Stabilization of the high-temperature phase and total conductivity of yttrium-doped lanthanum germanate oxyapatite

Kiyoshi Kobayashi*, Yukihito Igarashi, Noriko Saito, Tohru Higuchi, Yoshio Sakka, Tohru S. Suzuki

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)


The high-temperature phase of lanthanum germanate is useful due to its high oxide ion conductivity. While the transition from the high- to low-temperature phase could be suppressed by yttrium substitution in lanthanum sites, full stabilization of the high-temperature phase was difficult to achieve by yttrium substitution under conditions of different lanthanum-deficient compositions, as some X-ray diffraction (XRD) peaks were broadened after annealing at 873 K. With lattice constant analysis using the XRD peaks, the degree of lattice asymmetry for the low-temperature phase with triclinic lattice was found to decrease with increases in the deficiency of the lanthanum site and yttrium concentration. Formation of the low-temperature phase was difficult to detect even from Raman shift spectra. On the other hand, Raman shift spectra showed high sensitivity to detection of the La2GeO5 impurity phase. The influence of the total conductivity on the phase transition showed different trends with increases in the lanthanum deficiency and yttrium concentration. With tuning of the composition, the highest conductivity was observed in La8.51Y0.96(GeO4)6O2.205. This conductivity (6.12

Original languageEnglish
Pages (from-to)91-98
Number of pages8
JournalJournal of the Ceramic Society of Japan
Issue number2
Publication statusPublished - 2018 Feb
Externally publishedYes


  • Conductivity
  • Lanthanum germanate
  • Oxyapatite
  • Phase transition
  • Raman shift spectra
  • Yttrium doping

ASJC Scopus subject areas

  • Ceramics and Composites
  • General Chemistry
  • Condensed Matter Physics
  • Materials Chemistry


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