Electrical conductivity and structural conditionality of ion transfer in langasite La$_3$Ga$_5$SiO$_{14}$:Mn

The temperature dependence of the static electrical conductivity $\sigma_{dc}(T)$ of a single crystal of lanthanum gallium silicate (langasite) La$_3$Ga$_5$SiO$_{14}$ activated with an impurity of Mn (1000 ppm) has been studied by impedance spectroscopy. Impedance measurements of La$_3$Ga$_5$SiO$_{14}$ (sp. gr. $P321$, $Z = 1$) were carried out along crystallographic axes $a$ (double symmetry axis) and $c$ (triple symmetry axis). It was found that the values of $\sigma_{\parallel a}$ are significantly higher than the electrical conductivity $\sigma_{\parallel c}$, the anisotropy of the electrical conductivity is $\sigma_{\parallel a}/\sigma_{\parallel c}$ = 170 at 773 K. The activation energy of electrotransport is $E_{\sigma}$ =0.75 $\pm$ 0.05 and 1.09 $\pm$ 0.02 eV along the a and c axes, respectively. The electrical conductivity mechanism has an ionic nature and an impurity character; oxygen vacancies $V_{\mathrm{O}}^{\bullet\bullet}$ are the most probable current carriers.