Mechanism of ionic conduction in oxy and hydroxyapatite structures

Knowledge of the ionic transport properties of apatites is important in uderstanding their physical and chemical properties. This report reviews and updates results obtained on the alternating current impedance characteristics of synthetic apatites. The possible mechanism of the conduction properties of various oxy and hydroxyapatites are discussed on the basis of the structural data. It is deduced that charge carrying protons are responsible for the observed conductivities in M10(PO4)6(OH)2. The H+ migration between the electoattractive ion (O2−) to give molecular H2O in matrix channels. However, in some vanadium oxyapatites containing lanthanum Ca10−xLax(VO4)6O1+x/2, the ionic conductivities observed are explained by the frequent hopping of oxygen ion along the c axis of the hexagonal matrix. The study of the conductivity relaxation shows structural aspects of these electrolytes.