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 dominates the nonlinear portion of both the dielectric and piezoelectric responses in piezoelectric ceramics. Analysis of these contributions supports an earlier theoretical model inferring that non-180° domain wall motion in bulk ferroelectric ceramics is a major factor in the piezoelectric and dielectric responses. These results link the observed Rayleigh law behavior to the mechanistic domain wall model commonly employed to describe the extrinsic response of ferroelectric ceramics.

The bismuth-based perovskite solid solution (100−x)BiScO3−xPbTiO3 (BSPT) was investigated for use at temperatures up to 400°C and above. The high-temperature resistivity, together with dielectric and piezoelectric behaviors of the shear mode for manganese-modified BSPT ceramics near the morphotropic phase boundary composition were studied. The resistivity and time constant were found to be 3×107Ωcm and 0.08s, respectively, at 450°C for modified BSPT66. The dielectric constant Κ11T and dielectric loss were found to be 1112 and 1%, respectively, at room temperature, showing a Curie temperature at 468°C. The electromechanical coupling factor k15 was calculated to be 61%, staying nearly constant up to 440°C, expanding the temperature usage range significantly. The properties indicate that the modified BSPT66 material is a promising candidate for high-temperature shear sensor applications.

The perovskite solid solution system (1-x)BiScO3-(x)PbTiO3 represents an interesting new family of high-temperature piezoelectric materials. Compositions near the morphotropic phase boundary (x approximately 0.64) have been reported to have high Curie temperatures (Tc > 450 degrees C) and good piezoelectric coefficients (d33 approximately 460 pC/N). In this work, manganese additions were used to improve the high-temperature electrical resistivity and RC time constant of compositions near the morphotropic phase boundary. The addition of manganese was found to shift Tc to slightly lower temperatures (442 degrees C and 456 degrees C for x = 0.64 and x = 0.66, respectively). The piezoelectric activities of the modified materials were found to be reduced slightly due to the hardening effect of manganese; however, the temperature stability and resistivity of the modified materials were significantly enhanced. In this paper we present, for the first time, a complete set of materials constants, including the elastic (sij, cij), piezoelectric (dij, eij, gij, hij), dielectric (epsilonij, betaij), and electromechanical (kij) coefficients and compare them to both unmodified 0.36BiScO3-0.64PbTiO3 and PZT5A ceramics.

(1-x)BiScO3-xPbTiO3 (BSPT) polycrystalline material with a morphotropic phase boundary (MPB) composition (x=0.64) exhibits a high Curie temperature (TC) about 450°C and good piezoelectric properties with d33 values around 460pC/N. Manganese (Mn) modified BSPT was utilized in order to increase the electric resistivity and RC time constant. At 450°C, BSPT66-Mn ceramic exhibited a resistivity of 3x107 Ohm.cm and RC value of 0.08s, respectively, significantly higher than the values for undoped BSPT and commercial PZT5 materials. The manganese additive shifts TC of BSPT materials to lower temperatures, which were found to be 442°C and 462°C for modified BSPT64 and BSPT66, respectively. The piezoelectric behavior for the modified BSPT material was found to deteriorate slightly owing to the hardening effect of manganese, but showed superior temperature stability and enhanced resistivity. The detailed temperature dependent properties were studied in this work and compared to commercial PZT5 materials. The complete set of materials constants, including the elastic sij, cij, piezoelectric dij, eij, gij, hij, dielectric and electromechanical kij values were determined using resonance technique and derived from the experimental data.

Recently, a new family of piezoelectric perovskite materials based on the solid solution (1 - x)BiMeO3-xPbTiO(3) (where Me is one or a combination of cations with sum valance +3) have been developed. Specifically, the (1 - x)BiScO3-xPbTiO(3) (BSPT) system is noted for its high Curie temperature (T-C = 450degreesC) and large piezoelectric coefficient (d(33) > 460 pC/N). Lanthanum additions, as a donor dopant in the piezoelectric system Pb(Zr,Ti)O-3 and other lead based perovskite materials, are commonly utilized to both lower Curie temperature and increase piezoelectric coefficients. In the current work, the effect of lanthanum substitution in the BS-PT system is reported. The results of lanthanum additions in the BS-PT system show no large enhancement of the piezoelectric properties. However, fine grain sized materials (<1 mum), desirable for improved mechanical properties, with Curie temperature of 365degreesC and high piezoelectric coefficient (d(33) = 465 pC/N) were successfully produced. The results of this study suggest that for low lanthanum additions, <5 mol%, internal compensation mechanisms in the BS-PT system dominate piezoelectric performance. Further grain size effects in lanthanum doped BS-PT compositions provide the first experimental evidence of significant extrinsic contributions to the piezoelectric properties in this system.

Building on the ferroelectric family based on the Bi(Me+3)O3–PbTiO3 solid solutions, the complex solid solution (1−x)Bi(Mg3∕4W1∕4)O3–xPbTiO3 [(1−x)BMW–xPT] was investigated. This system was found to exhibit a broad morphotropic phase boundary at x∼0.48mol% PbTiO3 with a corresponding Curie temperature of 205°C separating pseudocubic and tetragonal ferroelectric phases. Based on dielectric, x-ray diffraction (XRD), and calorimetric data, a simple dielectric phase field diagram was established. On further structural analysis with diffraction contrast transmission electron microscopy along with XRD, evidence of B-site chemical ordering was found for the (1−x)Bi(Me′Me″)O3–xPbTiO3 perovskite family.

The effect of Sn substitution on the dielectric and piezoelectric properties of BiScO3–PbTiO3 was investigated in the ternary system, (1-x){(1-y)BiScO3–yPbO·SnO2}–xPbTiO3 (x=0.43–0.63, y=0.25–0.75). The ferroelectric phase transition temperature near morphotropic phase boundary (MPB) decreased with increasing Sn content from 450°C (x, y=0.64, 0) down to ∼250°C for the composition with x, y=0.46, 0.75. Piezoelectric activity (d 33=460–465 and k p=0.54) in Sn-substituted MPBs remained at similar levels to the pure 0.46BiScO3–0.64PbTiO3 MPB, with Sn content of up to y=0.5. However, further Sn-additions lead to decreased electromechanical performance and the formation of secondary phases such as SnO2. Broad temperature dependence of the permittivity near the ferroelectric phase transition was assessed by a diffuseness parameter δ, which generally decreased with firing temperature in the range of 1050–1250°C. The temperature of the permittivity maximum (T max) increased with measuring frequency, a characteristic consistent with relaxor ferroelectric materials.

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.

A new ternary system (1 - x)BiScO3-x{(l - y)PbTiO3-y(Ba0.294Sr0.706)TiO3}was studied in relation to morphotropic phase boundaries (MPB). Analogous to modified PZT ceramics, barium and strontium were introduced to the recently developed MPB (1 - x)BiScO3-xPbTiO(3) for x > 0.60, in order to investigate Curie temperature and piezoelectric property variations. With increasing barium and strontium substitution up to y = 0.3, the MPB line moved from x = 0.64 to 0.70 and d(33) and k(p) gradually decreased. X-ray diffraction phase analysis correlated the variations in piezoelectric properties showing a maximum in the compositions near rhombohedral-tetragonal phase boundary. Grain sizes were around 2 mum for all compositions and tetragonality decreased with the downward shifting of T-c in the range of 216-371degreesC. The frequency dependence of dielectric properties about the Curie maximum shows a dispersion in both epsilon' and tan delta. This relaxation behavior becomes more pronounced with increasing (Ba,Sr)TiO3 content, and high Curie maximum temperatures T-max's are found compared to lead based perovskites with complex B-sites.

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 diagram for BiScO3−PbTiO3 has been modified.

X-ray diffraction and transmission electron microscopy have been performed on samples in the solid solution series (BiFeO3)x–(PbTiO3)1−x in which a morphotropic phase boundary occurs at x≈0.7. BiFeO3 exhibits superlattice reflections at 12{hkl}p positions in some electron diffraction patterns, the distribution of which unambiguously demonstrates that the FeO6 octahedra are rotated in anti-phase about the pseudocubic [111] axis, consistent with the rhombohedral (R) space group R3c. The amplitude of the rotations decreases in the R phase as PbTiO3 content increases and superlattice reflections are absent in electron diffraction patterns from the tetragonal (T) phase (x=0.6), indicating that it is untilted with space group P4mm. Electron diffraction patterns from samples where x=0.7 reveal superlattice reflections not associated with octahedral rotations and consistent with an intermediate phase with lower symmetry than T and R.

Dielectric spectra of high-temperature piezoelectric (1−x)BiScO3–xPbTiO3 of composition near the morphotropic phase boundary (x≅0.64) were investigated in the frequency range of 100 Hz–1 THz at temperatures between 10 and 900 K. Below the ferroelectric phase transition Tc≅700 K, in addition to polar phonons, two other polarization mechanisms were detected: one, centered in the 100 MHz–1 GHz range probably caused by sound generation due to ferroelectric-ferroelastic domain wall motion; another evidences dynamic disorder of some ions. The former process, characterized by the temperature-independent mean relaxation time, vanishes below ∼250 K. The latter mechanism, caused by compositional disorder, results in the nearly frequency-independent losses (1/f noise) at low temperatures.

The dielectric and piezoelectric properties of the new perovskite solid solution system (1-x)BiScO3–xPbTiO3 were investigated. This system is representative of a new group of high temperature piezoelectrics that includes Bi(Me)O3–PbTiO3, where Me+3 is a relatively large cation, Sc, Y, Yb, In, etc., and combinations thereof. In the (1-x)BiScO3–xPbTiO3 series, perovskite stability was achieved for x>50 mol% PbTiO3 being ferroelectric rhombohedral and transforming to ferroelectric tetragonal in the region x=64 mol% PbTiO3, designated as the morphotropic phase boundary (MPB). Analogous to (1-x)PbZrO3–xPbTiO3 (PZT), the dielectric and piezoelectric properties were enhanced for compositions near the MPB. Piezoelectric coefficient d33 values reached 450 pC/N, comparable to soft PZT's with a transition temperature of 450°C, more than 100°C higher than commercial PZT. The combination of high TC and excellent piezoelectric activity make (1-x)BiScO3–xPbTiO3 materials candidates for high temperature, and temperature stable actuators and transducers.

New morphotropic phase boundary (MPB) piezoelectrics, with ferroelectric phase transition (T c) exceeding that of PbZrO3–PbTiO3 (PZT), were investigated. Based on a perovskite tolerance factor-T c relationship, new high T c MPB systems were projected in the Bi(Me)O3–PbTiO3 system, where Me is a relatively large B+3-site cation. For the (1-x)BiScO3–(x)PbTiO3 solid solution, a MPB was found at x-0.64 separating the rhombohedral and tetragonal phases, with correspondingly enhanced dielectric and piezoelectric properties. A transition temperature T c of ∼ 450°C was determined with evidence of T c's on the order of ≥ 600°C in the BiInO3 and BiYbO3 analogues, though issues of perovskite stability remain for the smaller tolerance end-member systems.