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0.70BiFeO3‐0.30BaTiO3 (0.70BF‐0.30BT) ceramics have been widely concerned because of their potential applications for high‐temperature piezoelectric devices. In this work, a series of dense 0.70BF‐0.30BT ceramics with average grain size variation from 0.55 to 6.0 μm were prepared. XRD results indicate that 0.70BF‐0.30BT ceramics show the coexistence of rhombohedral and pseudo‐cubic phases and the volume fraction of the rhombohedral phase increase with the grain size. The dielectric, ferroelectric and piezoelectric properties increase with the grain size initially from 0.55 to 5.0 μm and then decrease slightly. Values of d33, Pr, and εr, of 0.70BF‐0.30BT ceramics with the grain size of 5.0 μm are 185 pC/N, 21.2 μC/cm2, and 638, respectively, about five times higher than those ceramics with fine‐grain of 0.55 μm. Of particular importance is that 0.70BF‐0.30BT ceramics with large grain sizes possess better piezoelectric thermal stability due to the much stabler poled domain state with the rising temperature. The detailed structural studies indicate that the enhanced electric properties are owing to the significantly improved domain motion and the increased lattice distortion. This clarifying the relationship between electrical properties and grain size offers a novel way of improving the performances of piezoceramics. [ABSTRACT FROM AUTHOR]

Lead‐free 0.75BiFeO3–0.25BaTiO3 (0.75BF–0.25BT) ceramics have been extensively studied because of their high Curie temperature. The aging behavior and thermal stability of piezoceramics play decisive roles in their device applications. In this work, effects of Mn doping on the phase structure, aging behavior, and thermal stability of 0.75BF–0.25BT ceramics were characterized and related mechanisms were investigated. With the increase in Mn content, the typical rhombohedral phase of 0.75BF–0.25BT ceramics changed to the coexistence of pseudo‐cubic and rhombohedral phases. Mn modification enhanced the aging behavior and thermal stability of ceramics obviously. The aging rates of d33 and kp for 0.75BF‐0.25BT ceramics with 1.0 mol% Mn are 1.3% and 1.1%, respectively, which are only 1/4 those values for the undoped ceramics. The variation of εr of 0.75BF‐0.25BT ceramics with 1.0 mol% Mn is half of undoped ceramics under 500℃. The depoling temperature of 0.75BF‐0.25BT ceramics with 1.0 mol% Mn was 450℃, which is about 200℃ higher than that of undoped ceramics. The enhanced aging behavior results from the decreased defect concentrations, and the better thermal stability is owing to the significantly improved poling state due to the enhanced resistivity, large grain size, and decreased crystal distortion by Mn modification. These results reflect that a proper amount of Mn doping is an effective way to enhance the aging behavior and electric thermal stability. [ABSTRACT FROM AUTHOR]

The xBiFeO3‐(1‐x)Ba(Zr0.02Ti0.98)O3 + 1.0 mol% MnO2 (xBF‐BZT) lead‐free piezoelectric ceramics were prepared by conventional solid‐state reaction method. The structure, dielectric, and piezoelectric properties were studied. X‐ray diffraction (XRD) analysis showed that xBF‐BZT ceramics exhibited pure perovskite structure with the coexistence of tetragonal and rhombohedral phases (0.66 ≤ x ≤ 0.74). The Curie temperature Tc, the dielectric constant εr (1 kHz), dielectric loss tanδ (1 kHz), piezoelectric constant d33, coercive field Ec (80 kV/cm), and remnant polarization Pr (80 kV/cm) of 0.7BF‐0.3BZT‐Mn ceramics were 491°C, 633, 0.044, 165 pC/N, 35.6 kV/cm, and 22.6 μC/cm2, respectively. The unipolar strain of 0.7BF‐0.3BZT reached up to 0.20% under the electric field of 60 kV/cm, which is larger than that (0.15%) of BiFeO3–BaTiO3 ceramics. These results indicated that the xBF‐BZT ceramics were promising candidates for high‐temperature piezoelectric materials. [ABSTRACT FROM AUTHOR]

BiFeO3‐BaTiO3 (BF‐BT) solid solutions are lead‐free candidates for high‐temperature piezoelectric applications. BF‐BT ceramics with compositions near the morphotropic phase boundary (MPB) separating rhombohedral (R) and pseudo‐cubic (PC) phases were fabricated by the conventional high temperature sintering method, and their thermal stability and aging properties were studied in detail. BF‐BT ceramics with rhombohedral (R) phase show much better thermal stability and aging properties than those with pseudo‐cubic (PC) or coexistence of PC and R phases. The thermal degradation and aging rates of BF‐BT ceramics with R phase are on the order of 1% and 1.2% per decade, respectively. X‐ray diffraction results reveal that the domain state of poled rhombohedral BF‐BT ceramics is stable up to its Curie temperature, which is responsible for the high thermal stability. The Rayleigh analysis shows that the low aging rate is attributed to the low domain wall contribution to the overall piezoelectric response. The high thermal stability and low aging rates indicate that the lead‐free BF‐BT ceramics with R phase are potential candidates for sensor and transducer applications over a broad temperature range. [ABSTRACT FROM AUTHOR]