Effects of cation- or oxide ion-defect on conductivities of apatite-type La–Ge–O system ceramics

A series of apatite-type La–Ge–O ceramics were prepared and their cation-defect at the 4f+6h sites and oxide ion-defect at 2a site were investigated. In LaxGe6O12+1.5x ceramics of x=6–12, the higher conductivities were obtained in the region of apatite composition, Lax(GeO4)6O1.5x−12 (x=8–9.33), and the highest conductivity was achieved for La9(GeO4)6O1.5 (x=9), where the number of cation (La3+) occupying the 4f+6h sites is 9 and the number of oxide ion occupying the 2a site is 1.5. The ceramics with cation- and oxide ion-defects were La9−0.66xSrx(GeO4)6O1.5 (x=0–1), La9−1.33xZrx(GeO4)6O1.5 (x=0–1), La9−xSrx(GeO4)6O1.5−0.5x (x=0–3), La9−xZrx(GeO4)6O1.5+0.5x (x=0–1), Lax(GeO4)3x−21(AsO4)27−3xO1.5 (x=0–3), Lax(GeO4)33−3x(AlO4)3x−27O1.5 (x=0–3), La9(GeO4)6−x (AlO4)xO1.5−0.5x (x=0–3), La9(GeO4)6−x(AsO4)xO1.5+0.5x (x=0–1), La9.33−xSrx(GeO4)6O2−0.5x (x=0–1.2) and Lax(GeO4)4.5(AlO4)1.5O1.5x−12.75 (x=8.8–9.83), which were prepared by the partial substitution of La3+and GeO44−of the basic apatite La9(GeO4)6O1.5 with Sr2+ or Zr4+ and AlO45− or AsO43−. Such substitutions lowered the conductivity of La9(GeO4)6O1.5. These results were discussed by the electrostatic interaction between Sr2+, Zr4+, AlO45− or AsO43− and oxide ion as a conductive species.