New Publications

Phase transitions in bismuth pyrostannate upon substitution of tin by iron ions

Udod, L., V; Aplesnin, S. S.; Sitnikov, M. N.; Romanova, O. B.; Molokeev, M. N. Source: JOURNAL OF ALLOYS AND COMPOUNDS, 804 281-287; 10.1016/j.jallcom.2019.07.020 OCT 5 2019

The Bi2(Sn1-хFeх)2O7 (х = 0, 0.1, 0.2) compounds have been synthesized by the solid-state reaction technique. The structure of the synthesized compounds has been investigated in the temperature range of 80–500 K using the thermal expansion and ultrasound damping coefficients and IR spectroscopy. The shift -type structural transitions for the composition with х = 0.2 in the low-temperature region has been established. The effect of iron ions on the phase boundaries of the polymorphic transitions in the Bi2Sn2O7 compound has been observed. Softening of the phonon modes near the phase transitions at different iron concentrations has been found.

Soft modes condensation in Raman spectra of (Pb-La)(Zr-Sn-Ti)O-3 ceramics

Vtyurin, Alexander N.; Krylov, Alexander S.; Krylova, Svetlana N.; Oreshonkov, Alexander S.; Wei, Xiaoyong; Feng, Yujun; Xu, Ran; Zhao, Tian Source: JOURNAL OF ADVANCED DIELECTRICS, 9 (3):10.1142/S2010135X19500243 JUN 2019

Low frequency Raman spectra of (Pb0.97La0.02)(Zr0.864Sn0.04Ti0.096)O3 ceramic samples have been studied near cubic to antiferroelectric phase transition at about 200C. A set of low frequency soft modes were observed restoring below the transition point, in addition to the known one above 100cm1. These modes show strong damping anomalies at the transition point that supposes considerable intermode interactions via dampings.

Magnetic Properties of Soft Magnetic Alloys 5BDSR and 82K3HSR

Svetlichnyi, V. A.; Balashov, V. B.; Lapin, I. N.; Sokolov, A. E.; Cherepanov, V. N. Source: RUSSIAN PHYSICS JOURNAL, 62 (3):411-415; 10.1007/s11182-019-01728-6 JUL 2019

The paper explores the size and morphology of microparticles of soft magnetic alloys 5BDSR and 82K3HSR and nanoparticles first obtained from these alloys using pulsed laser ablation in gas. The magnetic properties of particles are studied depending on their size, composition and production method.

Tunnel Conductivity and Tunnel Magnetoresistance of the Fe-SiO Films: Interplay of the Magnetotransport and Magnetic Properties

Balaev, D. A.; Balaev, A. D. Source: PHYSICS OF THE SOLID STATE, 61 (7):1203-1210; 10.1134/S1063783419070047 JUL 2019

The electrical properties of a system of nanogranular amorphous Fe–SiO films with a SiO concentration between 0 and 92 vol % have been investigated. The samples with a low SiO content are characterized by the metal-type conductivity. With an increase in the dielectric content x in the films, the concentration transition from the metal to tunneling conductivity occurs at x ≈ 0.6. At the same concentration, the ferromagnet–superparamagnet transition is observed, which was previously investigated by the magnetic method. The temperature dependences of the electrical resistivity ρ(T) for the compositions corresponding to the dielectric region obey the law ρ(T) ~ exp(2(C/kT)1/2), which is typical of the tunneling conductivity. The estimation of the metal grain sizes from the tunneling activation energy C has shown good agreement with the sizes obtained previously by analyzing the magnetic properties. In the dielectric region of the compositions, the giant magnetoresistive effect attaining 25% at low temperatures has been obtained.

Orientational structures in cholesteric droplets with homeotropic surface anchoring

Krakhalev, Mikhail N.; Rudyak, Vladimir Yu.; Prishchepa, Oxana O.; Gardymova, Anna P.; Emelyanenko, Alexander V.; Liu, Jui-Hsiang; Zyryanov, Victor Ya. Source: SOFT MATTER, 15 (28):5554-5561; 10.1039/c9sm00384c JUL 28 2019

The dependency of orientational structures in cholesteric droplets with homeotropic surface anchoring on the helicity parameter has been studied by experiment and simulations. We have observed a sequence of structures, in which the director configurations and topological defects were identified by comparison of polarized microscopy pictures with simulated textures. A toron-like and low-symmetry intermediate layer-like structures have been revealed and studied in detail. The ranges of stability of the observed structures have been summarized in a general diagram and explained by the helicity parameter dependence of the free energy terms.

Structure and electrophysical properties of thin-film SnO2-In2O3 heterostructures

Zhilova, O. V.; Pankov, S. Yu.; Sitnikov, A. V.; Kalinin, Yu. E.; Volochaev, M. N.; Makagonov, V. A. Source: JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS, 30 (13):11859-11867; 10.1007/s10854-019-01503-w JUL 2019

The structure and electrical properties of In2O3 and SnO2 oxide semiconductors and heterostructures based on them has been experimentally investigated. The films were prepared by the method of layer-by-layer deposition using the ion-beam sputtering. The transition from the two-phase film of amorphous SnO2 and In2O3 islands, formed during the layer-by-layer deposition, to a multilayer structure consisting of the amorphous SnO2 and In2O3 continuous layers occurs with an increase in the bilayer thickness. The electrophysical properties of the (SnO2/In2O3)69 heterostructures are determined by the transition from the random distribution of SnO2 and In2O3 amorphous phases to a multilayer structure and the temperature range of measurement. For all studied systems, a consistent change in the prevailing mechanism of conductivity is observed at temperatures from 77 to 300 K. In (SnO2/In2O3)69 thin films with a bilayer thickness hbl < 2.5 nm, change of the prevailing conduction mechanism takes place according to the next sequence: variable range hopping conduction over localized states near the Fermi level, hopping conduction over the nearest neighbors and hopping transfer of carriers excited into localized states near the band edges at temperatures close to room temperature.

Effect of CuO2 Lattice Strain on the Electronic Structure and Properties of High-T-c Cuprate Family

Makarov, I. A.; Gavrichkov, V. A.; Shneyder, E. I.; Nekrasov, I. A.; Slobodchikov, A. A.; Ovchinnikov, S. G.; Bianconi, A. Source: JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 32 (7):1927-1935; 10.1007/s10948-018-4936-9 JUL 2019

Doping and strain dependences of the electronic structure of the CuO6-octahedra layer within LDA+GTB method in the frameworks of six-band p-d model are calculated. Band structure and Fermi surface of the quasiparticle excitations in the effective Hubbard model are characterized by inhomogeneous distribution of the k-dependent spectral weight. Doping results in reconstruction of the band structure, redistribution of the spectral weight over dispersion surface, and reconstruction of Fermi surface from small hole pockets in the underdoped region to large hole contour in the overdoped region through two quantum phase transitions (QPT). Strain increasing leads to displacement of the valence and conductivity bands, bandwidths decreasing, and shift of the concentrations corresponding to QPTs. Strain dependences of the antiferromagnetic exchange coupling and DOS at the Fermi level determining superconducting temperature Tc are obtained. Effective exchange coupling in the equation for Tc demonstrates monotonic strain dependence.

Effect of Short-Range Correlations on Spectral Properties of Doped Mott Insulators

Kuz'min, Valerii; Nikolaev, Sergey; Ovchinnikov, Sergey Source: JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 32 (7):1909-1919; 10.1007/s10948-018-4927-x JUL 2019

In the framework of the cluster perturbation theory for the 2D Hubbard and Hubbard-Holstein models at low hole doping, we have studied the effect of local and short-range correlations in strongly correlated systems on the anomalous features in the electronic spectrum by investigating the fine structure of quasiparticle bands. Different anomalous features of spectrum are obtained as the result of intrinsic properties of strongly correlated electron and polaron bands in the presence of short-range correlations. Particularly, features similar to the electron-like Fermi-pockets of cuprates at hole doping p ∼ 0.1 are obtained without ad hoc introducing a charge density wave order parameter within the Hubbard model in a unified manner with other known peculiarities of the pseudogap phase like Fermi-arcs, pockets, waterfalls, and kink-like features. The Fermi surface is mainly formed by dispersive quasiparticle bands with large spectral weight, formed by coherent low-energy exications. Within the Hubbard-Holstein model at moderate phonon frequencies, we show that modest values of local electron-phonon interaction are capable of introducing low-energy kink-like features and affecting the Fermi surface by hybridization of the fermionic quasiparticle bands with the Franck-Condon resonances.

Structural Evolution and Effect of the Neighboring Cation on the Photoluminescence of Sr(LiAl3)(1-x)(SiMg3)(x)N-4:Eu2+ Phosphors

Author Full Names: Fang, Mu-Huai; Mahlik, Sebastian; Lazarowska, Agata; Grinberg, Marek; Molokeev, Maxim S.; Sheu, Hwo-Shuenn; Lee, Jyh-Fu; Liu, Ru-Shi Source: ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 58 (23):7767-7772; 10.1002/anie.201903178 JUN 3 2019

In this study, a series of Sr(LiAl3)1−x(SiMg3)xN4:Eu2+ (SLA‐SSM) phosphors were synthesized by a solid‐solution process. The emission peak maxima of SLA‐SSM range from 615 nm to 680 nm, which indicates structural differences in these materials. 7Li solid‐state NMR spectroscopy was utilized to distinguish between the Li(1)N4 and Li(2)N4 tetrahedra in SLA‐SSM. Differences in the coordination environments of the two Sr sites were found which explain the unexpected luminescent properties. Three discernible morphologies were detected by scanning electron microscopy. Temperature‐dependent photoluminescence and decay times were used to understand the diverse environments of europium ions in the two strontium sites Sr1 and Sr2, which also support the NMR analysis. Moreover, X‐ray absorption near‐edge structure studies reveal that the Eu2+ concentration in SLA‐SSM is much higher than that in in SrLiAl3N4:Eu2+ and SrSiMg3N4:Eu2+ phosphors. Finally, an overall mechanism was proposed to explain the how the change in photoluminescence is controlled by the size of the coordinated cation.

Site-Selective Occupancy of Eu2+ Toward Blue-Light-Excited Red Emission in a Rb3YSi2O7:Eu Phosphor

Qiao, Jianwei; Ning, Lixin; Molokeev, Maxim S.; Chuang, Yu-Chun; Zhang, Qinyuan; Poeppelmeier, Kenneth R.; Xia, Zhiguo Source: ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 10.1002/anie.201905787

Establishing an effective design principle in solid‐state materials for a blue‐light‐excited Eu2+‐doped red‐emitting oxide‐based phosphors remains one of the significant challenges for white light‐emitting diodes (WLEDs). Selective occupation of Eu2+ in inorganic polyhedra with small coordination numbers results in broad‐band red emission as a result of enhanced crystal‐field splitting of 5d levels. Rb3YSi2O7:Eu exhibits a broad emission band at λmax=622 nm under 450 nm excitation, and structural analysis and DFT calculations support the concept that Eu2+ ions preferably occupy RbO6 and YO6 polyhedra and show the characteristic red emission band of Eu2+. The excellent thermal quenching resistance, high color‐rendering index Ra (93), and low CCT (4013 K) of the WLEDs clearly demonstrate that site engineering of rare‐earth phosphors is an effective strategy to target tailored optical performance.

Probing Quantum Chaos in many-body quantum systems by the induced dissipation

Bychek, Anna A.; Muraev, Pavel S.; Kolovsky, Andrey R. Source: PHYSICAL REVIEW A, 100 (1):10.1103/PhysRevA.100.013610 JUL 11 2019

We theoretically analyze the depletion dynamics of an ensemble of cold atoms in a quasi-one-dimensional optical lattice where atoms in one of the lattice sites are subject to decay. Unlike the previous studies of this problem in Labouvie et al., Phys. Rev. Lett. 116, 235302 (2016), we focus on the case where the system is brought to the chaotic regime, which crucially modifies the depletion dynamics as compared to the regular case. It is shown that depletion of the affected site results in gradual depletion of the neighboring sites according to the t1/3 scaling law. We also show that by measuring occupations of the lattice sites one can extract important information on chaotic dynamics of the original conservative system.

Magnon-polaron excitations in the noncollinear antiferromagnet Mn3Ge

Sukhanov, A. S.; Pavlovskii, M. S.; Bourges, Ph; Walker, H. C.; Manna, K.; Felser, C.; Inosov, D. S. Source: PHYSICAL REVIEW B, 99 (21):10.1103/PhysRevB.99.214445 JUN 28 2019

We present detailed inelastic neutron scattering measurements of the noncollinear antiferromagnet Mn3Ge. Time-of-flight and triple-axis spectroscopy experiments were conducted at the temperature of 6 K, well below the high magnetic ordering temperature of 370 K. The magnetic excitations have a 5-meV gap and display an anisotropic dispersive mode reaching 90 meV at the boundaries of the magnetic Brillouin zone. The spectrum at the zone center shows two additional excitations that demonstrate characteristics of both magnons and phonons. Ab initio lattice-dynamics calculations show that these can be associated with the magnon-polaron modes resulting from the hybridization of the spin fluctuations and the low-energy optical phonons. The observed magnetoelastic coupling agrees with the previously found negative thermal expansion in this compound and resembles the features reported in the spectroscopic studies of other antiferromagnets with similar noncollinear spin structures.

Collective lattice resonances in disordered and quasi-random all-dielectric metasurfaces

Zakomirnyi, Vadim, I; Karpov, Sergei, V; Agren, Hans; Rasskazov, Ilia L. Source: JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS, 36 (7):E21-E29; 10.1364/JOSAB.36.000E21 JUL 1 2019

Collective lattice resonances in disordered 2𝐷 arrays of spherical Si nanoparticles (NPs) have been thoroughly studied within the framework of the coupled dipole approximation. Three types of defects have been analyzed: positional disorder, size disorder, and quasi-random disorder. We show that the positional disorder strongly suppresses either the electric dipole (ED) or the magnetic dipole (MD) coupling, depending on the axis along which the NPs are shifted. Contrarily, size disorder strongly affects only the MD response, while the ED resonance can be almost intact, depending on the lattice configuration. Finally, random removing of NPs from an ordered 2𝐷 lattice reveals a quite surprising result: hybridization of the ED and MD resonances with lattice modes remains observable even in the case of random removing of up to 84% of the NPs from the ordered array. The reported results could be important for rational design and utilization of metasurfaces, solar cells, and other all-dielectric photonic devices.

Interference of nonpolarized light in liquid crystal domains on a polymer surface

Parshin, Alexander M.; Barannik, Alexey, V; Zyryanov, Victor Y.; Shabanov, Vasily F. Source: JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS, 36 (7):1845-1849; 10.1364/JOSAB.36.001845 JUL 1 2019

The interference of nonpolarized light transmitted through an ensemble of nematic liquid crystal domains formed on a polycarbonate surface has been investigated. A model based on the superposition of the ordinary and extraordinary beams passing through domains with a radial structure has been developed. Expressions for the phase difference and intensity of the interfering beams have been derived that take into account the distribution of the liquid crystal director field. The dependences of the optical transmittance of a domain layer on the applied voltage have been calculated with regard to the material and optical constants of a liquid crystal and structural features and averaged morphological parameters of individual domains in the experimental sample. The results of the calculation are consistent with the experimental data, which confirms the validity of the proposed model.

Inducing magnetism in non-magnetic alpha-FeSi2 by distortions and/or intercalations

Zhandun, Vyacheslav; Zamkova, Natalia; Korzhavyi, Pavel; Sandalov, Igor Source: PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 21 (25):13835-13846; 10.1039/c9cp02361e JUL 7 2019

By means of hybrid ab initio + model approach we show that the lattice distortions in non-magnetic α-FeSi2 can induce a magnetic state. However, we find that the distortions required for the appearance of magnetism in non-magnetic α-FeSi2 are too large to be achieved by experimental fabrication of thin films. For this reason we suggest a novel way to introduce magnetism in α-FeSi2 using “chemical pressure” that is, intercalating the α-FeSi2 films by light elements. Theoretical study of the distortions resulting from intercalation reveals that the most efficient intercalants for formation of magnetism and a high spin polarization are lithium, phosphorus and oxygen. Investigation of the dependency of the magnetic moments and spin polarisation on the intercalation atoms concentration shows that the spin polarization remains high even at small concentrations of intercalated atoms, which is extremely important for modern silicate technology.

Heat capacity, thermal expansion and sensitivity to hydrostatic pressure of (NH4)(3)SiF7 at successive structural phase transitions

Bogdanov, Evgeniy V.; Pogoreltsev, Evgeniy I.; Gorev, Mikhail V.; Kartashev, Andrey V.; Laptash, Natalia M.; Flerov, Igor N. Source: JOURNAL OF SOLID STATE CHEMISTRY, 276 152-158; 10.1016/j.jssc.2019.04.029 AUG 2019

Heat capacity, thermal dilatation, permittivity and sensitivity to external pressure of were studied. Due to the absence of cubic phases and , a strong decrease in the total entropy change  J/mol K associated with four successive transformations was found in silicate in comparison with other double fluoride salts (Me: Ge, Ti, Sn) Using analysis of the excess heat capacity in the framework of the thermodynamic theory, the entropies associated with each individual phase transition were determined. In accordance with the entropic parameters, the complete ordering of the structural elements occurs in the monoclinic phase . Further change in symmetry is associated with small entropy changes which prove insignificant displacement of structural units. A phase diagram was constructed and good agreement was found between measured and calculated baric coefficients.

Giant hydrogen effect on the structure and physical properties of ZnO and Co-doped ZnO films fabricated by the RF magnetron sputtering in Ar + H-2 atmosphere

Edelman, I. S.; Chou, Hsiung; Samoshkina, Yu E.; Petrov, D. A.; Lin, Hsien C.; Chan, Wen L.; Sun, Shih-Jye; Zharkov, S. M.; Bondarenko, G., V; Platunov, M. S.; Rogalev, A. Source: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 489 10.1016/j.jmmm.2019.165461 NOV 1 2019

ZnO and Co-doped ZnO films were synthesized by the radio frequency magnetron sputtering in mixed atmosphere of Ar + 20% O2 and Ar + 20–50% H2. The morphology, chemical composition, crystal structure, optical transmission, electrical resistance, and magnetic circular dichroism of the films were investigated. It was established that the films thickness decreased several times when Ar was partly replaced by hydrogen in the sputtering chamber. At the same time, for the Co-doped ZnO films, the increase in the relative Co content with the increasing hydrogen concentration was observed. These phenomena are explained by the formation of gaseous ZnH2 because of the hydrogen reaction with the growing films under the conditions of the high substrate temperature (450 °C) and, respectively, the decrease in the Zn component in the films. The hydrogenated Co-doped ZnO films exhibit an increase in electric conductivity and ferromagnetic behavior at room temperature. The magnetic nature of the films is explained by a combination of the intrinsic ferromagnetism (due to the formation of the Co-H-Co complex) with the inclusion of metallic Co clusters.

Fractal Dimension Effect on the Magnetization Curves of Exchange-Coupled Clusters of Magnetic Nanoparticles

Komogortsev, S. V.; Iskhakov, R. S.; Fel'k, V. A. Source: JOURNAL OF EXPERIMENTAL AND THEORETICAL PHYSICS, 128 (5):754-760; 10.1134/S1063776119040095 MAY 2019

The effect of the fractal dimension of exchange-coupled clusters of magnetic nanoparticles on their magnetization curves is predicted by scaling estimates. These predictions form the basis for the experimental technique used for determining the fractal dimension of nanoparticle clusters from the magnetization curves. We estimate the reliability of determining the dimension by such methods with the help of micromagnetic simulation. It is shown that the effective dimension of magnetic correlation volumes, which is determined from analysis of the magnetization approaching saturation, is in conformity with the dimension of fractal clusters determined from analysis of their morphology. The dimension estimated from analysis of the coercive field on the particle size in a physically natural situation of the dipole–dipole interaction between nanoparticles provides estimates of the cluster dimension, which strongly differs from estimates obtained from analysis of their morphology.

Nematic and Cholesteric Liquid Crystal Structures in Cells with Tangential-Conical Boundary Conditions

Krakhalev, Mikhail N.; Bikbaev, Rashid G.; Sutormin, Vitaly S.; Timofeev, Ivan, V; Zyryanov, Victor Ya Source: CRYSTALS, 9 (5):10.3390/cryst9050249 MAY 2019

Orientational structures formed in nematic and cholesteric layers with tangential-conical boundary conditions have been investigated. LC cells with one substrate specifying the conical surface anchoring and another substrate specifying the tangential one have been considered. The director configurations and topological defects have been identified analyzing the texture patterns obtained by polarizing microscope in comparison with the structures and optical textures calculated by free energy minimization procedure of director field and finite-difference time-domain method, respectively. The domains, periodic structures and two-dimensional defects proper to the LC cells with tangential-conical anchoring have been studied depending on the layer thickness and cholesteric pitch

Optical and calorimetric studies of K2TaF7

Mel'nikova, Svetlana, V; Bogdanov, Evgeniy, V; Molokeev, Maxim S.; Laptash, Natalia M.; Flerov, Igor N. Source: JOURNAL OF FLUORINE CHEMISTRY, 222 75-80; 10.1016/j.jfluchem.2019.04.016 JUN 2019

Optical and calorimetric experiments on K2TaF7 are performed in a wide temperature range. No features were found in the behavior of the birefringence Δnb(T), the angle of rotation of the indicatrix ϕ(T) and the heat capacity ΔCp(T) except for those associated with the PnmaP21/c phase transition. Structural transformation was characterized as strong first order “proper” ferroelastic accompanied by a huge angle ϕ ≈40° and strong pre-transition phenomena in Δnb(T). Two contributions to the anomalies of the optical properties were found associated with the photoelastic effect and the transition parameter related linearly to the spontaneous deformation. Thermal treatments cause correlated changes in temperature and enthalpy of the phase transition, which leads to the invariance of the large magnitude of the corresponding entropy ΔS = 22 J/mol·K which does not match the model with the absence of structural disorder in the Pnma phase.

Understanding perceived color through gradual spectroscopic variations in electrochromism

Mishra, Suryakant; Yogi, Priyanka; Chaudhary, Anjali; Pathak, Devesh K.; Saxena, Shailendra K.; Krylov, Alexander S.; Sagdeo, P. R.; Kumar, Rajesh Source: INDIAN JOURNAL OF PHYSICS, 93 (7):927-933; 10.1007/s12648-018-1353-7 JUL 2019

A bias-dependent in situ Raman scattering and UV–Vis absorption spectroscopic change has been correlated with the corresponding color change of an electrochromic device in an attempt to explain how to understand the relationship between actual perceived color and its absorption/transmittance spectra. For this, the bias across an electrochromic device was increased gradually, rather than abruptly turning ON and OFF, to see subtle variations in Raman and absorption spectra due to bias. Raman scattering establishes that viologen changes its oxidation state reversibly between two redox species (EV2+ to EV+•) as a result of bias-induced dynamic redox process. A gradual variation in Raman and absorption spectra, which shows maximum absorption corresponding to the yellow light, accompanies similar variation in color change of the device as visible by naked eye. These spectroscopic results are correlated with the perceived blue color, in the reflected light, by the eye to understand the actual reason behind this. Maximum absorption of yellow light by the device resulting in blue appearance has been explained using the concept of additive and subtractive primary colors.

Brownian dynamics of the self-assembly of complex nanostructures in the field of quasi-resonant laser radiation

Kornienko, Victoria S.; Tsipotan, Aleksey S.; Aleksandrovsky, Aleksandr S.; Slabko, Vitaliy V. Source: PHOTONICS AND NANOSTRUCTURES-FUNDAMENTALS AND APPLICATIONS, 35 10.1016/j.photonics.2019.100707 JUL 2019

Self-assembly of nanoparticles under the action of laser field can be an universal method for the formation of nanostructures with specific properties for application in sensorics and nanophotonics. For prognosis of the self-assembly processes, the model of movement of an ensemble of nanoparticles in a viscous media under the action of laser radiation with the account for interaction of laser-induced polarizations and Brownian dynamics is developed. This model is applied to the investigation of the self-assembly process of a triple of nanoparticles into three-particle structure with a predetermined geometry.Two specific cases of formation of nanostructure from a preliminarily formed pair of particles are studied: either for the pair fixed in space or from the unfixed pair of nanoparticles. The geometry of resulting nanostructures is shown to be determined by the polarization direction of laser radiation and the laser wavelength. Under proper choice of these parameters the formation of structures is shown to be highly efficient. E. g., maximum probability of structures formation is as hig as 36–46% per single laser pulse of 10 ns duration.

Phase transitions in Rb2KLuF6 crystal

Krylov, A. S.; Vtyurin, A. N.; Voronov, V. N.; Krylova, S. N. Source: FERROELECTRICS, 538 (1):28-34; 10.1080/00150193.2019.1569982 2019

The Raman spectra of Rb2KLuF6 elpasolite crystal have been studied in a wide temperature range, including two phase transitions: from the cubic phase to the tetragonal phase and then to the monoclinic phase. The results of an analysis of the temperature dependences of the parameters of spectral lines are in good agreement with the thermodynamic data on the phase transitions. The analysis of Raman spectra shows that the transition from cubic to tetragonal phase is a second-order transition and the transition from the tetragonal to the monoclinic phase is a weak first-order transition.

Thermal expansion and polarization of (1-x)PNN-xPT solid solutions

Gorev, M. V.; Flerov, I. N.; Bormanis, K.; Kalvane, A. Source: INTEGRATED FERROELECTRICS, 196 (1):60-63; SI 10.1080/10584587.2019.1591957 FEB 12 2019

The paper presents the results of detailed studies of the thermal expansion of (1-x)PbNi1/3Nb2/3O3-xPbTiO3 solid solutions with x = 0-0.8. The anomalous and lattice contributions to deformation and the thermal expansion coefficient are analyzed and the mean square polarization Pd is determined. The results obtained are discussed within the framework of the thermodynamic theory and the Landau 2-4-6 coefficients for solid solutions are estimated.

Toroidal Configuration of a Cholesteric Liquid Crystal in Droplets with Homeotropic Anchoring

Krakhalev, M. N.; Rudyak, V. Yu.; Gardymova, A. P.; Zyryanov, V. Ya. Source: JETP LETTERS, 109 (7):478-481; 10.1134/S0021364019070075 APR 2019

Orientational structures formed in cholesteric droplets with homeotropic surface anchoring have been studied by means of polarization optical microscopy and computer simulations. It has been found that, when the ratio of the size of droplets to the pitch of a cholesteric helix ranges from 1.4 to 2.9, an axisymmetric toroidal cholesteric structure is formed with a topological linear defect in the form of an equatorially located surface ring. The features of the toroidal structure in cholesteric droplets and their optical textures for various observation schemes are examined in detail.

The Influence of the Interface on the Magnetic State in Two-Layer Films of the Fe-Bi System

Patrin, G. S.; Yakovchuk, V. Yu; Yarikov, S. A.; Shiyan, Ya G.; Furdyk, V. P. Source: TECHNICAL PHYSICS LETTERS, 45 (5):507-510; 10.1134/S1063785019050262 MAY 2019

Results of the experimental investigation of two-layer films in the Fe–Bi system are presented. It is found that the order of sequential deposition of the magnetic and nonmagnetic layers influences both the character of magnetization process and the magnetic resonance behavior. The obtained results are explained by the formation of a strongly anisotropic sublayer of nanogranular iron in the Bi/Fe film structure.

A Highly Selective Bandpass Filter Based on Suspended Substrate Resonators with a Two-Sided Stripline Pattern

Belyaev, B. A.; Serzhantov, A. M.; Bal'va, Ya. F.; Leksikov, An. A.; Grushevskii, E. O. Source: TECHNICAL PHYSICS LETTERS, 45 (5):485-488; 10.1134/S1063785019050225 MAY 2019

New resonator design employing a hairpin stripline conductor with a stub situated on one side of a dielectric substrate and regular stripline conductors (connected to a screen) on the other side. Eigenfrequencies of the first three oscillation modes of this resonator can be made closer to each other, so that the resonances of two modes are involved in the formation of the passband while the third mode resonance forms a minimum of the transmission coefficient adjacent to the passband. A structure comprising four resonators of this type has the characteristic of an eighth-order bandpass filter arranged in a case with 45 × 16 × 6.25-mm internal dimensions possessing   f0 = 0.52 GHz central frequency with a 14% relative bandwidth. The filter is highly selective due to the attenuation poles being close to the pass band and a wide high-frequency stopband extending above a fivefold   f0  value at a level of  –100 dB.

Linear Zero Thermal Expansion in a Deep-Ultraviolet Transparent Crystal of BPO4 with Cristobalite-like Structure

Wang, Naizheng; Jiang, Xingxing; Molokeev, Maxim S.; Song, Gaomin; Guo, Shibin; Huang, Rongjin; Li, Laifeng; Wu, Yicheng; Lin, Zheshuai Source: CRYSTAL GROWTH & DESIGN, 19 (6):3109-3112; 10.1021/acs.cgd.9b00361 JUN 2019

We report the discovery of the zero thermal expansion (ZTE) effect in BPO4, a famous deep-ultraviolet (DUV) optical material with cristobalite-like structure. It is revealed that BPO4 has a linear ZTE coefficient of −0.16(5) MK–1 along the c-axis as temperature increases from 13 to 300 K, which originates from the subtle counterbalance between the rotation-induced expansion and contraction effects among BO4 and PO4 groups. BPO4 is a unique DUV cristobalite-like material exhibiting the linear ZTE behavior.

Study of the Physical Properties and Electrocaloric Effect in the BaTiO3 Nano- and Microceramics

Kartashev, A. V.; Bondarev, V. S.; Flerov, I. N.; Gorev, M. V.; Pogorel'tsev, E. I.; Shabanov, A. V.; Molokeev, M. S.; Guillemet-Fritsch, S.; Raevskii, I. P. Source: PHYSICS OF THE SOLID STATE, 61 (6):1052-1061; 10.1134/S1063783419060088 JUN 2019

The specific heat, thermal expansion, permittivity, and electrocaloric effect in bulk of BaTiO3 (BT) samples in the form of nano- (nBT-500 nm) and micro- (mBT-1200 nm) ceramics fabricated using spark plasma sintering and solid-state plasma techniques have been investigated. The size effect has been reflected, to a great extent, in the suppression of the specific heat and thermal expansion anomalies and in the changes in the temperatures and entropies of phase transitions and permittivity, and a decrease in the maximum intensive electrocaloric effect: ΔTmaxAD = 29 mK (E = 2.0 kV/cm) for nBT and ΔTmaxAD = 70 mK (E = 2.5 kV/cm) for mBT. The conductivity growth at temperatures above 360 K leads to the significant irreversible heating of the samples due to the Joule heat release in the applied electric field, which dominates over the electrocaloric effect.

Influence of the Coulomb Repulsions on the Formation of the Superconducting Gap of the Spin-Polaron Quasiparticles in Cuprates

Val'kov, V. V.; Korovushkin, M. M.; Barabanov, A. F. Source: JOURNAL OF LOW TEMPERATURE PHYSICS, 196 (1-2):242-252; 10.1007/s10909-018-02120-3 JUL 2019

Taking into account the real crystalline structure of the CuO2 plane and the strong spin-fermion coupling, the influence of the on-site Coulomb repulsion of holes Up and the intersite Coulomb repulsion V2 between holes located at the next-nearest-neighbor oxygen ions on the formation of the superconducting gap with the d-wave symmetry of the order parameter of the spin-polaron quasiparticles is studied. It is shown that the formation of the resulting superconducting gap within the spin-fermion model is caused by three components. The dependence of the narrowing of the superconducting gap on the values Up and V2 is analyzed.

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