Chemical strain in perovskite-like materials

Pseudo-cubic perovskites based upon substituted oxides RBO3-δ as well as double perovskites RBaB2O6-δ and Sr2BMoO6, where R=rare-earth element and B=3d-transition metal, with A-site and B-site, respectively, cation ordering are very promising materials for a variety of different devices for moderate high temperature applications. The unique feature of the oxides is their ability to undergo both thermal strain and that induced by the defects of oxygen nonstoichiometry in the oxide crystal lattice. The latter is called as chemical or defect-induced strain, which is extremely sensitive to the defect structure of the oxide material. This property was shown recently to be isotropic for pseudo-cubic perovskites unlike that of double perovskites. The crystal lattice of a double perovskite expands along a-axis and simultaneously contracts along c-axis with the decreasing lattice oxygen content. The model of the oxide lattice chemical strain based on a change of mean ionic radius due to reduction of most reducible cation has been recently developed by us. In this work we introduced the new feature in the model such as change of preferable coordination of cations caused by change of oxygen content in the oxide. The modified model was shown to enable correct prediction of chemical expansion upon increasing oxygen nonstoichiometry along a-axis for both pseudo-cubic and double perovskite oxides and simultaneous lattice contraction along c-axis in double perovskites. Thus most important finding is that simultaneous lattice contraction along c-axis in double perovskites is caused by aforementioned change of preferable coordination

Hydration thermodynamics of proton-conducting perovskite Ba4Ca2Nb2O11

The oxygen nonstoichiometry index δ, i.e. number of oxygen vacancies per formula unit, in perovskite-type BaCa(1+y)/3Nb(2-y)/3O3–δ (BCNy) oxides can be tailored by varying the Ca–Nb ratio y, and equals . These oxygen vacancies can be hydrated under humid atmosphere, providing nonstoichiometric BCNy oxides with good proton conductivity. It makes them promising materials for proton-conducting solid oxide fuel cell (SOFC) electrolytes and high-temperature humidity sensors. The present work aimed to partly address the lack of fundamental thermodynamic studies on BCNy by investigating the heat of low-temperature hydration-induced phase transition as well as the higher-temperature thermodynamics of hydration and related defect chemistry of BCN50 oxide. Please click Additional Files below to see the full abstract

Experimental thermochemical verification of trends in thermodynamic stability of hybrid perovskite-type organic-inorganic halides

Hybrid perovskite-type methylammonium lead halides have received great attention in recent years due to high conversion efficiency obtained in solar cells based on such materials. Since the time of the first demonstration photovoltaic devices based on the hybrid perovskites CH3NH3PbX3 (X = Cl, Br, I) have showed huge progress in increase of conversion efficiency reaching currently 20.1%. However, despite very promising achievements fundamental chemistry and physics of hybrid organic-inorganic (HOIP) perovskites is far from being completely understood. In particular it is true for thermodynamic properties of HOIP perovskite-type halides ABX3 and A2BX4 (A=CH3NH3, formamidinium, Cs, Rb, etc; B=Sn, Pb, 3d-element; X = Cl, Br, I). Moreover, reported results of DFT calculations aiming at estimating the stability of these materials often give controversial results. In addition, some of the HOIP perovskites (for example, CH3NH3PbX3 (X = Cl, Br, I)) are known to be entropy-stabilized phases. Therefore experimental verification of the stability trends in HOIP perovskite-type halide systems is strongly required. This is especially important for assessment of the stability of these materials under particular working conditions. Therefore, the main aim of this work was to study the thermodynamics of formation of HOIP perovskite-type halides ABX3 and A2BX4 (A=CH3NH3, formamidinium, Cs, Rb, etc; B=Sn, Pb, 3d-element; X = Cl, Br, I). Their standard formation enthalpy at 298 K was measured by solution calorimetry. Heat capacity was measured in the temperature range 2-298 K using PPMS system. Standard entropy was obtained by integration of the Cp/T vs T curve. Standard Gibbs free energy of ABX3 and A2BX4 (A=CH3NH3, formamidinium, Cs, Rb, etc; B=Sn, Pb, 3d-element; X = Cl, Br, I) was evaluated using measured formation enthalpy and entropy. Trends in variation of the thermodynamic functions with chemical composition and crystal structure of HOIP perovskite-type halides were analyzed and compared with available results of DFT calculations. This work was supported by the Russian Science Foundation (grant No. 18-73-10059)

In situ and ex situ study of cubic La0.5Ba0.5CoO3–δ to double perovskite LaBaCo2O6– δ transition

Double perovskites REBaCo2O6–δ (RE – rare-earth element) have received great attention in past decades as promising materials for various electrochemical devices because of their high mixed ionic-electronic conductivity and catalytic activity for the reaction of oxygen reduction. Among these compounds, cobaltite LaBaCo2O6–δ can serve as a good example of structural flexibility, since it is able to form either A-site disordered cubic “simple” perovskite or layered A-site ordered double perovskite. However, the exact limits of the thermodynamic stability of LaBaCo2O6–δ double perovskite with respect to temperature (T) and oxygen partial pressure (pO2) have not been determined so far. Furthermore, synthesis and study of selected properties of either cubic or layered LaBaCo2O6–δ oxide were mostly of interest for researchers, whereas the transition from “simple” to double perovskite was not addressed in detail so far. At the same time, it is generally recognized that such transition significantly improves oxide ion transport in the perovskite-type oxides and, therefore, understanding this order-disorder transition is of key importance for successful development of new materials for practical application. Therefore, the present work aims at providing some insights into the nature of the aforementioned order-disorder transformation of LaBaCo2O6–δ, as well as into thermodynamic stability of both ordered and disordered phases, using a set of complementary techniques such as transmission electron microscopy, in situ X-ray diffraction and solid state coulometric titration. As a result, formation of complex domain textured intermediate products during the phase transition “ordered LaBaCo2O6–δ – disordered La0.5Ba0.5CoO3–δ” was revealed. These products were found to exhibit strong affinity to oxygen and fast oxygen exchange with ambient atmosphere even at temperature as low as 70 °C. This particularity seems to provide a unique possibility to develop a new class of advanced materials for IT SOFCs, ceramic membranes and catalysis. The thermodynamic stability limits of the cubic and double perovskites were determined as log(pO2) = f(1/T) dependencies. The stability diagram of the LaBaCo2O6–δ – La0.5Ba0.5CoO3–δ system was plotted as a result. Oxygen nonstoichiometry of the thermodynamically stable cubic perovskite La0.5Ba0.5CoO3–δ was measured as a function of pO2 in temperature range between 1000 and 1100 °C using coulometric titration technique. Acknowledgement: This study was supported by the Russian Foundation for Basic Research (Grant No. 18-33-20243)

High resolution thermochemical study of phase stability and rapid oxygen incorporation in YBaCo4-xZnxO7+δ 114-cobaltites

The formation enthalpies of YBaCo4-xZnxO7+δ (x = 0, 1 and 3) oxides were measured by high temperature oxide melt solution calorimetry. All the studied oxides were shown to be thermodynamically metastable at low temperature with respect to a mixture of binary oxides Y2O3, BaO, Co3O4, CoO and ZnO. The tendency of cobalt to increase oxidation state under oxidizing conditions as well as significant bond valence sum mismatch for Ba and Y in 114-oxides are the main destabilizing factors. As a result, the studied 114-oxides are thermodynamically stable in air only at relatively high temperatures (\u3e ca. 900 °C) when CoO is stable. Oxygen absorption in YBaCo4-xZnxO7+δ (x = 0, 1 and 3) at 350-400 °C was studied by calorimetry combined with precise oxygen dosing. Complex phase evolution in YBaCo4O7+δ upon oxygen absorption was revealed. Several single and two phase fields were identified and a sketch of the phase diagram for YBaCo4O7+δ was proposed. The calorimetric results support observations using in situ XRD. At the same time, thermochemical measurements were shown to have higher resolution with respect to the amount of oxygen absorbed by YBaCo4-xZnxO7+δ sample under equilibrium conditions. This work was supported by the Ural Federal University within the framework of Act 211 of Government of the Russian Federation, agreement № 02.A03.21.0006. The thermochemistry work at Davis was supported by US Department of Energy Grant DE-FG02-03ER46053

DIGITAL TWIN AND DIGITAL IDENTITY: CONCEPT, CORRELATION, MEANING IN THE PROCESS OF COMMITTING CYBERCRIMES AND IN LAW IN GENERAL

The modern development of computer technologies is accompanied by an increasing immersion of a person into the virtual world, where he often spends many hours. The longer a person uses a computer and various electronic gadgets, the more traces he leaves. In fact, there is a situation in which a digital copy or digital twin of a person appears in the virtual world. This phenomenon is new to legal science and requires its own research. The purpose of the article is to analyze the concept of «digital twin» and its development, to study the approaches of foreign and Russian authors from various fields of knowledge to the definition of this term, to identify the possibilities of using this concept in the legal sphere. When writing the article, the following methods are used: comparative legal, analysis and synthesis. The following results are obtained: every computer and gadget user has his «digital copy», a kind of «digital twin», on behalf of which a person performs various, including criminal actions in the virtual space. Public relations in the cyberspace are largely not regulated by law, and when developing a framework for regulating such specific legal relations, it is necessary to begin with the definition of the subject. The authors pay special attention to the question of equating a digital identity with a real one, as well as the lack of legislative regulation of the legal status of a digital twin. The discrepancy between such categories as «digital identity» and «digital twin» is shown. A more correct definition of a digital twin is proposed for legal regulation, in particular for identifying the account with which the Internet crime was committed – a digital identity twin. The paper also proposes the basic principles for the subsequent legal regulation of public relations arising and developing in the cyberspace and lays the foundation for further research on the topic of legal regulation of the digital twin

Crystal structure, oxygen nonstoichiometry, hydration and conductivity BaZr1- xMxO3-d (M=Pr, Nd, Y, Co)

Partially substituted perovskite-like barium zirconates with general formula BaZr1-хМхО3-d possess oxygen-ion and proton conductivity and, therefore, may be promising as electrolytes for intermediate temperature solid oxide fuel cells. The aim of this work was to study the crystal structure, thermal and chemical expansion, water uptake, oxygen nonstoichiometry, total conductivity and Seebeck coefficient of zirconates BaZr1-xMxO3-d (M=Pr, Nd, Y, Co) in the atmospheres with different levels of humidity (log(pH2O/atm.) = -1.75; -2.5; -3.5) as a function of oxygen partial pressure (log(pO2/atm) = -20 - -0.67) and temperature (T = 25 – 1050 °C). Synthesis of the samples was carried out by glycerol-nitrate method. The phase composition of the as-prepared powders was analyzed by the X-ray diffraction (XRD). Room temperature and high temperature XRD studies were carried out using Shimadzu XRD-7000 diffractometer equipped with high temperature chamber HTK 16N (Anton Paar GmbH). Thermal and chemical expansion was also measured using DIL 402 C dilatometer (Netzsch GmbH). Oxygen nonstoichiometry was studied by solid state coulometric titration and thermogravimetry. Electrical conductivity and Seebeck coefficient were measured simultaneously in the same setup. This work was supported by the Russian Science Foundation (project No.18-73-00022)

Oxygen Content and Thermodynamic Stability of YBaCo2O6-delta Double Perovskite

The thermodynamic stability of the double perovskite YBaCo2O6−δ was studied using the coulometric titration technique and verified by measurements of the overall conductivity depending on oxygen partial pressure at a given temperature. As a result, the stability diagram of YBaCo2O6−δ was plotted. YBaCo2O6−δ was found to be thermodynamically stable in air at 850°C and higher temperatures, whereas its thermodynamic stability at 900°C is limited by the range of oxygen partial pressures −3.56 ≤ log(pO2/atm) ≤ −0.14. Oxygen content in YBaCo2O6−δ slightly decreases at 900°C from 5.035 at log(pO2/atm) = −0.14 to 4.989 in the atmosphere with log(pO2/atm) = −3.565 indicating a crucial role which variation of Co+3/Co+2 ratio plays in its stability. YBaCo2O6−δ decomposes into the mixture of YCoO3 and BaCoO3−z at the high pO2 stability limit, whereas YBaCo4O7, BaCo1−xYxO3−γ, and Y2O3 were identified as the products of its decomposition at the low pO2 one