Kinetics of reactive diffusion between solid La₂GeO₅ and gases [GeO + 1/2O₂]

Abstract

We successfully prepared the polycrystalline lanthanum germanate oxyapatite (LGO) by the reactive diffusion between solid La₂GeO₅ and gases [GeO + 1/2O₂] during isothermal heating at 1573–1723 K for 2–50 h. The reaction products were investigated by polarizing-microscopy for microtexture characterization, Raman spectroscopy for phase identification, and X-ray diffractometry for determination of the {00l}_LGO texture fractions. The LGO polycrystals were highly c*-axis-oriented, and hence the Lotgering factor f_00l ranged, regardless of annealing temperatures, between 0.94 and 0.99. The thickness (l/m) of LGO layer steadily increased with the increase of annealing time (t/s) in accordance with a parabolic relationship of l = [exp(−1.502 × 10⁴/T − 5.233)] × t^1/2. The growth of LGO layer was predominantly controlled by volume diffusion of GeO₂ component, with the activation energy being ca. 125 kJ mol⁻¹.