Search

Here we report the 0.94(BiNa)TiO-0.06Ba(ZrTi)O (0.94BNT-0.06BZT) lead-free ceramics was synthesized by two-step solid state reaction route. The structural, dielectric, ferroelectric, piezoelectric and electromechanical properties of the ceramics were studied, and showed excellent electric properties ( P = 39.9 μC/cm, P = 33.7 μC/cm, E = 2.79 kV/mm, S = 0.20%, d = 174 pC/N, k = 0.33). The depolarization temperature ( T ) of the ceramics is about 65 °C, which is determined from the first hump of relative dielectric constant. The electromechanical factor k disappears at 65 °C, is consistent with the depolarization temperature ( T ) and the ferroelectric-antiferroelectric phase transition temperature ( T ) determined from the temperature-dependent P- E and bipolar S- E curves. These results indicate the 0.94BNT-0.06BZT ceramics has a good thermal stability in range of − 60-60 °C, and meets the actual demand. [ABSTRACT FROM AUTHOR]

The structures, Curie temperature, dielectric relaxor behaviors, ferroelectricity, ferromagnetism, and magnetocapacitance of the (1− x) Ba0.70 Ca0.30 TiO3- x BiFeO3 [(1− x) BCT- x BF, x = 0-0.90] solid solutions have been systematically investigated. The ceramics have coexisted tetragonal (T) and orthorhombic (O) phases when x ≤ 0.06, coexisted pseudocubic (PC) and O phases when x = 0.065, coexisted cubic and O phases when 0.07 ≤ x ≤ 0.12, PC phase when 0.21 ≤ x ≤ 0.42, coexisted T and rhombohedral (R) phases when 0.52 ≤ x ≤ 0.70, and R phase when x ≥ 0.75. Significantly, composition-dependent microstructures and Curie temperature are observed, the average grain size increases from 1.9 μm for x = 0, reaches 12.0 μm for x = 0.67, and then decreases to 1.3 μm for x = 0.90. At room temperature, the ceramics with x = 0.42-0.70 show piezoelectric properties and multiferroic behaviors, characterized by the polarization-electric field, polarization current intensity-electric field, and magnetization-magnetic field curves, the composition with x = 0.67 has maximum polarization, remnant polarization, maximum magnetization, and remnant magnetization of 15.0 μC/cm2, 9.1 μC/cm2, 0.33 emu/g, and 0.14 emu/g, respectively. In addition, the magnetocapacitance is evidenced by the increased relative dielectric constant with increasing the applied magnetic field ( H). With Δ H = 8 kOe, the composition with x = 0.67 shows the largest values of (εr( H) − εr(0))/εr(0) = 2.96% at room temperature. The structure-property relationship is discussed intensively. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric ceramics of (1 − x) Ba0.70 Ca0.30 TiO3- x BiFeO3 [(1 − x) BCT- x BF, x = 0-0.065] have been prepared and investigated. The ceramics with x ≤ 0.06 have diphasic tetragonal and orthorhombic crystal structures, whereas tetragonal phase is suppressed by the introduction of BF. As a result, the composition with x = 0.065 is found to have diphasic pseudocubic and orthorhombic phases. Significantly composition-dependent grain size is observed. With increasing x from 0 to 0.065, the ferroelectric-paraelectric phase transition temperature decreases monotonically from 128°C to 50°C, accompanied by enhanced ferroelectric relaxor behavior, as indicated by the widened diffused phase transition temperature. The room temperature polarization-electric field ( P-E) hysteresis loops and strain-electric field ( S-E) curves indicate that the ferroelectricity enhances slightly and reaches the maximum near x = 0.05, and then weakens with increasing x. On the other hand, the piezoelectric coefficient ( d 33) and electromechanical coupling coefficient ( kp) decrease simultaneously with increasing x, whereas the mechanical quality factor ( Qm) reaches the maximum near x = 0.05. The structure-property relationship is discussed intensively. Our results may be helpful for further understanding and designing BaTiO3-related lead-free ferroelectric/piezoelectric materials. [ABSTRACT FROM AUTHOR]

Highlights: [•] The effects of Mn doping on structures, electric, magnetic, and magnetocapacitive properties of the 0.33Ba0.70Ca0.30TiO3–0.67BiFeO3 + x wt%MnO2 (BCT-67BF:Mn100x, x =0–0.6) ceramics have been intensively investigated. [•] The BCT-67BF:Mn100x ceramics with x =0–0.6 have diphasic tetragonal–rhombohedral phases. Mn doping improves the densification and significantly decreases the grain size. [•] As x increases, the relaxor degree increases, the ferroelectricity and piezoelectricity weaken monotonically, while the magnetism enhances firstly, reaching the maximum near x =0.5, and then decreases. [•] The room temperature relative dielectric constant shows an obvious increase with increasing applied magnetic fields (H), the magnetocapacitive coefficient (ε r(H)− ε r(0))/ε r(0) decreases with increasing Mn content, from 2.96% for x =0 – 0.86% for x =0.6 . [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]