DC and AC conductivity of Li4/3Ti5/3O4 spinel

The electrical conductivity of polycrystalline Li4/3Ti5/3O4 is reported between ∼ 300 K and ∼ 1000 K. Sintered and commercial pressed pellets were used for measurements. Impedance spectroscopy was applied (20 Hz–1 MHz) to determine the DC conductivity σDC and AC conductivity σAC. Anomalies of σDC were observed at higher temperatures as a consequence of presumed order–disorder phase transitions, coupled to diffusion of Li+ between various spinel sites, as concluded in earlier work. There was a broad transitional region of σDC in this temperature range characterized by varying differential activation energies EA. For sintered pellets, consisting of ∼ 0.8–1.5 μm grains, after run 1 up to ∼ 960 K, EA values were EA ∼ 0.80 eV above ∼ 740 K and EA ∼ 0.57 eV below ∼ 500 K for effective σDC deduced from the sum of bulk and grain boundary resistivities, while in the transitional temperature range the values were lower with the data taken under flowing N2. Typically, σDC(500 K) ∼ 10− 4–10− 6 Ω− 1 cm− 1 and σDC(300 K) ∼ 3 × 10− 10 Ω− 1 cm− 1; predominant conduction is due to ionic Li+ charge transport. For commercial ∼ 0.1–0.3 μm grain pellets, after run 1 up, the respective values were EA ∼ 0.87 eV above ∼ 800 K and EA ∼ 0.61 eV between 495 K and 380 K. Below ∼ 620 K, for both materials bulk σDC could be determined, which is a factor of 3–10 above the effective σDC. For the frequency dependence of σAC of commercial Li4/3Ti5/3O4, a power law behaviour was established between 349 and 443 K. Applying DC voltage measurements, for sintered Li4/3Ti5/3O4 the electronic fraction of σDC was estimated to be <∼1% of the ionic fraction between 465 and 830 K.