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.     

Investigation of solid solution of ZrP<Subscript>2</Subscript>O<Subscript>7</Subscript>–Sr<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>

In this study, ZrP₂O₇ was synthesized by the solid state reaction of ZrO₂ and NH₄H₂PO₄ at 900 °C. Then, in set 1; 10, 5, 1, 0.5, 0.1, 0.05, 0.03% previously prepared Sr₂P₂O₇ were doped into ZrP₂O₇, and Sr₂P₂O₇ slightly affect the unit cell parameter of cubic ZrP₂O₇ (a = 8.248(6)–8.233(8) Å). The reverse of this process was also applied to Sr₂P₂O₇ system (set 2). ZrP₂O₇ changes the unit cell parameters of orthorhombic Sr₂P₂O₇ in between a = 8.909(5)–8.877(5) Å, b = 13.163(3)–13.12(1) Å, and c = 5.403(2)–5.386(4) Å. Analysis of the vibrations of the P₂O ₇ ^4? ion and approximate band assignments for IR and Raman spectra are also reported in this work. Some coincidences in infrared and Raman spectra both sets were found and strong P–O–P bands were observed. Surface morphology, EDX analysis, and thermoluminescence properties of both sets were given the first time in this paper.     

Kinetics of Thermal Transformation of Mg<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript> · 8H<Subscript>2</Subscript>O to Mg<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The kinetics of thermal dehydration of Mg₃(PO₄)₂ · 8H₂O was investigated using thermogravimetry at four different heating rates. The activation energies of the dehydration step of Mg₃(PO₄)₂ · 8H₂O were calculated through the isoconversional Ozawa and Kissinger-Akahira-Sunose (KAS) methods and iterative methods, which were found to be consistent and indicate a single mechanism. The possible conversion function of the dehydration reaction for Mg₃(PO₄)₂ · 8H₂O has been estimated through the Coats and Redfern integral equation, and a better kinetic model such as random nucleation of the “Avrami–Erofeev equation (A _3/2 model)” was found. The thermodynamic functions (ΔH*, ΔG*, and ΔS*) of the dehydration reaction are calculated by the activated complex theory and indicate that it is a non-spontaneous process when the introduction of heat is not connected.     

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.     

Facile Synthesis of Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/CoO Nanoparticles by Thermal Treatment of Ball-Milled Precursors

Co₃O₄/CoO nanoparticles have been synthesized by a simple method which is based on the ball-milling and calcination of cobalt acetate and citric acid. The samples were characterized using X-ray diffraction, transmission electron microscope, and Fourier transform infrared spectroscopy. The results show that Co₃O₄ nanoparticles with an average particle size of ∼40 nm can be obtained by calcination of ball-milled precursors at relatively low temperature (350 °C) for 3 hours. It should be noted that it is possible to control the size of Co₃O₄ particles by calcination temperature, calcination time and also by ball-milling duration using this method. Meanwhile, the pure CoO nanoparticles were obtained successfully by thermal decomposition of Co₃O₄ at 950 °C and quickly quenching to liquid nitrogen.     

Impact of Particle Size on Room Temperature Ferrimagnetism of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript>

In this paper, we report the control of important hysteresis parameters, which are useful for memory devices, viz. M _s , H _c and M _r /M _s , by changing the particle size/calcination temperature. An investigation of SrFe₁₂O₁₉ nanopowder from the structural and magnetic aspect is performed using X-ray diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM), Scanning Electron Microscopy (SEM) and Vibrating Sample Magnetometer (VSM). The average particle size (APS) of SrFe₁₂O₁₉(nanopowder) increases from 26 to 600 nm with calcination temperatures of 400 and 1100 °C in air, respectively. With the increase in calcination temperature, saturation magnetization (M _s ) increases with the decrease in coercivity for the respective sample. The change in saturation magnetization and coercive field are explained on the basis of transition from single domain structure to multi-domain geometry with an increase in the heating temperature. The sample heated at 1000 °C shows a minimum coercive field (2.71 kOe) and an appropriate squareness ratio (M _r /M _s ) compared to other calcined samples.     

Increased Solubility of Mg at Ca Site in Cu<Subscript>0.5</Subscript>Tl<Subscript>0.5</Subscript>Ba<Subscript>2</Subscript>Ca<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>10−<Emphasis Type="Italic">δ</Emphasis></Subscript> Superconductor

The Cu_0.5Tl_0.5Ba₂Ca_2?y Mg _y Cu₃O_10?δ (y=0, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 1.5, 2.0) superconductor has been synthesized at the atmospheric pressure by the solid-state reaction method. The zero resistivity critical temperature is found to increase to 98 K with Mg concentration of y=0.6, but saturates to 97 K with further enhancement of Mg to y=0.8, 1.0, and 1.5. The Mg doped material grows in tetragonal structure and follows P4/mmm symmetry with a &; c-axes lengths of 3.894 Å &; 15.091 Å for y=1.5. The axes lengths were decreased with the increase of Mg content in the unit cell, which shows that anisotropy of the material decreases. The critical current density and the quantity of diamagnetism in the samples with Mg contents are higher than in the samples without Mg. In order to realize the effects of decreased axes lengths on the phonon modes of Cu_0.5Tl_0.5Ba₂Ca_2?y Mg _y Cu₃O_10?δ , we have carried out FTIR absorption measurements.     

BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript> films produced from BaFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> heterostructures

BaFe₁₂O₁₉ hexaferrite films have been produced on thermally oxidized single-crystal silicon (SiO₂/Si) substrates by sequential ion-beam sputtering of BaFe₂O₄ and α-Fe₂O₃ targets in an argon-oxygen atmosphere. Their crystal structure has been studied, and the origin of the impurity phases forming during heat treatment has been identified. The results show that heat treatment may lead to the formation of eutectic melts. As a result, the hexaferrite films may contain spherulites.     

Enhanced microwave dielectric properties of Ba<Subscript>0.40</Subscript>Sr<Subscript>0.60</Subscript>TiO<Subscript>3</Subscript>–Zr<Subscript>0.80</Subscript>Sn<Subscript>0.20</Subscript>TiO<Subscript>4</Subscript> composite ceramics

The (1−x) Ba_0.40Sr_0.60TiO₃ (BST)−xZr_0.80Sn_0.20TiO₄ (ZST) composite ceramics with x = 10, 20, 30, and 40 wt% were fabricated by conventional solid-state reaction method. With increasing of ZST content, the dielectric constant of composite ceramics was decreased and dielectric loss increases. The effect of ZnO addition to 70 wt% BST–30 wt% ZST composition on the microstructure and dielectric properties was investigated. The improvements in dielectric constant, dielectric loss, and microwave dielectric properties of composite ceramics can be achieved by ZnO addition. The sample with 98 wt% (70 wt% BST–30 wt% ZST)–2 wt%ZnO composition exhibits promising dielectric properties, with dielectric constant, loss tangent and tunability at 4 kV/mm, of 125, 0.0016 and 12%, at 10 kHz and room temperature. At ~2 GHz, it possesses a dielectric constant of 101 and a Q factor of 187, which makes it a good candidate for tunable microwave device applications.     

The Influence of Neutron Irradiation on the Critical Temperature and Normal Phase Resistance of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">δ</Emphasis></Subscript> High Temperature Superconductors

The variation of the normal phase resistance, transition width and critical temperature T _c by the irradiation bulk samples of Y123 with different doses of neutrons at the temperature range of 70<T<300 K has been investigated comparatively. The nonirradiated sample shows a superconducting transition temperature of T _c=86 K (zero-resistance temperature). The irradiation produced clear enhancement of normal phase resistance at all investigated temperatures, which provides the evidence for the enhancement of residual resistance, so the results of experiments showed that the transition width and critical temperature of specimens varies nonlinearly with increasing irradiation fluencies. These results are explained in terms of oxygen declension, and some defects induced by neutrons.      

Ionic conductivity ageing behaviour of 10 mol.% Sc<Subscript>2</Subscript>O<Subscript>3</Subscript>–1 mol.% CeO<Subscript>2</Subscript>–ZrO<Subscript>2</Subscript> ceramics

The long-term ionic conductivity behaviour of samples of zirconia co-doped with 10 mol.% of Sc₂O₃ and 1 mol.% CeO₂ is evaluated in oxidizing and reducing atmospheres at 600 °C. After 3,000 h, the sample kept in reducing atmospheres exhibits 20% loss in the ionic conductivity, while the sample kept in air shows 6% degradation. No phase transitions were observed in the samples after both the ageing studies. The main contribution towards the loss in the ionic conductivity of the sample kept in air comes from grain boundaries; however, for the sample aged in reducing conditions, both grain and grain boundary contribute similarly towards the increase in the total resistivity. This is tentatively explained by the reduction of Ce⁴⁺ cations, dissolved in the fluorite lattice of ZrO₂.     

Temporal Stability of Magnetization of ε-In<Subscript>0.24</Subscript>Fe<Subscript>1.76</Subscript>O<Subscript>3</Subscript> Nanoparticles

The kinetics of spontaneous demagnetization in nanoparticles of the exotic epsilon-phase of indium-doped iron(III) oxide (ε-In_0.24Fe_1.76O₃) has been studied using the method of accelerated testing of magnets for temporal stability in a magnetization-reversal field. Time dependences of the magnetization of nanoparticles measured in a wide range of magnetic fields exhibited rectification in semilogarithmic coordinates. The dependence of the magnetic viscosity on the magnetic field has been measured and used for determining the fluctuation field and activation volume. A relationship between the magnetic viscosity and magnetic noise caused by random thermoinduced magnetization reversal in separate nanoparticles is established.     

Catalytic combustion of methane over Pt and PdO-supported CeO<Subscript>2</Subscript>–ZrO<Subscript>2</Subscript>–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

Catalytic combustion of methane was investigated on Pt and PdO-supported CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts prepared by a wet impregnation method in the presence of polyvinylpyrrolidone. The catalysts were characterized by X-ray fluorescence analysis, X-ray powder diffraction, X-ray photoelectron spectra, transmission electron microscopy, and BET specific surface area measurements. The Pt/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ and PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts were selective for the total oxidation of methane into carbon dioxide and steam, and no by-products such as HCHO, CO, and H₂ were obtained. The catalytic activities of the PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts were relatively higher than those of the Pt-supported catalysts, due to the facile re-oxidation of metallic Pd into PdO based on lattice oxygen supplied from the CeO₂–ZrO₂–Bi₂O₃ bulk. A decrease in the calcination temperature during the preparation process was found to be effective in enhancing the specific surface area of the catalysts, whereby particle agglomeration was inhibited. Optimization of the PdO amount and calcination temperature enabled complete oxidation of methane at temperatures as low as 320 °C on the 11.6 wt% PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalyst prepared at 400 °C.     

Microwave dielectric properties of temperature-stable (Mg<Subscript>0.95</Subscript>Co<Subscript>0.05</Subscript>)<Subscript>2</Subscript>TiO<Subscript>4</Subscript>–Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> composite ceramics for LTCC applications

In this paper, the effects of Li₂O–B₂O₃–Bi₂O₃–SiO₂ (LBBS) glass on the phase formation, sintering characteristic, the microstructure and microwave dielectric properties of temperature-stable (Mg_0.95Co_0.05)₂TiO₄–Li₂TiO₃ ceramics were investigated. (Mg_0.95Co_0.05)₂TiO₄–Li₂TiO₃ powders were obtained by using the traditional solid-state process. A small amount of LBBS doping can effectively reduce sintering temperature and promote the densification of the ceramics. X-ray diffraction analysis revealed not only the primary phase (Mg·Co)₂TiO₄ associated with Li₂TiO₃ minor phase but also a third phase (Mg·Co)TiO₃. The dielectric constant and Qf values vary with the doping amount of LBBS and sintering temperatures. With the compensation of the positive temperature coefficient (τ _f ) of Li₂TiO₃ and the negative τ _f of (Mg_0.95Co_0.05)₂TiO₄, the τ _f of the specimens fluctuates around zero. The (Mg_0.95Co_0.05)₂TiO₄ ceramic with 2.5 wt% LBBS addition and sintering at 900?°C for 4 h exhibited excellent microwave dielectric properties: ? _r ?=?19.076, Qf?=?126100 GHz, and τ _f ?=?0.98 ppm/°C.     

Growth of bulk β-BaB<Subscript>2</Subscript>O<Subscript>4</Subscript> crystals of high optical quality in the BaB<Subscript>2</Subscript>O<Subscript>4</Subscript>-NaBaBO<Subscript>3</Subscript> system

Phase equilibria along the BaB₂O₄-NaBaBO₃ join of the BaO-B 2 O 3 -Na 2 O system are studied by differential thermal analysis and modified visual thermal analysis. The join is shown to be suitable for growing - BaB₂O₄ crystal of high optical quality.Translated from Neorganicheskie Materialy, Vol. 41, No. 1, 2005, pp. 64–69. Original Russian Text Copyright © 2005 by Kokh, Kononova, Fedorov, Bekker, Kuznetsov.     

Electrical Properties and Leakage Current Mechanisms of Bi<Subscript>3.2</Subscript>Gd<Subscript>0.8</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> Thin Films Prepared by a Sol-Gel Method

Bi_3.2Gd_0.8Ti₃O₁₂ (BGTO) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates using the sol-gel method and rapid thermal annealing in an oxygen atmosphere. The effects of annealing temperature (500–800°C) on microstructure and electrical properties of thin films were investigated. X-ray diffraction analysis shows that the BGT thin films have a bismuth-layered perovskite structure with preferred (117) orientation. The intensities of (117) peaks increases with increasing annealing temperature. The leakage current density (J) was 3.69×10⁻⁸ A/cm² at 200 kV/cm. It was found that the leakage current was affected not only by the microstructure but also by the interface between the Pt electrode and BGTO thin films. In the low electric field region, the leakage current was controlled by Poole–Frenkel emission. In addition, the mechanism can be explained by Schottky emission from the Pt electrode in the high electric field region.     

Effect of gamma radiation on electrical and optical properties of (TeO<Subscript>2</Subscript>)<Subscript>0·9</Subscript> (In<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>0·1</Subscript> thin films

We have studied in detail the gamma radiation induced changes in the electrical properties of the (TeO₂)_0·9 (In₂O₃)_0·1 thin films of different thicknesses, prepared by thermal evaporation in vacuum. The current–voltage characteristics for the as-deposited and exposed thin films were analysed to obtain current versus dose plots at different applied voltages. These plots clearly show that the current increases quite linearly with the radiation dose over a wide range and that the range of doses is higher for the thicker films. Beyond certain dose (a quantity dependent on the film thickness), however, the current has been observed to decrease. In order to understand the dose dependence of the current, we analysed the optical absorption spectra for the as-deposited and exposed thin films to obtain the dose dependences of the optical bandgap and energy width of band tails of the localized states. The increase of the current with the gamma radiation dose may be attributed partly to the healing effect and partly to the lowering of the optical bandgap. Attempts are on to understand the decrease in the current at higher doses. Employing dose dependence of the current, some real-time gamma radiation dosimeters have been prepared, which have been found to possess sensitivity in the range 5–55 μGy/μA/cm². These values are far superior to any presently available real-time gamma radiation dosimeter.     

Growth and structure of Mg(Fe<Subscript>0.8</Subscript>Ga<Subscript>0.2</Subscript>)<Subscript>2</Subscript>O<Subscript>4 − δ</Subscript> films

Films 150–200 nm in thickness, with the nominal composition Mg(Fe_0.8Ga_0.2)₂O_{4 − δ} have been grown on (100) single-crystal silicon substrates by ion-beam sputtering in vacuum. The effect of growth and annealing conditions on the crystal structure and morphology of the films has been studied, and the thermal conditions for the growth of spinel-structure films have been optimized.     

A physicochemical study of the Sb<Subscript>2</Subscript>Se<Subscript>3</Subscript>–Nd<Subscript>2</Subscript>Se<Subscript>3</Subscript> system

We have studied phase relations in the Sb₂Se₃–Nd₂Se₃ system and mapped out its T–x phase diagram using differential thermal analysis, X-ray diffraction, microstructural analysis, microhardness tests, and density measurements. The system contains one compound, with the composition NdSbSe₃, which melts incongruently at 865 K and crystallizes in orthorhombic symmetry with the following lattice parameters: а = 12.77(1) Å, b = 14.08(1) Å, and c = 5.82(5) Å (Z = 8, ρ_meas = 6.20 g/cm³, ρ_x = 6.38 g/cm³). At room temperature, the Nd₂Se₃ solubility in Sb₂Se₃ is 5 mol % and the Sb₂Se₃ solubility in Nd₂Se₃ is 2.5 mol %. The Sb₂Se₃–Nd₂Se₃ system has a eutectic located at 15 mol % Nd₂Se₃, with a melting point at 755 K. The electrical conductivity and thermoelectric power of the (Sb₂Se₃)_1–x (Nd₂Se₃) _x solid solutions have been measured as functions of temperature.     

Angular-Dependent Vortex Pinning Properties of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">δ</Emphasis></Subscript>/Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Quasi-Multilayers

A series of quasi-multilayers of YBa₂Cu₃O_7?δ (YBCO)/Y₂O₃ specifically 70 × (m YBCO/n Y₂O₃) were prepared on SrTiO₃ single crystal using pulsed-laser deposition (PLD) with a controlled deposition pulses of m = 40 and n = 2, 5, and 10 for YBCO and Y₂O₃, respectively. The x-ray diffraction patterns indicate that all the present quasi-multilayers exhibit good c-axis orientation. The angular dependence of critical current density (J _c ) on applied magnetic field directions are systemically measured to study the anisotropic vortex pinning performances for those quasi-multilayers. It is revealed that compared with the pure YBCO films, the quasi-multilayers with n = 2, i.e., a proper constituent pulse of Y₂O₃, exhibits the enhanced vortex pinning abilities in all angles between c-axis orientation and the applied magnetic field direction. As well, such a quasi-multilayer film (n = 2) shows the higher lift factor J _c (Θ)/ J _c (90°) and much better vortex pinning properties at high fields and high temperatures, showing promising potential for coated conductor application.