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Slovensko   English2024-05-24

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In collaboration with co-workers from China, Germany, Australia, and Switzerland, Prof. dr. Tadej Rojac from the Electronic Ceramics Department has recently published a paper in the journal of Advanced Functional Materials titled Piezoelectric properties of BiFeO₃ exposed to high temperatures. The study reports on an unusual phenomenon in ferroelectric bismuth ferrite (BiFeO3), which has been extensively studied in recent years due to its high Curie temperature (TC = 830°C) and therefore its potential for high-temperature piezoelectric applications. The researchers discovered that the piezoelectric response, which disappeared at temperatures above ~400°C, was recovered upon cooling of the material. In contrast to the commonly assumed explanation related to thermal depoling of the ceramics and thus permanent loss of piezoelectricity, in this case, it is a reversible phenomenon stemming from the thermally activated electrical conductivity of the ferrite. The discovery of this phenomenon has paved the way for optimizing the poling conditions of BiFeO3, which may have practical significance in the development of BiFeO3-related environmentally friendly lead-free piezoceramics.

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Journal Physical Review Letters published a paper Dynamics and Topology of Symmetry Breaking with Skyrmions, by Jaka Pišljar, Andriy Nych, Uliana Ognysta, Andrej Petelin, Samo Kralj and Igor Muševič, from Jožef Stefan Institute, Faculty of Mathematics and Physics UL, Faculty of Natural Sciences and Engineering UL and Institute of Physics, Kyiv. The authors showed how the formation of the half-skyrmions-vortices from the high temperature isotropic phase dramatically changes as the chiral liquid crystal sample is confined to thickness below 100 nm. They observed unusally slow fluctuations, which represent spontanoeus formation and decay of individual half-skyrmions, also shown in the accompanying figure. The rate of such dynamics is 4 orders of magnitude slower of what was expected and is explained by the mechanism of thermal hopping between states, which become energetically accessible due to the strong confinement effects. This phenomenon is interesting from the topological point of view as well, as the experiments reveal the mechanisms of topological charge conservation at the phase transition. The paper was also highlighted in the journal Physics.

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Doctoral student Petruša Borštnar from the Department for Advanced Materials at Jožef Stefan Institute, under the mentorship of Assoc. Prof. Dr. Nina Daneu, and in collaboration with colleagues from the National Institute of Chemistry and Cheng Kung University in Taiwan, published a paper Transient Ruddlesden–Popper-Type Defects and Their Influence on Grain Growth and Properties of Lithium Lanthanum Titanate Solid Electrolyte in the journal ACS Nano. The research describes the development of a coarse-grained microstructure in lithium lanthanum titanate (LLTO) ceramics under the influence of Ruddlesden-Popper-type planar defects. Based on quantitative high-resolution scanning transmission electron microscopy (HAADF-STEM) analyses, the authors explain the process from the formation of defects in the initial grain growth stage to the exaggerated growth of grains with RP-type defects and finally, to recrystallization of the RP-type sequences to LLTO perovskite. The results are a contribution to the development of solid electrolytes for applications in lithium-ion batteries, where the total ionic conductivity is directly related to the number of highly resistive grain boundaries.

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Prof. dr. Svjetlana Fajfer, the Department of Theoretical Physics of the Jožef Stefan Institute gave a Theory Summary talk at the Electroweak Interactions & Unified Theories 2024 conference, which took place from March 24 to 31, 2024 in La Thuile, Italy. The Rencontres de Moriond are series of the most prestigious conferences in the field of particle physics around the world, which every year present important results, more than 100 lecturers appeared with presentations of collaborations from CERN ATLAS, CMS, LHCb, Belle II, BaBaR, astroparticle experiments LUXE, LUXE 2, neutrino experiments Katrin, T2K, No a, CUORE, FASER, ICECUBE, Alpha-g, search for axions in experiments LIDA and 21 cm. There were a total of 77 talks of which 54 were from the field of experimental research and 23 from the field of theoretical research. Young researchers presented their results in young scientist forums as five-minute lectures. In the closing lecture of the conference, Svjetlana Fajfer presented an overview of the theoretical talks at the conference and the prospects of theoretical physics of elementary particles.

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