Crystal structure and imperfection of the perovskite-like proton conductor Ba4Ca2Nb2O11

The crystal structure complex oxide Ba4Ca2Nb2O11 in anhydrous and hydrated forms was studied by the method of neutron diffraction, the preferred localizations 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 of 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

Electrical properties of Ba2(In1-x Al x )2O5 solid solutions

The electric conductivity of perovskite-like Ba2(In 1-x Al x )2O5 solid solutions (0 < x ≤ 0.20) characterized by structural disordering in the oxygen sublattice was studied as a function of temperature and partial pressure of oxygen in an atmosphere with a low content of water vapors (pH2O = 3 Ч 10-5 atm). When In3+ was partially replaced by Al3+, the oxygen ion conductivity increased because of the disordering of oxygen structural vacancies, leading to a significant increase in the total electric conductivity of the samples. © 2013 Pleiades Publishing, Ltd

Effect of anion doping on mobility of ionic charge carriers in solid solutions based on Ba2In2O5

In the work, mobilities of oxygen and protons are determined for F --substituted solid solutions based on brownmillerite Ba 2In2O5 and their concentration dependences are analyzed. It is found that small additives of the more mobile anion (F - ions) promote an increase in oxygen mobility as a result of additional effects of repulsion of ions of different nature in the anion sublattice. Mobility of oxygen at high fluoride concentrations decreases due to the overlapping of migration paths of diffusion, as both anions, fluoride ions and oxygen ions, move via oxygen vacancies. Concentration dependences of mobility of proton carriers have a similar character, which is related to the effect of the oxygen sublattice. The anion doping method used in the work can be recommended as the general method for improvement of the transport characteristics of oxygen-ionic and protonic conductors with a perovskite-like structure. © 2013 Pleiades Publishing, Ltd

Fluorine and chlorine doping in oxygen-deficient perovskites: A strategy for improving chemical stability

The present work describes the effect of fluorine and chlorine doping on the chemical stability of proton conductors Ba2In2O5, Ba4In2Zr2O11, and Ba4Ca2Nb2O11 against carbon dioxide and water steam. It was proved that both undoped and halide-doped compositions demonstrate good chemical stability under H2O treatment without degradation and without any hydrolytic decomposition. The hydration process leads to the change in the crystal structure only. The treatment in the CO2/air (1:1) atmosphere (500 °C, 10 h) leads to the decomposition of undoped samples only. Halide-doped samples retain their structure without detectable products, that is, they are more chemically stable compared with undoped compositions. The method of halide doping can be used as the promising technique for obtaining the new perovskite-related materials with high level of chemical stability. © 2019 Académie des sciencesRussian Science Foundation, RSF: 18-73-00006This work was financially supported by the Russian Science Foundation (project 18-73-00006 )

Electric properties of oxyfluorides Ba2In2O 5-0.5x F x with brownmillerite structure

Synthesis of fluoro-substituted substances based on brownmillerite Ba 2In2O5 is carried out. The width of the homogeneity region of the Ba2In2O5-0.5x F x (0 < x ≤ 0.25) solid solution was established using X-ray analysis. Measurement of temperature dependences of conductivity in atmospheres with different partial pressure of water vapor (pH2O = 3.3 and 2 Ч 103 Pa) showed an increase in conductivity at T ≤ 550 C in a humid atmosphere, which is due to appearance of proton transport. The dependence of conductivity on partial oxygen pressure (pO2 = 0.21 Ч 105 to 10-15 Pa) is studied in the temperature range of 500-1000 C; ion transport numbers are calculated. The method of polarization measurements was used to determine transport numbers of fluoride. Total conductivity is divided into ion (proton, oxygen, and fluoride ion) and electron components. Analysis of concentration dependences of conductivities showed that low concentrations of fluoride allow increasing both the total and partial conductivities (oxygen-ion and proton) and, besides, allow shifting the "order-disorder" phase transition by 100 C to the low temperature range. © 2013 Pleiades Publishing, Ltd

Electrical Properties of (1–x)La2Mo2O9-xLa2Mo3O12 (x = 0.15) Composite System

Electrical properties of (1–x)La2Mo2O9 –xLa2Mo3O12 (x = 0.15) composite system areinvestigated. Introduction of an inert additional phase La2Mo3O12 (adjacent phase to La2Mo2O9 in the phase diagram) results in an increase in conductivity of composite by approximately one order of magnitude. This increase is associated with the appearance of a composite effect. The dominant ionic conductivity is maintained in the wide range of oxygen partial pressures. The calculated ion transport numbers are close to 1. Keywords: lanthanum molybdate, LAMOX, heterogeneous doping, composites, oxide–ion conductivit

Materials AIILnInO4 with Ruddlesden-Popper Structure for Electrochemical Applications: Relationship between Ion (oxygen-ion, proton) Conductivity, Water Uptake, and Structural Changes

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 perov-skites AIILnInO4 are novel and prospective class of functional materials which can be used in the different electrochemical devices in the near future. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.This article was financially supported by the Ministry of Education and Science of the Russian Federation (state assignment no. 075-03-2021-051/5)

Proton and Oxygen-Ion Conductivities of Hexagonal Perovskite Ba5In2Al2ZrO13

The hexagonal perovskite Ba5 In2Al2ZrO13 and In3+-doped phase Ba5 In2.1Al2Zr0.9O12.95 were prepared by the solid-state synthesis method. The introduction of indium in the Zr-sublattice was accompanied by an increase in the unit cell parameters: a = 5.967 Å, c = 24.006 Å vs. a = 5.970 Å, c = 24.011 Å for doped phase (space group of P63 /mmc). Both phases were capable of incorporating water from the gas phase. The ability of water incorporation was due to the presence of oxygen deficient blocks in the structure, and due to the introduction of oxygen vacancies during doping. According to thermogravimetric (TG) measurements the compositions of the hydrated samples corresponded to Ba5 In2Al2ZrO12.7 (OH)0.6 and Ba5 In2.1Al2Zr0.9O12.54 (OH)0.82. The presence of different types of OH−-groups in the structure, which participate in different hydrogen bonds, was confirmed by infrared (IR) investigations. The measurements of bulk conductivity by the impedance spectroscopy method showed that In3+-doping led to an increase in conductivity by 0.5 order of magnitude in wet air (pH2O = 1.92·10−2 atm); in this case, the activation energies decreased from 0.27 to 0.19 eV. The conductivity−pO2 measurements showed that both the phases were dominant proton conductors at T < 500◦C in wet conditions. The composition Ba5 In2.1Al2Zr0.9O12.95 exhibited a proton conductivity ~10−4 S·cm−1 at 500◦C. The analysis of partial (O2−, H+, h•) conductivities of the investigated phases has been carried out. Both phases in dry air (pH2O = 3.5·10−5 atm) showed a mixed (oxygen-ion and hole) type of conductivity. The obtained results indicated that the investigated phases of Ba5 In2Al2ZrO13 and Ba5 In2.1Al2Zr0.9O12.95 might be promising proton-conducting oxides in the future applications in electrochemical devices, such as solid oxide fuel cells. Further modification of the composition and search for the optimal dopant concentrations can improve the H+-conductivity. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.Russian Science Foundation, RSF: 22-23-20003Funding: This research was supported by the Russian Science Foundation and Government of Sverdlovsk region, Joint Grant 22-23-20003 https://rscf.ru/en/project/22-23-20003/

The Effect of Simultaneous Homo- and Heterogeneous Doping on Transport Properties of Ba2In2O5

In this article, the possibility of application of simultaneous homogeneous and heterogeneous doping has been described for the first time. The composite 0.7Ba1.95In2O4.9F0.1⋅0.3Ba2 InNbO6 has been obtained by in situ solid-state method. The scanning electron microscopy and thermogravimetry investigations have beencarried out; the electrical properties have been examined. It has been proved that simultaneous homogeneous and heterogeneous doping is a prospective method for obtaining high-conductive proton electrolytes. Keywords: brownmillerite, composite, anionic doping, fluorin

Layered and Hexagonal Perovskites as Novel Classes of Proton-Conducting Solid Electrolytes. A Focus Review

Received: 15 September 2022. Accepted: 28 September 2022.Solid oxide electrolytes have attracted significant attention due to their possible applications in energy conversion devices, including solid oxide fuel cells (SOFCs) and electrolysis cells (SOECs). Although a large amount of data has been accumulated to date, the design of new representatives of ionic electrolytes is of unquenchable interest. In this paper, a review of the new classes of proton-conducting solid electrolytes is provided. The physicochemical and transport properties of layered perovskites (BaNdInO4, BaNdScO4, SrLaInO4, BaLaInO4) and hexagonal perovskites (Ba7Nb4MoO20, Ba5Er2Al2ZrO13 and Ba5In2Al2ZrO13) were analyzed and summarized. Based on the performed analysis, the most promising compositions among the considered phases were identified and the effective approaches aimed at improving their functional characteristics were provided.This work was supported by the Russian Science Foundation (grant no 22-79-10003)