferroelectrics with ternary solid solutions. One of the high-temperature compositions based on the xBiScO3-yPb(Mg1∕3Nb2∕3)O3-zPbTiO3 (xBS-yPMT-zPT) ternary system exhibited a high permittivity maxima of ∼17 000 and a Tmax of 500–550 K. These materials are compared to complex lead perovskite relaxor ferroelectrics by determination of the activation energy, EA, and freezing temperature, Tf, from the Vogel-Fulcher relationship and also a high-temperature deviation temperature, TD, from the Curie-Weiss behavior. It was found that these parameters scale within the perovskite relaxor systems and from the self-consistent trends of these defining parameters. It is suggested that a general comparison for relaxor ferroelectrics may exist. The highest EA, Tf, and TD values all exist within the xBS-yPMT-zPT ternary system within the relaxor ferroelectri...

Sol-gel processing of composite PbTiO3/PLZT thin films

Abstract A novel sol-gel fabrication approach was developed for the fabrication of composite PbTiO3/PLZT thin films. The approach involves the deposition of a perovskite (PbTiO3) interlayer prior to deposition of the PLZT film. Composite PbTiO3/PLZT sol-gel thin films were prepared on (110) sapphire, platinum-coated sapphire, and platinum-coated silicon substrates. These films were highly crystalline and exhibited preferred crystallographic orientation. This perovskite interlayer approach is applicable to a wide variety ferroelectric thin film and substrate materials.