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

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)

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

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)

Expression Level of the DREB2-Type Gene, Identified with Amplifluor SNP Markers, Correlates with Performance, and Tolerance to Dehydration in Bread Wheat Cultivars from Northern Kazakhstan

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.A panel of 89 local commercial cultivars of bread wheat was tested in field trials in the dry conditions of Northern Kazakhstan. Two distinct groups of cultivars (six cultivars in each group), which had the highest and the lowest grain yield under drought were selected for further experiments. A dehydration test conducted on detached leaves indicated a strong association between rates of water loss in plants from the first group with highest grain yield production in the dry environment relative to the second group. Modern high-throughput Amplifluor Single Nucleotide Polymorphism (SNP) technology was applied to study allelic variations in a series of drought-responsive genes using 19 SNP markers. Genotyping of an SNP in the TaDREB5 (DREB2-type) gene using the Amplifluor SNP marker KATU48 revealed clear allele distribution across the entire panel of wheat accessions, and distinguished between the two groups of cultivars with high and low yield under drought. Significant differences in expression levels of TaDREB5 were revealed by qRT-PCR. Most wheat plants from the first group of cultivars with high grain yield showed slight up-regulation in the TaDREB5 transcript in dehydrated leaves. In contrast, expression of TaDREB5 in plants from the second group of cultivars with low grain yield was significantly down-regulated. It was found that SNPs did not alter the amino acid sequence of TaDREB5 protein. Thus, a possible explanation is that alternative splicing and up-stream regulation of TaDREB5 may be affected by SNP, but these hypotheses require additional analysis (and will be the focus of future studies)

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)

Seroimmunotyping of African swine fever virus

The extreme genetic and immunobiological heterogeneity exhibited by the African swine fever virus (ASFV) has been a significant impediment in the development of an efficacious vaccine against this disease. Consequently, the lack of internationally accepted protocols for the laboratory evaluation of candidate vaccines has become a major concern within the scientific community. The formulation of such protocols necessitates the establishment of a consensus at the international level on methods for the determination of homologous and heterologous isolates/strains of ASFV. The present article provides a comprehensive description of biological techniques employed in the classification of ASFV by seroimmunotypes. These techniques involve a holistic evaluation of ASFV isolates/strains based on their antigenic properties as determined by the hemadsorption inhibiting test (HAdI) using type-specific sera and an immunological test (IT) conducted on pigs inoculated with attenuated strains. The article outlines the methods for setting up the HAdI test, an IT on pigs, and the processes involved in the acquisition of type-specific serums for the HAdI test. It is pertinent to note that the definitive classification of seroimmunotype can only be ascertained after conducting an IT on pigs. The findings from the HAdI test or the phylogenetic analysis of the EP402R gene should be considered preliminary in nature

The General Transcription Repressor TaDr1 Is Co-expressed With TaVrn1 and TaFT1 in Bread Wheat Under Drought

The general transcription repressor, TaDr1 gene, was identified during screening of a wheat SNP database using the Amplifluor-like SNP marker KATU-W62. Together with two genes described earlier, TaDr1A and TaDr1B, they represent a set of three homeologous genes in the wheat genome. Under drought, the total expression profiles of all three genes varied between different bread wheat cultivars. Plants of four high-yielding cultivars exposed to drought showed a 2.0–2.4-fold increase in TaDr1 expression compared to controls. Less strong, but significant 1.3–1.8-fold up-regulation of the TaDr1 transcript levels was observed in four low-yielding cultivars. TaVrn1 and TaFT1, which controls the transition to flowering, revealed similar profiles of expression as TaDr1. Expression levels of all three genes were in good correlation with grain yields of evaluated cultivars growing in the field under water-limited conditions. The results could indicate the involvement of all three genes in the same regulatory pathway, where the general transcription repressor TaDr1 may control expression of TaVrn1 and TaFT1 and, consequently, flowering time. The strength of these genes expression can lead to phenological changes that affect plant productivity and hence explain differences in the adaptation of the examined wheat cultivars to the dry environment of Northern and Central Kazakhstan. The Amplifluor-like SNP marker KATU-W62 used in this work can be applied to the identification of wheat cultivars differing in alleles at the TaDr1 locus and in screening hybrids

Diagnostics of functioning of controllable restored stochastic systems

The aim to be attained is development of mathematical models of the controllable restored systems and technique of calculation of stationary characteristics. Models of selective control of restored systems have been studied, an effective technique of calculation of stationary characteristics has been developed, the problems of selecting the optimal control moment are being solved. A complex of programs of statistical simulation of the controllable restored systems for calculation of the models characteristics has been developedAvailable from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio

ТЕХНОЛОГІЧНІ АСПЕКТИ НИТРУВАННЯ КРОХМАЛЮ АЗОТНО-СІРЧАНОКИСЛОТНОЮ СУМІШШЮ

Aim. To establish patterns of starch nitration process, allowing to justify the choice of the composition of the nitrating mixture and the regime parameters of nitration. Methods. The degree of nitration was expressed in terms of the nitrogen content in the resulting starch nitrate, which was determined by the ferrosulfate method. We also carried out an assessment of the surface state of the starch grains and starch nitrate at a 300-fold magnification using an optical microscope. Results. It was established that the dependences of the nitrogen content in starch nitrate on the composition of the nitrating mixture and the operating parameters of the process pass through maxima. At certain values of the composition of the nitrous mixture, the nitration process is disturbed, which is associated with side reactions. When starch is nitrated with a nitrogen-sulfuric acid mixture, the resulting starch nitrate retains the granular structure of the original starch, but characteristic defects are formed on the surface of its grains. Conclusions. The maximum nitrogen content in starch nitrate is achieved at H2SO4/HNO3 ≈ 3, a water concentration in the nitrating mixture 8 – 10 %, temperature 35 – 40 °C, nitration time 30 – 35 minutes and nitration module 30–40. The ratio of the rates of the nitration process and side reactions determines the stability of the nitration process. It is broken when H2SO4/HNO3 ≤ 0.5 and H2SO4/HNO3 ≥ 7.0 as well as when the concentration of water in the nitrous mixture СH2O ≥ 20 %. The surface defects of starch nitrate grains are associated with dissolution and extraction into a nitrating mixture of amylose nitrate, as a result of which one should expect changes in the internal structure of starch nitrate grains.В статье представлены результаты экспериментального исследования процесса нитрования картофельного крахмала, целью которого являлось установление его закономерностей, позволяющих обосновать выбор режимов технологии изготовления взрывчатого вещества – нитрата крахмала. Показано, что зависимости содержания азота в получаемом нитрате крахмала от состава нитрующей смеси и режимных параметров процесса нитрования характеризуются наличием максимумов, которые обусловлены протеканием побочных реакций. Особенностью зависимостей содержания азота от состава нитрующей смеси является также нарушение процесса нитрования при определенном массовом отношении кислот и концентрации воды в нитрующей смеси, что связано с растворением крахмала и его гидролизом. Получаемый нитрат крахмала сохраняет зернистую структуру исходного крахмала, но в процессе нитрования изменяется состояние поверхности зерен. На ней образуются характерные дефекты, которые свидетельствуют об изменении внутренней структуры зерен в результате экстрагирования нитрата амилозы серной кислотой из аморфных областей зерен. Предполагается, что такое изменение внутренней структуры может влиять на характеристики конечного продукта, а присутствие растворенного нитрата амилозы в отработанной нитрующей смеси необходимо учитывать при ее регенерации.В статті представлені результати експериментального дослідження процесу нітрування картопляного крохмалю, метою якого було встановлення його закономірностей, що дозволяють обґрунтувати вибір режимів технології виготовлення вибухової речовини – нітрату крохмалю. Показано, що залежності вмісту Нітрогену в нітраті крохмалю, що отримується, від вмісту нітруючої суміші та режимних параметрів процесу нітрування характеризуються наявністю максимумів, які обумовлені протіканням побічних реакцій. Особливістю залежності вмісту Нітрогену від складу нітруючої суміші є порушення процесу нітрування при певному масовому співвідношенні кислот і концентрації води в нітруючій суміші, що пов'язано із розчиненням крохмалю та його гідролізом. Одержаний нітрат крохмалю зберігає зернисту структуру вихідного крохмалю, але у процесі нітрування змінюється стан поверхні зерен. На ній утворюються характерні дефекти, які свідчать про зміну внутрішньої структури зерен у результаті екстрагування нітрату амілози сульфатною кислотою з аморфних областей зерен. Передбачається, що така зміна внутрішньої структури може визначати характеристики кінцевого продукту, а присутність розчиненого нітрату амілози у відпрацьованій нітруючій суміші необхідно враховувати при її регенерації