An unconventional temperature dependence of infrared absorption spectra of rare-earth cobalt oxides LaCoO3 and GdCoO3 has been studied experimentally and theoretically in the temperature range of 3.2–550 K. A quite strong softening of the optical phonon mode has been detected, which cannot be explained by standard lattice anharmonicity. It has been shown that the redshift of the phonon spectrum is due to the e-lectron–phonon coupling quadratic in the lattice displacement and to fluctuations of the multiplicity of Co3+ ions.

The effect of surfactants on the structure, morphology, and magnetic properties of Fe x S y iron-sulfide nanoparticles synthesized by thermal decomposition is studied. Oleylamine, hexadecylamine, and octadecylamine are used as surfactants. It is established by X-ray and electron-diffraction analysis combined with Mössbauer spectroscopy that, in samples 1 and 2 prepared using oleylamine and hexadecylamine, respectively, the Fe 3 S 4 greigite phase dominates, with an inverse spinel structure isostructural to the iron oxide Fe 3 O 4 magnetite with minor Fe 9 S 11 impurities. Deviations in the distribution of iron cations over the tetrahedral and octahedral sites relative to the bulk greigite crystals are observed. The nanoparticles synthesized using octadecylamine (sample 3) are found to be multiphase with a greigite fraction of ~20%. In all three cases, as showed the results of transmission electron microscopy and Fourier transform infrared spectroscopy together with thermogravimetry analysis, the magnetic nanoparticles have an organic shell chemically bonded to their magnetic core, which prevents the agglomeration of the particles. This shell is much more massive in samples 2 and 3. The magnetization values for samples 1 and 2 are similar to those of greigite nanoparticles reported in publications, while the magnetization of sample 3 is several times lower, in accordance with the greigite fraction in it. The combination of fairly high magnetization with a massive organic shell allows one to consider hexadecylamine to be a promising surfactant for the synthesis of iron-sulfide nanoparticles protected from external impact and agglomeration.

A composite based on nanorod-shaped greigite (Fe3S4) crystallites with adsorbed ferrihydrite (Fe2O3 center dot nH(2)O) nanoparticles has been synthesized. The synthesis has been performed by biomineralization of the bacterial wall of a sulfate-reducing Desulfovibrio sp. A2 bacteria. The phase composition of the synthesized composite has been investigated by X-ray powder and electron diffraction, as well as Fourier-transform infrared, extended X-ray absorption fine structure, and Mossbauer spectroscopy. The magnetic measurement data have shown that the sample under study contains two magnetic phases: multidomain nanorod-shaped greigite and ultrasmall ferrihydrite nanoparticles. The constant atomic fraction of the greigite crystalline phase in the range of 4-300 K (similar to 20%) revealed by Mossbauer spectroscopy is indicative of a blocked magnetic moment of nanorod-shaped Fe3S4. It is shown that nanorod-shaped Fe3S4 crystallites are strongly magnetically bound with adsorbed Fe2O3 center dot nH(2)O (E-int similar to 1200k(B)) nanoparticles. This significantly slows down the superparamagnetic relaxation of the magnetic moments of ferrihydrite nanoparticles. Therefore, the blocking temperature noticeably increases and attains, according to the Mossbauer spectroscopy data, a value of T-B = 140 K (the magnetic measurements yield T-B = 72 K). The processes of superparamagnetic blocking of the magnetic moments of ferrihydrite nanoparticles manifest themselves in the evolution of the magnetic properties of the investigated sample (a significant increase in the coercivity and remanent magnetization). In support of the Mossbauer spectroscopy data, a sufficiently high superparamagnetic blocking temperature has been established, which discloses the effect of magnetizing of ferrihydrite nanoparticles by coarser greigite formations, analogously to the effect of interparticle magnetic interactions. (C) 2022 Elsevier B.V. All rights reserved.

Morphological parameters, reflection spectra, IR absorption spectra, and glass transition temperatures of submicron-sized spheres of poly(methyl methacrylate) (PMMA) formed in a water-acetone dispersion medium were studied in comparison with similar spheres obtained in distilled water. Dependence of a shrinkage degree of the submicrospheres on the concentration of acetone in water is studied. Features of the formation of periodic structures based on the water-acetone dispersions of PMMA in four different ways are considered. 2D (photonic crystal films) and 3D (artificial and inverse opals) resonance structures were obtained.

In polycrystalline cerium iron garnet films, the gap in the electron excitation spectrum and electronic transitions between di- and tetravalent iron and cerium impurity ions have been established from the IR absorption spectra. The temperatures of delocalization of the ferrous states of iron have been found from the impedance spectroscopy, electrical resistance, and IR spectroscopy data. The difference between the ac and dc magnetoresistances has been established and explained using a model of a dielectrically inhomogeneous medium.

Методом цепной радикальной безэмульгаторной полимеризации метилметакрилата в воде синтезированы партии высококачественных сферических частиц полиметилметакрилата с полидисперсностью менее 5 %. Средние диаметры в партиях составили от 237 нм до 447 нм. Модифицируя классическую технологию синтеза и заменяя от 4 об.% до 10 об.% дисперсионной среды на ацетон, удается варьировать физико-химические свойства получаемых субмикросфер, делая их более стабильными и прочными. На основе сфер полиметилметакрилата субмикронного размера получены двух- и трехмерные фотонно-кристаллические структуры — опалы. Кристаллическая структура опалов исследована методами инфракрасной спектроскопии и электронной сканирующей микроскопии. Спектроскопия показала, что частицы полиметилметакрилата содержат значительное количество воды, испарение которой приводит к усадке сфер. Кроме того, исследована стереорегулярность полимера, синтезированного в этой работе, а также определены температуры стеклования полученных образцов.

The effect of magnetic nanoparticles coated with arabinogalactan on the viability of Ehrlich ascites carcinoma (EAC) cells was studied. The nanoparticles were studied by transmission electron microscopy, Mössbauer spectroscopy, IR spectroscopy, and ferromagnetic resonance. A correlation between the proportion of dead EAC cells in suspension and the intensity of the EPR signal of dinitrosyl iron complexes was found. This result may be due to the presence of NO molecules.

BaLaCuS3 powder was prepared by sulphidation method. The shape of powder particles is irregular and place in the range of 10-100 The electronic, elastic and vibrational properties were evaluated with the use of DFT method. According to the electronic band structure calculation the BaLaCuS3 is a direct wide band gap semiconductor with E-g(d) = 2.0 eV while the energy of indirect transition is equal to 2.2. eV and it indicates that the BaLaCuS3 is a promising material for efficient underwater solar cells. Calculated compressibility of BaLaCuS3 is found to be identical to germanium and zinc blende modification of zunc sulfide.

В поликристаллических пленках цериевого феррита граната найдена величина щели в спектре электронных возбуждений, электронные переходы между примесными двухвалентными и четырехвалентными ионами железа и церия из ИК-спектров поглощения. Найдены температуры делокализации двухвалентных состояний железа из импедансной спектроскопии, электросопротивления и ИК-спектров. Найдено отличие магнитосопротивления на переменном и постоянном токе, которое объясняется в модели диэлектрически неоднородной среды. Ключевые слова: магнитоимпеданс, ИК-спектроскопия, цериевый феррит гранат, тонкие пленки.

Single crystals of SmAl3(BO3)4 were synthesized by the group growth on seeds method. The crystal structure was solved using a single-crystal experiment and the purity of the bulk material was proved by the Rietveld method. This borate crystallizes in the monoclinic C2/c space group with unit-cell parameters a = 7.2386 (3), b = 9.3412 (5), c = 11.1013 (4) Å and β = 103.2240 (10)°. IR and Raman spectroscopic analyses confirmed the monoclinic structure of SmAl3(BO3)4. Under 532.1 nm excitation, luminescence spectra exhibit bands assignable to the transitions from 4G5/2 to 6H5/2, 6H7/2, 6H9/2 and 6H11/2. The similarity of the luminescence spectra of the trigonal and monoclinic polymorphs is explained by the minor role of Sm-O bond distortion and the primary role of rotational distortion of SmO6 octahedra. The smaller covalency of the Sm-O bond in alumoborates is deduced in comparison with galloborates. Calorimetric measurements did not reveal high-temperature structural phase transitions up to a temperature of 720 K.

Eu2(SO4)3 was synthesized by chemical precipitation method and the crystal structure was determined by Rietveld analysis. The compound crystallizes in monoclinic space group С2/с. In the air environment, Eu2(SO4)3 is stable up to 670°C. The sample of Eu2(SO4)3 was examined by Raman, Fourier-transform infrared absorption and luminescence spectroscopy methods. The low site symmetry of SO4 tetrahedra results in the appearance of the IR inactive ν1 mode around 1000cm−1 and ν2 modes below 500cm−1. The band intensities redistribution in the luminescent spectra of Eu3+ ions is analyzed in terms of the peculiarities of its local environment.

AbstractThe results of structural and magnetic investigations of nanogranular Co–Al_2O_3 films formed from Co_3O_4/Al thin-film layered structures upon vacuum annealing are reported. The Co_3O_4/Al films have been obtained by sequential reactive magnetron sputtering of a metallic cobalt target in a medium consisting of the Ar + O_2 gas mixture and magnetron sputtering of an aluminum target in the pure argon atmosphere. It is shown that such a technique makes it possible to obtain nanogranular Co–Al_2O_3 single- and multilayer thin films with a well-controlled size of magnetic grains and their distribution over the film thickness.

The results of structural and magnetic investigations of nanogranular Co–Al2O3 films formed from Co3O4/Al thin-film layered structures upon vacuum annealing are reported. The Co3O4/Al films have been obtained by sequential reactive magnetron sputtering of a metallic cobalt target in a medium consisting of the Ar + O2 gas mixture and magnetron sputtering of an aluminum target in the pure argon atmosphere. It is shown that such a technique makes it possible to obtain nanogranular Co–Al2O3 single- and multilayer thin films with a well-controlled size of magnetic grains and their distribution over the film thickness.

Two ammonium oxofluorovanadates, (NH4)3VO2F4 and (NH4)3VOF5, have been investigated by temperature-dependent infrared and Raman spectroscopy methods to determine the nature of phase transitions (PT) in these compounds. Dynamics of quasioctahedral groups was simulated within the framework of semi-empirical approach, which justified the cis-conformation of VO2F43 − (C2v) and the C4v geometry of VOF53 −. The observed infrared and Raman spectra of both compounds at room temperature (RT) revealed the presence at least of two crystallographically independent octahedral groups. The first order PT at elevated temperatures is connected with a complete dynamic disordering of these groups with only single octahedral state. At lower temperatures, the octahedra are ordered and several octahedral states appear. This PT is the most pronounced in the case of (NH4)3VOF5, when at least seven independent VOF53 − octahedra are present in the structure below 50 K, in accordance with the Raman spectra. Ammonium groups do not take part in PTs at higher and room temperatures but their reorientational motion freezes at lower temperatures.

The vibrational spectroscopy investigation of phase transitions in NdF3 crystal is reported. Spectra were obtained in temperature range from 300 to 10K. It has been shown that, down to 10K, the trigonal tysonite structure of NdF3 trifluoride remains stable.

The GdCoO3–δ perovskite is a semiconductor with the energy gap E g ≈ 0.5 eV from electrical transport measurements. It reveals unusual optical absorption spectra without transparency window expected for semiconductors. Instead we have measured the narrow transmittance peak at the photon energy ε0 = 0.087 eV. To reconcile the transport and optical data we have studied the effect of oxygen vacancies on the electronic structure of the GdCoO3–δ. We have found that oxygen vacancies result in the in-gap states inside the charge-transfer energy gap of the GdCoO3. It is a multielectron effect due to strong electron correlations forming the electronic structure of the GdCoO3–δ. These in-gap states decrease the transparency window and result in a narrow absorption minimum. The predicted temperature dependence of the absorption spectra has been confirmed by our measurements.

Infrared absorption spectra of the bismuth pyrostannate Bi2(Sn0.95Cr0.05)2O7 were investigated in the frequency range 350−1100cm−1 at temperatures of 110−525K. Four frequency regions with split absorption lines are distinguished. Softening of frequencies at the structural transitions was observed. The maxima of permittivity measured in the frequency range 1−200kHz at temperatures 100−400K were determined. It was found that the magnetic susceptibility changes its sign in the low-temperature region. The correlation between anomalies in the magnetic susceptibility, permittivity, and absorption line intensity was established. Softening of frequencies is explained by the variation in the coefficient of thermal expansion of the lattice. The temperature behavior of permittivity is described using the Debye model.