Proton Conductivity in Acceptor-Doped LaVO4

Electrical characterization of nominally undoped LaVO4, La0.99Ca0.01VO4−δ and La0.95Ca0.05VO4−δ was performed in various partial pressures of oxygen, water vapor and hydrogen isotopes, from 300 to 1100°C by impedance spectroscopy, AC conductivity measurements (10 kHz) and EMF-measurements. XRD, SEM and EDS were used for structural, micro structural and compositional analysis. Acceptor doped LaVO4 is a pure ionic conductor in oxidizing atmospheres in the entire measured temperature range; dominated by proton conductivity at low temperatures (T < 450°C) under wet conditions and oxide ion conductivity at high temperatures. A maximum in the partial proton conductivity of ∼ 6 × 10−5 S/cm was reached at 900°C ( atm). Thermodynamics of hydration and transport parameters for charge carriers in La0.99Ca0.01VO4 were derived from relations between defect chemistry, transport properties and the measured conductivity data and revealed: =− 130 ± 10 J/mol K, ΔS0 hydr,corr =− 142 ± 10 J/mol K, =− 110 ± 10 kJ/mol, = 50 ± 6 cm2 K/Vs, = 75 ± 10 kJ/mol, = 120 ± 20 cm2 K/Vs and = 85 ± 10 kJ/mol. The tetrahedron (XO4) volume and migration enthalpy were found to be correlated for the series of monoclinic LaXO4.