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The BiFeO3-BaTiO3 (BF-BT) ceramics were here prepared through the solid-state reaction of Bi2O3, Fe2O3 and nano-sized BT powders. The crystal structures and piezoelectric properties were investigated in both quenched (AQ) and slowly cooled (SC) 0.7BF-0.3BT ceramics. Prior work has shown that rhombohedral and pseudo-cubic phases coexist in 0.7BF-0.3BT ceramics. In this work, the crystal structure of the pseudo-cubic phase was refined as a non-polar orthorhombic Pbnm phase in the SC sample and as a polar orthorhombic Pmc21 phase in the AQ sample. In addition to a sharp dielectric peak at about 620 °C, corresponding to the Curie temperature of the rhombohedral phase, a broad dielectric peak with strong frequency dispersion and a sharp frequency-independent dielectric peak were observed at around 500 °C in the SC and AQ samples, respectively. We determine that the dielectric anomalies around 500 °C were caused by a relaxor phase transition of the non-polar orthorhombic phase in the SC sample and a ferroelectric–paraelectric phase transition of the polar orthorhombic phase in the AQ sample. The AQ sample showed better ferroelectric and piezoelectric properties than the SC sample. The 0.7BF-0.3BT ceramic slowly cooled in a nitrogen atmosphere showed a well-saturated P-E curve and a similar temperature-dependent dielectric constant as the AQ sample. Our results indicate that large concentrations of oxygen vacancies produce a more distorted polar orthorhombic phase and better piezoelectric properties in the AQ sample than in the SC sample. [ABSTRACT FROM AUTHOR]

The electrocaloric effect (ECE) in lead-free (Bi0.5Na0.5)TiO3-SrTiO3 (BNT-ST) ceramics was investigated by direct and indirect measurements. Polarization-electric field hysteresis loops of the BNT-ST ceramics changed from well-saturated shapes at room temperature to constricted shapes around the depolarization temperature due to an electric field-induced phase transition. A large adiabatic temperature change due to ECE (ΔTEC) was obtained around the phase transition temperature (TFR) by indirect measurements, which was confirmed by direct measurements. The 0.85BNT-0.15ST sample showed a large negative ΔTEC in the indirect measurements below TFR where the polarization increases, while the directly measured ΔTEC displayed positive values. It suggests that the indirect method using the Maxwell relation is not valid in the temperature range where the polarization increases with temperature. The X-ray diffraction structural refinements showed that the poled 0.85BNT-0.15ST sample has mixed phases of a rhombohedral R3C and a tetragonal P4bm in the temperature range where the polarization increases below TFR. [ABSTRACT FROM AUTHOR]

Solid solutions of xBiFeO[sub 3]–yPrFeO[sub 3]–zPbTiO[sub 3] (x+y+z=1) and (1-w)BiFeO[sub 3]–wPbTiO[sub 3] have been explored for finding ferroelectromagnetic bulk material, in which ferroelectricity and ferromagnetism coexist simultaneously. The coexistence has been observed only in some ternary composition samples, that is, 0.2BiFeO[sub 3]–0.2PrFeO[sub 3]–0.6PbTiO[sub 3] and 0.4BiFeO[sub 3]–0.2PrFeO[sub 3]–0.4PbTiO[sub 3]. In the ternary solid solutions, spontaneous magnetic moments disappear with the decrease of PrFeO[sub 3] content to y<0.2 independently of BiFeO[sub 3] content. When PrFeO[sub 3] content remains constant at y=0.2, the ternary solid solutions become paraelectric with the decrease of PbTiO[sub 3] content to z≤0.2. The ferroelectromagnetic solid solutions have the noncentrosymmetric and doubled perovskite unit cell with a space group I4cm (a=bapprox. 5.4 Å, capprox. 7.9 Å). Addition of Ta[sub 2]O[sub 5] dopant substantially changes the polarization–electric-field and magnetization–magnetic field curves of the 0.2BiFeO[sub 3]–0.2PrFeO[sub 3]–0.6PbTiO[sub 3]. The binary solid solutions of (1-w)BiFeO[sub 3]–wPbTiO[sub 3] do not exhibit spontaneous magnetic moments down to 10 K over the entire composition range. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The binary and ternary solid solutions, BiFeO3-BaTiO3, BiFeO3-BaTiO3, and BiFeO3-BaFeO2.5-BaTiO3 were explored in order to attain ferro-electricity and ferromagnetism in bulk ceramics. The change carrier mediation in the antiferro magnetic lattice is caused by the weak ferromagnetization.

The 0.97(Na0.5K0.5)(Nb1−xSbx)O3‐0.03CaZrO3 ceramic with x = 0.09 exhibits a high d33 of 518 pC/N and a strain of 0.13% at 4.0 kV/mm owing to its orthorhombic‐pseudocubic polymorphic phase boundary (PPB) structure. However, these values decreased considerably above 90°C owing to its low Curie temperature (TC), indicating that its thermal stability is not sufficient for practical applications. Li2O was added to the specimen with x = 0.11 to improve its thermal stability of the strain and d33 by increasing the TC without degrading the actual d33 and strain values. The 0.97(Li0.04Na0.46K0.5)(Nb0.89Sb0.11)O3‐0.03CaZrO3 ceramic, having an orthorhombic‐tetragonal PPB structure, exhibits a d33 of 502 pC/N and a strain of 0.16%. This large strain was maintained up to 150°C and the d33 slightly decreased to 475 pC/N at 130°C. Therefore, this lead‐free ceramic displays excellent piezoelectric characteristics with improved thermal stability, indicating that it can be applied to piezoelectric actuators. [ABSTRACT FROM AUTHOR]