Crystal structure and ionic conductivity of Mg-doped apatite-type lanthanum silicates La₁₀Si_6−xMg_xO_27−x (x = 0–0.4)

Lanthanum silicates La₁₀Si_6−xMg_xO_27−x (x = 0–0.4) were prepared by solid state synthesis to investigate the effect of Mg doping on crystal structure and ionic conductivity. Rietveld analysis of the powder XRD patterns reveals that Mg substitution on Si site results in significant enlargement of channel triangles, favoring oxide-ion conduction. Furthermore, an increase of Mg concentration significantly influences the linear density of interstitial oxygen, which plays an important role in ionic conductivity. The Arrhenius plots of La₁₀Si_6−xMg_xO_27−x (x = 0–0.4) suggest that Mg-doped samples present higher conductivity and lower activation energy than non-doped La₁₀Si₆O₂₇, and La₁₀Si_5.8Mg_0.2O_26.8 exhibits the highest conductivity with a value of 3.0×10⁻² S ·cm⁻¹ at 700 °C. Such conductive behavior agrees well with the refined results. The corresponding mechanism has been discussed in this paper. (interdisciplinary physics and related areas of science and technology)