Preparation of high-oxygen-content apatite silicates through Ti-doping: effect of Ti-doping on the oxide ion conductivity

In this paper we show that through Ti-doping it is possible to synthesise high-oxygen-content silicate-based apatites, La10Si6−xTixO27 (0.25 ≤ x ≤ 2.0), and report conductivity data for this series. The results show that Ti-doping leads to a general decrease in the conductivity, and an increase in activation energy, particularly for the range 1.0 ≤ x ≤ 2.0. With reference to computer modelling and 29Si NMR data, this decrease in conductivity is attributed to trapping of the interstitial oxide ions around the Ti dopant. Attempts to prepare similar compositions containing La cation vacancies, i.e. La10−ySi6−xTixO3−3y/2, have a tendency to result in La2Ti2O7 impurities, particularly for high values of y.