Springer Online Journal Archives 1860-2000
Abstract Apatite is a mineral with general formula M10(XO4)6Z2, where M are metallic elements such as Li+, Na+, K+, Ca2+, Sr2+, Ba2+, Ln3+ etc.; X=P, V, S, Si, Ge, Re, Cr etc; Z=F−, Cl−, I−, OH−, O2−, S2− etc. Some materials with apatite structure (S.G. P63/m) exhibit quite high cationic (Li+, H+ etc.) and/or anionic (F−, Cl− etc.) conduction. Recently, it was reported that some rare earth silicates, e.g., La10(SiO4)6O3, exhibit quite high oxide-ion conductivity. In this paper, we discuss chemical composition, structure, synthetic procedure and ionic conduction of apatite-type materials. Recent improvements are briefly reviewed. High ionic conductivity has been observed for both cation deficient, oxygen stoichiometric La9.33(SiO4)6O2 and cation stoichiometric, oxygen excess La10(SiO4)6O3 compositions. Grain boundary conductivity is usually low, which tends to dominate the impedance response. The resistance, particularly the grain boundary resistance is also found to depend on pO2.
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