EVALUATION OF THE INSTABILITY OF LATTICE HYDROXIDE IONS OF HYDROXYAPATITE IN TERMS OF PROTONIC CONDUCTIVITY AT HIGH TEMPERATURES

Abstract

The instability of the lattice OH^- ions of hydroxyapatite was evaluated in terms of high temperature conductivity, the charge carriers of which was confirmed protons by the measurements of electromotive force. The instability of the ions was observed as the aging phenomenon of the conductivities, in which the values increased with the order of 102 in S·cm^-1 at the initial stage, then gradually decreased with time after the maximum of ca. 10^-3 S·cm^-1. The range of aging change was found dependent on the thickness as well as the annealing conditions. The H₂O vapor in the ambience of sintering was also found to have considerable influence the characteristics of the aging; the specimens sintered in air was independent of time, although their conductivities were negligible in comparison with those of specimens sintered under steam stream.