Conductivity and hydration of lanthanum-substituted barium calcium niobates Ba4 − x La x Ca2Nb2O11 + 0.5x (x = 0.5; 1; 1.5)

Abstract

A double perovskite Ba4(Ca2Nb2)O11 known as the oxygen-ionic and protonic conductor is modified by substitution of La atoms for Ba atoms in its composition. Three phases with different lanthanum contents Ba4 − xLaxCa2Nb2O11 + 0.5x with x = 0.5; 1; 1.5 are studied. The temperature dependences of conductivity are measured and the thermogravimetric studies are carried out. The thermogravimetric curves of heating are close for all three compounds, whereas their curves of cooling strongly differ from one another. For compositions with x = 0.5 and 1.5, the dependences of conductivity on the partial oxygen pressure \(P_{O_2 }\) and the partial water vapor pressure \(P_{H_2 O}\) are measured. The total transport numbers of ions and the transport numbers of protons are calculated. It is shown that the slope of the \(log\sigma _{tot} \left( {logP_{H_2 O} } \right)_T\) dependence reaches 1/3 in the range of medium \(P_{H_2 O}\) under the condition of electroneutrality 2[O″V] = [H*i], which coincides with the result obtained earlier for the Ba4Ca2Nb2O11 (x = 0) composition and the solid solutions on its basis with different Ba/Ca ratios. The obtained results are compared with the literature data describing the incorporation of water into Ba2In2O5 and BaCe0.89(Y0.2)O2.9.