Исследование размытого фазового перехода в твердых растворах BiFeO3-BaTiO3 вблизи ромбоэдрической-псевдокубической фазовой границы

Работа выполнена с использованием оборудования УЦКП «Современные нанотехнологии» УрФУ. Работа выполнена при поддержке Российского фонда фундаментальных исследований (проект № 19-52-04015) и Белорусского республиканского фонда фундаментальных исследований (проект № F19RM-008)

Impact of Alkali Ions Codoping on Magnetic Properties of La(0.9)A(0.1)Mn(0.9)Co(0.1)O(3) (A: Li, K, Na) Powders and Ceramics

The aim of the work was to check how the introduction of alkali and cobalt ions into a manganese structure can affect the structural disorder and, in consequence, lead to the changes (improvements) of magnetic properties. The high-pressure sintering technique was applied to check if the external factor can modify the magnetization of manganites. Nanocrystalline La0.9A0.1Mn0.9Co0.1O3 (where A is Li, K, Na) powders were synthesized by the combustion technique. The respective powders were used for nanoceramics preparation by the high-pressure sintering technique. The structure and morphology of the compounds were studied by X-ray powder diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Magnetization studies for all compounds were performed in order to check the changes induced by either codoping or the sintering pressure. It was found that the type of the dopant ion and sintering pressure produced significant changes to the magnetic properties of the studied compounds. Alkali ions lead to the stabilization of Co ions in the +2 oxidation state and the formation of positive exchange interactions Mn3+–Mn4+ and Co2+–Mn4+ and the subsequent increase in remanent magnetization. High sintering pressure leads to a decrease in grain size and reduction of long-range ferromagnetic order and lower magnetization. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.This project has 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. Part of this work was developed within the scope of the project CICECO‐Aveiro Institute of Materials, UIDB/50011/2020 and UIDP/50011/2020, financed by national funds through the Portuguese Foundation for Science and Technology/MCTES. The equipment of the Ural Center for Shared Use “Modern nanotechnology” UrFU was used. The work has been supported in part by the Ministry of Science and Higher Education of the Russian Federation under Project № FEUZ‐2020‐0054

Local polarization reversal in polycrystalline BiFeO3-based solid solutions

The equipment of the Ural Center for Shared Use “Modern Nanotechnology” Ural Federal University was used. The study was funded by RFBR (grant No. 19-52-04015) and BRFFR (grant No. F19RM-008). This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 778070

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

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

Crystal structure and magnetic properties of Bi1-xSmxFeO3 ceramics across the phase boundary: effect of high pressure

The solid solutions Bi1-xSmxFeO3 with chemical composition across the morphotropic phase boundary region specific for rhombohedral - orthorhombic structural transition were investigated by X-ray diffraction, electron microscopy and magnetometry. Structural measurements showed a concentration driven transition from the single phase rhombohedral structure to the single phase nonpolar orthorhombic structure through the formation of antipolar orthorhombic phase which coexists with the rhombohedral phase in the compounds with x < 0.15 followed by a coexistence with nonpolar orthorhombic phase in the compounds with x <= 0.18. Application external pressure provides a stabilization of the orthorhombic phase, viz. the polar rhombohedral phase diminishes and transforms to the anti-polar orthorhombic phase, while the anti-polar orthorhombic phase transforms to the non-polar orthorhombic phase. Magnetic properties of the compounds subjected to external pressure demonstrate an increase in the magnetization of the compounds having dominant rhombohedral phase, wherein coercivity significantly increases, while the spontaneous magnetization remains nearly constant. Твердые растворы Bi1-xSmxFeO3 с химическим составом в области морфотропной границы раздела фаз, характерной для ромбоэдрально-орторомбического структурного перехода, были исследованы методами рентгеновской дифракции, электронной микроскопии и магнитометрии. Структурные измерения показали обусловленный концентрацией переход от однофазной ромбоэдрической структуры к однофазной неполярной орторомбической структуре путем образования антиполярной орторомбической фазы, которая сосуществует с ромбоэдрической фазой в соединениях с x < 0,15, за которым следует сосуществование с неполярной орторомбической фазой в соединениях с x <= 0,18. Применение внешнего давления обеспечивает стабилизацию орторомбической фазы, а именно. полярная ромбоэдрическая фаза уменьшается и переходит в антиполярную орторомбическую фазу, в то время как антиполярная орторомбическая фаза переходит в неполярную орторомбическую фазу

RELATIONSHIP BETWEEN STRUCTURAL STATE AND LOCAL PIEZOELECTRIC PROPERTIES IN xBiFeO3-(1-x)BaTiO3 SOLID SOLUTIONS

Relationship between structural state and local piezoelectric properties was studied in BFO-BTO solid solution by macroscopic X-ray diffraction and piezoresponse force micros-copy. Gradual lattice transformation and changes of domain structure in the dependence to doping level was demonstrated.The equipment of the Ural Center for Shared Use “Modern nanotechnology” Ural Federal University was used. The study was funded by RFBR (grant No. 19-52-04015) and BRFFR (grant No. F19RM-008). This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when appro-priate co-financed by FEDER under the PT2020 Partnership Agreement. This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 778070