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Ba 0.70 Ca 0.30 Ti 1- x (Nb 0.5 Fe 0.5) x O 3 lead-free ceramics (abbreviated as BCTNF x , x = 0–0.12) were prepared by solid-state reaction method. The influence of B-site (Fe 0.5 Nb 0.5)4+ substitution on phase structure, microstructure, dielectric, ferroelectric and piezoelectric properties of Ba 0.70 Ca 0.30 TiO 3 ceramics were systematically studied. The BCTNF x ceramics consist of diphasic tetragonal (T) and orthorhombic (O) phases at x = 0–0.04, pseudocubic (PC) and O phases at x = 0.05–0.08, cubic (C) and O phases at 0.08 < x ≤ 0.12. Increase of (Fe 0.5 Nb 0.5)4+ doping improves sinterability, depresses the ferroelectric - paraelectric phase transition temperature (T m) monotonically from 128 °C at x = 0 to -86 °C at x = 0.12, induces enhanced relaxor behavior and weakens piezoelectric properties. The room temperature relative dielectric constant (ε r) and dielectric loss tangent (tan δ) increase with increasing x and reach the maximum values of 4869 and 0.06 respectively at x = 0.06. Whereas the average grain size (abbreviated as AGS), ferroelectric properties and electric field induced strain increase significantly by introducing 2.0 mol% B-site complex cations (Fe 0.5 Nb 0.5)4+ into Ba 0.70 Ca 0.30 TiO 3 ceramics. The BCTNF0.02 ceramics achieve optimal electrical properties with ε r = 1268, tan δ = 0.03, T m = 102 °C, P max = 12.8 μC/cm2, P r = 6.1 μC/cm2, E C = 6.0 kV/cm, d 33 = 117 pC/N, k p % = 0.18%, Q m = 236, bipolar S max % = 0.20%, unipolar S max % = 0.16% and d 33 ∗ = 314 pm/V. The variation of electrical properties of BCTNF x ceramics is attributed to the combined action of grain size effect, phase transition, weakness of octahedral distortion, clamping effects of the internal bias electric field E i on domain wall motion induced by B-site cations (Fe 0.5 Nb 0.5)4+ displacement. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric ceramics of Ba0.70Ca0.30Ti1−x Fe x O3 (x=0–0.03) have been synthesized by a conventional solid state reaction method. The influence of Fe content on the microstructure, phase transition, dielectric, ferroelectric, and piezoelectric properties is investigated systematically. The ceramics with x≤0.02 are diphasic composites of tetragonal Ba0.80Ca0.20TiO3:Fe and orthorhombic Ba0.07Ca0.93TiO3:Fe solid solutions. The tetragonal phase is gradually suppressed as x increases, the ceramic with x=0.03 is found to have diphasic pseudocubic and orthorhombic phases. And the grain size is dependent on Fe content significantly. Introduction of Fe at B-sites improves the densification and decreases the sintering temperature. As x increases from 0 to 0.03, the room temperature relative dielectric permittivity enhances, dielectric loss decreases, and the Curie temperature decreases monotonically from 128°C to 58°C. However, the ferroelectricity enhances slightly and reaches the maximum near x=0.005, and then weakens with increasing x. On the other hand, the piezoelectric coefficient (d 33) and the electromechanical coupling coefficient (k p ) decrease simultaneously with increasing x, whereas the mechanical quality factor (Q m ) increases significantly. The structure–electrical properties relationship is discussed intensively to give more information on (Ba,Ca)TiO3-based lead-free piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

Abstract: The effects of sintering temperature and poling conditions on the electrical properties of tetragonal and orthorhombic diphasic Ba0.70Ca0.30TiO3 (BCT) lead-free ceramics have been systematically investigated. On the one hand, with increasing sintering temperature from 1270°C to 1400°C, the bulk density increases monotonically and the Curie temperature keeps almost constant with the value of ∼120°C, whereas the grain size, the maximum relative dielectric constant, room temperature polarization reach the maximum values for samples sintered at 1340°C. On the other hand, it is found that the piezoelectric property depends on poling electric field and poling temperature significantly. An enhanced piezoelectric behavior of d 33=126pC/N, k p =0.29, and Q m =588 is obtained for the BCT ceramics poled at 100°C with 30kV/cm field for 20min. The aging behavior of the piezoelectric property is also investigated. [Copyright &y& Elsevier]