Study On Preparation And Properties Of Multicomponent Potassium Sodium Niobate-based Lead-free Piezoelectric Ceramics

Multicomponent potassium sodium niobate–based lead–free piezoelectricceramics （0.94–y）(K_0.49Na_0.51-xLi_x)NbO₃–y(Bi_0.5K_0.5)TiO₃–0.06BaZrO₃(KNNL_x–yBKT–BZ) and (K_0.49Na_0.51)_0.98–xLi_0.02+x(Nb_0.77Ta_0.18–ySb_0.05+y)O₃–0.005BaZrO₃(KNNLTSBZ_x–y) were prepared in the laboratory and enterpriseby the traditional ceramic technology, respectively. The effects of Li and BKTco–doping, Li and Sb co–doping on the phase, microstructure, piezoelectricand dielectric properties of samples were investigated. The(K_0.49Na_0.51)_0.96Li_0.04(Nb_0.77Ta_0.17Sb0.06)O₃–0.005BaZrO₃multicomponentpotassium sodium niobate–based lead–free piezoelectric ceramic will besuitable for practical.First, The effects of Li content （x=0⁰.05） and BKT content （y=0⁰.04）co–doping on the performance of KNNL_x–yBKT–BZ lead-free piezoelectricceramic were investigated. The results show that all samples possess a singleperovskite structure within the composition range, with Li content xincreasing, the crystal structure of KNNL_x–0.02BKT–BZ ceramics istransformed from rhombohedral phase to tetragonal phase, therhombohedral–tetragonal morphotropic phase boundary （MPB） locates in thecomposition range of0.01﹤x﹤0.03. With y increasing, the crystal structureof KNNL_0.03–yBKT–BZ ceramic transformed from orthorhombic to tetragonalsymmetry across a MPB region with the composition range of0.01﹤y﹤0.03.Li doping can effectively improve the Curie temperature （T_c）. With theincrease of BKT amount, both the Curie temperature （T_c） and theorthorhombic–tetragonal phase transition temperature (T_o–t) descend,meanwhile dielectric relaxation is enhanced for KNNL_0.03–yBKT–BZceramics. Composition with x=0.03, y=0.02exhibits optimal electricalproperties: piezoelectric constant d₃₃=227pC/N, planar electromechanicalcoefficient k_p=39.3%, mechanical quality factor Q_m=69, dielectric constantε^T₃3/ε₀=1642, dielectric loss tanδ=2%, remanent polarization P_r=13.3μC/cm2,and coercive field strength E_c=1.64kV/mm. Li doping can obviouslyimprove the temperature stability of KNNL_x–0.02BKT–BZ materials, afterheat treatment at200oC, remanent properties is still above80%of originalperformance when x≥0.03. The d₃₃and k_pare185pC/N and32%after heattreatment for x=0.03, which is a promising application of piezoelectric ferroelectric materials.Second, in an enterprise environment, the effects of Li and Sb content onthe crystal structure, microstructure and electrical properties ofKNNLTSBZ_x–y ceramics were studied systematically. The results show that:all the samples possess pure perovskite structure, with the increase of x, thecrystal structure of KNNLTSBZ_x–0 ceramics is transformed fromorthorhombic to tetragonal symmetry across a polymorphic phase transition（PPT） region0.02﹤x﹤0.04, KNNLTSBZ_x–0 ceramics with x=0.02exhibitoptimal electrical properties: d₃₃=240pC/N，k_p=44.7%，ε^T₃3/ε₀=2090，tanδ=2.7%. With the increase of y, the crystal structure of KNNLTSBZ0.02–yceramics always keep orthorhombic phase, the electrical properties ofKNNLTSBZ_0.02–y ceramics decrease gradually, decline slowly within therange of y=0⁰.015, then decreased rapidly when y≥0.02. The dielectrictemperature spectrum indicated: with the increase of x, T_cand T_o–tof theKNNLTSBZ_x–0 ceramics is shifted to upward and downward respectively, andT_o–tdrops to below room temperature when x≥0.03; with y increasing, T_cofKNNLTSBZ_0.02–y ceramics increases, then decreases when y﹥0.01, themaximum value is224oC for y=0.01, T_o–tremains50⁶0oC.