Synthesis and characterization of TiO<Subscript>2</Subscript>–NiO and TiO<Subscript>2</Subscript>–WO<Subscript>3</Subscript> nanocomposites

TiO₂–NiO and TiO₂–WO₃ nanocomposites were prepared by hydrothermal and surface modification methods. The samples were analyzed using X-ray diffraction, Scanning Electron Microscope images, Transmission Electron Microscope, Energy dispersive analysis, Zeta potential, Electrophoretic mobility and Photocatalysis activity measurement. XRD data sets of TiO₂–NiO, TiO₂–WO₃ powder nanocomposite have been studied for the inclusion of NiO, WO₃ on the anatase-rutile mixture phase of TiO₂ by Rietveld refinement. The cell parameters, phase fraction, the average grain size, strain and bond lengths between atoms of individual phases have been reported in the present work. Shifted positional co-ordinates of individual atoms in each phase have also been observed.     

Syntheses and proton conductivity of mesoporous Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> and NdOCl–SiO<Subscript>2</Subscript> composites

Two mesoporous oxide composites of Nd₂O₃–SiO₂ and NdOCl–SiO₂ were synthesized using SBA-15 as a template and neodymium nitrate or neodymium chloride as a precursor. The porous Nd₂O₃–SiO₂ with a SBA-15-like structure has amorphous walls and the porous NdOCl–SiO₂ with a replicated structure of SBA-15 has crystalline walls. These porous materials were characterized by X-ray diffraction, transmission electron microscopy and nitrogen adsorption/desorption. They exhibited significant proton conductivities in the presence of moisture at low temperatures and the highest conductivity observed was 4.55 × 10⁻⁴ S/cm at 47 °C in wet air (RH = 28.6%).     

Atomistic structure and energetics of interface between Mn-doped γ-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> and MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript>

The interface between an Mn-doped γ-gallium oxide (Ga₂O₃) thin film and an MgAl₂O₄ (001) substrate has been investigated using high-resolution transmission electron microscopy (HRTEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and first-principles calculations. A high-quality Mn-doped γ-Ga₂O₃ film with a defective spinel structure has been epitaxially grown by pulsed laser deposition. The γ-Ga₂O₃ crystal shows an uniform tetragonal distortion with a tetragonality of 1.05 throughout the film thickness of 75 nm. HRTEM and HAADF-STEM observations reveal that the γ-Ga₂O₃ and MgAl₂O₄ crystals form a coherent interface without any interfacial layers or precipitates. The atomistic structure and energies are theoretically evaluated for the interfaces with two types of termination plane, i.e., Mg- and Al₂O₄-termination of MgAl₂O₄. The cation sublattice is found to be continuous for both interfaces despite the defective spinel structure of Mn-doped γ-Ga₂O₃ with some vacant cation sites. The Al₂O₄-termination shows a lower interfacial energy than the Mg-termination under most conditions of the chemical potentials. This behavior is attributed to the energetic preference of the Mn–Al₂O₄ local configuration at the interface.     

Magnetic Anomalies and Electronic Structure of Ce<Subscript>2</Subscript>Cu<Subscript>2</Subscript>Mg and Ce<Subscript>2</Subscript>Pd<Subscript>2</Subscript>Mg

The intermetallic compounds RE ₂Cu₂Mg and RE ₂Pd₂Mg (RE=La, Ce) were prepared and characterized by magnetic susceptibility and heat-capacity measurements. They crystallize with an ordered U₃Si₂ type structure (space group P4/mbm) and the cerium compounds contain stable trivalent cerium ions, which undergo antiferromagnetic ordering at ∼7.5 and ∼4 K, respectively. In high magnetic fields Ce₂Cu₂Mg exhibits spin reorientation with critical field strength of 40 kOe at 5 K. The data are compared to the non-magnetic isotypic compounds La₂ T ₂Mg (T=Cu, Ni, Pd) and to the already reported intermediate valent Ce₂Ni₂Mg.     

Synthesis and optical limiting studies of HA<Subscript>P</Subscript> and HA<Subscript>P</Subscript>@SiO<Subscript>2</Subscript> core–shell nanoparticles

We report the spectral and optical limiting properties of two kinds of HA_P nanoparticles (pure HA_P and HA_P@SiO₂ core–shell nanoparticles) that were wet-chemically prepared and coated with silica by means of Stober method. The size, framework substitution and silica coating formation of the resultant particles were confirmed by Transmission Electron Microscopy, X-ray diffraction, Fourier Transform Infrared Spectroscopy and Thermogravimetric analysis. The nonlinear optical limiting properties of HA_P and HA_P@SiO₂ nanoparticles suspended in ethylene glycol is studied at 532 nm using 5 ns Nd:YAG laser pulses. Observations indicate that effective three-photon absorption is found to be responsible for strong optical limiting characteristics in these nanoparticles and it is seen that the optical nonlinearity is enhanced in core–shell structures as compared with single counterparts. The nonlinear optical parameters calculated from the data show that these materials are efficient optical limiters.     

High-damping and high-rigidity composites of Al<Subscript>2</Subscript>TiO<Subscript>5</Subscript>–MgTi<Subscript>2</Subscript>O<Subscript>5</Subscript> ceramics and acrylic resin

High-damping materials are widely used in engineering fields. In order to increase the precision of vibration control to different levels, high-damping materials with high-rigidity are required. This study attempts to develop a new high-damping high-rigidity material using ductile ceramics based on the Al₂TiO₅–MgTi₂O₅ system, which has many continuous microcracks along the grain boundaries. Ductile ceramics have high internal friction (Q ⁻¹ = 0.01–0.037), but very low rigidity (<10 GPa). The rigidity of Al₂TiO₅–MgTi₂O₅ ceramics was improved by combining them with a polymer such as acrylic resin. The Young’s modulus and internal friction of the composites of Al₂TiO₅–MgTi₂O₅ ceramics and acrylic resin are investigated. They show high-damping capacity (Q ⁻¹ = 0.03–0.04) with high rigidity (E = 50–60 GPa), and their properties depend on those of the polymer. Thus, the composites fabricated using the above method can serve as high-damping high-rigidity materials.     

Growth and properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and SiO<Subscript>2</Subscript> nanolayers on III–V semiconductors

We describe atomic layer deposition of silica and alumina layers on GaAs, InAs, and InSb substrates. The conditions for layer-by-layer growth of surface nanostructures are established, and some of their dielectric parameters are evaluated.     

Structure and ferroelectric properties of stoichiometric and Sr-deficient–SrBi<Subscript>4</Subscript>Ti<Subscript>4</Subscript>O<Subscript>15</Subscript> thin films

SrBi₄Ti₄O₁₅ (SBTi) and Bi-excess and Sr-deficient SBTi (Sr-deficient SBTi, Sr_0.8Bi_4.13Ti₄O₁₅) thin films were deposited on Pt/Ti/SiO₂/Si (100) substrates using a sol–gel method. Structure and electric properties were investigated systematically. These films were random oriented. The remnant polarization (2P _r) of SBTi film was about 25.3 μC/cm², which was larger than the reported value of SBTi thin film. The film with Sr-deficient and Bi-excess composition showed a very large remnant polarization of 36.6 μC/cm². The capacitance–voltage (C–V) characteristics of both the films showed normal ferroelectric behavior. The Curie temperatures of the same Sr-deficient and Bi-excess component ceramics sample increased slightly in comparison with that of SBTi. More importantly, the Sr-deficient and Bi-excess SBTi thin film showed high fatigue resistance against continuous switching up to 4.4 × 10¹⁰ cycles.     

Optical and photoelectric properties of α-Dy<Subscript>2</Subscript>S<Subscript>3</Subscript> and α-Dy<Subscript>2</Subscript>S<Subscript>3</Subscript>〈Pb〉 films

A process is described for the growth of thin crystalline α-Dy₂S₃ films by thermal evaporation from separate dysprosium and sulfur sources. The films were doped with Pb, and their reflection and transmission spectra were measured at room temperature and photon energies in the range (0.3−5.2) × 10⁻¹⁹ J. The α-Dy₂S₃ films were shown to have an exponential absorption edge. The photoconductivity of the doped films was measured at photon energies in the range (0.3−5.2) × 10⁻¹⁹ J and temperatures from 115 to 400 K.     

Synthesis and study of sodium uranate Na<Subscript>2</Subscript>U<Subscript>2</Subscript>O<Subscript>7</Subscript>·6H<Subscript>2</Subscript>O and of products of its dehydration and thermal decomposition

Previously unknown sodium uranate of the composition Na₂U₂O₇·6H₂O was synthesized by precipitation from solution under hydrothermal conditions at 200°С. The composition and structure of this compound were determined by chemical analysis, X-ray diffraction, IR spectroscopy, and thermal analysis. The dehydration and thermal decomposition of the compound were studied.     

Microstructure and properties of the Ba<Subscript>0.75−x</Subscript>Ca<Subscript>x</Subscript>La<Subscript>0.25</Subscript>Fe<Subscript>11.6</Subscript>Co<Subscript>0.25</Subscript>Ti<Subscript>0.15</Subscript>O<Subscript>19</Subscript> hexaferrites

In the case of Ti⁴⁺ remain unchanged, the Ca²⁺ substituted Ba_0.75?xCa_xLa_0.25Fe_11.6Co_0.25Ti_0.15O₁₉ (0?≤?x?≤?0.05) were prepared by conventional solid-state reaction method at temperature of 1280 °C. A ball-to-power weight ratio of 10:1. Their crystal structure and magnetic properties were mainly investigated. The results show that the single magnetoplumbite phase structure transformed into the multiphase structure. Meanwhile, the small amount of α-Fe₂O₃ phase existed in M-type phase. The micrographs were observed by a field emission scanning electron microscopy (SEM). Vibrating sample magnetometer (VSM) was used to analyze the magnetic properties. The saturation magnetization (M _s ) first increases then decreases when x from 0 to 0.03. But, when x from 0.03 to 0.05, the saturation magnetization (M _s ) first increases then decreases too. The maximum value is at x?=?0.04 (M _s ?=?70.73 emu/g). The value of coercivity (H _c ) first increases then decreases when x from 0 to 0.04. But, the value increased when x from 0.04 to 0.05. The maximum value is at x?=?0.02 (H _c ?=?1691 Oe).     

Microwave and photoluminesent characterizations of (Ca<Subscript>2</Subscript>Mg<Subscript>3</Subscript>)(X<Subscript>1.75</Subscript>Sb<Subscript>0.25</Subscript>)TiO<Subscript>12</Subscript> [X = Nb and Ta] ceramics

(Ca₂Mg₃)(X_1.75Sb_0.25)TiO₁₂ [X = Nb and Ta] ceramics are prepared through the conventional solid-state route. The samples are calcined at 1,100 and 1,180 °C, and are sintered at 1,250 and 1,375 °C. The substitution of Sb decreases the calcination and sintering temperatures of pure (Ca₂Mg₃)(Nb/Ta)₂TiO₁₂. The structure of the samples is analyzed using X-ray diffraction method. The microstructure of the sintered pellet is studied using scanning electron microscopy. The dielectric properties such as dielectric constant (ε_r), quality factor (Q_uxf) and temperature coefficient of resonant frequency (τ_f) are measured in the microwave frequency region. By Sb substitution, thermal stability is achieved, with the increase in dielectric constant, without much change in the quality factor. The materials have intense emission lines in the wavelength region 500–700 nm. The compositions have good microwave dielectric properties and photoluminescence and hence are suitable for dielectric resonator and ceramic laser applications.     

Superconducting Bands Stabilizing Superconductivity in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subscript> and MgB<Subscript>2</Subscript>

It is shown that the ceramic superconductor YBa₂Cu₃O₇ as well as the superconducting intermetallic compound MgB₂ possesses a narrow, partly filled “superconducting band” with Wannier functions of special symmetry in their band structures. This result corroborates previous observations about the band structures of numerous superconductors and non-superconductors showing that evidently superconductivity is always connected with such superconducting bands. These findings are interpreted in the framework of a nonadiabatic extension of the Heisenberg model. Within this new group-theoretical model of correlated systems, Cooper pairs are stabilized by a nonadiabatic mechanism of constraining forces effective in narrow superconducting bands. The formation of Cooper pairs in a superconducting band is mediated by the energetically lowest boson excitations in the considered material that carry the crystal-spin angular momentum 1⋅ℏ. These crystal-spin-1 bosons are proposed to determine whether the material is a conventional low-T _c or a high-T _c superconductor. This interpretation provides the electron–phonon mechanism that enters the BCS theory in conventional superconductors.     

Structure and properties of CaF<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

FTIR spectroscopy has been employed to investigate the structure of CaF₂–B₂O₃ glasses. It is proposed that CaF₂ partially modifies the borate network forming \textCa _{1 / 2} ²⁺ [\textBO _{3 / 2} \textF] ^- {\text{Ca}}_{ 1 / 2}^{ 2+ } [{\text{BO}}_{ 3 / 2} {\text{F]}}^{ - } units. The rest of CaF₂ is assumed to build an amorphous network formed of CaF₄ tetrahedra. Analysis of density and molar volume revealed that the volume of CaF₄ tetrahedron in the studied glasses is slightly greater than that in the crystalline form. Data of density, molar volume, and electric conductivity have been correlated with the glass structure. As far as the authors know, CaF₂–B₂O₃ glasses are investigated for the first time.     

Synthesis and study of structural,dielectric, magnetic and magnetoelectric properties of K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>NbO<Subscript>3</Subscript>–CoMn<Subscript>0.2</Subscript>Fe<Subscript>1.8</Subscript>O<Subscript>4</Subscript> composites

Magnetoelectric (ME) composites consisting of K_0.5Na_0.5NbO₃ (KNN) as ferroelectric phase and CoMn_0.2Fe_1.8O₄ (CMFO) as ferrite phase with general formula (x) CoMn_0.2Fe_1.8O₄–(1???x) K_0.5Na_0.5NbO₃ (x?=?10, 20, 30, 40 and 50 wt%) were synthesized using solid state reaction method. X-ray diffraction analysis asserts the existence of component phases including spinel phase of CMFO and orthorhombic phase of KNN. Field emission scanning electron microscopy has been used for studying the morphology and calculation of average grain size. The temperature dependent dielectric properties including dielectric constant (\(\varepsilon ^{\prime}\)) and dielectric loss (tan δ) at different frequencies has been studied and both are found to increase with incorporation of CMFO. Magnetic hysteresis loops have been measured at temperatures of 300 and 5 K. Variation of magnetization versus temperature has been studied in field cooled and zero field cooled modes. Polarization versus electric field (P–E) hysteresis loops are obtained at room temperature indicating presence of ferroelectric ordering in the composites at room temperature. The remnant polarization (2P_r) and coercive field (2E_c) are found to decrease linearly with incorporation of CMFO. ME voltage coefficient (α_ME) has been measured. The maximum value of α_ME is found to be 5.941 mV/cm-Oe for 10% CMFO–90% KNN bulk composite.     

Structural,magnetic and magnetocaloric investigation of La<Subscript>0.67</Subscript>Ba<Subscript>0.33</Subscript>Mn<Subscript>1−x</Subscript>Ni<Subscript>x</Subscript>O<Subscript>3</Subscript> (x = 0, 0.025 and 0.075) manganite

In this paper, we report the structural, magnetic and magnetocaloric properties of Ni-doped La_0.67Ba_0.33Mn_1?xNi_xO₃ (x?=?0, 0.025 and 0.075) manganites. Our compounds were synthesized using the sol–gel method. The structural analysis using Rietveld refinement shows that Ni-doped LaBaMnO₃ system crystallizes in the rhombohedral symmetry with \({\text{R}}\bar {3}{\text{c}}\) space group. Magnetization measurements versus temperature in a magnetic applied field of 0.05 T reveal that all the compositions exhibit a transition from a ferromagnetic to paramagnetic phase with increasing temperature. A systematic decrease in the transition temperature is clearly observed upon Ni doping and a near room temperature T_C (302 K) is achieved with x?=?0.075 composition. The maximum magnetic entropy change \(\left( { - ~\Delta {\text{S}}_{{\text{M}}}^{{\hbox{max} }}} \right)\) in a magnetic field change of 5 T is found to be 2.12, 2.78 and 1.78 J/kg K for x?=?0, 0.025 and 0.075, respectively. At this value of magnetic field, large relative cooling power values are obtained in our samples, especially for x?=?0.075 (271 J/kg) making it a promising candidate for magnetic refrigeration near room temperature.     

Laser and electromagnetic loss properties of Perovskite SmNi<Subscript>x</Subscript>Fe<Subscript>1−x</Subscript>O<Subscript>3</Subscript>

SmNi_xFe_1?xO₃ (0?≤?x?≤?0.5) with perovskite-type structure has been successfully prepared by conventional solid-state reaction as a microwave and laser multi-functional material. The optimized synthesis temperature and the effects of Ni doping on the reflectivity, electromagnetic loss properties were investigated in details. XRD results shown that synthesis temperature did not change the perovskite structure of SmFeO₃. The reflectivity at 1.06 μm was about 0.33% at 1200–1300?°C. Doping Ni did not cause the change of perovskite structure. The incorporation of Ni in SmFeO₃ contributed to the decrease of reflectivity at a wider wavelength, SmNi_0.3Fe_0.7O₃ possessed the lowest reflectivity at 1.06 μm. Moreover, electromagnetic property was very sensitive to Ni content. The real and imaginary parts of complex permeability were enhanced remarkably at a certain frequency. The changes in magnetic performance provided possibility of choosing specific frequency of magnetic loss. The difference in electric and magnetic losses caused by Ni concentration could result in microwave absorption at different frequency. In a word, SmNi_xFe_1?xO₃ could be a promising candidate for a multi-functional material with compatible camouflage capability for radar and laser waveband.     

Ferroelectric and piezoelectric properties of new NaNbO<Subscript>3</Subscript>–Bi<Subscript>0.5</Subscript>K<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> lead-free ceramics

New lead-free ceramics (1–x)NaNbO₃–xBi_0.5K_0.5TiO₃ have been fabricated by the conventional ceramic sintering technique, and their ferroelectric and piezoelectric properties have been studied. The results of X-ray diffraction reveal that Bi_0.5K_0.5TiO₃ diffuses into the NaNbO₃ lattices to form a new perovskite-type solid solution with orthorhombic symmetry. The addition of a small amount of Bi_0.5K_0.5TiO₃ (x ≥ 0.025) transforms the ceramics from antiferroelectric to ferroelectric. The ceramic with x = 0.10 possesses the largest remanent polarization P _r and thus exhibits the optimum piezoelectric properties, giving d ₃₃ = 71 pC/N, k _p = 16.6% and k _t = 39.7%. The ceramics with low doping level of Bi_0.5K_0.5TiO₃ are normal ferroelectrics and the ferroelectric-paraelectric phase transition becomes diffusive gradually with the doping level x of Bi_0.5K_0.5TiO₃ increasing. Our results show the (1–x)NaNbO₃–xBi_0.5K_0.5TiO₃ ceramics is one of the good candidates for lead-free piezoelectric and ferroelectric materials.     

Microscopic and macroscopic magnetic properties of MgAl<Subscript>x</Subscript>Cr<Subscript>x</Subscript>Fe<Subscript>2 − 2x</Subscript>O<Subscript>4</Subscript> spinel ferrite system

In order to study the effect of co-substitution of Al^{3 +} and Cr^{3 +} for Fe³⁺ in MgFe₂O₄ on its structural and magnetic properties, the spinel system MgAl _x Cr_xFe_{2 ? 2x}O₄ (x = 0.0–0.8) has been characterized by X-ray diffraction, high field magnetization, low field a.c. susceptibility and ⁵⁷Fe Mössbauer spectroscopy measurements. Contrary to the earlier reports, about 50% of Al^{3 +} is found to occupy the tetrahedral sites. The system exhibits canted spin structure and a central paramagnetic doublet was found superimposed on the magnetic sextet in the Mössbauer spectra (0.5 > x > 0.2). Thermal variation of a.c. susceptibility exhibits normal ferrimagnetic behaviour.     

Characterization and electrical conductivity of La<Subscript>1−x</Subscript>Sr<Subscript>x</Subscript>CrO<Subscript>3</Subscript> NTC ceramics

The La_1?xSr_xCrO₃ (x?=?0–0.1) negative temperature coefficient (NTC) ceramics have been prepared by the traditional solid state reaction method. X-ray diffraction (XRD) analysis has revealed that the as-sintered ceramics crystallize in a single perovskite structure. Scanning Electron Microscope (SEM) images show that the doped Sr²⁺ contributes to in the decrease in porosity. X-ray photoelectron spectroscopy (XPS) analysis indicates the existence of Cr³⁺ and Cr⁶⁺ ions on lattice sites, which result in hopping conduction. The presence of the Cr⁶⁺ is one of the key factors that affect the electrical conductivity of La_1?xSr_xCrO₃. Resistance–temperature characteristics were studied in the range of ?80 to 10?°C for the ceramic samples, the electrical characterizations show that the electrical resistivity and material constant B decrease with the increase of the strontium content.