Indirect Measurement of Energy Density of Soft PZT Ceramic Utilizing Mechanical Stress

This paper reports on an indirect measurement of energy density of soft PZT ceramic utilizing mechanical stress. The method works analogous to the Olsen cycle and allows for a large amount of electro-mechanical energy conversion. A maximum energy density of 350 kJ/m³/cycle was found under 0–312 MPa and 1–20 kV/cm of applied mechanical stress and electric field, respectively. The obtained result is substantially higher than the results reported in previous studies of PZT materials utilizing a direct piezoelectric effect.     

Stress-dependent ferroelectric properties of Pb(Zr1/2Ti1/2)O3–Pb(Zn1/3Nb2/3)O3 ceramic systems

Effects of compressive stress on the ferroelectric properties of ceramics in PZT–PZN systems were investigated. (1 − x)Pb(Zr_1/2Ti_1/2)O₃(xPb(Zn_1/3Nb_2/3)O₃ or (1 − x)PZT–(x)PZN (x = 0.1–0.5) ceramics were prepared by a conventional mixed-oxide method. The ferroelectric properties under compressive stress of the PZT–PZN ceramics were observed at stress levels up to 170 MPa using a compressometer in conjunction with a modified Sawyer–Tower circuit. It was found that with increasing compressive stress the area of the ferroelectric hysteresis (P–E) loops, the saturation polarization (P_sat), the remanent polarization (P_r), and the coercive field (E_c) decreased. These results were interpreted through the non-180° ferroelectric domain switching processes.     

Effects of uniaxial stress on dielectric properties of 0.9PMN–0.1PT ceramics

This study deals with the influence of uniaxial stress on the dielectric properties of electrostrictive PMN–PT ceramic. The dielectric properties of lead magnesium niobate-lead titanate prepared by a mixed-oxide method with composition ratio 9:1 were measured under uniaxial compressive stress up to 22 MPa. The experimental results revealed that the superimposed compression load significantly reduced both the dielectric constant and the dielectric loss tangent in every measuring frequency. The observations were interpreted in terms of clamping of domain walls and de-poling under the compressive loading. The change of the dielectric properties with stress was attributed to competing influences of the intrinsic contribution of non-polar matrix and the extrinsic contribution of re-polarization and growth of micro-polar regions. In addition, the results reported here also suggested a significant influence of the experimental conditions on the uniaxial stress dependence of dielectric properties of the PMN–PT ceramic.     

Local Structure of Magnetoelectric BiFeO3–BaTiO3 Ceramics Probed by Synchrotron X-Ray Absorption Spectroscopy

The novel Cu- and Mn-doped and Cu/Mn codoped 0.75BiFeO₃–0.25BaTiO₃ magnetoelectric ceramics were successfully prepared by a solid-state reaction method. The dielectric, ferroelectric, ferromagnetic, and magnetoelectric properties were determined and all the results suggested that Cu and Mn dopants occupied different B-site lattices in the 0.75BiFeO₃–0.25BaTiO₃ structure. To identify the preferential sites of Cu and Mn in the lattice, Synchrotron X-ray Absorption Spectroscopy (SXAS) measurements were carried out. A combination of both measured and simulated XAS results with a linear combination fitting (LCF) revealed that in Cu- and Mn-doped 0.75BiFeO₃–0.25BaTiO₃ ceramics both Mn and Cu substituted at Fe-site and Ti-site with slightly different proportion. On the other hand, both dopants were found to occupied different sites in Cu/Mn codoped 0.75BiFeO₃–0.25BaTiO₃ ceramics.     

Estimation of energy density of PMN-PT ceramics utilizing mechanical stress

Abstract

Present study introduces an indirect measurement of energy density of (1-x)Pb(Mg_1/3Nb_2/3)O₃-(x)PbTiO₃ (PMN-PT) ceramics under compressive stress and electric field. The method works analogous to Olsen cycle which is a demonstration of a novel cycle converting mechanical energy into electrical energy. A large amount of electro-mechanical energy conversion can be achieved via this method. The ceramics were investigated under 0–75?MPa and 1–15?kV/cm of applied mechanical stress and electric field, respectively. A maximum energy density of 68?kJ/m³/cycle was achieved in 0.7PMN-0.3PT ceramic. The obtained result is significantly greater than that of linear piezoelectric phenomena.     

Dielectric and Ferroelectric Properties of Complex Perovskite Ceramics Under Compressive Stress

Dielectric and ferroelectric properties of complex perovskite PZT-PZN ceramic system were investigated under the influence of the compressive stress. The results showed that the dielectric properties, i.e. dielectric constant ( εr ) and dielectric loss ( tan δ), and the ferroelectric characteristics, i.e. the area of the ferroelectric hysteresis loops, the saturation polarization ( P(sat) ), and the remnant polarization (Pr) changed significantly with increasing compressive stress. These changes depended strongly on the ceramic compositions. The experimental results on the dielectric properties could be explained by both intrinsic and extrinsic domain-related mechanisms involving domain wall motions, as well as the de-aging phenomenon. The stress-induced domain wall motion suppression and non-180° ferroelectric domain switching processes were responsible for the changes observed in the ferroelectric parameters. In addition,a significant decrease in those parameters after a cycle of stress was observed and attributed to the stress induced decrease in switchable part of spontaneous polarization. This study clearly show that the applied stress had significant influence on the electrical properties of complex perovskite ceramics.     

Fabrication and electrical properties of Pb(Co1/3Nb2/3)O3 ceramics

Pb(Co_1/3Nb_2/3)O₃ (PCN) ceramics have been produced by sintering PCN powders synthesized from lead oxide (PbO) and cobalt niobate (CoNb₂O₆) with an effective method developed for minimizing the level of PbO loss during sintering. Attention has been focused on relationships between sintering conditions, phase formation, density, microstructural development, dielectric and ferroelectric properties of the sintered ceramics. From X-ray diffraction analysis, the optimum sintering temperature for the high purity PCN phase was found at approximately 1050 and 1100 °C. The densities of sintered PCN ceramics increased with increasing sintering temperature. However, it is also observed that at very high temperature the density began to decrease. PCN ceramic sintered at 1050 °C has small grain size with variation in grain shape. There is insignificant change of dielectric properties with sintering temperature. The P–E hysteresis loops observed at −70 °C are of slim-loop type with small remanent polarization values, which confirmed relaxor ferroelectric behavior of PCN ceramics.     

Thermal expansion behavior and estimated total polarizations of lead zirconate titanate-lead nickel niobate ceramics

Thermal expansion properties of lead zirconate titanate-lead nickel niobate ((1 − x)PZT-xPNN, x = 0.1-0.5) ceramics were determined in the temperature range of approximately − 100 to + 450 °C by dilatometer thermal expansion measurement. The observed deviation from the straight line below a Burns-like temperature for all the compositions was interpreted as due to the contribution from the dynamic polarization fluctuations of the relaxor part of the compositions. The Burns temperature was determined and found to increase with increasing PZT concentration. The local polarization was calculated from the thermal expansion data. Various aspects of understanding the polarization behavior and other effects in this ferroelectric system were also examined and discussed.     

Local Structure Investigation in Multiferroic BiFeO3–BaTiO3 Ceramics by XAS Technique and Their Relevant Properties

The (1?x)BiFeO₃‐xBaTiO₃ (with x = 0.1, 0.2, 0.3, and 0.4) ceramics were fabricated successfully by solid‐state reaction method. Single‐phase perovskite was obtained in all ceramics, as confirmed by XRD technique. It was observed that 0.7BiFeO₃–0.3BaTiO₃ was the morphotropic phase boundary (MPB) between rhombohedral and cubic phases, as also revealed from ferroelectric and magnetic properties. The simulated and experimental X‐Ray Absorption Spectroscopy (XAS) study revealed that BT in 0.75BF‐0.25BT is possibly taken a rhombohedral structure. Furthermore, the rounded ferroelectric hysteresis loops observed for 0.9BiFeO₃–0.1BaTiO₃ and 0.8BiFeO₃–0.2BaTiO₃ compositions could be attributed to their microstructure and surface charge effects and electron transfer between Fe³⁺ and Fe²⁺ ions. It was also found that high dielectric constant of 0.9BiFeO₃–0.1BaTiO₃ composition was a result of grain and grain‐boundary effects, as observed in SEM micrographs. In addition, a strong signature of dielectric relaxation behavior was observed in this ceramic system with the activation energy 0.467 eV obtained from the Arrhenius' law. Finally, the local structure investigation with XAS technique provided additional information to better understand the electric and magnetic properties in the BF‐BT ceramic system.