Preparation, Enhancement And Toughening Of Pbszt Piezoelectric Ceramics

The piezoelectric ceramic (Pb_0.70Ba_0.26Sr_0.04) (Zr_0.52 Ti_0.48) O₃ (PBSZT) is choosed as a basic material for the present investigation. To improve the mechanical properties of PBSZT, three approaches including Bi ions doping, addition of K₂Ti₆O₁₃ whiskers (KTOw) and composite of Bi ions doping and addition of K₂Ti₆O₁₃ whiskers were carried out. The improvements were conformed by measurements of bending fracture strength (σ_b) and fracture distortion (△p). The microstructure and phase compositions were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The composition was analyzed by energy dispersive spectrometer (EDS). The parameters such as relative dielectric constant (ε_r), dielectric loss(tanб), electric hysteresis loops, piezoelectric coefficient (d₃3,d₃₁) and electromechanical coupling coefficient(k_p) were measured to investigate effects of the modification approaches on the functional properties of the modified PBSZT ceramics.The experimental results of Bi₂O₃ doped PBSZT (Bi-PBSZT) indicate that an appropriate Bi₂O₃ substitution (Bi₂O₃ wt.%=0-0.3) can reduce the ceramic grain size and increase sintering density, enhance the bending fracture strength. While and d₃₁ values exhibit a reduction tendency with the Bi₂O₃ substitution due to the lattice distortion. The glassy matter in which Pb is enriching in grain boundary area will suppress of Bi³⁺and Pb²⁺ion vacancy dipole moments. It is found that when the Bi₂O₃ content at 0.3 wt% the Bi-PBSZT ceramics possess the optimized characteristics withσ_b=140.37 MPa,ε_r=5520, d₃₁=518 x10^-12m/V.The PBSZT ceramics with KTO_W (PBSZT/KTOw) show a large fracture distortion, which develops the toughening mechanism of micro poles arising from the addition of KTO_w.With the increase of KTO_W, the density and strength reduce, and for the functional properties,ε_r and tanбdecrease, while the variation of d33 like a parabola which opens downward. The change of kp is consist with d₃₃ Compared with PBSZT, at the 0.5 wt.% KTO_W, d₃₃ achieves a maximum value 471.4 x10^-12 m/V, with an increase 26.2%, and Ap is increased 4.2%. At the 1.0 wt.% KTOw incorporation, d33 is decreased 3.9% and Ap achieves a maximum 2.45 mm, increased 28.9%. The effect of "both increase" makes KTO_W as a good candidate for toughening piezoelectric ceramics.The composite approach (Bi-PBSZT/KTO_w) shows that the bending fracture strength and functional properties for the composites combining theindividual characteristics. With 0.3 wt.% Bi₂O₃ and 1.0 wt.% KTO_w, the Ap achieves a maximum 3.18 mm, which increases 67.3% compared with PBSZT, and other parameters characterized asσ_b:101.51 MPa, d₃3:362.5 x10^-12 m/V. For all other samples:0.3 wt.% Bi₂O₃ and 1.8 wt.% KTO_W,0.5 wt.% Bi₂O₃ and 1.0 wt.% KTO_w,0.5 wt.% Bi₂O₃ and 1.8 wt.% KTOW, ther fracture distortion and piezoelectric coefficients are increased. The phenomenon of "both increase" on toughness and piezoelectric properties confirms the advantage of this composite approach.