Lithium-cation conductivity in the systems Li4ЭO4-Li4Zn(PO4)2

Solid solutions in the systems Li₄SiO₄ – Li₄Zn(PO₄)2 и Li₄GeO₄ – Li₄Zn(PO₄)₂ have been prepared by solid state reactions and their crystal structure and temperature and concentration dependences of electroconductivity have been researched. In both systems solid solutions based on Li₄ЭO₄ reach the level up to 20 mol.% of Li₄Zn(PO₄)₂. In the silicate system solid solutions have the same structure as Li₄SiO₄ and in the germanate one crystal structure have become orthorhombic and close to γ-Li₃PO₄. This structure is more preferable for the fast ion transport so Lf-ion conductivity in the germanate system is essentially higher than in the silicate one and is of the same order as compared with the best lithium ion conductors.
By NMR spectroscopy it was revealed that mobilities of the lithium cations in each type of the solid solutions are rather different. In the germanate solid solutions having crystal structure based on γ-Li₃PO₄ part of Li⁺ ions are in the host lattice and not participate in elcctromigration. On the contrary, the interstitial Li⁺ cations are weakly bonded with the host lattice and have high mobility. In silicate solid solutions different mobility of Li⁺ cations may be caused both with differ in their coordination number by oxygen and with coexisting in the samples ordered and disordered forms of Li₄SiO₄.