Abstract
The crystal structure complex oxide Ba4Ca2Nb2O1 inanhydrous and hydrated forms was studied by the method of neutron diffraction, the preferred localization of protons were set. The hydration process with temperature variation and the partial pressure of water vapor was studied. It is established that the crystallographic non-equivalence OH-groups in the structure determines their different thermal stability. The quasi-chemical approach was proposed that describes the formation of proton defects in oxides with structural disordering.
Highlights
Proton conductors are widely used as components of electrochemical devices such as gas sensors, electrolysers, fuel cell membranes, etc [1,2,3]
In high temperature proton conductors (HTPC) hydrogen is not part of chemical formula, its appearance in the structure of the complex oxide is provided by the equilibrium with Н2О/Н2-containing atmosphere and is described as the process of dissociative dissolution of water vapor/hydrogen [4]
Since the presence of oxygen vacancies is the main factor responsible for the appearance of proton defects, the value of the proton conductivity is determined by the complex oxide defectiveness
Summary
Proton conductors are widely used as components of electrochemical devices such as gas sensors, electrolysers, fuel cell membranes, etc [1,2,3]. In complex oxide compounds with the structural typical disorder of the oxygen sublattice, in contrast to phases with impurity disordering, the number of vacancies in the oxygen sublattice may be considerably higher, the high oxygen deficiency is able to provide a significant level of concentration of protons (and proton conductivity) [5]. Such features allow us to consider these compounds as a distinct class of proton conductors and suggest the need to devise new ways to describe them. In the present work we report a detailed study of the crystal structure of proton conductor Ba4Ca2Nb2O11 and set the preferred places of localization of protons, and developed a quasichemical approach to describe the processes of formation of proton defects
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