Coworkers of the Department of Complex Matter from Jožef Stefan Institute, Peter Medle Rupnik, Luka Cmok, Nerea Sebastián, and Alenka Mertelj have published a paper in the journal Advanced Functional Materials entitled Viscous Mechano-Electric Response of Ferroelectric Nematic Liquid. They report on mechano-electric transduction phenomena in ferroelectric liquid at room temperature. They show that the actuation of a cell filled with ferroelectric nematic liquid crystal causes changes in electric polarisation structure and consequently electric current is generated. As described the observed phenomena fundamentally differ from the piezoelectric effect, due to their viscous character, i.e. the polarisation changes with flow. This indicates a high technological potential since already a very soft touch leads to electric signals, which depend on the touch strength. Ferroelectric liquids are therefore promising for use in fields from tactile sensorics to energy harvesting at low actuation frequencies. |
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. |
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. |
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. |
