No abstract

In this paper the preparation, structure and dielectric parameters of ceramics from different powders of pure potassium sodium niobate (KNN) and KNN doped with 1.0 wt% of Li 2 O, CdO, Bi 2 O 3 , MnO 2 , V 2 O 5 and WO 3 have been studied. The dopping of sintering aids did not affect the crystallographic structure of the ceramics significantly; all ceramic samples had a single-phase perovskite structure. Added elements Li 2 O, CdO, MnO 2 , V 2 O 5 effectively decreased the sintering temperature of KNN (50 • -80 • C). All sintering aids influenced sinterability, microstructure and dielectric properties of ceramics. Dielectric constant for doped samples increased from 6000 up to 8000.

We investigated the effect of uniaxial pressure (0 ÷ 1000 bars) applied parallely to the ac electric field on dielectric properties of PLZT-x/65/35 (2 x 13) ceramics. There was revealed a significant effect of the external stress on these properties. The application of uniaxial pressure leads to the change of the peak intensity of the electric permittivity (ε), of the frequency dispersion as well as of the dielectric hysteresis. The peak intensity ε becomes diffused/sharpened and shifts to a higher/lower temperatures with increasing the pressure. It was concluded that the application of uniaxial pressure induces similar effects as increasing the Ti ion concentration in PZT system. We interpreted our results based on the domain switching processes under the action of combined electromechanical loading.

No abstract

Lead-free piezoelectric ceramics (K 0.5 Na 0.5 )(Nb 1−x Sb x )O 3 +0.5 mol.%MnO 2 , where x = 0 ÷ 0.10, with single phase structure and rhombohedral symmetry at room temperature were prepared by conventional ceramic technology. The optimal sintering temperatures of compositions were within 1100 • -1140 • C. MnO 2 functions as a sintering aid and effectively improves the densification. The samples reached density from 4.26 g/cm 3 for undoped (K 0.5 Na 0.5 )NbO 3 to 4.40 g/cm 3 for Mn/Sb 5+ co-doped ceramics. The co-effects of MnO 2 doping and Sb 5+ substitution lead to significant improvement in dielectric and piezoelectric properties: ε at the T c increased from 6000 (KNN) to 12400 (x = 0.04), d 33 = 92 ÷ 192 pC/N, k p = 0.32 ÷ 0.46, k t = 0.34 ÷ 0.48.