Structure, Phonon Vibration, and Spin Correlation of LaBa2Cu3?xCoxOy

Polycrystalline samples LaBa₂Cu_3–xCo _x O _y (0 x 1.0) were synthesized by solid state reaction method. The structure, phonon vibration, conduction, and spin correlation were investigated by means of X-ray diffraction, infrared spectra, resistivity, and electron spin resonance. It is found that there are orthorhombic–tetragonal and tetragonal–orthorhombic structural transitions with Co doping, and the conduction behavior changes from metallic to semiconducting. With the increase of Co content, the Cu(1)—O(1) phonon mode around 531 cm^–1 softens, the Cu(2)—O(2) phonon mode around 657 cm^–1 hardens, and the Cu(1)—O(4) mode around 583 cm^–1 is nearly unchanged. The Cu²⁺ spins tend to localize with Co doping. The changes in structure, phonon vibration, and spin correlation with Co doping are analyzed and discussed.     

Characterization and photocatalytic activity of TiO2–MxOy (MxOy?=?SiO2, Al2O3, and ZrO2) mixed oxides synthesized by microwave-induced solution combustion technique

Titania–silica, titania–alumina, and titania–zirconia mixed oxides (1:1 molar ratio) were prepared by a microwave-induced solution combustion synthesis technique. The prepared materials were characterized by thermogravimetry/differential thermal analysis, X-ray diffraction (XRD), Raman spectroscopy, BET surface area, X-ray photoelectron spectroscopy (XPS), ultraviolet–visible diffuse reflectance spectroscopic (UV–Vis DRS), and Fourier transform infrared (FTIR) techniques to assess their physicochemical properties. Their photocatalytic activity for the degradation of phenol in aqueous solution under sunlight was studied. XRD and Raman studies revealed the presence of titania in the form of anatase phase in all the mixed oxides synthesized. The XRD studies further suggested that titania–zirconia contains an additional (Ti,Zr)O₂ phase. UV–Vis DRS results reveal that all samples exhibit absorption maxima near visible region. FTIR results revealed the presence of Ti–O–Si linkages in the titania–silica sample, which are responsible for its higher activity in the photocatalytic degradation of phenol under sunlight.     

Synthesis, and study of magnetic properties, of Bi1?xCdxFeO3

Ceramic Bi_1−x Cd _x FeO₃ (x = 0.0, 0.05, and 0.1) samples were prepared by a citrate-gel method. The as-prepared compounds were calcined at 600 °C for 3 h to obtain nearly single-phase materials. The crystal structure, examined by X-ray powder diffraction (XRD) and Rietveld analysis, confirmed that the samples crystallize in a rhombohedral (space group, R-3c no. 161) structure. Magnetic measurements were carried out on the resultant powders from 300 to ~2.5 K. Magnetic hysteresis loops showed a significant increase in magnetization as a result of Cd doping in BiFeO₃.     

Single step synthesis of nanosized CeO2–MxOy mixed oxides (MxOy?=?SiO2, TiO2, ZrO2, and Al2O3) by microwave induced solution combustion synthesis: characterization and CO oxidation

Various CeO₂ –M _x O _y (M _x O _y  = SiO₂, TiO₂, ZrO₂, and Al₂O₃) mixed oxides were prepared by microwave induced solution combustion method and analyzed by different complimentary techniques, namely, X-ray diffraction (XRD), Raman spectroscopic (RS), UV–Vis diffuse reflectance spectroscopy (UV-DRS), X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG-DTA), and BET surface area. XRD analyses revealed that CeO₂ –SiO₂ and CeO₂ –TiO₂ mixed oxides are in slightly amorphous form and exhibit only broad diffraction lines due to cubic fluorite structure of ceria. XRD lines due to the formation of cubic Ce_0.5Zr_0.5O₂ were observed in the case of CeO₂ –ZrO₂ sample. RS results suggested defective structure of the mixed oxides resulting in the formation of oxygen vacancies. The UV-DRS measurements provided valid information about Ce⁴⁺ ← O²⁻ and Ce³⁺ ← O²⁻ charge transfer transitions. XPS studies revealed the presence of cerium in both Ce³⁺ and Ce⁴⁺ oxidation states. The ceria–zirconia combination exhibited better oxygen storage capacity (OSC) and CO oxidation activity when compared to other samples. The significance of present synthesis method lays mostly on its simplicity, flexibility, and the easy control of different experimental factors.     

Growth and Accurate Characterization of Bi2Sr2?xLaxCuO6+δ Single Crystals

High-quality and various doped Bi₂Sr_2−x La _x CuO_6+δ (x=0–0.90) single crystals were obtained by floating-zone method. Analysis of the thermal behavior indicated an incongruent melt for all the doped compounds. The segregation coefficient of La related to Sr was estimated to be ∼1.02. Chemical compositions including the La doping in the crystals were accurately determined to study the effect of doping on the structural, chemical and superconducting property of the compounds. Raman spectra were performed to show the high-frequency modes 627 cm⁻¹ softened with increasing the doping level of La. Implications of the doping effect on crystals for understanding the superconductivity are discussed.     

Magnetic and dielectric properties of Mg1+x Mnx, Fe2?2x, O4 ferrite system

Ferrites with the general formula Mg_1+xMn_xFe_2–2xO₄(where x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9) were prepared by the standard ceramic technique and studied by means of X-ray diffraction, magnetization, a.c. susceptibility and dielectric constant measurements. The X-ray analysis confirmed the single-phase formation of the samples. The lattice parameter is found to increase up to x = 0.3 and thereafter it decreases as x increases. The cation distribution has been studied by X-ray analysis and magnetization. Magnetization results exhibit collinear ferrimagnetic structure for x 0.3 and thereafter structure changes into non-collinear for x > 0.3. Curie temperature (T_C) obtained from a.c. susceptibility data decreases with increasing x. The dielectric constant (), loss tangent (tan ) show strong frequency dependence.     

Synthesis and abrasive properties of nanoparticulate MoO2-modified Al2 ? xFexO3 and Fe2 ? yAlyO3 solid solutions

X-ray diffraction, IR spectroscopy, particle-size analysis, and chemical analysis are used to elucidate the general mechanisms of the formation of nanoparticulate molybdenum-dioxide-modified Al_{2 − x} Fe _x O₃ and Fe_{2 − y} Al _y O₃ solid solutions prepared via heat treatment of ammonium hydroxycarbonate complexes, (NH₄)₂Al₂Fe(OH)₅(CO₃) · nH₂O. The addition of molybdenum dioxide (within 0.005 mol %) is shown to enhance the polishing performance of the oxides for final polishing of nonferrous metals and alloys (copper and brass) by a factor of 6–7 relative to unmodified aluminum iron oxides, which is attributable to the increased chemical activity of the abrasive material. The surface roughness value R _a achieved is below 0.005 μm.     

Preparation, characterization and conductivity studies of Li3?2xAl2?xSbx(PO4)3

New NASICON type materials of composition, Li_3−2x Al_2−x Sb _x (PO₄)₃ (x = 0·6 to 1·4), have been prepared and characterized by powder XRD and IR. D.C. conductivities were measured in the temperature range 300–573 K by a two-probe method. Impedance studies were carried out in the frequency region 10²−10⁶ Hz as a function of temperature (300–573 K). An Arrhenius behaviour is observed for all compositions by d.c. conductivity and the Cole-Cole plots obtained from impedance data do not show any spikes on the lower frequency side indicating negligible electrode effects. A maximum conductivity of 4·5 × 10⁻⁶ S cm⁻¹ at 573 K was obtained for x = 0·8 of the Li_3−2x Al_2−x Sb _x (PO₄)₃ system.     

Electrical and magnetic properties of the diluted magnetic semiconductors Cd1 ? xMnxGeP2 and Cd1 ? xMnxGeAs2 at high pressures

The structural and magnetic phase transitions and magnetoresistance of the diluted magnetic semiconductors Cd_{1 − x} Mn _x GeAs₂ and Cd_{1 − x} Mn _x GeP₂ have been studied at high hydrostatic pressures, up to 7 GPa. The normal and anomalous Hall coefficients of the samples have been determined graphically from experimental data.     

Optical Properties, Electronic Structure and Magnetism of α′-NaxV2O5

The optical properties of sodium-deficient -Na _x V₂O₅ (0.85 x 1.00) single crystals are analyzed using ellipsometry, and infrared reflectivity techniques. In sodium deficient samples, the optical absorption peak associated to the fundamental electronic gap develops in the middle of the pure -NaV₂O₅ gap at 0.44 eV, and the material remains insulating up to the maximal achieved hole concentration of about 15%. Nonmetallic behavior under hole doping provoked reinterpretation of the -NaV₂O₅ optical spectra. We argue that the absorption peak at about 0.9 eV corresponds to the photoionization energy of a large polaron.     

Experimental determination of the spatial distribution of electron defects in La2 ? xSrxCuO4 and Nd2 ? xCexCuO4 crystal lattices

The data of M?ssbauer emission spectroscopy on ⁶⁷Cu(⁶⁷Zn) and ⁶⁷Ga(⁶⁷Zn) isotopes show that holes appearing as a result of the Sr²⁺ substitution for La³⁺ in the La_{2 − x} Sr _x CuO₄ crystal lattice are localized predominantly at oxygen atoms occurring in the same atomic plane as the copper atoms. In contrast, electrons appearing as a result of the Ce⁴⁺ substitution for Nd³⁺ in the Nd_{2 − x} Ce _x CuO₄ crystal lattice are localized in the copper sublattice. These results are consistent with the model assuming that a mechanism responsible for the high-temperature superconductivity in La_{2 − x} Sr _x CuO₄ and Nd_{2 − x} Ce _x CuO₄ crystal lattices is based on the interaction of electrons with two-site two-electron centers possessing negative correlation energies (negative-U centers).     

Saturation magnetization and structural analysis of Ni0.6Zn0.4NdyFe2?yO4 by XRD, IR and SEM techniques

Compositions having general formula Ni_0.6Zn_0.4Nd _y Fe_2−y O₄ (where y = 0, 0.01, 0.02 and 0.03) were prepared by oxalate co-precipitation method from high purity sulphates. The samples were characterized by XRD, IR and SEM techniques. X-ray diffraction measurements confirmed the formation of single phase cubic spinel structure. Lattice constant increases with rise in Nd³⁺ content and obeys Vegard’s law. Crystallite size of the samples lies in the range 29.98–31.15 nm. The IR spectra shows two strong absorption bands in the frequency range 400–600 cm⁻¹. Further, it shows that Nd³⁺ occupies B-site. SEM studies show that the grain size of the samples decreases with increase in Nd³⁺ content. Saturation magnetization of Nd³⁺ substituted Ni–Zn ferrites is higher than unsubstituted ferrite.     

Magnetic order and evolution of the electronic state aroundx=0.12 in La2?xBaxCuO4 and La2?xSrxCuO4

Muon spin rotation ( ⁺SR) measurement provides clear evidence of the antiferromagnetic order of Cu moments below 35 K for La_2–x Ba _x CuO₄ and below 15 K for La_2–x Sr _x CuO₄ in the narrow range ofx where the high-T _c superconductivity (SC) is suppressed remarkably. The results suggest that the change of the electronic state coupled with the lattice instability is relevant to the local suppression of SC and freezing of spin fluctuations of the Cu moment.     

A Study of the Magnetic Properties of?Bi1.64?xPb0.36CdxSr2Ca2Cu3Oy Superconductor

The flux pinning energy and magnetic properties of Bi_1.64−x Pb_0.36Cd _x Sr₂Ca₂Cu₃O _y (BPCSCCO) with x=0.0, 0.02, 0.04 and 0.06 were studied. A series of Bi-2223 superconductor samples with a nominal composition of BPCSCCO was synthesized and the effect of Cd substitution for Bi was investigated. As a result, Cd addition has been found to improve the superconducting properties of the Bi-Pb-Sr-Ca-Cu-O system. The effects of the annealing time and the amount of Cd doping on the structure, AC magnetic susceptibility, ρ–T curves and flux pinning energy were investigated. Also, for all samples the relation between the current and voltage in the mixed state was found to follow the model relationship V=α I ^β . The maximum value of β is 22.30, which is obtained for the sample with an annealing time of 270 h and a Cd content of 0.04.     

Preparation and thermophysical properties of (NdxGd1?x)2Zr2O7 ceramics

Ceramic powders of (Nd _x Gd_1−x )₂Zr₂O₇ (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0) were synthesized by chemical-coprecipitation followed by calcination method, and were then pressureless-sintered at 1,600 °C for 10 h in air. Phase constituents and morphologies of the synthesized powders and sintered ceramics were identified by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). A high-temperature dilatometer and a laser-flash method were used to analyze the thermal expansion coefficient and thermal diffusion coefficient of different ceramics from room temperature up to 1,400 °C. Thermal conductivity was calculated from thermal diffusivity, density, and specific heat. (Nd _x Gd_1−x )₂Zr₂O₇ (0.1 ≤ x ≤ 1.0) ceramics are with a pyrochlore-type structure; however, pure Gd₂Zr₂O₇ exhibits a defective fluorite-type structure. The average linear thermal expansion coefficients of different (Nd _x Gd_1−x )₂Zr₂O₇ ceramics decrease with increasing the value of x from 0 to 1.0 in the temperature range of 25–1,400 °C. The thermal conductivities of (Nd _x Gd_1−x )₂Zr₂O₇ ceramics are located within the range of 1.33 to 2.04 W m⁻¹ K⁻¹ from room temperature to 1,400 °C.     

The Effects of Substitution of Sn for Cu in Bi1.75Pb0.25Sr2CaCu2.3?xSnxSnxOy

The influence of Sn doping on superconductivity in the Bi-based 2212 phase is studied in this paper. For the samples R–T relations and magnetic hysteresis loops were measured. X-ray powder diffraction analysis was also performed. For Bi_1.75Pb_0.25Sr₂CaCu_2.3–x Sn _x O _y , the experimental results show that by adding the proper amount of Sn the superconductivity of the samples can be improved. As x = 0.15, the critical temperature T _c, the critical current density J _c, and the magnetic pinning force density F reach a maximum. At T = 11 K, the critical state parameters H _c1, H _c2, , , and are calculated and compared with the results reported by other researchers. The experimental results also show that the Sn doping is able to speed up the growth of the 2223 phase. In brief, Sn doping is an effective way of improving the superconductivity in Bi-based superconductors.     

Preparation of Ce1?xFexO2 solid solution and its catalytic performance for oxidation of CH4 and CO

A series of Ce_1−x Fe _x O₂ (0 < x ≤ 0.5) catalysts were prepared by the co-precipitation method, and their catalytic performances were investigated for the total oxidation of CO and CH₄ as model reactions. X-ray diffraction (XRD) and Raman spectroscopy results show that Ce_1−x Fe _x O_2−δ solid solutions are formed with x ≤ 0.2. Ce_0.9Fe_0.1O₂ solid solution presents superior catalytic performance for CH₄ and CO oxidation, while Ce_1−x Fe _x O₂ with x > 0.2 shows less active for CO and CH₄ oxidation. The results of H₂-temperature programmed reduction (H₂-TPR), CH₄-temperature programmed surface reaction (CH₄-TPSR) and CO-TPSR reveal that, the surface oxygen of catalyst is relevant to CO oxidation, which was promoted by the oxygen vacancies formed in Ce–Fe–O solid solution, while the easier lattice oxygen migration property and the favorable reducibility of the catalysts is responsible for the promoted catalytic performance for CH₄ oxidation.     

Relation of Structure and Superconductivity in Self-compensated Y1?xCaxBa2Cu3?xAlxOz System

The co-doped compounds of Y_1−x Ca _x Ba₂Cu_3−x Al _x O _z , with x from 0.1 to 0.4, were synthesized through a solid-state reaction method. Structural and superconducting properties have been investigated by X-ray diffraction, Rietveld refinement, and DC magnetization measurement. The lattice constant a decreases while b increases with the addition of x. The difference between a and b diminishes gradually. Careful study of the crystalline structure shows that the critical temperature (T _c ) changes monotonically with some local structural parameters, such as the difference between Ba and Cu(2) atoms’ Z coordinates, the bond length of Cu(2)–O(4), and the bond angle of Cu(2)–O(2)–Cu(2), which are all closely related to the interaction between the perovskite block and the rock salt block in the unit cell. The results indicated that the influence of the crystalline structure on superconductivity is important and independent of the carrier concentration.     

Superconductivity of YBa2?xNdxCu3Oy Solid Solution

The solubility of Nd at the Ba sites and the superconductivity of YBa_2–x Nd _x Cu₃O _y were investigated by X-ray powder diffraction and measurements of the electrical resistance and ac susceptibility. The single Re123 phase was obtained for x0.30. The onset transition temperature is insensitive to the Nd content x in the region of x0.40. All are higher than 95 K. The zero resistance transition temperatures , however, exhibits two-step variation with the increase of x. For x0.25, are all above 92 K. The highest of 94 K was obtained for x=0.25. For x0.3 drops sharply to about 84 K. Finally falls to 30 K and is below 10 K for x=0.5. The two-step variation of T _c might be an indication of the existence of two trap levels for holes.