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  • Magnetic Sensitive Ceramic Composites based on La0.7Sr0.3MnO3

    Biphasic composite materials were synthesized near the La0.7Sr0.3MnO3-based percolation threshold and the second phase, which is an inorganic or organic compound — polyvinyl acetate, paraffin, carboxymethylcellulose, sucrose, and ultrafine silver particles. For composites with an organic matrix, the magnetoresistance values ​​do not exceed 2%, and for composites with silver particles - 8%. The values ​​of isotropic negative magnetoresistance for ceramic samples of 80% LSMO / 20% GeO2 (mass%) reach 13% in a 15 kOu magnetic field with a sensitivity of about 1% / ke in the low-field region. High chemical and radiation stability of these glass composites should be noted. The magnetoresistive properties of such compounds slightly decreased after 60 days of being in water with a salinity of 35 ppm. Composites of 80% LSMO / 20% GeO2 were exposed to X-rays with a dose of 7 Sv from the Co57 source. The magnetoresistive properties and electrical resistance of these composites did not change after that.

    Keywords: lanthanum strontium manganite, ceramic two-phase material, one-step synthesis, radiation exposure, magnetoresistance, percolation threshold, dielectric constant, barrier layer, spin-dependent tunneling, spin polarization

  • Electrical properties of magnetoresistive composites based on manganites

    The electrical properties of composites based on La0.7Sr0.3MnO3 (LSMO) synthesized at the percolation threshold have been studied: LSMO / Li4P2O7, LSMO / Sb2O3, LSMO / GeO2. The activation energies of these compounds have been determined. New ceramic materials with silver interlayers between LSMO manganite crystallites have been synthesized. The current-voltage characteristics for the LSMO / GeO2 series are given. The nonlinearity of the characteristics is most pronounced for compositions near the percolation threshold, 85% LSMO / 15GeO2.

    Keywords: lanthanum strontium manganite, composite material, ceramics, one-step synthesis, magnetoresistance, percolation threshold, dielectric constant, barrier layer, tunneling, spin polarization

  • A new class of magnetodielectric materials based on manganites

    A new class of materials is proposed that change their dielectric permittivity as a function of the magnetic field strength. Such materials are two-phase composites of composition La0.7Sr0.3MnO3 / I, where I is the isolating phase, Li4P2O7 or GeO2. The ratio of components is close to the percolation threshold: from 10% to 20% by weight. Dielectric properties have been studied in the frequency range of the measuring field from 1 kHz to 1 MHz in magnetic fields from 0 to 15 kOe. Samples have an inductive impedance, their permittivity is negative. In a magnetic field, the permittivity increases in absolute value and at room temperature the values of the magnetodielectric coefficient reach 28%.

    Keywords: lanthanum strontium manganite, composite material, ceramics, one-step synthesis, magnetoresistance, percolation threshold, dielectric constant, barrier layer, tunneling, spin polarization

  • Influence of barrier substances on magneto-resistive properties of composites based on strontium lanthanum manganite

    Based on our own, as well as literary experimental data, the analysis of the Influence of a barrier material used to create heterogeneous composites based on La0.7Sr0.3MnO3 on their magnetoresistive properties is carried out. Such composites differ in existence of an isotropic negative magnitorezistivnost (MR) connected from backs - dependent tunneling of carriers in magnetic field. The largest value MR up to 15% in the field of 15 kOe are shown when using glass-like GeO2 oxide at a percolation ratio of components.

    Keywords: lanthanum strontium manganite, composite material, ceramics, one-step synthesis, magnetoresistance, percolation threshold, dielectric constant, barrier layer, tunneling, spin polarization

  • Electric properties and structure of the new layered oxides LnSr2CuTiO6,5 (Ln = La, Nd, Pr)

    Many complex oxides of transition metals show effect of enormous dielectric permeability. New complex layered oxides LnSr2CuTiO6,5 (Ln = La, Nd, Pr) are synthesized. Their structure by means of x-ray diffraction on the Shimadzu XRD-7000 S is investigated. Processing of XRD was carried out in the program FULLPROF-2013. The main X-ray reflexes are indicated in space group I4/mmm (№ 139). The data of the crystal-chemical analysis which are carried out taking into account a charge state and coordination environment of cations show that distortion of coordination polyhedrons is significantly reduced in series Ln = La→Nd. The unit cell parameters naturally decrease according to reduction of ionic radiuses of La→Nd. Dielectric properties of materials investigated using the universal analyzer of a frequency response Solartron 1260A in the range of frequencies 1mHz - 16МHz with a signal amplitude 500-900 mV. Increasing the dielectric constant is possible due to the charge ordering caused by uneven distribution of charge. Frequency dependences of an imaginary and real part of dielectric constant are given.

    Keywords: dielectric constant , complex oxide, transition metal, perovskite, x-ray diffraction, microstructure, crystal-chemical analysis, impedance- spectroscopy, charge ordering, coordination polyhedron

  • Composite ceramic materials based on La0,67Sr0,33MnO3 with positive and negative magnetoresistive

    Lanthanum strontium manganite La0,67Sr0,33MnO3 which has a high spin polarization of the carriers has been used to create composite materials with different barrier materials - GeO2, Li4P2O7, C. The magnetoresistive properties of the synthesized ceramics at room temperature have been investigated. It has been found that the magnetoresistive isotropic negative values ​​for samples with germanium oxide at room temperature in a magnetic field of 18 kOe reach a value of 15%, with the barriers of lithium pyrophosphate - 16%. It has been determined that the samples which contain 10-85% graphite at a field of 15 kOe exhibit positive magnetoresistance reaching a value of 15% .

    Keywords: lanthanum strontium manganite, composite material, ceramics, magnetoresistance, X-ray diffraction, microstructure, barrier layer, tunneling, percolation transition, spin polarization, the Seebeck effect

  • Structure and dielectric properties of B-substituted lanthanum nickelates

    Ceramic materials based on solid solutions La2-xSrxMO4, where M is Ni, Fe, Co, Cu, x = 0, 2 with layered K2NiF4 structure (structure of Ruddlesden-Popper) have been synthesized and investigated. The correlation of dielectric properties with a normalized bond lengths of the metal-oxygen has been observed. The existence of nickel atoms in the 2+ oxidation state for nickelates has been shown.

    Keywords: solid solutions, colossal dielectric constant, resistivity, x-ray diffraction, dielectric spectrum, XANES, low-resistivity semiconductors, the activation energy, the distortion of the coordination polyhedra, oxygen non-stoichiometry

  • Glass composites based on magnetic semiconductor La0,67Sr0,33MnO3 as functional materials

    Composites La0,67Sr0,33MnO3 (SiO2, Sb2O3) with different weight ratios have been synthesized. Their magnetoresistive and dielectric properties have been investigated. It has been established that in the frequency range from 10 to 106 Hz for SiO2 concentration of 10% the colossal magnitudes of the dielectric constant ( ~ 4 • 104) take place. The values of the negative isotropic magnetoresistance for samples with silica at room temperature is 8.6%, with abarriers of antimony oxide reaches 12%, which makes it possible to use such materials in spintronics.

    Keywords: Magnetoresistance, colossal dielectric permittivity, glass composites, X-ray diffraction, spin polarization, barrier layers, tunneling, microstructure, dielectric spectrum, Maxwell-Wagner effect.

  • The strontium hexaferrite - compound with colossal dielectric constant

    The presence of colossal dielectric constant in the low frequency region is observed in the strontium ferrite with hexagonal structure. This result can be explained in the framework of the "grain-layer" and the polarization of Maxwell - Wagner in the ceramic medium. The effect of negative capacitance in ceramic strontium hexaferrite at a frequency of less than 2.10 Hz has been detected.

    Keywords: hexaferrite strontium, ferromagnetic, insulator, semiconductor, colossal dielectric constant, negative capacitance, high-temperature annealing, X-ray structural analysis, full-profile analysis, electron microscopy.

  • Nonferroelectric ceramic of La2-xSrxNiO4 with colossal permittivity

    By self-propagating high-temperature synthesis (SHTS) prepared fine powder оf La2-xSrxNiO4 composition , which is used to obtain dense ceramics exhibiting the properties of n-type semiconductor. Prolonged annealing of the samples resulted in a decrease of the conductivity on the order of 3-4, and the changing nature of the dielectric spectrum: dielectric constant ε' has a stable value of 4·104 Hz in the range of 0,4 − 1·105 Hz .

    Keywords: dielectric constant, phase separation, nikelate of strontium lanthanum, self-extending high-temperature synthesis

  • Synthesis and electrochemical characteristics of the new composite cathode material of LiMn2O4@LiCoO2 for lithium-ion battery

    The composite cathode material of the core@shell type with the LiMn2O4@LiCoO2 formula of has been successfully synthesized using the solid-state reactions in several stages. Its structure has been studied by means of X-ray diffraction, scanning and transmission electron microscopy and vibrational infrared spectroscopy. Electrochemical investigation in two-electrode cell has been showed improvement of characteristics of the synthesized cathode material than the constituent components. The specific power of LiMn2O4@LiCoO2 is 650 mWh/g, against 450 and 500 mWh/g for LiCoO2 and LiMn2O4, respectively.

    Keywords: lithium-ion batteries, cathode materials, Delafosse, X-ray structural analysis, electron microscopy, electrochemical properties

  • Synthesis and electrochemical properties of LiMn1/3Cr1/3Fe1/3O2 solid solution with the structure of α-NaFeO2

    The solid solution of  LiMn1/3Cr1/3Fe1/3O2 with the structure of α-NaFeO2  isostructural with the widely used LiCoO2  has been synthesized and investigated as a cathode material. Rated voltage of LiMn1/3Cr1/3Fe1/3O2  relative to the lithium is 4 V.  The possibility of charging − discharging the material to a specific capacity of 220-250 mAh/g at currents of C/15-C/50 without phase transformations has been experimentally demonstrated. 

    Keywords: lithium-ion batteries, cathode materials, Delafosse, solid solution, X-ray structural analysis, electrochemical properties