Pyro-paraelectric and flexocaloric effects in barium strontium titanate: A first principles approach

This is the author accepted manuscript. The final version is available from AIP Publishing via https://doi.org/10.1063/1.4947010Inhomogeneous strain allows the manifestation of an unexplored component of stress-driven caloric effect (flexocaloric effect) and enhanced pyroelectric performance, obtainable significantly beyond the Curie point. A peak temperature change of 1.5 K (at 289 K) was predicted from first-principles-based simulations for Ba0.5Sr0.5TiO3 under the application of a strain gradient of 1.5 μm−1. Additionally, enhanced pyro-paraelectric coefficient (pyroelectric coefficient in paraelectric phase) and flexocaloric cooling 11 × 10−4 C m−2 K−1 and 1.02 K, respectively, could be obtained (at 330 K and 1.5 μm−1). A comparative analysis with prevailing literature indicates huge untapped potential and warrants further research.One of the authors (RV) acknowledges support from the Indian National Science Academy (INSA), Delhi, India, through a grant by the Department of Science and Technology (DST), Delhi, under INSPIRE faculty award-2011 (ENG-01) and INSA Young Scientists Medal-2013. AC would like to acknowledge the support of SERB, India in the form of Cambridge India Ramanujan fellowship. IP acknowledges support from the National Science Foundation Grant No. DMR-1250492 and MRI CHE-1531590

Управление транспортными услугами в условиях действия случайных факторов

The article deals with possible approaches to improve the quality of transport service management using information technology in terms of random factors. Particular attention is given to further improvement of accuracy of transport efforts’ estimation. The procedure provided by the authors, can be used for drawing up a typology and comparative analysis of the activities of various companies and comparison of different types of activities within the transport company.Демонстрируются возможные подходы к повышению качества управления транспортными услугами с использованием информационных технологий в условиях действия случайных факторов. Особое внимание уделяется дополнительному повышению точности оценки транспортных усилий. Методику, представленную авторами, можно использовать для составления типологии и сравнительного анализа деятельности различных компаний или сравнения различных видов деятельности внутри транспортной компании

Aluminum anodization in deionized water as electrolyte

Thin oxide films were prepared electrochemically on the aluminum surface using the high-voltage discharge and potentiostatic methods in deionized water as an electrolyte. The growth of continuous films occurred only at potentials lower than the breakdown potential. The films obtained by the discharge method are more uniform and can grow to a higher thickness in comparison to those formed by the potentiostatic mode, as demonstrated by electrochemical impedance spectroscopy (EIS), transmission electron microscopy (TEM), and scanning Kelvin probe force microscopy (SKPFM). The data herein obtained can be used as a reference to understand better the properties of the films produced in conventional electrolytes where apart from water other species are present

Geometric frustration in compositionally modulated ferroelectrics

Geometric frustration is a broad phenomenon that results from an intrinsic incompatibility between some fundamental interactions and the underlying lattice geometry1-7. Geometric frustration gives rise to new fundamental phenomena and is known to yield intriguing effects, such as the formation of exotic states like spin ice, spin liquids and spin glasses1-7. It has also led to interesting findings of fractional charge quantization and magnetic monopoles5,6. Geometric frustration related mechanisms have been proposed to understand the origins of relaxor behavior in some multiferroics, colossal magnetocapacitive coupling and unusual and novel mechanisms of high Tc superconductivity1-5. Although geometric frustration has been particularly well studied in magnetic systems in the last 20 years or so, its manifestation in the important class formed by ferroelectric materials (that are compounds exhibiting electric rather than magnetic dipoles) is basically unknown. Here, we show, via the use of a first-principles-based technique, that compositionally graded ferroelectrics possess the characteristic "fingerprints" associated with geometric frustration. These systems have a highly degenerate energy surface and exhibit original critical phenomena. They further reveal exotic orderings with novel stripe phases involving complex spatial organization. These stripes display spiral states, topological defects and curvature. Compositionally graded ferroelectrics can thus be considered as the "missing" link that brings ferroelectrics into the broad category of materials able to exhibit geometric frustration. Our ab-initio calculations allow a deep microscopic insight into this novel geometrically frustrated system.Comment: 14 pages, 5 Figures; http://www.nature.com/nature/journal/v470/n7335/full/nature09752.htm

Elastic excitations in BaTiO_{3} single crystals and ceramics: Mobile domain boundaries and polar nanoregions observed by resonant ultrasonic spectroscopy

The dynamic properties of elastic domain walls in BaTiO3 were investigated using resonance ultrasonic spectroscopy (RUS). The sequence of phase transitions is characterized by minima in the temperature dependence of RUS resonance frequencies and changes in Q factors (resonance damping). Damping is related to the friction of mobile twin boundaries (90° ferroelectric walls) and distorted polar nanoregions (PNRs) in the cubic phase. Damping is largest in the tetragonal phase of ceramic materials but very low in single crystals. Damping is also small in the low-temperature phases of the ceramic sample and slightly increases with decreasing temperature in the single crystal. The phase angle between the real and imaginary part of the dynamic response function changes drastically in the cubic and tetragonal phases and remains constant in the orthorhombic phase. Other phases show a moderate dependence of the phase angle on temperature showing systematic changes of twin microstructures. Mobile twin boundaries (or sections of twin boundaries such as kinks inside twin walls) contribute strongly to the energy dissipation of the forced oscillation while the reduction in effective modulus due to relaxing twin domains is weak. Single crystals and ceramics show strong precursor softening in the cubic phase related to polar nanoregions (PNRs). The effective modulus decreases when the transition point of the cubic-tetragonal transformation is approached from above. The precursor softening follows temperature dependence very similar to recent results from Brillouin scattering. Between the Burns temperature (≈586 K) and Tc at 405 K, we found a good fit of the squared RUS frequency [∼Δ (C11−C12)] to a Vogel–Fulcher process with an activation energy of ∼0.2 eV. Finally, some first-principles-based effective Hamiltonian computations were carried out in BaTiO3 single domains to explain some of these observations in terms of the dynamics of the soft mode and central mode

Creating Nanoscale luminescence Centres in Silver Halides Suitable for Infrared Application

This study shows the possibility of creating luminescence centres in silver halide media using substances based on rare-earth elements such as neodymium, ytterbium and dysprosium. These luminescent substances in the form of fine particles of both nanoscale and microscale dimensions can be introduced into the AgCl0.25Br0.75 ceramic matrix highly transparent in the spectral range of 0.5–35 μm. Our theoretical and experimental studies showed that the introduction of luminescent nanoparticles or microparticles at the amount of 0.5 wt.% into AgCl0.25Br0.75 ceramics neither reduces the level of its transmission in the MIR region nor shortens the range of transmission. What is more, we proved that the luminescent properties of nanoparticles remain well preserved after doping silver halide ceramic media with them. Therefore, silver halides doped with rare-earth elements in question can be used for developing the sources of coherent middle infrared radiation, with appropriate energy levels being excited by optical radiation or pulsed electric field. © 2021 Institute of Physics Publishing. All rights reserved.This work was supported by the Russian Science Foundation (No. 21-73-10108)