Structure, Water Uptake, and Electrical Conductivity of TiP2O7

Authors


  • J. Stevenson—contributing editor

†Author to whom correspondence should be addressed. e-mail: nalini.vajeeston@kjemi.uio.no

Abstract

We report here on the structure of TiP2O7 and electrical properties of nominally acceptor (Sc, Fe)-doped TiP2O7 synthesized by an aqueous phosphoric acid route. Structural characterization, including studies of the high-temperature phase transition in TiP2O7, was carried out by powder X-ray and neutron diffraction. Ceramic disks were sintered by the spark plasma technique and their conductivities were characterized as a function of p(O2) and p(H2O) in the temperature range of 500°–1000°C by means of AC constant frequency measurements and impedance spectroscopy. As reported earlier, the acceptor doping appears not to influence the defect structure of TiP2O7 significantly. Effects of H+/D+ isotope shift were utilized to identify proton conduction. The conductivity was independent of p(O2) at 500°–900°C under oxidizing conditions suggesting predominantly protonic conduction at these temperatures. Under reducing atmosphere n-type conductivity contributed to the total conductivity at the higher temperatures. p(H2O) dependencies of the conductivities are interpreted in terms of a defect-chemical model involving protons and oxygen interstitials as the dominating defects. The uptake of water was studied by thermogravimetry at high p(H2O) and the thermodynamics of the hydration reaction was derived. Finally, parameters for the mobility of protons were extracted by combining the conductivity and thermogravimetry data.

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