Optical, Dielectric and Magnetic Properties of La1−xNdxFeO3 Powders and Ceramics

Nanocrystalline La1−xNdxFeO3 powders with different concentrations of Nd3+ have been synthesized using a modified Pechini method. Their structures were studied by X-ray powder diffraction (XRD). Furthermore, La1−xNdxFeO3 nanoceramics were prepared using a high pressure sintering technique. The luminescence spectra of the powders were investigated as a function of concentration of active dopant to check the possible energy transfers observed due to Nd3+ concentration changes. The electrical and magnetic properties of the powders and ceramics were investigated to determine the effect of Nd3+ doping on the dielectric permittivity and magnetization in the wide frequency range. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.Funding: 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 the 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

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

Magnetic Penetration Depth in Unconventional Superconductors

This topical review summarizes various features of magnetic penetration depth in unconventional superconductors. Precise measurements of the penetration depth as a function of temperature, magnetic field and crystal orientation can provide detailed information about the pairing state. Examples are given of unconventional pairing in hole- and electron-doped cuprates, organic and heavy fermion superconductors. The ability to apply an external magnetic field adds a new dimension to penetration depth measurements. We discuss how field dependent measurements can be used to study surface Andreev bound states, nonlinear Meissner effects, magnetic impurities, magnetic ordering, proximity effects and vortex motion. We also discuss how penetration depth measurements as a function of orientation can be used to explore superconductors with more than one gap and with anisotropic gaps. Details relevant to the analysis of penetration depth data in anisotropic samples are also discussed.Comment: topical review, 57 pages, 219 reference

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

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

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

Point contact Andreev reflection spectroscopy of NdFeAsO_0.85

The newly discovered oxypnictide family of superconductors show very high critical temperatures of up to 55K. Whilst there is growing evidence that suggests a nodal order parameter, point contact Andreev reflection spectroscopy can provide crucial information such as the gap value and possibly the number of energy gaps involved. For the oxygen deficient NdFeAsO0.85 with a Tc of 45.5K, we show that there is clearly a gap value at 4.2K that is of the order of 7meV, consistent with previous studies on oxypnictides with lower Tc. Additionally, taking the spectra as a function of gold tip contact pressure reveals important changes in the spectra which may be indicative of more complex physics underlying this structure.Comment: 11 pages, 3 figures. New references included, extra discussion. This version is accepted in Superconductor Science and Technolog

Postmodern Literary Labyrinths: Spaces of Horror Reimagined

Cox examines horror in Angela Carter’s The Passion of New Eve (1977) and Mark Z. Danielewski’s House of Leaves (2000) as the confrontation with labyrinthine architecture that represents bodily and psychological reflections of self as monstrous, disorientating, and feminine. The reimagined space (re)absorbs and so threatens the protagonists with existential nothingness. Drawing on the abject body, there is an inevitable confrontation with an active maternal origin. Horror is elicited, not by the expected confrontation with the monster, but by encounter with the anthropomorphic labyrinth’s ability to entrap, nullify, and transform. Surprisingly, the experience of these labyrinths, as a reimagined space of horror, typically results in positive transformation. The labyrinth is both the locus of horror and a means to understand and move on from trauma