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Lead-free piezoelectric ceramics (Bi0.5Na0.5)0.94(Ba1-xSrx)0.06TiO3 (abbreviated as BNBST-100x, with x ranges from 0.02 to 0.1) have been investigated. Effects of amount of Sr-substitution on the electrical properties and crystal structure of the ceramics were studied. The BNBST-100x ceramics sintered at 1200°C for 2h in air have high density around 5.69~5.75g/cm3. X-ray diffraction (XRD) analysis shows that all of the BNBST-100x ceramics have pure perovskite structure. At high amount level of Sr-substitution, the crystal structure of the samples changes from rhombohedral to tetragonal symmetry. Piezoelectric and dielectric measurements reveal that Sr-substitution amount within a certain range will lead to the increase of piezoelectric coefficient (d33), electromechanical coupling factor (kp), and relative dielectric constant (ε33 T/ε0). At 6 mol% Sr-substitution level, the d33 and kp of the ceramics reach maximum, with values of 168 pC/N and 34%, respectively.

The anti-reducing sintering of (Ca,Sr,Ba)TiO3-based dielectrics was achieved by the cooperating effect of Mn2+, Ca2+, Mg2+, Dy3+ and Yb3+. A small quantity of Zr4+ partly substitution for Ti4+ can improve the temperature dependence of dielectric constant. But ZrO2 will also reduce the solid solubility of BaTiO3-SrTiO3-CaTiO3 ternary system, and may cause phase separation. The separated ferroelectric phase increases the capacitance change under DC bias. Non-reducible (Ca,Sr,Ba)(Ti,Zr)O3-based dielectrics with single orthorhombic phase of perovskite structure was obtained. The dielectric and DC bias properties are: .C/C (DC bias: 1.5kV/mm) <0.05%, ε =250~300, tgδ < 0.5%.

A lead-free piezoelectric ceramic ternary system based on (Bi0.5Na0.5)TiO3 (BNT)-(Bi0.5 K0.5)TiO3(BKT)-BaTiO3(BT) near the morphotropic phase boundary (MPB) between the tetragonal and rhombohedral phases has been investigated. The samples were prepared by a conventional sintering technique. Piezoelectric properties, dielectric properties and microstructures of BNT-BKT-BT lead-free piezoelectric ceramic were studied. The X-ray diffraction (XRD) patterns show that the ceramics possess a single-phase perovskite structure. The measurements of piezoelectric properties reveal that this system has a relatively high piezoelectric performance: the piezoelectric constant d33 reached to 178pC/N and planar electromechanical coupling factor kp enhanced to 0.325. The BNT-BKT-BT ternary system ceramics could be well sintered at 11500C with a high-density ratio of more than 95% of the theoretical density.

It has been reported that formation of Mo(Al,Si)2 phases by the addition of aluminum can improve the mechanical and oxidation properties of MoSi2, however, the constancy of the Mo(Al,Si)2 phase was not explored. In this study, MoSi2 preforms were added with Al whose contents were 1, 5, 10wt%, respectively, and these performs were sintered at 1150°C-1550°C, respectively. These MoSi2 specimens with the Al addition were heat-treated at 1350°C-1550°C in N2 atmosphere. Results showed that single Mo(Al,Si)2 phase existed only when the aluminum content was above 5 wt%. It was difficult to form single Mo(Al,Si)2 phase for the samples with 1wt% Al addition. For the samples with 5wt% Al, only the single Mo(Al,Si)2 phase was formed at 1350°C; and a large number of the tetragonal MoSi2 were re-appeared at 1450°C, 1550°C. For the samples with 10wt% Al addition, the single Mo(Al,Si)2 phase would always formed at individual sintering temperatures. The formation temperature of the single Mo(Al,Si)2 phase was decreased with increment of aluminum content. For the samples composed of the single Mo(Al,Si)2 phase, the Mo(Al,Si)2 phase disappeared gradually and was substituted for MoSi2 and a little of other phases, such as Mo3Al4Si2, by heat treatment at temperatures mentioned above for 40 min. This indicated that the Mo(Al,Si)2 phase was unstable at the temperatures above 1350°C.

The effect of Ho2O3 doping on the electrical properties and microstructure of ZnO base varistor was investigated. It was found that Ho2O3 is an effective dopant for increasing the breakdown electric filed. The Ho2O3 doping can also improve the nonlinear performance both in low and high current area. But excessive doping of Ho2O3 will decrease the withstanding surge current. With 0.8mol% Ho2O3 doping, the varistor samples exhibit a breakdown voltage of about 400V/mm, a nonlinear coefficient of 80 and the withstanding surge current of 8/20μs, waveshape is higher than 5kA. Ho2O3 dopant can hinder ZnO grain growth and make the crystal grains more uniform.