| In order to satisfy the requirements of high-power multilayered piezoelectric transformers and piezoelectric speaker for practical applications, the properties of piezoelectric ceramics should combine high electrical properties and a low sintering temperature. PbZrO3-PbTiO3-Pb(Mg1/3Nb2/3)O3-Pb(Z1/3Nb2/3)O3 (PZT-PMN-PZN) and PbZrO3-PbTiO3-Pb(Ni1/3Nb2/3)O3-Pb(Mg1/2W1/2)O3-Pb(Sbi/2Nb1/2)O3(PZT-PNN-PMW-PSN) piezoelectric ceramics were investigated in this work from the aspects of process, dopants addition and sintering aids addition. Moreover, the devices with the favorable properties were fabricated and investigated from the aspects of process and structure.PZT-PMN-PZN ceramics were fabricated by the conventional mixed-oxide method. The density, microstructure, dielectric and piezoelectric properties of PZT-PMN-PZN ceramics as a function of Li2CO3,LiSbO3,ZnO-Li2CO3,Pb3O4, CuO and Ba(W1/2Cu1/2)O3 content and sintering temperature were investigated. The results indicated that the composition calcined at 800℃and sintered at 1020℃showed the optimized values of d33,Kp, Qm,εr and tanδ, which were 249 pC/N,0.57,1954,1122 and 0.0059, respectively. The piezoelectric transformers with the composition of PMN-PZN-PZT calcined at 800℃and sintered at 1020℃were fabricated and measured at different resistance loads. The optimized values were high step-up ratio of 120, high efficiency of 90%,low temperature rise of 5℃at 250 kΩand broad frequency band, respectively. Otherwise, the 5 W cold cathode fluorescent lamps (CCFL) were successfully driven using the fabricated transformer with optimized PZT-PZN-PMN composition ceramics. The proper additions of 0.10 wt.%ZnO-Li2CO3 with 0.10 wt.%Pb3O4 content could modified the electrical properties of PZT-PMN-PZN ceramics, which were listed as follows:d33=256 pC/N,Kp=0.60, Qm=1910,εr=1032, tanδ=0.0070 and r=2.09 Q, respectively. The step-down piezoelectric transformers with the optimal composition of PZT-PMN-PZN ceramics sintered at 995℃were fabricated and measured at different output power and resistance loads, respectively. The step-down piezoelectric transformers showed the favorable characteristics with a higher gain G of 0.204 and a lower temperature rise of 6℃when the output power was 5 W, and the driving frequency was approximately constant(-126 kHz) when the output power was from 5 W to 13 W. In addition, the maximum efficiency (90.2%)was obtained at load resistance of 10Ω. To further decreased the sintering temperature and improved the electrical properties of the ceramics, PZT-PMN-PZN-0.10 wt.%Bi2O3+0.10 wt.% ZnO-Li2CO3+0.10 wt.%Pb3O4 ceramic were investigated by doping CuO and Ba(W1/2Cu1/2)O3. The influence of CuO content and Ba(W1/2Cu1/2)O3 on the phase structure, microstructure, dielectric, piezoelectric properties and the temperature stability of the ceramics were investigated in details.It was found that the sintering temperature of the ceramics with adding 0.10 wt.% CuO reduced from 995℃to 920℃.Meanwhile, the ceramics exhibited good properties, which were d33=280 pC/N,Kp=0.53,Qm=1645,tanδ=0.0090,εr=982 and Tc=321℃.And the composition sintered at 920℃with 0.13 wt.% Ba(W1/2Cu1/2)O3 content also showed a uniform microstructure with fewer pores and higher values, which were listed as follows:d33=351 pC/N,Kp=0.63,Qm=1415,tanδ=0.0078,εr =1023,Tc=322℃, Pr=45μC/cm2 andEc=5.69 kV/cm. The material was a good candidate for high-power multilayered piezoelectric transformer applications.To satisfy the requirement of multilayer piezoelectric speaker and decrease cost, the properties of Pb(Ni1/3Nb2/3)O3-PZT with Pb(W1/2Mg1/2)O3,Pb(Sb1/2Nb1/2)O3 and Zr/Ti ratios were investigated. The results revealed that 0.36PbTiO3-0.23PbZrO3-0.38Pb(Ni1/3Nb2/3)O3-0.02Pb(Mg1/2W2/3)O3-0.01Pb(Sb1/2Nb1/2)O3 ceramics sintered at 1150℃gave the desirable piezoelectric and dielectric properties, which were d33=833 pC/N,Kp=0.72,Qm>m=42, tanδ=0.0243,εr=4843,Tc=180℃,Δr/fr25℃=3.01%,Δεr/εr25℃=15.79%,ΔKp/Kp25℃=1-15% andΔQm/Qm25℃=2.11%.In order to decrease the sintering temperature, LiSbO3 and Ba(W1/2Cu1/2)O3 addtition were added to the ceramics, which could make the sintering temperature decrease from 1150℃to 900℃and 930℃, respectively. The liquid phase was formed and the pyrochlore phase was inhibited by LiSbO3 and Ba(W1/2Cu1/2)O3 additive. With increasing LiSbO3 content, d33,Kp and Qm increased at first, and then decreased. The optimal values of the ceramics sintered at 900℃were obtained by doping 0.06 wt.% LiSbO3,which were listed as follows:d33=665 pC/N, Kp=0.62, Qm=25,tanδ=0.0224 andεr=5600. In addition, it was also found that the addition of Ba(W1/2Cu1/2)O3 significantly improved the sinterability of the ceramics sintered at 930℃.The favorable piezoelectric and dielectric properties were obtained by doping 0.13 wt.% Ba(W1/2Cu1/2)O3 addition, which were listed as follows:d33=661 pC/N,Kp=0.63,Qm=36,εr=4206, tanδ=0.0209, Tc=200℃,Δfr/fr25℃=2.8% andΔKp/Kp25℃=-1.15%.The compositions with 0.13 wt.% Ba(W1/2Cu1/2)O3 additives were fabricated multilayer piezoelectric speaker. The piezoelectric speaker sintered at 930℃had homogenous microstructure, low porosity, well-grown grains and the Ag/Pd alloy joint at the interface. As increasing sintering temperature,f0 decreased, but SPL increased. With increasing thickness, fo increased, but SPL changed inslightly. The f0 and SPL increased with increasing layer number. The f0 decreased, and SPL changed inslightly with-L/W Ratio of the speaker decreased. Piezoelectric speakers sintered at 930℃obtained low f0(≤2.0 kHz) and high SPL (≥70 dB), which satisfied the requirement of multilayer piezoelectric speaker.
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