Effect of orthorhombic–tetragonal phase transition on structure and piezoelectric properties of KNN-based lead-free ceramics

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Abstract

Lead free piezoelectric ceramics have been prepared by the conventional solid state reaction method and the effects of SrZrO ₃ content on polymorphic phase transition are investigated.

Abstract

(1 − x)(K _0.5Na _0.5) _0.95Li _0.05Nb _0.93Sb _0.07O ₃- xSrZrO ₃ ((1 − x)KNLNS- xSZ) lead free piezoelectric ceramics have been prepared by the conventional solid state reaction method, via adjusting the orthorhombic–tetragonal phase transition temperature to near room temperature with doping SrZrO ₃, and the effects of SrZrO ₃ content on polymorphic phase transition have been investigated. These results show that the phase structure of the ceramics was changed from orthorhombic to tetragonal at x ≥ 0.02 mol, and the orthorhombic–tetragonal phase transition temperature was modified to around room temperature with increasing SrZrO ₃. Remarkable piezoelectric and ferroelectric properties has been obtained in (1 − x)KNLNS- xSZ system with x = 0.02, which showed a piezoelectric parameter of d ₃₃ = 256 pC N ⁻¹, Curie temperature T _c = 270 °C, strain levels of 0.16% at 50 kV cm ⁻¹, remnant polarization P _r = 24.9 μC cm ⁻² and coercive field E _c = 10.6 kV cm ⁻¹.

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Lead-free piezoceramics.

Yasuyoshi Saito, Hisaaki Takao, Toshihiko Tani … (2004)

Lead has recently been expelled from many commercial applications and materials (for example, from solder, glass and pottery glaze) owing to concerns regarding its toxicity. Lead zirconium titanate (PZT) ceramics are high-performance piezoelectric materials, which are widely used in sensors, actuators and other electronic devices; they contain more than 60 weight per cent lead. Although there has been a concerted effort to develop lead-free piezoelectric ceramics, no effective alternative to PZT has yet been found. Here we report a lead-free piezoelectric ceramic with an electric-field-induced strain comparable to typical actuator-grade PZT. We achieved this through the combination of the discovery of a morphotropic phase boundary in an alkaline niobate-based perovskite solid solution, and the development of a processing route leading to highly textured polycrystals. The ceramic exhibits a piezoelectric constant d33 (the induced charge per unit force applied in the same direction) of above 300 picocoulombs per newton (pC N(-1)), and texturing the material leads to a peak d33 of 416 pC N(-1). The textured material also exhibits temperature-independent field-induced strain characteristics.