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

Apatite-type lanthanum germanates La10-x(GeO4)(6)O3-1.5x, have been successfully prepared at room temperature in a planetary ball mill by dry milling for only 6 hours (rotating disc speed = 350 rpm), stoichiometric mixtures of hexagonal A-La2O3 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 degrees C, are similar to those found for the same phases but prepared by conventional solid state reaction and sintered at higher temperatures (alpha(dc) = 4 x 10(-3) Scm(-1) at 650 degrees C and 3 x 10(-2) S cm(-1) at 950 degrees C. Two different regimes are identified in the Arrhenius plots with activation energies of around 1 eV (below 650 degrees C and 0.6 eV (above 650 degrees C. (c) 2006 Elsevier SAS. All rights reserved.