At the spring meeting of E-MRS we presented our findings on chemical and crystal chemical reactions of sodium cobaltate, a potential thermoelectric material. The chemistry of the material is governed by a high mobility of interlayer sodium and high oxidation state of cobalt. This renders sodium cobaltate reactive with atmospheric moisture and carbon dioxide. Furthermore high temperature causes reduction of cobalt resulting in the formation of secondary phase. The results of thermal and electron microscopy analyses were discussed.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 26592295We described a possibility of spontaneous texturing of Na0.75CoO2 which is brought about by sintering in the atmosphere of pure oxygen, which allows use of temperatures above the decomposition temperature in air. Preferential grain growth occurs in [010] and [100] crystallographic directions perpendicular to the direction of pressing of ceramic powder before sintering. The consequence of texturing is a strong increase in electrical conductivity.
B.03 Paper at an international scientific conference
We described structural and microstructural changes during reaction of Na0.75CoO2 in detail. Reacting of water molecules with interlayer sodium causes the formation of sodium hydroxide which further reacts with carbon dioxide resulting in the formation of carbonates on the surface of the ceramics. Stability can be increased by partial substitution of Na with Ca which triggers coherent intergrowth of two structural types that results in considerable reduction of thermal conductivity.
B.03 Paper at an international scientific conference