Peculiarities of the crystal structure evolution of Bifeo3-batio3 ceramics across structural phase transitions

Evolution of the crystal structure of ceramics BiFeO3-BaTiO3 across the morphotropic phase boundary was analyzed using the results of macroscopic measuring techniques such as X-ray diffraction, differential scanning calorimetry, and differential thermal analysis, as well as the data obtained by local scale methods of scanning probe microscopy. The obtained results allowed to specify the concentration and temperature regions of the single phase and phase coexistent regions as well as to clarify a modification of the structural parameters across the rhombohedral-cubic phase boundary. The structural data show unexpected strengthening of structural distortion specific for the rhombohedral phase, which occurs upon dopant concentration and temperature-driven phase transitions to the cubic phase. The obtained results point to the non-monotonous character of the phase evolution, which is specific for metastable phases. The compounds with metastable structural state are characterized by enhanced sensitivity to external stimuli, which significantly expands the perspectives of their particular use. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.Instituto Nacional de Ciência e Tecnologia para Excitotoxicidade e Neuroproteção, INCT-EN: UID/04564/2020, UIDB/50011/2020, UIDP/50011/2020Russian Science Foundation, RSF: 18-19-00307Funding: This work was supported by the RSF (project #18-19-00307). Investigations performed at the Center for Physics of the University of Coimbra were supported by Fundação para a Ciência e a Tecnologia (project UID/04564/2020). M.V.S. acknowledges Russian academic excellence project “5-100” for Sechenov University. Part of work done at the University of Aveiro was developed within the scope of the project CICECO-Aveiro Institute of Materials, refs. UIDB/50011/2020 & UIDP/50011/2020, financed by national funds through the FCT/MEC

Oxygen nonstoichiometry and magnetic properties of doped manganites La0.7Sr0.3Mn0.95Fe0.05O3-δ

Based on the investigation of the dynamics of changes in the oxygen index (3 – δ) during heating of the samples, the formation of a stressed state in their grains as a result of annealing was established. This results in a decrease in the mobility of oxygen vacancies during the reduction of cations and explains the decrease of released oxygen amount with an increase of δ as well as the heating rate of the samples. It was found that the temperature dependence of the magnetization obeys the Curie–Weiss law and as the oxygen defficiency increases, the Curie temperature for solid solutions decreases. It was found that with an increase of temperature in the low-temperature region, magnetic ordering is disturbed due to the excitation of magnons with a quadratic dependence of the energy from the wave vector, the number of which increases in proportion to T3/2. This results in a decrease in the manganite magnetization. The observed temperature dependence of the magnetization measured in the “field-cooling mode” was approximated taking into account the quadratic and non-quadratic dispersion laws of the magnon spectrum

Crystal Structure and Concentration-Driven Phase Transitions in Lu(1−x)ScxFeO3 (0 ≤ x ≤ 1) Prepared by the Sol–Gel Method

The structural state and crystal structure of Lu(1−x)ScxFeO3 (0 ≤ x ≤ 1) compounds prepared by a chemical route based on a modified sol–gel method were investigated using X-ray diffraction, Raman spectroscopy, as well as scanning electron microscopy. It was observed that chemical doping with Sc ions led to a structural phase transition from the orthorhombic structure to the hexagonal structure via a wide two-phase concentration region of 0.1 < x < 0.45. An increase in scandium content above 80 mole% led to the stabilization of the non-perovskite bixbyite phase specific for the compound ScFeO3 . The concentration stability of the different structural phases, as well as grain morphology, were studied depending on the chemical composition and synthesis conditions. Based on the data obtained for the analyzed samples, a composition-dependent phase diagram was constructed. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.Funding: This project received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 778070—TransFerr— H2020-MSCA-RISE-2017. G.N. gratefully acknowledges the Center of Spectroscopic Characterization of Materials and Electronic/Molecular Processes (SPECTROVERSUM Infrastructure) for use of Raman spectrometer. A.L.Z. and A.P.T. acknowledge BRFFR (project № T21RM-040) and RFBR (project № 20-52-04011) respectively. M.V.S. acknowledges Ministry of Science and Higher Education of the Russian Federation within the framework of state support for the creation and development of World-Class Research Centers “Digital biodesign and personalized healthcare” № 075-15-2020-926. D.A. acknowledges the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement

Morphotropic phase boundary in Sm-substituted BiFeO3 ceramics: Local vs microscopic approaches

Samarium substituted bismuth ferrite (BiFeO3) ceramics prepared by sol-gel synthesis method were studied using both local scale and microscopic measurement techniques in order to clarify an evolution of the crystal structure of the compounds across the morphotropic phase boundary region. X-ray diffraction analysis, transmission and scanning electron microscopies, XPS, EDS/EDX experiments and piezoresponse force microscopy were used to study the structural transitions from the polar active rhombohedral phase to the anti-polar orthorhombic phase and then to the non-polar orthorhombic phase, observed in the Bi1−xSmxFeO3 compounds within the concentration range of 0.08 ≤ x ≤ 0.2. The results obtained by microscopic techniques testify that the compounds in the range of 0.12 ≤ x ≤ 0.15 are characterized by two phase structural state formed by a coexistence of the rhombohedral and the anti-polar orthorhombic phases; two phase structural state observed in the compounds with 0.15<x<0.18 is associated with a coexistence of the anti-polar orthorhombic and the non-polar orthorhombic phases. Local scale measurements have revealed a notable difference in the concentration range ascribed to the morphotropic phase boundary estimated by microscopic measurements, the obtained results testify a wider concentration range ascribed to a coexistence of different structural phases, the background of the mentioned difference is discussed. © 2021 Elsevier B.V.This work was supported by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 778070 . M.V.S acknowledges Ministry of Science and Higher Education of the Russian Federation within the framework of state support for the creation and development of World-Class Research Centers “Digital biodesign and personalized healthcare” №075-15-2020-926 . Diffraction measurements and analysis (A.A.D. and D.V.K.) were supported by RFBR (projects # 20-58-00030 ) and BRFFR (project # F20R-123 ). Piezoresponse force microscopy investigations were made possible by the Russian Science Foundation (grant 19-72-10076 ). The equipment of the Ural Center for Shared Use “Modern nanotechnology” UrFU was used

Nanoscale Ferroelectricity in Pseudo-cubic Sol-gel Derived Barium Titanate - bismuth Ferrite (BaTiO3– BiFeO3) Solid Solutions

Single phase barium titanate–bismuth ferrite ((1-x)BaTiO3-(x)BiFeO3, BTO-BFO) solid solutions were prepared using citric acid and ethylene glycol assisted sol-gel synthesis method. Depending on the dopant content the samples are characterized by tetragonal, tetragonal-pseudocubic, pseudocubic and rhombohedral structure as confirmed by Raman spectroscopy and XRD measurements. An increase of the BFO content leads to a reduction in the cell parameters accompanied by a decrease in polar distortion of the unit cell wherein an average particle size increases from 60 up to 350 nm. Non zero piezoresponse was observed in the compounds with pseudocubic structure while no polar distortion was detected in their crystal structure using X-ray diffraction method. The origin of the observed non-negligible piezoresponse was discussed assuming a coexistence of nanoscale polar and non-polar phases attributed to the solid solutions with high BFO content. A coexistence of the nanoscale regions having polar and non-polar character is considered as a key factor to increase macroscopic piezoresponse in the related compounds due to increased mobility of the domain walls and phase boundaries. © 2020 Elsevier B.V.The work has been done in frame of the project TransFerr. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 778070 . The scanning probe microscopy study was funded by RFBR (grant No. 19-52-04015 ) and BRFFR (grant No. F19RM-008 ). The equipment of the Ural Center for Shared Use “Modern nanotechnology” UrFU was used. Sample structural characterization was funded by RFBR (grant № 18-38-20020 mol_a_ved). M.S. also acknowledges Russian academic excellence project “5–100″ for Sechenov University. This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, refs. UIDB/50011/2020 & UIDP/50011/2020, financed by national funds through the FCT/MEC

Магниторезистивный эффект в наноразмерном ферромолибдате стронция с диэлектрическими прослойками

Single phase strontium ferromolybdate nanopowder with a double perovskite structure has been synthesized using the citrate gel technique at pH = 4. A superstructural ordering degree of the iron and molybdenum cations of 88% has been obtained. X−ray diffraction of pressed Sr2FeMoO6−δ pellets subjected to annealing at T = 700 K and p(O2) = 10 Pa has revealed the formation of the SrMoO4 phase at grain boundaries. The temperature dependence of the electrical resistivity in the 4.2 to 300 K range changes from a metal type one in the single phase Sr2FeMoO6−δ to a semiconductor type one in the Sr2FeMoO6−δ – SrMoO4 – Sr2FeMoO6−δ structure containing dielectric interlayers, indicating variable charge hopping in the latter structure. In the applied magnetic fields the temperature dependence does not change qualitatively; however, the resistivity decreases with increasing field, i.e., a negative magnetoresistance of up to 41% at T = 10 K and B = 8 T is observed. The external field forms a collinear spin structure, thus increasing the spin−polarized current through the barriers in the granular Sr2FeMoO6−δ – SrMoO4 – Sr2FeMoO6−δ heterostructure

Магнитомягкие композиты на основе порошков железа для создания компонентов двухстаторного комбинированного электродвигателя

An experimental prototype of electric motor on permanent (FeNdB) magnets with switchable magnetic flux with two sectioned stators and a rotor using SMC material based on encapsulated metal powders has been developed. The method of manufacture of magnetic cores by powder metallurgy method on the basis of magnetically soft encapsulated titanium dioxide composites has been developed, including computer modeling of magnetic cores components, creation of tooling for their manufacture by pressing and selection of technological modes of pressing. Press set for manufacturing stator components by pressing in the form of a mold was made of hardened 5XHB steel. With its use magnetic components for twostator combined electric motor are pressed. The main electromagnetic characteristics of the components were measured with an express magnetometer. Complex studies showed that the magnetic components have sufficient strength and the necessary electromagnetic characteristics to create a two-stator combined electric motor of this type. An experimental sample of electric motor with maximum power of 15 kW was created on the basis of manufactured magnetic components. Advantages of composite material over electrical steel and other soft magnetic alloys allow providing their wider application in electric machines in order to increase specific power at high speed of rotation with less losses.Разработан экспериментальный образец электродвигателя с переключаемым магнитным потоком с двумя секционированными статорами и ротором на постоянных (FeNdB) магнитах с применением SMC-материала на основе капсулированных металлических порошков. Создана методика изготовления магнитопроводов на основемагнитомягких капсулированных диоксидом титана композитов методом порошковой металлургии, включающая в себя компьютерное моделирование компонентов магнитопроводов, создание оснастки для их изготовления методом прессования и выбор технологических режимов прессования. Оснастка для компонентов статора методом прессования в виде пресс-формы изготовлена из закаленной стали 5ХHB. С ее применением спрессованы магнитныекомпоненты для двухстаторного комбинированного электродвигателя. Основные электромагнитные характеристики компонентов измерены с помощью экспресс-магнетометра. Комплексные исследования показали, что магнитные компоненты обладают достаточной прочностью и необходимыми электромагнитными характеристиками длясоздания двухстаторного комбинированного данного типа электродвигателя. На основе изготовленных магнитных компонентов создан экспериментальный образец электродвигателя с максимальной расчетной мощностью 15 кВт. Преимущества композиционного материала перед электротехнической сталью и другими магнитомягкими сплавами позволяют обеспечить более широкое их применение в электрических машинах с целью повышения удельной мощности при высокой скорости вращения с меньшими потерями

СТЕПЕНЬ ПРЕВРАЩЕНИЯ И МЕХАНИЗМ КРИСТАЛЛИЗАЦИИ МЕТАЛЛООКСИДНОГО СОЕДИНЕНИЯ Sr2FeMoO6–δ

Polythermic dependences of the phase transformation degree during Sr2FeMoO6–d crystallization by the solid phase method have been studied for powders synthesized from the stoichiometric mixture of the oxides SrCO3 Fe2O3, MoO3 and from the partially reduced precursors SrFeO3–x and SrMoO4–y. It is found that the general rule for all samples is a transition from the kinetic mode of interaction to the diffusion one. In this case, the reaction product layer is formed and is increased with its blocking action. However, it should be mentioned that for the samples synthesized from a mixture of simple oxides, the kinetic stage of solid-phase interactions is mixed with the presence of some fraction of the diffusion part due to the formation of intermediate reaction products. When α is increased, the fraction of the diffusion part grows. The use of the partially reduced precursors SrFeO3–x and SrMoO4–y with submicron grains allows one to synthesize the single-phase compound Sr2FeMoO6–d with the superstructure ordering of Fe3+/Mo+5 cations. In this case, the kinetic difficulties of the Sr2FeMoO6–d phase formation are significantly reduced by increase in the diffusion mobility of Fe3+ and Mo+5 cations and by decrease in the distance of their motion to the reaction zone.В сообщении рассмотрена скорость кристаллизации ферромолибдата стронция из исходных реагентов с различной предысторией их получения. На основании изучения политермических зависимостей степени превращений при кристаллизации Sr2FeMoO6–d установлено, что при синтезе образцов, состоящих из смеси исходных реагентов стехиометрического состава MoO3, Fe2O3, SrCO3 и SrFeO3–х и SrMoO4–у, общей закономерностью является переход от кинетического режима взаимодействия к диффузионному, при котором происходит образование слоя продукта реакции и рост с увеличением его блокирующего действия. Однако следует указать, что для образцов, синтезированных из смеси исходных реагентов MoO3, Fe2O3, SrCO3, кинетическая стадия твердофазных взаимодействий является смешанной с присутствием некоторой доли диффузионной части, ввиду образования промежуточных продуктов реакции, и по мере увеличения α доля диффузионной части увеличивается. Использование частично восстановленных прекурсоров SrFeO3–х и SrMoO4–у с зернами субмикронной величины позволяет синтезировать однофазное соединение Sr2FeMoO6–d со сверхструктурным упорядочением катионов Fe3+ и Mo5+. В этом случае значительно снижаются кинетические трудности фазообразования Sr2FeMoO6–d за счет увеличения диффузионной подвижности катионов Fe3+ и Mo5+ и уменьшения дальности их движения в реакционную зону