Highly polycrystalline and pure delafossite phase CuAlO 2 powder has been synthesised within a short annealing period, shorter than most conventional processes. This is an improvement over the conventional synthesis procedures. Conventional synthesis procedure has seen CuAlO 2 only formed at high annealing temperatures ≥ 1100°C over long annealing time, some as long as 96 hours. In the current process, a pure phase devoid of impurities has been obtained at reduced calcination time of 1.5 hours in an argon atmosphere at a temperature of 1150°C. This was confirmed by XRD and SEM/EDX. High temperature DC/AC electrical measurements show a change in conduction mechanism from mixed conductivity (ionic + p-type) in the temperature range of 375 ≥ T ≥ 25°C to intrinsic type behavior above 375°C. The activation energies for these two regimes are 0.27 eV and 0.08 eV respectively. This change from mixed to DC conductivity is confirmed by spectral analysis too. Spectral analysis using the power law also revealed that conduction is of long range hopping. Use of platinum as a contact electrode at elevated temperatures has a detrimental effect on the electrical properties since it encourages the formation of CuAl 2 O 4 at the interface due to the formation of more stable Cu−Pt alloy by virtue of the chemical reaction Pt + 2CuAlO 2 − → CuAl 2 O 4 + Pt Cu .

Although AC conductivity measurements of NASICON is well documented in literature, thick film conductivity and ion dynamic studies, important for planar, are scarcely reported. Most thick film measurements are performed using four point probe methods (DC method) and are quite limited in that, they cant give information on ion dynamics and cannot seperate contributions from grains, grain boundaries and electrode effects. However, in this paper we report the electrical properties of NASICON, x = 1.95 thick films of different thicknesses (20-32 µm), screen printed on alumina substrates, in light of ionic dynamics using the AC conductivity formalism. Surface resistivities of thick films from impedance data in the frequency range 0.1 ≤ f (HZ) ≤ 3.2 × 10 7 is obtained. Impedance Cole-Cole plots shows grain interior and electrode effects. The hopping frequency and AC/DC conductivity are thermally activated and show Arrhenius-type behaviour, with activation energies in the range of 0.44 ≤ E a (eV ) ≤ 0.46. Scaling in conductivity and Modulus shows that the relaxation mechanisms are independent of temperature and film thickness. Conductivity was independent of film thickness at high temperatures. SEM reveals that there is a minimum thickness for which NASICON on alumina substrate can be printed and used in high temperature planar electrochemical devices.

This is a repository copy of Electrochemical determination of activity of Na2O in Na2Ti6O13-TiO2 two phase system between 803-1000 K.

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