Isothermal Onsager matrices and acceptor size effect on mass/charge transport properties of La1.9A0.1NiO3.95+δ (A = Ca, Sr)

Abstract

Isothermal Onsager transport coefficient matrices have been established experimentally for the systems of La_1.9A_0.1NiO_3.95+δ doped with different-sized acceptors A = Ca²⁺ and Sr²⁺, in the range of oxygen activity −6 < log a_O2 < 0 at 800°, 900° and 1000 °C, respectively. The oxygen self-diffusivity, oxygen defect (interstitial) diffusivity, hole mobility, and partial conductivities in the reversible electrode condition are thereby evaluated against defect concentration, and compared with those of the host La₂NiO_4+δ. It has been found that acceptor-doping suppresses the oxygen defect diffusivity by ca. an order of magnitude compared with the undoped host by increasing the migrational enthalpy by 0.3 eV or so. Hole mobility is in the range of 0.15 to 0.20 cm² V⁻¹ s⁻¹ for both the undoped and Ca-doped specimens, and 0.21–0.25 cm² V⁻¹ s⁻¹ for the Sr-doped specimens, with their temperature dependence indicating band conduction. The ionic charge-of-transport, corresponding phenomenologically to the number of holes dragged by an oxygen interstitial upon its transfer, appears to increase with increasing defect concentration and decreasing temperature in the range of 0 to 0.5. The ionic and electronic mobilities depending on the types of dopants are discussed in terms of dopant size.