Facile synthesis, characterization and electrical properties of apatite-type lanthanum germanates

Apatite-type lanthanum germanates La10−x(GeO4)6O3−1.5x, have been successfully prepared at room temperature in a planetary ball mill by dry milling for only 6 hours (rotating disc speed =350rpm), stoichiometric mixtures of hexagonal ALa2O3 and GeO2. As obtained powders are not amorphous and show XRD patterns as well as IR and Raman spectra characteristic of the apatite-type lanthanum germanates. The domain size of the as prepared samples grows gradually with the temperature of post-milling thermal treatment with an activation energy of about 20 kJ mol−1 K−1. The IR and Raman spectra suggest increasing ordering with firing temperature. The electrical properties of the as prepared materials, sintered at temperatures as low as 1200 °C, are similar to those found for the same phases but prepared by conventional solid state reaction and sintered at higher temperatures (σdc=4×10−3Scm−1 at 650 °C and 3×10−2Scm−1 at 950 °C). Two different regimes are identified in the Arrhenius plots with activation energies of around 1 eV (below 650 °C) and 0.6 eV (above 650 °C).

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