Ionic conductivity of Li3TaO4 depending on polymorphism and non-stoichiometric defects

Ionic conductivity of complex rock-salt Li3TaO4 was studied using low-temperature (LT; disordered) and hightemperature (HT; ordered) polymorphs modified with Li/Ta non-stoichiometry. For each of LT and HT derivatives, samples were prepared with four different nominal compositions of Li3.05Ta0.99O4, Li3TaO4, Li2.99Ta1.002O4, and Li2.98Ta1.004O4. The synchrotron X-ray diffraction analysis showed that the ordered HT phases have larger lattice volume than the disordered LT phases by & AP;0.5%. Among both LT and HT sample groups, the lattice volume was smallest in the stoichiometric phases Li3TaO4. The X-ray diffraction line broadening analysis implied that the disordered LT phases contain local distortions that resemble the ordered HT phases. The solid-state magic-angle-spinning 7Li nuclear magnetic resonance spectroscopy revealed that LT phases have the larger LiO6 octahedra and the shorter Li-Li distances than HT phases. According to the ac impedance measurement and equivalent circuit analysis, the disordered LT phases had higher ionic conductivities (& sigma;i) than the ordered HT phases, by more than two orders of magnitudes. Particularly, the & sigma;i of Li2.98Ta1.004O4 (at & AP;390 degrees C) was evaluated to be 10_ 2.4 S/cm and 10_4.8 S/cm for LT and HT phases, respectively. Meanwhile, the Li/Ta non-stoichiometry contributed to increase the & sigma;i of Li3TaO4, by more than an order.

Automated summary

The ionic conductivity of complex rock-salt Li3TaO4 was studied by modifying the low-temperature and high-temperature polymorphs with Li/Ta non-stoichiometry. The results showed that the disordered low-temperature phase had higher ionic conductivity than the ordered high-temperature phase, and the Li/Ta non-stoichiometry contributed to an increase in the ionic conductivity of Li3TaO4.