Non-Fermi-Liquid Behavior in CePt1+xSi1−x and CePtSi1−yGey

The heavy-fermion system CePtSi is located close to a magnetic instability. In order to study the influence of composition on the physical properties of CePtSi we prepared slightly off-stoichiometric CePt_1+xSi_1–x polycrystals. CePt_1+xSi_1–x with x=–0.04 exhibits typical non-Fermi-liquid behavior (C/TlnT, T^–0.21, T^1.5). A scaling analysis of the thermodynamic quantities at magnetic fields up to 10T and temperatures up to 6K points to a quantum phase transition described by some unknown non-Gaussian fixed point. In contrast substitution of Si by Ge leads to a quantum phase transition involving weak-coupling spin fluctuations for CePtSi_0.89Ge_0.11, which can be described within the framework of the self-consistent renormalization theory.     

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.     

Dielectric properties of the system Ba1−xLaxTi1−xCo x O3

The dielectric behaviour of compositions withx=0.01, 0.05, 0.10 and 0.20 in the system Ba_1–x La _x Ti-_1-x Co _x O₃ was studied in the temperature range 300–473 K. The compositions withx = 0.01 and 0.05 show a diffuse ferroelectric-paraelectric phase transition, while other compositions do not show this transition in this temperature range. The frequency dependence of dielectric constant and dielectric loss in the samples withx0.05 indicates that spacecharge polarization contributes significantly to their observed dielectric parameters.     

Precipitation in CdxHg1−xTe

An electron microscope study has been made of the precipitation effects at the boundaries of the pseudobinary sphalerite Cd _x Hg_1–x Te phase. Te precipitation is frequently found for alloys with compositions of 51 to 53 at. %Te but rarely in the 50 at. % stoichiometric alloy. Annealing of specimens under Hg overpressure leads to the formation of a new crystalline phase, which appears to be strongly related to the Cd–Hg phase.     

Augmenting 2 n−1 Designs

After a 2 ^n?k fractional factorial has been analysed, an experimenter may wish to carry out a further fraction to improve some estimates and break chains of aliases. The problem of augmenting a 2 ^n?1 half replicate by a nonoverlapping 2 ^n?k design is discussed. In each alias set for the 2 ^n?k fraction the effects occur in pairs as aliases from the half replicate. If only one of these pairs in a given alias set contains two nonnegligible effects, then that chain is broken. If more than one pair has both effects nonnegligible, no chains are broken. Procedures are given for augmenting four-letter plans for four or six factors.     

Phonon Vibration and Conduction of La2 − xSrxCuO4 − δ and La1.85 − xSr0.15 + xCu1 − xCoxO4 − δ

Polycrystalline samples La_{2 ? x} Sr _x CuO_{4 ? δ} (0.06 ≤ x ≤ 0.5) and La_{1.85 ? x} Sr_{0.15 + x} Cu_{1 ? x} Co _x O_{4 ? δ} (0 ≤ x ≤ 1) were synthesized by a conventional solid state reaction method. The structure, phonon vibration, and conduction were investigated by means of XRD, infrared (IR) spectra, and resistance. It is found that the increase of itinerant hole carriers could mask the in-plane ${\text{Cu}}{\kern 1pt} - {\kern 1pt} {\text{O(1)}}$ stretching vibration mode (689 cm^?1). The softening of the ${\text{Cu}}{\kern 1pt} - {\kern 1pt} {\text{O(1)}}$ phonon vibration mode gives an index of the weakening of ${\text{Cu}}{\kern 1pt} - {\kern 1pt} {\text{O}}$ hybridization. The distortion of CuO₆ octahedron and the microstructural inhomogeneity induced by Co doping lead to the widening of the IR absorption peaks.     

Valence compensated perovskite oxide system Ca1−xLaxTi1−xCrxO3 Part III Impedance spectroscopy

Electrical behaviour of the compositions with x 0.50 in the Ca_1–x La _x Ti_1–x Cr _x O₃system has been studied by employing complex plane impedance and spectroscopic analysis in the temperature range 100 K–550 K. These studies have revealed the contribution of three processes to the total electrical conductivity of these samples. An equivalent electrical circuit model, which contains series arrangement of three paralle RC elements, is proposed to represent the electrical characteristics of these materials. Out of these three, two processes correspond to the activated hopping processes within the bulk while the third process corresponds to the barrier layer formation in these ceramics. Immittance spectroscopic analysis shows that conduction occurs through localized as well as long range movement of charge carriers.     

Pb1−x Bi x /Bi/Pb1−x Bi x Josephson junction

A superconductor/semimetal/superconductor (S/SM/S) Josephson junction has been developed. We have used an alloy of Pb_1–x Bi _x (0x 0.6) as the superconductor and Bi as the semimetal. By irradiating at X-band microwave of 10 GHz, Shapiro steps were observed for various bismuth barrier thicknesses inÅ and bismuth weight ratiosx. Finally, we obtained the empirical relationship for barrier thickness, below which microwaves could be detected for various bismuth weight ratiosx at the temperature of 4.2 K.     

Lattice-matched epitaxial Pb1 − x Mn x Se/PbSe1 − x S x heterojunctions

This paper examines the possibility of producing lattice-matched p-n heterojunctions based on epitaxial n-Pb_{1 ? x} Mn _x Se (x = 0.02) and p-PbSe_{1 ? x} S _x (x = 0.04) films. The heterojunctions have been grown by molecular beam epitaxy in a single processing cycle, without breaking the vacuum, using a compensating Se vapor source in the growth process. Optimal conditions have been found for the growth of structurally perfect (W _1/2 = 90″-100″) epitaxial films and fabrication of lattice-matched heterojunctions based on such films, photosensitive in the IR spectral region.     

Preparation,structure and dielectric properties of the system Sr1−xLaxTi1−xNixO3

Attempts have been made to synthesize the solid solution Sr_1–x La _x Ti_1–x Ni _x O₃ for x0.50 and its electrical behaviour has been studied. It was found that a solid solution forms for compositions up to x=0.10. The structure remained cubic. These compositions exhibited dielectric relaxator behaviour. The average grain size in these materials was very small.     

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.     

Valence compensated perovskite oxide system Ca1−xLaxTi1−xCrxO3 Part II Electrical transport behavior

Electrical transport behaviour of the valence compensated system Ca_1–x La _x Ti_1–x Cr _x O ₃ (x 0.50) has been investigated by studying the Seebeck co-efficient, DC and AC conductivity as a function of temperature. Seebeck co-efficient, DC conductivity of different compositions has been measured in the temperature range 300 K–1000 K. AC conductivity for different compositions were determined in the temperature range 100–550 K and frequency range 10 Hz–10 MHz. Positive values of Seebeck co-efficient show that holes are the majority charge carriers. Conduction seems to occur by correlated barrier hopping of holes among Cr³⁺and Cr⁴⁺ions or V_O and V_O . Almost equal values of activation energies obtained for DC conductivity and dielectric relaxation process show that both the processes occur by the same mechanism.     

High-Pressure Studies on Superconductivity in LaFeAsO1−x F x and SmFeAsO1−x F x

The pressure dependence on the superconducting transition temperature (T _c ) was investigated for the iron-based superconductors LaFeAsO_1−x F _x and SmFeAsO_1−x F _x . The T _c ’s increase largely for LaFeAsO_1−x F _x with a small increase of pressure, while a sharp decrease of T _c was observed for SmFeAsO_1−x F _x . The electrical resistivity measurements reveal pressure-induced superconductivity for undoped LaFeAsO and SmFeAsO. These pressure effects seem to be related to an anisotropic decrease of the lattice constants under high pressure from the x-ray diffraction measurements up to 10 GPa for the LaFeAsO_1−x F _x system.     

Composition gradients in bridgman-grown Hg1−xMnxTe

The growth of Hg_1−xMn_xTe, a material from which infrared detectors can be made, has been studied. As with other members of the HgTe-based pseudobinary family, this material is prone to large longitudinal composition gradients. These gradients have been studied as a function of growth speed.     

Dielectric properties of the Sr1−x La x Sn1−x Co x O3 system

The possibility of the formation of a solid solution in the Sr_1–x La _x Sn_1–x Co _x O₃ system has been explored. Single-phase solid solution forms in the compositions for x0.10. All single-phase solid solution compositions have a cubic structure similar to SrSnO₃. The dielectric behaviour of these solid solution compositions has been studied as a function of temperature and frequency. The frequency dependence of dielectric constant and dielectric loss in these materials indicates that space charge polarization contributes significantly to their observed dielectric parameters. Microstructural studies show the presence of well-faceted grains. The average grain size in these samples is small.     

Valence compensated perovskite oxide system Ca1−xLaxTi1−xCrxO3 Part I Structure and dielectric behaviour

Attempts have been made to synthesize compositions with x = 0.01, 0.03, 0.05, 0.10, 0.20, 0.30 and 0.50 in the valence compensated system Ca_1–x La _x Ti_1–x Cr _x O₃by solid state ceramic method. Solid solutions form upto x 0.50. All the compositions have been found to have orthorhombic structure. The structure of the compositions upto x 0.10 is similar to that of CaTiO₃. The structure changes gradually from CaTiO₃to LaCrO₃in the composition range 0.10 < x < 0.50. Dielectric constant, at room temperature, has been found to increase with increasing substituent concentration upto x= 0.30 and thereafter it decreases with increasing xupto 0.50. Orientational and space charge polarizations contribute to the dielectric behaviour of these materials.     

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.     

Dielectric properties of the system Ca1−xYxTi1−xCoxO3(0.00 ⩽ x ⩽ 0.15)

The dielectric behaviour of the compositions withx0.15 in the system Ca_1–x Y _x Ti_1–x Co _x O₃ sintered and cooled in air has been studied. Space-charge polarization which arises due to the presence of chemical inhomogeneities at the micro-level contributes significantly to their dielectric constant. The composition with x=0.05 exhibits temperature and frequency-independent dielectric constant and very small dielectric loss.