Preparation and properties of Mn1.1Sb1 − y Al y and Mn1.1Sb1 − y Si y solid solutions

We have prepared Mn_1.1Sb_{1 ? y} Al _y (0 < y ≤ 0.2) and Mn_1.1Sb_{1 ? y} Si _y (0 < y ≤ 0.1) solid solutions with the B8 structure, in which the aluminum and silicon atoms substitute for antimony in the anion sublattice of manganese antimonide. Magnetic measurements have shown that substitutions within the stability region of the B8 phase have little effect on the mass magnetization and Curie temperature of the material. Mössbauer spectroscopy results confirm the anion nature of the substitutions.     

The relationship between the mean dopant-ion radii and conductivity of co-doped ZnO systems, Zn1−x−y M x M′ y O (M, M′ = Al, In, Ga, Y)

The conductivities of the Zn_1–x–y M _x M _y O (M, M = Al, In, Ga, Y) and Zn_1–x M _x O (M = Al, In, Ga) systems were measured from room temperature to 1173 K in order to elucidate a dominant parameter of the conducting mechanism. The conductivity at 873 K first increased with the dopant content. However, it showed a maximum value at a given dopant content, and then gradually decreased. For the samples with the same dopant content, their conductivity at 873 K was strongly dependent on the mean dopant-ion radii, and reached a maximum value at around 0.51 Å of the mean dopant-ion radii. The results suggested that the conductivity of the system would be influenced not only by the dopant content, but also by the mean dopant-ion radii. It was found that the co-doped ZnO system of Zn_0.995Al_0.003In_0.003O had a conductivity higher than that of the other usual mono-doped system.     

Structural and Magnetic Study of Zn-Substituted NiGa y Fe 2−y O 4 Ferrite

Single-phase spinel ferrite Ni _1?x Zn _x Ga _y Fe _2?y O ₄ with (0.0≤x≤0.5) and y=0.5 samples were synthesized using solid-state reaction technique. These ferrites were investigated using X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and Mössbauer effect (ME) spectroscopy. XRD patterns confirmed the formation of single-phase cubic spinel ferrites for all samples. Lattice parameter was found to decrease with the introduction of Ga ³⁺ in NiFe ₂ O ₄, and then to increase with the increasing of Zn ²⁺ content x. ME measurements illustrated a strong dependence on the zinc concentration. The cation distribution calculated from the ME spectra at room temperature indicated that the Ga ³⁺ ion substituted iron in both octahedral B and tetrahedral A- sites. Zn ²⁺ ions firstly introduced in A- site, and for higher x, they distribute in both B- and A- sites. VSM measurements indicated that the change in the value of saturation magnetization can be explained using the cation distribution obtained from ME measurements. The coercivity values can be interpreted on the basis of magneto-crystalline anisotropy.     

Preparation and characterization of in1−xGaxAsyP1−y epilayers by liquid-phase epitaxy

In_1–x Ga _x As _y P_1–y epilayers with three different solid compositions of ln_0.73Ga_0.27As_0.60P_1.40, In_0.59Ga_0.41As_0.87P_0.13 and ln_0.53Ga_0.47As were grown on (1 0 0) InP substrate at 623° C by the step cooling technique of liquid-phase epitaxy. From the optical transmission measurements, the corresponding wavelengths of the InGaAsP epilayers were 1.30, 1.55 and 1.69 m, respectively, which are in good agreement with those obtained from the calculations using Vegard's law. The full widths at half maximum of the photoluminescent spectra at 14 K of these layers were as low as 18.6, 22.5 and 7.9meV, respectively. The electron mobility of the InGaAsP epilayers is a function of the solid composition with the ln_0.53Ga_0.47As epilayer having the highest electron mobility. The mobility and concentration of this layer are 8,873cm²V^–1 sec^–1, 9.7×10¹⁵cm^–3 and 22,900 cm²V^–1 sec^–1, 8.5×10¹⁵cm^–3 at 300 and 77 K, respectively. The compensation ratio is between 2 and 5.     

Nonstoichiometry and physical properties of the perovskite BaxLa1−xFeO3−y system

A series of samples in the Ba _x La_1–x FeO_3–y system (x=0.00, 0.25, 0.50, 0.75, and 1.00) have been prepared at 1200°C under an atmospheric air pressure. The solid solutions of the system were analysed from the X-ray diffraction spectra and thermal analyses. X-ray diffraction studies assigned the compositions of the x=0.00 and 1.00 to the orthorhombic system and the compositions of the x=0.25, 0.50, and 0.75 to the cubic system. The reduced lattice volume increased with the x value in the system. The mole ratios of the Fe⁴⁺ ion in the solid solutions, or values, were determined by Mohr salt analyses and the non-stoichiometric chemical formulae of the system were formulated from the x, , and y values. From the results of the Mössbauer spectroscopy, the coordination and the magnetic property of the iron ion have been discussed. The electrical conductivities were measured as a function of temperature under atmospheric air pressure. The activation energy was minimum at the composition of x=0.50. The conduction mechanism can be explained by the hopping model between the mixed valences of the Fe³⁺ and Fe⁴⁺ ions.     

Superconducting Density of States from the Magnetic Penetration Depth of Electron-Doped Cuprates La2−x Ce x CuO4−y and Pr2−x Ce x CuO4−y

From measurements of the magnetic penetration depth, (T), from 1.6 K to T _c in films of electron-doped cuprates La_2–x Ce _x CuO_4–y and Pr_2–x Ce _x CuO_4–y we obtain the normalized density of states, N _s(E) at T=0 by using a simple model. In this framework, the flat behavior of ^–2(T) at low T implies N _s(E) is small, possibly gapped, at low energies. The upward curvature in ^–2(T) near T _c seen in overdoped films implies that superfluid comes from an anomalously small energy band within about 3k _B T _c of the Fermi surface.     

Mössbauer study of vacancy ordering in the system SrTi1−xFexO3−y (0.50 ≤ x ≤ 0.70)

The synthesis of the system SrTi_1−xFe_xO_3−y with 0.50 ≤ x ≤ 0.70 has been performed in order to study the nature of the oxygen vacancy ordering. By means of Electron Microscopy and Diffraction and Mössbauer spectroscopy, we have obtained the main features of vacancy ordering in this system. The results are compared with the predictions of Komornicki-Grenier model of anion vacancies distribution in perovskites.     

The Effect of Zn-Substitution on the Anomalous Resistance Behavior of La1−x Ca x Mn1−y Zn y O3 Compounds

We have studied the effect of Zn substitution on the temperature dependence of the resistivity and the Curie temperature T _p of La_1–x Ca _x Mn_1–y Zn _y O₃ system (with x=0, y=0, and x=0.33, 0.00y0.15) during their pass to the paramagnetic conducting phase. All the specimens show a clear metal-insulator transition passing through the Curie temperature T _p . With increasing Zn concentration, T _p decreases for La/Ca substitution and also for Zn/Mn substitution with fixed 33 at.% of Ca. T _p is found to be slightly decreases for low concentrations of Zn (up to y=0.075) followed by a sharp decrease up to y=0.15. A possible explanation is given. Moreover, the activation energy E _a is calculated in the three different temperature regions characterized in the (-T) curve. Decreasing the temperature below T _p can increase the parallel alignment of the Mn spins and, thus decreases the resistivity of the samples. E _a increases with Zn content (up to y=0.075) followed by a sharp decrease. A strong correlation in the behavior of the normal state and residual resistivity as well as T _p and E _a with Zn content is reported.     

Hydrothermal synthesis and magnetic properties of CoxFe1−x/CoyLazFe3−y−zO4 composites

A series of iron–cobalt alloy and cobalt–ferrite composites doped with La³⁺ (Co_xFe_1−x/Co_yLa_zFe_3−y−zO₄) in which the Fe–Co alloy has either a bcc or a fcc structure and the oxide is a spinel phase, have been synthesized by using the disproportionation of Fe (OH)₂ and the reduction of Co (II) by Fe⁰ in a concentrated and hot KOH solution. when x ≤ 0.1, the structures of the Fe_xCo_1−x alloy and cobalt–ferrite are fcc structure; and when x ≥ 0.25, the structures of the Fe_xCo_1−x alloy is bcc structure. The fcc structure of alloy is favored for [KOH] close to 9 N, Co(II)/Fe(II) ratios between 0.5 and 0.9 and short reaction time of synthesis. And the bcc structure of the alloy is favored for [KOH] close to 1 N, Co(II)/Fe(II) ratios between 0.1 and 0.5 and long reaction time of synthesis. A low [KOH] favors nucleation leading to octahedral of 1 μm. And [KOH] of 9–12 N favors particle growth. The metal occurs in square particles of 100–150 nm included within the spinel. Powder X-ray diffraction (XRD), thermal gravity analysis (TGA) and different thermal analysis (DTA), scanning electron microscope (SEM), transmission electron micrograph (TEM) and vibrating sample magnetometer (VSM) were employed characterize the crystallite sizes, structure, morphology and magnetic properties of the composites. And the effect of the Co(II)/Fe (II) ratio (0 ≤ Co/Fe ≤ 1), concentration of KOH, reaction time and substitution Fe³⁺ ions by La³⁺ ions on structure, magnetic properties of the composites were investigated.     

High temperature mechanical properties of La1−x Sr x Cr1−y Co y O3 for SOFC interconnect

Solid oxide fuel cells (SOFC) require an interconnect for fabrication into stacked cells. This is typically La(Sr, Ca)CrO₃, of which much data on the electrical and physical properties already exists. However, very little information exists on the high temperature mechanical properties of the material, which is a necessity for future design improvements. La_1–x Sr _x Cr_1–y Co _y O₃ samples were fabricated into green dry-pressed bars and pellets, and sintered under various heating and cooling regimes. The sinterability and high temperature mechanical properties of the material was then investigated as a function of the dopant concentration. It was observed, for example, that the modulus of rupture of the dry pressed La_0.7Sr_0.3Cr_1–yCo_yO₃ (y 0.3) gave a value of over 110 MPa at 1000 °C. This paper will provide data on the high temperature mechanical properties of the material and its application to the SOFC system.     

Synthesis and Para-conductivity Analyses of TlBa2(Ca 3 − y Mg y )Cu4 O 1 2 − δ Superconductors

TlBa ₂(Ca _3?yMg _y)Cu ₄ O _12?δ (y=0,0.5,1.0, 1.5,2) superconductors are synthesized at normal pressure, and the influence of doped Mg atoms on the superconductivity parameters at the microscopic level is investigated by carrying out para-conductivity analyses of conductivity data. The samples have shown tetragonal structure, and the unit cell volume decreases with increased Mg doping. The onset temperature of superconductivity [ T _c(onset)] and zero resistivity critical temperature [ T _c(R=0)] decreases with Mg. Maximum magnitude of diamagnetism is observed in the samples with Mg of y=2. The apical oxygen mode of the type Tl-O _A-Cu(2) and CuO ₂ planar oxygen modes are softened as observed in fourier transform infrared spectrometer (FTIR) absorption measurements. The fluctuation-induced conductivity (FIC) analyses of conductivity data have shown the enhancement of inter-plane coupling and coherence length along the c-axis. These analyses have shown an increase in the coherence length along the c-axis and the inter-layer coupling J. The enhancement of inter-plane may possibly be arising due to a small decrease in the value of the order parameter of the carriers from ∣ψ∣ ²=1 in the CuO ₂ planes in Mg-doped samples. The values of B _c0(T), B _c1(T), J _c(0) are suppressed with the increased incorporation of Mg, which most likely arises due to the weak coupling of the grains induced by Mg doping.     

Crystalline structure and dielectric properties of Ba(Ti1−y Ce y )O3

Crystalline structure, microstructure and dielectric properties for Ba(Ti_1–y Ce _y )O₃ (0 y 0.5) ceramics have been studied. Dense ceramics with the relative density higher than 95% and grain size of 0.7–1.5 m have been obtained. The limit of the solid solubility is determined as y = 0.3 by the X-ray diffraction, SEM, and dielectric properties measurements. The crystalline symmetry is tetragonal for the sample with y = 0.02 and cubic for y 0.06 at room temperature, and the unit cell increases with increasing Ce content in the solid solution range. Correspondingly, the dielectric response exhibits three dielectric peaks for y = 0.02, and one pinched dielectric peak with ferroelectric relaxor behavior for y 0.06.     

Growth of Ga x In1 − x As y P1 − y /GaAs quantum dot arrays by ion beam deposition

Experimental data are presented that demonstrate the possibility of producing GaInAsP quantum dots on GaAs by ion beam deposition. The morphology of the quantum dots and the effect of GaAs substrate temperature on parameters of GaInAsP quantum dot arrays have been studied by atomic force microscopy and scanning electron microscopy. We have determined the elemental composition of the quantum dots and obtained photoluminescence spectra of the GaInAsP/GaAs heterostructures.     

Optical conductivity of a superconductor withd x 2− y 2 symmetry

Using a simplified Eliashberg formulation in which we keep only that part of the susceptibility which is separable and of $d_{x^2 - y^2 } $ symmetry in the pairing channel and keep the isotropic part in the renormalization channel, we have calculated the ac conductivity in the superconducting state. At zero temperature, in the clean limit, we find a finite amount of absorption at any frequency, however small, although it is substantially reduced over its normal-state value. Besides this boson-assisted absorption, when impurities are added a new channel is opened up in which momentum is given up to the impurity system and absorption proceeds directly through the creation of a hole-particle pair. Born and unitary impurity scattering are considered.     

Transport Properties of Heavy Fermion Compounds: YbIn1−x Cu4+x and YbIn1−y Ag y Cu4

The intermetallic compounds of Yb with In and Cu (YbIn_1–x Cu_4+x ) and Yb with In, Ag, and Cu (YbIn_1–y Ag _y Cu₄) exhibit interesting magnetic and transport properties. Of the compounds of Yb with In and Cu the compound with x=0, namely YbInCu₄, has attracted particular attention, because—while being a Curie–Weiss paramagnet—it undergoes a first-order isostructural phase transition at T _v =approx. 40 to 80 K and atmospheric pressure. Below T _v the ytterbium in this compound is in a mixed-valence state and the compound as a whole is sometimes called a light heavy-fermion system. Above T _v , the compound is known as a Curie–Weiss paramagnet of localized magnetic moments and, below T _v , a Pauli paramagnet in a nonmagnetic Fermi-liquid state. In the present paper the results of measurements of the thermal conductivity of polycrystalline samples, YbIn_1–x Cu_4+x with x=0,0.015, 0.095, and 0.17 and YbIn_1–y Ag _y Cu₄ with y=0, 0.3, 0.7, and 1.0, are reported. The thermal conductivity is separated into the phonon thermal conductivity ( _ph ) (i.e., related to the heat carried by phonons) and into the electronic thermal conductivity ( _e ) (related to the heat carried by electrons). The electrical resistivity of the compounds was measured to determine the temperature dependence of the Lorenz number. The results show that in the temperature interval 4.2 to 300 K the latter quantity behavior follows the theoretical predictions for heavy fermion materials.     

Transport Properties and Electronic Specific Heat of La2−x Ba x Cu1−y Zn y O4+d Bulk

The effect of the partial substitution of Cu by Zn and La by Ba in La: 214 prepared by conventional solid state reaction method has been investigated by using Hall coefficient, Seebeck coefficient and electronic specific heat measurements, over the wide temperature range between 4.2 K and 300 K, in magnetic fields up to 5 T. The samples with y=0 and d=0, showed superconductivity for x between 0.055 and 0.30. The critical temperature, the Hall and Seebeck coefficients strongly depend on Zn content. The phonon specific heat C _ph and electronic specific heat C _el have been extracted from the total specific heat C. Zn-doping effect on the (T)=C _el/T behavior suggests that the large range stripe order and the fluctuating stripe suppress the singlet formation and pseudo gap.     

Crystal structure and dielectric properties of (Pb1−x Ca x )(Zr1−y Sn y )O3 ceramics

There has been an increasing demand for dielectric resonator materials that operate in the microwave frequency range for applications in microwave communications. (Pb,Ca)ZrO₃ ceramics have a dielectric constant (_r), high quality factor (Q) and a small temperature coefficient of resonant frequency (_f). However, basic properties such as its crystal structure, temperature characteristics and the nature of its phase transformation are not yet fully understood. The temperature coefficient of resonant frequency can be controlled fairly well with the temperature coefficient of the dielectric constant. In this paper, we report the results of investigated crystal structure and the dielectric properties of (Pb_1–x Ca _x )(Zn₁– _y Sn _y )O₃ ceramics with the objective of elucidating the relationship between the crystal structure and the dielectric properties. The crystal structure refinement was performed by the Rietveld method. The dielectric properties were measured from-150–350 °C. The phase transformation was analysed from high and low temperature XRD data.     

Magnetization Fluctuation Analysis and Superconducting Parameters of La1.5−x Ba1.5+x−y Ca y Cu3O z Superconductor

In this work we report analysis of experimental data of the magnetization of La_1.5?x Ba_1.5+x?y Ca _y Cu₃O _z superconducting system. The data are analyzed in terms of thermal fluctuations on the magnetization excess M(T) for different values of temperature in each of the samples. We describe a procedure for extracting the penetration depth in the ab plane (1537–1650 Å) and the coherence length in the ab plane (21–23 Å) parameters from the magnetization, as a function of the applied magnetic field. This procedure was performed for polycrystalline samples using the theory of Bulaevskii, Ledvij and Kogan, which analyzes the vortex fluctuation in superconducting materials within the Lawrence-Doniach framework. These data allowed one to determine the characteristic temperature value T ^? (53–73 K) in the magnetization curves for several magnetic fields. We calculated the data of magnetization excess from the curves of the magnetization as a function of the logarithm of the applied field. We notice that the values for these superconducting parameters are in agreement with reports for high-temperature superconductors. The value obtained of the superconducting volumetric fraction is compared with the value obtained through the measure of the Meissner effect.