Defect and transport properties of the NdCoO3 catalyst and sensor material

The NdCoO₃ perovskite has been investigated using a combination of atomistic simulation and experimental techniques to examine its possible use as an oxidation catalyst and/or sensor material. The sensing properties of NdCoO₃ and Nd_0.8Sr_0.2CoO₃ towards CO have been investigated by employing thin films deposited by means of radio-frequency (RF) magnetron sputtering onto polycrystalline Al₂O₃. The response of the films was monitored by performing four-probe DC-conductivity measurements. The conductivity variation induced by switching between a CO-free atmosphere (air) and a CO-rich one with the same composition of residual gas was recorded and analysed as a function of temperature; results are compared for the two samples. Simulation studies focussed on the dopant, transport and redox properties of the pure material; the results indicate that Sr and Ca on the Nd site are the most soluble dopants and that when divalent dopants are incorporated in the structure, charge compensation occurs via oxygen ion vacancies. The low activation energy for oxygen vacancy migration suggests high oxide-ion mobility through the lattice. Particular attention is paid to the electronic processes because of their importance with respect to practical applications of the material.