Effects of Ge4＋ acceptor dopant on sintering and electrical properties of （K0.5Na0.5）NbO3 lead-free piezoceramics

Lead-free （K0.5Na0.5）（Nb1-xGex）O3 （KNN-xGe, where x = 0-0.01） piezo- electric ceramics were prepared by conventional ceramic processing. The effects of Ge4＋cation doping on the phase compositions, microstructure and electrical properties of KNN ceramics were studied. SEM images show that Ge4＋ cation doping improved the sintering and promoted the grain growth of the KNN ceramics. Dielectric and ferroelectric measurements proved that Ge4＋ cations substituted Nbs＋ ions as acceptors, and the Curie temperature （Tc） shows an almost linear decrease with increasing the Ge4＋ content. Combining this result with microstructure observations and electrical measurements, it is concluded that the optimal sintering temperature for KNN-xGe ceramics was 1020℃. Ge4＋ doping less than 0.4 mol.% can improve the compositional homogeneity and piezoelectric properties of KNN ceramics. The KNN-xGe ceramics with x = 0.2% exhibited the best piezoelectric properties： piezoelectric constant d33 = 120 pC/N, planar electromechanical coupling coefficient kp = 34.7%, mechanical quality factor Qm = 130, and tanδ = 3.6%.

Ca^2+ doping effects in(K,Na,Li)(Nb0.8Ta0.2)O3 lead-free piezoelectric ceramics

Lead-free(K0.5-x/2Na0.5-x/2Lix)(Nb0.8Ta0.2)O3(KNLNT)and(K0.49-x/2Na0.49-x/2-LixCa0.01)(Nb0.8Ta0.2)O3(KNLNT-Ca)ceramics were prepared by a conventional ceramic processing.Structural analysis shows that the Ca^2+ doping takes the A site of ABO3 perovskite and decreases the phase transition temperature.Property measurements reveal that as a donor dopant,the Ca^2+ doping results in higher room-temperature dielectric constant,lower dielectric loss,and lower mechanical quality factor.In addition,the Ca^2+ doping does not change the positive piezoelectric coefficient d33,but increases the converse piezoelectric coefficient d 33*significantly.This is likely due to the increase in the relaxation,as well as the appearance of(CaNa/K·-VNa/K’)defect dipoles.

Facile fabrication of cordierite-based porous ceramics with magnetic properties

In this paper,cordierite-based porous ceramics with magnetic properties have been firstly in-situ synthesized by using MgO,Al_(2)O_(3),and SiO_(2) powders as raw materials and Fe_(3)O_(4) as a functional additive.Combining with the foam freeze casting method,near net size fabrication(total linear shrinkage<2.86%)of the magnetic porous materials was realized by adjusting the amount of Fe_(3)O_(4).The porosity,compressive strength,and saturation magnetization of the prepared materials were 83.9%-87.8%,1.51-2.65 MPa,and 1.2-5.8 emu/g,respectively.The phase composition and microstructure evolutions during sintering were investigated briefly.The results showed that the synthesis temperature of cordierite was lowered about 100℃ due to the addition of Fe_(3)O_(4).Except for the main phase-cordierite,Mg-Al-Fe spinel and α-Fe_(2)O_(3) also existed in the final materials.The lattice parameters of the Mg-Al-Fe spinel and the amount of α-Fe_(2)O_(3) changed obviously with the change in the sintering temperature and Fe_(3)O_(4) amount,which mainly influenced the magnetic properties of the prepared materials.Thus,a facile fabrication method of the cordierite-based porous ceramics with the magnetic properties has been put forward in this paper.

Improvement in synthesis of （K0.5Na0.5）NbO3 powders by Ge4＋ acceptor doping

In this paper, the effects of doping with GeO2 on the synthesis temperature, phase structure and morphology of （K0.5Na0.5）NbO3 （KNN） ceramic powders were studied using XRD and SEM. The results show that KNN powders with good crystallinity and compositional homogeneity can be obtained after calcination at up to 900℃ for 2 h. Introducing 0.5 mol.% GeO2 into the starting mixture improved the synthesis of the KNN powders and allowed the calcination temperature to be decreased to 800℃, which can be ascribed to the formation of the liquid phase during the synthesis.