The new phases BaLa0.9M0.1InO3.95 (M = Ca2+, Sr2+, Ba2+) with a Ruddlesden-Popper structure were obtained. It was established that all investigated samples were capable for the water uptake from the gas phase. The ability of water incorporation was due to not only by the presence of oxygen vacancies, but also due to the presence of La-O blocks in the structure. The degree of hydration of the samples was much higher than the concentration of oxygen vacancies and the composition of the samples appear to be BaLaInO3.42(OH)1.16, BaLa0.9Ca0.1InO3.25(OH)1.4, BaLa0.9Sr0.1InO3.03(OH)1.84, BaLa0.9Ba0.1InO2.9(OH)2.1. The degree of hydration increased with an increase in the size of the dopant, i.e., with an increase in the size of the salt blocks. It was proven that doping led to the increase in the oxygen ionic conductivity. The conductivities for doped samples BaLa0.9M0.1InO3.95 were higher than for undoped composition BaLaInO4 at ~1.5 order of magnitude. The increase in the conductivity was mainly attributed to the increase of the carrier concentration as a result of the formation of oxygen vacancies during doping. The proton conductivities of doped samples increased in the order Ca2+–Sr2+–Ba2+ due to an increase in the concentration of protons. It was established that all doped samples demonstrated the dominant proton transport below 450 °C.

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In this paper, the review of the new class of ionic conductors was made. For the last several years, the layered perovskites with Ruddlesden-Popper structure AIILnInO4 attracted attention from the point of view of possibility of the realization of ionic transport. The materials based on Ba(Sr)La(Nd)InO4 and the various doped compositions were investigated as oxygen-ion and proton conductors. It was found that doped and undoped layered perovskites BaNdInO4, SrLaInO4, and BaLaInO4 demonstrate mixed hole-ionic nature of conductivity in dry air. Acceptor and donor doping leads to a significant increase (up to ~1.5–2 orders of magnitude) of conductivity. One of the most conductive compositions BaNd0.9Ca0.1InO3.95 demonstrates the conductivity value of 5∙10−4 S/cm at 500 °C under dry air. The proton conductivity is realized under humid air at low (<500 °C) temperatures. The highest values of proton conductivity are attributed to the compositions BaNd0.9Ca0.1InO3.95 and Ba1.1La0.9InO3.95 (7.6∙10−6 and 3.2∙10−6 S/cm correspondingly at the 350 °C under wet air). The proton concentration is not correlated with the concentration of oxygen defects in the structure and it increases with an increase in the unit cell volume. The highest proton conductivity (with 95−98% of proton transport below 400 °C) for the materials based on BaLaInO4 was demonstrated by the compositions with dopant content no more that 0.1 mol. The layered perovskites AIILnInO4 are novel and prospective class of functional materials which can be used in the different electrochemical devices in the near future.

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