Electrical conductivity and X-ray diffraction analysis of oxyapatite-type lanthanum silicate and neodymium silicate solid solution

In this study, we determined the crystallographic nature and electrical transport properties of Nd9.20(SiO4)6O1.8 and (La0.46Nd0.54)9.33(SiO4)6O2, which are defect-containing oxyapatites. The intensity data measured by synchrotron powder X-ray diffraction were analyzed by a Rietveld method. From the total conductivity data, the oxygen partial pressure region where the oxygen ionic conductivity (σO2-) predominates was determined to narrow down owing to the substitution of neodymium ions. A comparison of various solid solutions under similar temperature conditions ranging from 873 K to 1273 K showed that the σO2- values were lowest for (La0.46Nd0.54)9.33(SiO4)6O2 samples. The activation energy of the oxygen ionic conductivity increased with an increasing neodymium content.