[en] We experimentally show that, in contrast to the data having been collected so far, some single crystals of NaNbO₃ exhibit a dielectric permittivity of several thousand, at low T, and this value is saturated when approaching 0 K on cooling. Other sodium niobate crystals (having larger dielectric losses) present a first-order phase transition to a ferroelectric phase on cooling (at 80-200 K). The width of the thermal hysteresis in these crystals increases when the temperature of the phase transition obtained on heating decreases. The dielectric permittivity at the phase transition obtained on cooling shows a tendency to increase and saturate, when the thermal hysteresis increases. We identify the ground state of the sodium niobate crystal exhibiting the smallest dielectric losses (in the studied set of crystals) as a novel quantum paraelectric state coexisting with a metastable ferroelectric state. In principle, the crystal presenting the state of quantum paraelectricity can be considered as having the largest (among the crystals studied) thermal hysteresis, for which the low boundary is below 0 K. (fast track communication)

[en] A solid solution of the three – component system 0.8NaNbO₃ – 0.15KNbO₃-0.05CdNb₂O₆ was prepared by two-stage solid-phase synthesis followed by sintering using conventional ceramic technology. An experimental study of the dielectric, piezoelectric, and ferroelastic characteristics of the latter in the low-temperature range (10÷330) K. The conclusion is made about the expediency of using the obtained results in the development of functional ferroactive materials based on sodium – potassium – cadmium niobates and devices with their participation. (paper)

[en] Alternative explanation to the effect of disappearance of the Morin transition on hematite nanoparticles with their size decreasing is proposed basing on an idea of the predominant role of the shape anisotropy for nanosize particles. Three types of the magnetic structure of hematite nanoparticles with various sizes are found by Mössbauer spectroscopy: coexistence of the well-pronounced antiferromagnetic and weakly ferromagnetic phases for particles with average diameters of about 55 nm, non-uniform distribution of the magnetization axes which concentrate on the vicinity of the basal plane (111) for prolonged particles with cross sections of about 20 nm, and uniform distribution of the easy axes in regard to the crystalline directions for 3-nm particles. Description of the temperature evolution of experimental data within novel model of the magnetic dynamics for antiferromagnetic particles which accounts the exchange, relativistic, and anisotropy interactions is provided, and the structural as well as energy characteristics of the studied systems are reconstructed.

[en] Polycrystalline samples of SrFe_2/3W_1/3O₃ (SFWO) ceramic were obtained by solid-phase reactions with subsequent sintering using conventional ceramic technology. X-ray diffraction analysis showed that at room temperature, the SFWO ceramic is single-phase and has a perovskite-type structure with tetragonal symmetry and parameters a = 3.941(9) Å, c = 3.955(6) Å, and c/a = 1.0035. In studying the magnetic properties and the Mössbauer effect in SFWO ceramics, it is found that the material is a ferrimagnet, and the iron ions are only in the valence state of Fe³⁺. It is suggested that in the temperature range of T = 150–210°C, a smeared phase transition from a cubic (paraelectric) phase to a tetragonal (ferroelectric) phase takes place in SFWO with decreasing temperature.

[en] A comprehensive study of the Jiddat Al Harasis 055 (L4-5 type) ordinary chondrite is conducted using 2D X-ray fluorescence spectroscopy, Mössbauer spectroscopy, X-ray absorption near edge structure (XANES) spectroscopy, X-ray diffraction, and vibrating sample magnetometry. The content of Fe, Ni, Si, Mg, S, Ca, Al, Mn, Ti, and Cr is determined; several components and areas with increased content of S, Ti, Cr, and Ni are detected along with several Ca–Al inclusions. According to XANES data, the Jiddat Al Harasis 055 sample contains iron with the average oxidation state 2.4+. This result is consistent with the data of Mössbauer spectroscopy used to identify iron phases which testifis that 46% and 54% of iron ions appear in Fe²⁺ and Fe³⁺ states, respectively. By comparing the pre-edge energy position and the area under the preedge peak of XANES spectra with literature data reported for geological materials, the average coordination number in the first coordination sphere of iron is found to be 5.3. According to the data of Xray diffraction and Mössbauer spectroscopy, the iron-containing meteorite phases consist mainly of olivine, pyroxene, hematite, and goethite. The observed magnetic properties of the sample can be attributed to small inclusions of ferromagnetic phases such as nickel nanoparticles, which cannot be reliably identified using laboratory spectral methods.

[en] Spinel Mn²⁺ Fe_2−x³⁺Ce_x³⁺O₄ (where x = 0.01–0.05) polycrystalline nanoparticles were fabricated by solution combustion method using glucose and urea as fuels. X-ray diffractogram (XRD) proved the witness of the cubic crystal consort of products which have the crystallite sizes in between 12 and 8 nm. The size of the sample was accomplished via transmission electron microscopy. The elemental composition of iron and manganese ions valences of MnCe_xFe_2−xO₄ samples were analyzed by X-ray photoelectron spectroscopy. XPS data reveals iron in all samples was trivalent; manganese was divalent, although tetravalent manganese ions were present on the surface of particles. Magnetic characterization of samples was done via Mössbauer spectroscopy at room temperature and at low temperatures (15 K). The Mössbauer analysis determines the consequence of Ce³⁺ substitution on isomer shift and quadrupole splitting of all samples. The low temperature Mössbauer spectroscopy results indicate that the presence of Ce³⁺ ions in the octahedron sites causes the decrease in the concentration of Fe³⁺ ions.

[en] Nanoparticles of Co_0.5Ni_0.5Fe_2−xCe_xO₄ (where x = 0.0, 0.01, 0.015 and 0.02) ferrites are prepared by the modified solution combustion method using a mixture of fuels and are characterized to understand their structural, microstructural and magnetic properties. The X-ray diffraction is used to confirm the formation of a single-phase cubic spinel structure. The average crystallite sizes are calculated using the Scherrer formula and are found to be less than 50 nm. The microstructural features are obtained by the scanning electron microscopy, and the compositional analysis is done by using the energy-dispersive spectroscopy. The transmission electron microscopy (TEM) investigations show that the synthesized ferrites are made up of very fine spherical nanoparticles. The influence of a rare-earth element (Ce³⁺) on the magnetic properties of the samples was studied using the Mössbauer spectroscopy. The Mössbauer spectroscopy reveals the formation of broadened Zeeman lines and quadrupole-split lines and the presence of the Fe³⁺ charge state at B sites in the samples. The quadrupole splitting shows that the orientation of the magnetic hyperfine field with respect to the principle axes of the electric field gradient was random. The magnetic hyperfine field values indicate that the A sites have more A-O-B superexchange interactions than the B sites. The coexistence of magnetic sextet and a doublet component on the room-temperature spectra suggests superparamagnetic properties of the nanoparticles. The low-temperature (15 K) Mössbauer spectroscopy explores the paramagnetic relaxation in the nanoparticles. The area under the sextet refers to Fe³⁺ concentrations in the tetrahedral and octahedral sites of the ferrite. This study confirms that the Ce³⁺ substitution of Fe³⁺ only for octahedron sites causes the decrease in Fe-O-Fe arrangement. The effect of Ce³⁺ doping on the magnetic properties of Co_0.5Ni_0.5Fe₂O₄ is examined from the vibrating sample magnetometry (VSM) spectra. Saturation magnetization values are decreased initially and then increased, as result of Ce³⁺ doping. This can be explained by Neel’s two-sub-lattice model. Further, the value of coercivity is found to be increasing with increasing Ce³⁺ concentration. The obtained results of M-H loop with improved coercivity (from 851 to 1039 Oe) by Ce³⁺ doping of Co_0.5Ni_0.5Fe₂O₄ demonstrate the usefulness for permanent magnet applications.

[en] 

Abstract—

: The concentration dependences of the magnetic phase transition temperature T_N, determined based on the changes in Mössbauer spectra, were investigated for a BiFeO₃ solid solution with ordered perovskite PbFe_0.5Sb_0.5O₃ and for a disordered BiFe_1 – xCr_xO₃ solid solution. It is established that the magnetic-order type in BiFe_1 – xCr_xO₃ changes from antiferromagnetic to spin-glass at a higher degree of Fe-sublattice dilution in comparison with the PbFe_0.5Nb_0.5O₃-based solid solutions presumably because of the smaller BiFeO₃ lattice parameter. Due to the local ordering of Fe³⁺ and Sb⁵⁺ ions, the T_N value decreases more rapidly (as compared to BiFe_1 – xCr_xO₃) with a decrease in the Fe³⁺ content in the lattice of (1 – x)BiFeO₃– xPbFe_0.5Sb_0.5O₃ solid solutions.

[en] In the present investigation, we have examined the evolution and influence of Sc³⁺ content on the structural, microstructural, UV–Visible, Dielectric, DC conductivity and humidity sensing performance of Cobalt chromate viz., Co_(1−x)Sc_xCr₂O₄ nanoparticle are synthesized by modified solution combustion method using mixture of carbamide and glucose as fuel. For sintered powder to study the Crystallinity, phase purity, Structure analysis are done by using X-ray diffractogram (XRD). The results of the XRD analysis give rise to all the samples are exhibit single phase with spinel cubic structure. Further the crystallite size was observed in nano region. The increase of the lattice parameter provides evidence for the effective substitution of Sc³⁺ at A site. The surface morphology, microstructure and elemental analysis are done by using SEM and EDS respectively. The SEM micrographs reveals that material are exhibits highly porous nature and producing agglomeration. The results of EDS confirms perfect elemental composition and there is no impurities in the samples. Particle size of both samples were estimated from particle size distribution diagram. The UV–Vis diffuse reflectance analysis were used to estimate the band gap of the samples. To understand the electrical behaviour of the samples we have done dielectric properties as a function of frequency. Dielectric measurements reveal that dielectric constant is loos tangent decreases with increasing frequency and it is constant for higher frequency side, this can be discussed using Koop’s theory. For estimate the activation energy DC conductivity measurements used. The specific surface range (SSA) are analyzed by using Brunauer–Emmett–Teller (BET) measurement and were found 165 Cm³/g STP and 40,790 Cm³/g STP. Further the average pore diameters were found 38 and 28 nm. To explore the response of the material at different humidity levels humidity sensing measurements carried out and humidity sensing response coefficient is estimated. From this study the fundamental behaviour of the synthesized materials at different standards were evaluated for various industrial applications.

[en] In the present work, the HoFeO₃ and HoFe_0.8Sc_0.2O₃ nanoparticles prepared by the solution combustion method have been studied to understand their structural, dielectric, and magnetic properties. The refined X-ray diffraction pattern (XRD) confirms the single-phase formation with orthorhombic structure having space group Pbnm (D_2h¹⁶). The average crystallite size observed in nanometer for both samples and field emission-scanning electron microscopy (FE-SEM) confirms that the grain sizes were about in the region of micrometer. The temperature-dependent dielectric parameters were obtained such as the real part of the dielectric constant, dielectric loss tangent, and AC conductivity studied with frequency. The real part of the dielectric constant is high at lower frequencies and it is constant at higher frequency region. This sort of dielectric behavior can additionally be clarified based on various polarization mechanisms happening in various frequency ranges. The dielectric loss tangent increases with temperature. For both samples, the AC conductivity increases with temperature and frequency. The magnetic transitions and magnetic parameters were studied through the temperature-dependent susceptibility and field-dependent magnetization. For HoFeO₃ and HoFe_0.8Sc_0.2O₃, the Neel temperature transition at 5 and 8 K was observed which is characterized to the antiferromagnetic nature. The M-H loop confirms the antiferromagnetic nature at 5 K for HoFeO₃ and the ferromagnetic nature at 5 K for HoFe_0.8Sc_0.2O₃. Overall, it confirms the changes of nature from antiferromagnetic nature to ferromagnetic nature after substitution of Sc³⁺ on HoFeO₃.