Effect of Hydrothermal Treatment on the Piezoelectric Response of Oriented Barium Titanate Ceramics

The piezoelectric response of [11-oriented, fine-grained BaTiO3 ceramics was investigated. It was found that an exposure of the BaTiO3 compacts to high-pressure, high-temperature steam in an autoclave promoted the orientation of the sintered ceramics. As temperature in the autoclave increased, the orientation increased. A large small-field piezoelectric constant of d33 = 517 pC/N was observed for the oriented BaTiO3 ceramics with the grain size of 1.76 μm and the Lotgering factor of 85.3 %.

Influence of Sintering Conditions on Electric Performance of Textured 92BNT-6BT-2KNN Ceramics

0.92(Bi0.5Na0.5)TiO3-0.06BaTiO3-0.02(K0.5Na0.5)NbO3(92BNT-6BT-2KNN) is a high-stain material due to the volume change which come from antiferroelectric-ferroelectric (AFE-FE) phase transformation. Textured 92BNT-6BT-2KNN with a Lotgering factor of 67% was obtained by templated grain growth (TGG) method using plate-like (Bi0.5Na0.5)TiO3（BNT）particles as templates. The influences of sintering process on Lotgering factor and strain were investigated. It was found that the Lotgering factor increased as sintering temperature increase and then decreased with further temperature increase. The changing tendency of polar and unipolar strain did not keep the same accordance with that of Lotgering factor. The maximum of Lotgering factor (79%) and polar strain (0.36%) was obtained when the sintering temperature was 1240°C and 1220°C, respectively, due to the decrease of density when high sintering temperature was employed. Also it was found that the lotgering factor and polar strain reached its highest values when the soaking time was 4h. All these proved that the density and grain orientation codetermined the strain of 92BNT-6BT-2KNN ceramics.

Fabrication of Textured SrBi2Nb2O9 Ceramics by Templated Grain Growth

Textured SrBi2Nb2O9 (SBN) ceramics were fabricated by templated grain growth (TGG) method. The plated-like SBN particles with shape anisotropy prepared by molten salt method were used as the templates. The SBN powders prepared by conventional solid (CS) reaction were used as matrix powders. It was found that the textured SBN ceramics can be obtained by TGG method. The grain orientation (Lotgering factor, f) increased with the increase of sintering temperature and content of the templates. The textured SBN ceramics with f=0.86 could then be obtained after sintering at 1300 °C for 3 h with 20wt.% templates. The relative density keeps rising with increasing temperature until it reaches a peak value 91.22% at the sintering temperature 1300°C, after which it decreases.

Textured Pb(Mg1/3Nb2/3)O3-PbTiO3 Ceramics by Templated Grain Growth

Fiber textured 0.70PMN-0.30PT ceramics was fabricated using the Templated Grain Growth (TGG) process. Tabular SrTiO3 particles synthesized in molten NaCl-KCl salts were used as templates and oriented in fine 0.70PMN-0.30PT matrix during rolling. Tabular SrTiO3 particles can stabilize in sintering by SPS technique and annealing. A degree of [001] texture (Lotgering factor ~ 0.38) was obtained by heteroepitaxial growth of oriented single PMN-PT on the SrTiO3 template particles.

Texture Investigations on High Temperature Superconductors

The formation of a structure with strong crystallographic texture is an important requirement for high critical current densities at 77 K in high temperature superconductive materials (HTSC). In this work several methods for texture investigation in the superconductive phase of BiPbSrCaCuO/Ag- and YBaCuO/AgPd-composite conductors prepared according to the “powder in tube”-method as well as in YBaCuO-thick layers are presented. For the characterisation of the texture development in dependence on technological steps at the preparation of HTSC-composite conductors the determination of the halfwidth FWHM from the psi-scan or for one-phase specimens the determination of the Lotgering-factor is appropriate, if only a c-axis exists. The measurement of pole figures is necessary to determine, whether a rotation symmetry occurs or an orientation of the (a,b)-directions exists. The use of the omega-scan to determine the half-width is not useful, if the goniometer unit is intended and optimised for phase analysis and therefore the secondary monochromator cannot be relinquished.