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A manganese-doped BaTiOa was investigated with regard to the degradation of resistivity under a high d.c. electric field. Degradation was measured as a function of time, composition and temperature, using an electric field of 3 V #m -1. The activation energy of the process was found to be 1.13eV. to clarify the mechanism / against U characteristics and / against Tgraphs of new, degraded and relaxed samples were studied. Electron paramagnetic resonance and potential measurements were found to be useful in describing the degradation. Finally, a brief model is put forward to account for the observed phenomena. It is based on an injection of oxygen vacancies from the anode, which isaccompanied by a reduction of manganese in the lattice.* Based on a thesis submitted by J. R6del for the diploma degree at the

This article gives an overview about the preparation and characterization of asymmetric ceramic membranes that have been developed at our institute within the last years. Depending on the required pore size of the filter active layer for filtration applications ranging from microfiltration (MF) up to nanofiltration (NF) different preparation routes have to be applied.

Ceramics of the melilite‐type compound La1+xSr1−xGa3O7−δ were prepared by conventional ceramic processing. Samples prepared represented the entire homogeneity region of the phase (i.e., x=−0.15 to 0.60). Electrochemical characterization under variable temperature and atmospheric conditions in the vicinity of air entailed four‐point direct‐current conductivity measurements and electromotive force measurements. La1+xSr1−xGa3O7−δ samples exhibited a p‐type behavior with generally increased conductivity with increased substitution of lanthanum for strontium, which reached a saturation value of ∼10−1 S·cm−1 at 950°C.

Cylindrical constructs with parallel aligned pores were prepared by using ionotropic gelation of alginate/calcium phosphate hydroxyapatite (HAP) mixtures in regard to applications as scaffold for bone regeneration. The starting powder and stabilizing agents were characterized by measurement of electrosonic amplitude, particle size distribution, and specific surface. The shrinkage of the gels was investigated in dependence on the drying methods. The pore size relied on preparation conditions such as amount of HAP and concentrations of gelling agent or alginate sol. A wide field of pore sizes could be fabricated by varying the kind and concentration of additives. Micro computer tomography-investigations of freeze dried scaffolds demonstrated the pore progression over a length of 4 mm. The pore dimension and structure were adequate for cell seeding and blood capillary ingrowth. Biocompatibility was proven by in vitro experiments with human mesenchymal stem cells by fluorescence microscopy. A high stability of the wet gels was maintained under cell culture conditions for a period of 3 weeks.

Porous and mineralised scaffolds are required for various applications in hard tissue engineering. Scaffolds with oriented tube-like pores facilitate homogenous cell seeding, a sufficient nutrient supply during cell culture (even in big constructs) and a fast vascularisation after implantation. The phenomenon of ionotropic gelation has been known since more than 30 years which describes that alginate forms gels with capillary-like pores when covered with solutions of di-or trivalent cations [1]. This technique has been used here to develop scaffolds with tube-like and regular pores from alginate/calcium phosphate composites and to stabilise them by mineralisation with hydroxyapatite from solution.

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