Complete Documentation of All the Mass/Charge Transport Properties of La2NiO4+δ and Its Puzzling Thermomigration Behavior

All the mass/charge transport properties of mixed conducting La2NiO4+δ, with oxide ions O2– (= i) and holes h+ (= h) as the mobile charged components, may be exhaustively documented succinctly in terms of a 2 × 3 coupling coefficient matrix L of the Onsagerian causality between the fluxes of the mobile components, J k (k = i, h) and their driving forces, electrochemical potential gradients ∇η k (k = i, h) and temperature gradient ∇T. In this work, we introduce the simplest-ever rugged thermocell to measure the “non-isothermal” transport properties {L iT , L hT } of La2NiO4+δ across its entire stability range at elevated temperatures of 800, 900, and 1000 °C, respectively. We then complete documentation of all the mass/charge transport properties L of the system La2NiO4+δ by combining with its “isothermal” transport properties {L ii, L ih, L hi, and L hh} reported earlier (Kim, H.-S.; Yoo, H.-I. Phys. Chem. Chem. Phys. 2011, 13, 4651). Finally, we discuss its puzzling thermomigration behavior (L kT ), with the mobile component O being rendered from thermophilic (J O ∝ ∇T) to thermophobic (J O ∝ −∇T) with increasing T and δ.