Effect of Pb on the properties of Sr2YRu1‐xCuxO6 crystals grown from PbO‐PbF2 solutions at high temperatures

Single crystals of Sr₂YRu_1‐xCu_xO₆ with x=0 and x=0.1 were grown using PbO‐PbF₂ based solutions at different temperatures in the range 1150–1350°C. The influence of Pb from the solutions and the Cu from the solid solutions of Sr₂YRu_1‐xCu_xO₆ on the resulting crystals was studied using microstructure and magnetic property measurements. The peaks in the powder X‐ray diffraction patterns and Raman spectra do not change in the case of x=0 crystals but shift in the presence of Cu. A diamagnetic transition indicative of superconductivity was observed in the presence of Cu and an antiferromagnetic behavior with x=0. Based on these results it is concluded that Pb may not be incorporated in the crystals and even if it does the influence is not observed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure,microstructure and magnetic properties of mixed rare earth oxide (Dy1‐xErx)2O3

The mixed rare earth oxide (Dy_1‐xEr_x)₂O₃ (0.0 ≤ x ≤ 1.0) were synthesized by a sol–gel process. X‐ray and neutron diffraction data were collected and crystal structure and microstructure analyses were performed using Rietveld refinement method. All samples were found to have the same crystal structure and formed solid solutions over the whole range of x. Preferential cationic distribution is found for all samples but with different extent with Dy³⁺ preferring the 8b among the two non‐equivalent sites 8b and 24d of the space group Ia3. The lattice parameter is found to vary linearly with the composition x and a systematic variation is found in the r.m.s microstrain . Magnetization measurements were done in the temperature range 5‐300 K and a behavior in accordance with Curie‐Weiss law was found. Anomalous concentration dependence is found in magnetic susceptibility which is ascribed to the concentration dependence of effective crystal field combined with the contribution of ⁴I_15/2 and ⁶H_15/2 manifold at elevated temperature. The effective magnetic moments μ_eff is found to decrease linearly with composition parameter x, except for sample x=0.5 where the magnetization is enhanced. The Curie‐Weiss paramagnetic temperatures indicated antiferromagnetic interaction. These magnetic results are discussed in view of the cationic distribution. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase Formation,Crystal Structure and Electrical Properties of La212 Type Compound Substituted by Silver or Praseodymium

The La212 type compounds substituted by silver or praseodymium are prepared by solid state reaction method. It is found that compounds La_2‐xSr_xCa_0.5Pr_0.5Cu₂O₆, La_1.6Pr_0.4Ca_1‐xSr_xCu₂O₆ and La_2‐xPr_xCa_0.5Sr_0.5Cu₂O₆ can be formed for x=0.4‐1.1, 0‐0.5 and 0‐1.5, respectively. A new member of La212 type compounds, La_2‐xAg_xCaCu₂O₆ is also prepared. Their structures are verified by Rietveld structure refinement to belong to the structure type of La212 cuprate oxide with space group I4/mmm. Their electrical properties are investigated. La_1.65Ag_0.35CaCu₂O₆ displays metal‐like behavior and its resistivity decreases with the decrease of temperature from 300K to 4.2K.     

Microstructural,thermal, and electrical properties of Bi1.7V0.3Sr2Ca2Cu3Ox glass‐ceramic superconductor

A glass‐ceramic Bi_1.7V_0.3Sr₂Ca₂Cu₃O_x superconductor was prepared by the melt‐quenching method. The compound was characterized by scanning electron microscopy, x‐ray diffraction, differential thermal analysis, current‐voltage characteristics, transport resistance measurements, and Hall effect measurements. Two main phases (BSCCO 2212 and 2223) were observed in the x‐ray data and the values of the lattice parameters quite agree with the known values for 2212 and 2223 phases. The glass transition temperature was found to be 426 °C while the activation energy for crystallization of glass has been found to be E_a = 370.5 kJ / mol. This result indicates that the substitution of vanadium increased the activation energy for the BSCCO system. An offset T_c of 80 K was measured and the onset T_c was 100 K. The Hall resistivity ρ_H was found to be almost field‐independent at the normal state. A negative Hall coefficient was observed and no sign reversal of ρ_H or R_H could be noticed. The mobility and carrier density at different temperatures in the range 140‐300 K under different applied magnetic fields up to 1.4 T were also measured and the results are discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Predicting a major role of surface spins in the magnetic properties of ferrite nanoparticles

Room‐temperature magnetization hysterisis measurements were conducted on Mn_0.5Zn_0.5Gd_xFe_(2‐x)O₄ ferrite nanoparticles, with x = 0, 0.5, 1.0, 1.5. The structure of this ferrite is normal spinel where the added of Gd³⁺ ions occupied the octahedral sites and replaces Fe³⁺ ions. The saturation magnetization was found to increase with the initial addition of the Gd³⁺ ions followed by a sharp decrease with further addition of Gd³⁺ ions. The Curie temperature was found to increase up to Gd³⁺ concentration of x = 1.0, and then decreases at x = 1.5. These results were attributed to the surface spins. Because the size of Gd³⁺ ions is larger than that of Fe³⁺ ions, the substitution of Fe³⁺ ions with the Gd³⁺ ions results in surface disorder which results in surface spins. A core‐shell magnetization model was introduced where several factors were combined to explain our results. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magneto‐transport properties of polycrystalline YBa2(Cu1‐xMx)3O7‐δ (M = B and Mn)

The magnetic and transport properties of polycrystalline YBa₂ (Cu_1‐xM_x)₃ O_7‐δ (M = B and Mn) superconductor was investigated. Samples of YBa₂(Cu_1‐xB_x)₃O_7‐δ doped with several concentrations of boron B(x = 0.05 and 0.1) were investigated using magnetization measurements. A YBa₂(Cu_1‐xMn_x)₃O_7‐δ sample doped with Mn with concentration of x = 0.02 was investigated using current‐voltage (I‐V) measurements. Our results on the YBa₂(Cu_1‐xB_x)₃O_7‐δ samples reveal a considerable increase in the hysterisis width of the magnetization, M versus the applied magnetic field H with increasing boron concentration. The lower critical field was also found to be enhanced by boron doping. The critical current density, J_c was found to be significantly enhanced in the Mn‐doped sample. The enhancement of J_c was found to be more significant at the lower temperatures for all applied magnetic fields used (0 Oe, 300 Oe, and 500 Oe). Thus, chemical doping is suggested to enhance the vortex pinning forces in the YBCO samples. From the resistivity (R‐T) measurements, chemical doping of the samples was found to have no significant effect on the critical temperature, T_c. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Studies on electrical conduction behavior of La1‐3xCaxBaxSrxMnO3 synthesized by chemical route

In the manganite La_1‐xM_xMnO₃ (M = Ca, Ba, Sr) the doping concentration introduces a mixed valency (Mn³⁺, Mn⁴⁺) which governs the magnetic and electrical properties of the compound. The perovskite oxides La_1‐3xCa_xBa_xSr_xMnO₃ (x = 0.00, 0.05, 0.10) were prepared by chemical method. Single‐phase formation is confirmed by XRD studies. The electrical behavior of compositions with x = 0.00, 0.05 and 0.10 in the system La_1‐3xCa_xBa_xSr_xMnO₃ was studied in the temperature range 300‐420 K. It is observed that conductivity decreases with increasing temperature as well as dopants concentration. Metallic behavior of these compositions decreases with increasing dopants concentration (x). The microstructures of these samples have been characterized using scanning electron microscopy (SEM). (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of big single crystals of a new magnetic superconducting double perovskite Ba2PrRu1–xCuxO6

Single crystals of Ba₂PrRu_1–xCu_xO₆ with x = 0 to 0.2, have been grown from high temperature solutions of a mixture of PbO‐PbF₂ in the temperature range 1100–1200 °C. Thin crystals with mostly a hexagonal and triangular plate like habit measuring up to 1–2 mm across and 0.1–0.2 mm thick were obtained. The size, quality and morphology of the crystals were improved by varying the solution volume as well as additives like B₂O₃. Large crystals measuring up to 3 mm across and 0.3 to 0.5 mm thick were obtained with 5–7 wt% solute concentration and 0.51 wt% of B₂O₃. The ZFC curves exhibit a spin glass like behavior with x = 0 and a superconducting transition at 8 to 11 K depending on x = 0.05 to 0.1. The transition was also influenced by the growth temperature and post growth annealing. Powder x‐ray diffraction, EDS and Raman spectroscopic measurements confirm the presence of Cu in the crystals. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,X‐ray data,and Hall effect measurements of Li‐doped Tl‐Ba‐Ca‐Cu‐O superconductor

Lithium‐doped Tl‐based superconductor was prepared by adding an amount of 0.3 mol.% to the Tl_1.8Ba₂Ca_2.2Cu₃O_x compound. The usual solid‐state reaction method has been applied under optimum conditions. The x‐ray data of the sample show a tetragonal structure with a high ratio of Tl‐2223 superconducting phase. The sample showed a transition at 125 K and the zero resistance was observed at 117 K. Longitudinal (transport) and transverse (Hall) resistivities were measured at different temperatures under different magnetic fields and the data were interpreted. A positive Hall coefficient was observed at normal state and a sign reversal appears at temperatures lower than the critical temperature. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Oxygen potentials,stoichiometry, superconducting,and magnetic properties in the Y?Ba?Cu?O system

The relationship between stoichiometry in YBa₂Cu₃O_x and oxygen potential was investigated by barometry and compared with in-situ X-ray diffraction experiments between 300 and 1000 °C (6 < x < 7). The physical properties are influenced even by small deviations in x. Y₂BaCuO₅ was included in the investigations and found to be antiferromagnetic with T_N ≈ 30 K.     

Voltage‐current characteristics of Bi‐2223 superconducting tape near Tc under γ irradiation

Voltage‐current characteristics at four different applied magnetic fields (7, 20, 30, and 40 mT) of Bi₂Sr₂Ca₂Cu₃O_x superconducting tape were measured in the temperature range from 100 to 115 K. They were also measured at zero magnetic field before and after γ irradiations up to 10 MRad at different temperatures just below the critical temperature. The data were fitted to a power law expression V = I ^β(T) in which the exponential parameter β under 20 mT field and after irradiation is found to fluctuate around three and then drops to unity near the critical temperature which may be interpreted as a sign of Kosterlitz‐Thouless transition. The electrical properties of the tape were found to be very sensitive to γ irradiation where most of the changes take place in low γ doses. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,crystal structure,magnetic characterization and spectroscopic properties of a new dinuclear iron(III) complex asymmetrically bridged by a phenoxo and methoxo groups

Dinuclear iron(III) derivative of Fe₂L¹(OCH₃)Cl₂ (L¹=1,3‐bis[N‐(5‐bromo‐2‐hydroxybenzylidene)‐2‐aminoethyl]‐2‐(5‐bromo‐2‐hydroxyphenyl)imidazolidine) has been synthesized, its crystal structure determined and magnetically characterized. The title compound crystallizes in orthorhombic space group Pbcn with cell parameters a = 12.9770(10), 18.7930(10), 25.2950(10) Å, V = 6168.9(6)ų, Z = 8, D_cal = 1.951 Mg/m³. The two iron(III) ions are asymmetrically bridged by a phenoxo and methoxo groups in the compound. The iron(III) centers are separated by 3.166(3) Å. Magnetic susceptibilities of the complex were measured over the range 5 – 298 K and the observed data were successfully simulated by the equation based on the spin‐Hamiltonian operator. Magnetic susceptibility measurements indicate very weak antiferromagnetic coupling between the iron(III) ions with J = – 11.5 cm^‐1. The comparison of the magnetic and structural parameters of the investigated compound is given and the nature of the magnetic super‐exchange interaction of the title compound is compared with similar dinuclear iron(III) complexes. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magnetic properties of the Mg2FeV3O11−x site-disordered vanadate

The magnetic properties of the Mg₂FeV₃O_11−x ternary vanadate, characterized by disorder between diamagnetic Mg²⁺ and high-spin Fe³⁺ ions, are studied using dc magnetization and electron paramagnetic resonance (EPR). The dc susceptibility shows antiferromagnetic interactions between Fe³⁺ spins with a Curie–Weiss temperature of Θ = −50(1) K, followed by spin-glass-like freezing at T_f ≈ 2.8 K, suggesting significant spin frustration. Temperature-dependent EPR measurements confirm the antiferromagnetic coupling of Fe³⁺ spins at high temperatures, while a distinct divergence is observed at T ≈ 50 K. This behavior is associated with the formation of spin clusters providing two different energy scales for the magnetic interactions. The magnetic response of Mg₂FeV₃O_11−x is similar to that of the Zn-analogue compound, though the observed differences of the implicated energy scales indicate that magnetic inhomogeneity depends on the extent of cation disorder.     

Optical and magnetic properties of Nd‐doped ZnO nanoparticles

Nd‐doped ZnO nanoparticles with different concentration were synthesized by sol‐gel method. The structures, magnetic and optical properties of as‐synthesized nanorods were investigated. X‐ray diffraction (XRD) and x‐ray photoelectron spectroscopy (XPS) results demonstrated that Nd ions were incorporated into ZnO lattice; but Zn_1‐xNd_xO nanoparticles with Nd concentration of x = 0.05 showed Nd₂O₃ phase, so the saturation concentration of Nd in Zn_1‐xNd_xO is less than 5 at%. Vibrating sample magnetometer (VSM) measurements indicated that Nd doped ZnO possessed dilute ferromagnetis behaviour at room temperature. Photoluminescence spectroscopy (PL) showed that Nd ions doping induced a red slight shift and decrease in UV emission with increase of Nd concentration.     

X‐ray diffraction analysis of powder and thin film of (Gd1‐x Yx)2O3 prepared by sol‐gel process

The mixed oxide (Gd_1‐xY_x)₂O₃ (0.0 ≤ x ≤ 1.0) were synthesized, as powder and thin film, by a sol‐gel process. X‐ray diffraction data were collected and crystal structure and microstructure analysis were performed using Rietveld refinement method. All samples were found to have the same crystal system and formed solid solutions over the whole range of x. The cationic distribution, Gd³⁺ and Y³⁺, over the two non‐equivalent sites 8b and 24d of the space group Ia3 is found to be random for all values of (x). The lattice parameter is found to vary linearly with the composition (x). Replacing Gd³⁺ and Y³⁺ by each other introduces a systemic decrease in the x‐coordinate of cation position (24d) and slight changes in the oxygen coordinates. Crystallite size and microstrain analysis is performed along different crystallographic directions and anisotropic changes are found with the composition parameter (x). The average crystallite size ranges from 75 to 149 nm and the r.m.s strain from 0.027 to 0.068 x10^‐2. Textured Gd_1.841Y_0.159O₃ (400) buffer layers, with a high degree of alignment in both out‐plane and in‐plan, are successfully grown on cube textured Ni (001) tape substrates by sol–gel dip coating process. The resulting buffer layers are crack‐free, pinhole‐free, dense and smooth. YbBa₂Cu₃O_7‐x (YbBCO) thin film could be (00l) epitaxially grown on the obtained buffer layer using sol–gel dipping technique. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Twin Structure of (La,Nd)GaO3 Solid Solutions

For La_1‐xNd_xGaO₃ crystals the La‐Nd substitution leads to decrease of spontaneous strains and for composition with x≈0.32 the six possible twin states of orthorhombic phase (m3mFmmm) may be degenerated in three twin states inhered in m3mF4/mmm species when a distorted perovskite pseudocell becomes tetragonal. The {110} and {112} reflection twins and axial twins with compositional planes close to (211) and (21‐1) (S‐walls) were identified in La_1‐xNd_xGaO₃ (x=0.07, 0.12, 0.20) solid solutions crystals. All observed twins are typical for crystals with GdFeO₃ type perovskite‐like structure. It has been shown that for x≤0.2 and x≥0.5 orientations of S‐walls weakly depend on La/Nd ratio, whereas in the range of 0.2<x<0.5 they depend strongly on the solid solution composition. The tilt angle between two twin states across twin boundary in La_1‐xNd_xGaO₃ (x<0.6) solid solutions is smaller than that between two twins in pure LaGaO₃ or NdGaO₃.     

Local structure and redox state of copper in tellurite glasses

The local glass structure of tellurite glasses containing CuO with the nominal composition x(CuO) · (1−x)(TeO₂), where x=0.10, 0.20, 0.30, 0.40, and 0.50, as well as the valence state of the copper ions have been investigated by X-ray photoelectron spectroscopy (XPS) and magnetization measurements. The Te 3d core level spectra for all glass samples show symmetrical peaks (Te 3d_5/2 and Te 3d_3/2) at essentially the same binding energies as measured for TeO₂ indicating that the chemical environment of the Te atoms in the glasses does not vary significantly with the addition of CuO. The O 1s spectra, however, show slight asymmetry for all glass samples which results from two contributions, one from the presence of oxygen atoms in the Te-O-Te environment (bridging oxygen BO) and the other from oxygen atoms in an Te-O-Cu environment (non-bridging oxygen NBO). The ratio of NBO to total oxygen was found to increase with CuO content and to be in good agreement with calculated values for the TeO₄ trigonal bipyramid structure. Moreover, the appearance of a satellite peak in the Cu 2p spectra provides definitive evidence for the presence of Cu²⁺ ions in these glass samples where the asymmetry and broadening of the Cu 2p_3/2 and Cu 2p_1/2 peaks are indicative of the presence of both Cu²⁺ and Cu⁺ ions. The relative concentration Cu²⁺ determined from XPS is in good qualitative agreement with the determinations of Cu²⁺ from magnetic susceptibility measurements on the same glass samples. Furthermore the susceptibility data follow a Curie-Weiss temperature-dependent behavior (χ=C/(T−θ)) with negative Curie temperatures indicating that the predominant magnetic interactions between the Cu²⁺-Cu²⁺ exchange pairs are antiferromagnetic in nature.     

Growth,structure, and superconducting properties of Bi2Sr2Ca2Cu3O10 and (Bi,Pb)2Sr2Ca2Cu3O10‐y crystals

Large and high‐quality single crystals of both Pb‐free and Pb‐doped high temperature superconducting compounds (Bi_1‐xPb_x)₂Sr₂Ca₂Cu₃O_10‐y (x = 0 and 0.3) were grown by means of a newly developed “Vapour‐Assisted Travelling Floating Zone” technique (VA‐TSFZ). This modified zone‐melting technique was realised in an image furnace and allowed for the first time to grow Pb‐doped crystals by compensating for the Pb losses occurring at high temperature. Crystals up to 3×2×0.1 mm³ were successfully grown. Post‐annealing under high pressure of O₂ (up to 10 MPa at T = 500°C) was undertaken to enhance T_c and improve the homogeneity of the crystals. Structural characterisation was performed by single‐crystal X‐ray diffraction (XRD) and the structure of the 3‐layer Bi‐based superconducting compound was refined for the first time. Structure refinement showed an incommensurate superlattice in the Pb‐free crystals. The space group is orthorhombic, A2aa, with cell parameters a = 27.105(4) Å, b = 5.4133(6) Å and c = 37.009(7) Å. Superconducting studies were carried out by A.C. and D.C. magnetic measurements. Very sharp superconducting transitions were obtained in both kinds of crystals (ΔT_c ≤ 1 K). In optimally doped Pb‐free crystals, critical temperatures up to 111 K were measured. Magnetic critical current densities of 2�10⁵ A/cm² were measured at T = 30 K and μ₀H = 0 T. A weak second peak in the magnetisation loops was observed in the temperature range 40‐50 K above which the vortex lattice becomes entangled. We have measured a portion of the irreversibility line (0.1‐5 Tesla) and fitted the expression for the melting of a vortex glass in a 2D fluctuation regime to the experimental data. Measurements of the lower critical field allowed to obtain the dependence of the penetration depth on temperature: the linear dependence of λ(T) for T < 30 K is consistent with d‐wave superconductivity in Bi‐2223. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Ni1‐x Crx alloy for self controlled magnetic hyperthermia

It is known now that an increase in tumor temperature decreases the tumor resistance to chemo‐ and radiation therapies. Hyperthermia treatment of the tumor cells where damage to the healthy cells can be avoided is viable by using magnetic nanoparticles with controlled Curie temperatures. Nickel‐Chromium (Ni_1‐x Cr_x) particles with varying compositions have been investigated as thermoseeds for use in localized self controlled hyperthermia treatment of cancer. A series of Ni_1‐x Cr_x alloys, have been prepared to find the specific composition which has Curie temperature around 316‐317 K. The samples were cast by arc melting technique, and were annealed at 850 ^oC for 5 hours in sealed quartz tubes. Magnetic properties of the samples were investigated, including Curie temperature, saturation magnetization and hysterisis using Superconducting Quantum Interference Device (SQUID) and Vibrating Sample Magnetometer (VSM). The Curie temperatures of the alloys were found to decrease almost linearly from 401 K to 289 K as the Cr concentration was increased from x = 4.54 wt% to x = 5.90 wt%. The results showed that Ni_1‐x Cr_x alloys might be good candidates for self regulating magnetic hyperthermia applications. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Copper redox behavior, structure and properties of copper lead borate glasses

Copper oxidation states, structure and properties of xCuO · (50-x)PbO · 50B₂O₃ glasses were investigated. Both infrared (IR) and ¹¹B magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies were employed to determine the tetrahedral BO₄ fraction in the glasses as a function of CuO content. IR study indicates that the replacement of Pb²⁺ by Cu²⁺ ions increases the BO₃ units by converting BO₄- containing groups into ring type metaborate groups. The oxidation states of copper ions in the glasses have been studied using both X-ray photoelectron spectroscopy (XPS) and the wet chemical method. For high CuO containing (?30 mol%) glasses, high Cu⁺ ion concentrations (Cu⁺/Cu_tot.>0.3) result in a relatively slow disproportionation of B⁴-containing groups because of the small coordination number of Cu⁺ compared to Cu²⁺ ions. Effects of both glass structure and redox states of copper ions on glass properties including density, Vickers’ hardness, coefficient of thermal expansion, and chemical durability have been discussed.