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(KxNa0.96-xLi0.04)(Nb0.85Ta0.15)O3 lead-free piezoelectric ceramics were produced by conventional solid-state reaction method. The effects of K/Na ratio on the phase transitional behavior, Raman spectrum, microstructure, and dielectric, piezoelectric, and ferroelectric properties of the ceramics have been investigated. The phase structure of the ceramics undergoes a transition from orthorhombic to tetragonal phase with increasing x. A double-degenerate symmetric O–Nb–O stretching vibration v1 and a triply degenerate symmetric O–Nb–O bending vibration v5 are detected as relatively strong scattering in the Raman spectra. The peak shifts of v5 and v1 modes all have a discontinuity with x between 0.42 and 0.46, which may suggest the coexistence of orthorhombic and tetragonal phases in this range. Properly modifying x reduces the sintering temperature, promotes the grain growth behavior, and improves the density of the ceramics. The polymorphic phase transition (at To-t) is shifted to near room temperature by increasing x to 0.44 (K/Na ratio of about 0.85:1), and the coexistence of orthorhombic and tetragonal phases in the ceramics at x=0.44 results in the optimized electrical properties (d33=291 pC/N, kp=0.54, [variant_greek_epsilon]r=1167, tan δ=0.018, To-t=35 °C, TC=351 °C, Pr=27.65 μC/cm2, and Ec=8.63 kV/cm). The results show that the equal K/Na ratio is not an essential condition in obtaining optimized electrical properties in (KxNa0.96-xLi0.04)(Nb0.85Ta0.15)O3 ceramics. [ABSTRACT FROM AUTHOR]

Lead-free [(K0.458Na0.542)0.96Li0.04] (Nb1-xTax)O3 ceramics were prepared by ordinary sintering technique. The effects of Ta content on the phase transitional behavior, Raman spectrum, microstructure, and dielectric, piezoelectric, and ferroelectric properties of the ceramics were investigated. X-ray diffraction results indicate that the phase structure undergoes a transition from orthorhombic to tetragonal phase with the increase in x. The small and large peaks observed in the Raman spectra can all be attributed to the internal modes of the NbO6 octahedron, and both ν5 and ν1 modes slightly shift to lower frequency numbers by increasing x. Ta substitution for Nb leads to the disappearance of the abnormal grain growth behavior, inhibits the grain growth, and improves the density of the ceramics. Increasing x leads to the different variations of dielectric constants before and after poling and makes the ceramics more relaxorlike. The proper substitution of Ta shifts the polymorphic phase transition (at To-T) to near room temperature, and a coexistence of orthorhombic and tetragonal phases is formed, which leads to significant enhancements of the electrical properties. For the ceramics with x=0.15, the electrical properties become optimum, which are as follows: piezoelectric coefficient d33=298 pC/N, electromechanical coupling coefficient kp=0.52, dielectric constant [variant_greek_epsilon]r=1195, dielectric loss tan δ=0.016, To-T=35 °C, Curie temperature TC=366 °C, remanent polarization Pr=28.68 μC/cm2, and coercive field Ec=7.14 kV/cm. These properties are much higher than those of previously reported (K,Na,Li)(Nb,Ta)O3 systems with K:Na=1:1. [ABSTRACT FROM AUTHOR]

Abstract: Pb(Zr0.52Ti0.48)O3–Pb(Mg1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3 ceramics were prepared using the conventional mixed-oxide route. The effects of CuO addition on the phase transition and electrical responses were investigated. X-ray diffraction analysis indicated that the phase of the material changed from an rhombohedral structure to a MPB structure and then a tetragonal structure when the CuO content was increased from 0.00 to 0.30wt.%. The P–E hysteresis loops of CuO-doped PZT–PMN–PZN ceramics showed pinched shapes instead of the normal square-like P–E loops. The pinched loops were assumed to be the result of the pinning effect of the defect dipoles. Optimized electrical properties, such as d 33 =280pC/N, k p =0.53, tan δ =0.0090, Q m =1645 and ɛ r =982, were achieved by doping 0.20wt.% CuO in PZT–PMN–PZN ceramics sintered at 920°C. [Copyright &y& Elsevier]

Abstract: Effects of ZnO addition on electrical properties and low-temperature sintering of BiFeO3-modified Pb(Zr,Ti)O3–Pb(Fe2/3W1/3)O3–Pb(Mn1/3Nb2/3)O3 were investigated. The investigations revealed that the sintering temperature can be decreased to 950°C, and the favorable properties were obtained with 0.10wt% ZnO added ceramics. The electrical properties were as follows: d 33 =313pC/N, K p =0.56, tan δ =0.0053, ε r =1407 and T c =295°C, which showed that this system was a promising material for the multilayer devices application. [Copyright &y& Elsevier]