CaZrO3-based powders suitable for manufacturing electrochemical oxygen probes

Calcium zirconate powders doped with a small amount of CaO were synthesised using the Pechini method. X-ray analysis revealed that solid solution was formed in the concentration up to 51.5% mol CaO. For synthesis of stoichiometric CaZrO₃, the highest temperature was required (1150°C), but introduction of excess CaO from 50.5 to 51.5% mol enabled us to lower the synthesis temperature to 800°C. The sintering behaviour of such samples under non-isothermal conditions was studied by dilatometric methods. Deviations were found in stoichiometry; by increasing the CaO concentration in CaZrO₃ sinterability improved in comparison to CaZrO₃ with stoichiometric composition. The presence of CaO as second phase caused deterioration of the sinterability of the CaZrO₃-based samples. Pellets sintered at 1500°C for 2 h reached 96–98% of theoretical density. SEM and TEM observations were used to characterise the microstructure of the prepared samples. The electrical properties of CaZrO₃-based samples were investigated by the AC-impedance spectroscopy method. It was found that introduction of excess CaO into the CaZrO₃ structure caused an increase in ionic conductivity up to the solubility limit. The possibility of using CaZrO₃-based samples for constructing prototype electrochemical oxygen probes to determine activity of oxygen dissolved in molten copper is also demonstrated.