Synthesis of “stabilized Mn1−xMgxO” system (0.001 ⩽ x ⩽ 0.15) and its structural,thermal, optical and magnetic studies

A novel method of preparation, involving careful formation of a stoichiometric solid solution of stabilized Mn_1-x Mg _x O system for eight different concentrations ofx (0.001 x 0.15) is described. A variety of physicochemical techniques such as X-ray diffraction, DTA-TGA, reflectance spectra, magnetic susceptibility and XPS data are used to determine structure-property correlations in the solid solutions, which are (i) X-ray diffraction studies reveal the linear decrease of cubic lattice parameter with increasing x, (ii) DTA-TG-DTG studies which confirm the formation of solid solution and the stability of these solid solutions in air which increases from 515 to 565 K withx, (iii) the diffused reflectance spectra shows nearly perfect octahedral symmetry around Mn²⁺ ions, (iv) magnetic susceptibility data indicates the usual dilution effects of diamagnetic ions in antiferromagnetic host lattice, (v) XPS studies reveal the presence of mixed phase of Mn₂O₃-MgO on the surface which protects the bulk MnO from its further oxidation to higher oxides of manganese. This shows the important role of Mg²⁺ in the chemical passivation of manganous oxide.     

Electrical properties and phase transition of Ge1−x Sn x Se2.5 thin films

The Ge_1–x Sn _x Se_2.5 system was prepared by melting the correct ratio of high purity elements in quartz evacuated ampoules followed by quenching in ice. It was found that, within the Ge_1–x Sn _x Se_2.5 system, a glassy state can be formed when 0 x 0.4. On increasing x to 0.6 a glassy state could not be obtained, as is confirmed by X-ray diffraction. Differential thermal analysis (DTA) was carried out to study the effect of composition on the stability of amorphous phase. Ge_1–x Sn _x Se_2.5 (where 0 x 0.6) thin films have been prepared by the thermal evaporation technique. The electrical conductivity of the thin films have been studied as a function of composition and film thickness.     

Crystallographic studies of some mixed thiogallate semiconductors

A crystallographic study has been made of solid solutions of the tetragonal defect chalcopyrites (14), CdGa₂S₄ and CdGa₂Se₄. The compositions may be represented by CdGa₂S₄(1–x)Se_4x wherex = 0.0, 0.25, 0.50, 0.75 and 1.0. A complete solid solubility was observed between these two compounds. Thea-axis values varied linearly with composition, whilstc-axis values initially showed a slower rise forx<0.5 and then a marked rapid rise with increasing selenium content. Single crystals were grown of these compositions by the chemical transport method. Optimum conditions required for the growth of the crystals have been established. The crystals of CdGa₂S₄ and CdGa₂S₃Se had the biggest face parallel to (001) plane whereas crystals of compounds CdGa₂S₂Se₂, CdGa₂SSe₃ and CdGa₂Se₄ were triangular prisms with a face parallel to (112) plane and 110 as the growth axis. The parametersx, y andz for selenium position in CdGa₂Se₄ were obtained by comparing the calculated values ofF ² factors with those obtained from observed intensities. The best match was found forx=y=0.25 andz=0.15.     

Differential scanning calorimeter studies on Pb modified Ge–Se–Te glasses

Bulk glasses Pb _x Ge_{42 – x} Se₄₈Te₁₀(0 x 15) and Pb₂₀Ge _x Se_{70 – x} Te₁₀(17 x 24) have been prepared by quenching the melt. The non-isothermal properties of these glasses have been determined using a Differential scanning calorimeter (DSC). The composition dependence of the glass transition temperature, crystallisation temperature, excess heat capacity at glass transition, glass forming tendency and activation energy of glass transition and crystallisation show anomalous features near the composition at which the p- to n-type transition occurs. These observations reflect the changes occurring in the chemical bonding and the nature of the glassy network in these glasses. The results have been interpreted in terms of existing models and the majority charge carrier reversal phenomenon occurring in these glasses.     

p–T–x Phase Equilibria in the Cd–Zn–Te System

The p–T–x–y phase equilibria in the Cd–Zn–Te system are analyzed. The p–T and T–x–yprojections of the p–T–x–y phase diagram and a T–x–y isobar (for pressures at which Cd_1–x Zn _x Te_{1 ±} solid solutions sublime congruently in terms of Te) are mapped out. The key features of the sublimation behavior of the solid solution are examined. The p–T projection is studied by static vapor pressure measurements at temperatures from 700 to 1300 K and pressures of up to 101.3 kPa. The p–T sections of the phase diagram are constructed for x = 0.05, 0.10, 0.15, 0.25, 0.50, 0.75, 0.90, and 1. The solid solution containing 35 mol % ZnTe is found to phase-separate at 473 K.     

Determination of compositional fluctuation region in solid solution of lanthanum-modified lead zirconate titanate

A method was developed to determine a compositional fluctuation region in Pb_1–y La _y (Zr _x Ti_1–x )_1–(y/4)O₃ (PLZT) solid solution in the tetragonal region. The compositional fluctuation in PLZT extends two-dimensionally on the phase diagram. The method described in this paper utilized the fact that the compositional fluctuation region extends to the composition lines whose lattice spacing corresponds to the higher or lower fluctuation limit. The fluctuation limits of the lattice spacings were estimated from X-ray diffraction analysis. This method revealed that the compositional fluctuation in PLZT is difficult to be eliminated by using a conventional dry method (mixed oxide method). The shape of the region indicated that homogenization of Zr⁴⁺ and Ti⁴⁺ was more difficult as compared with that of Pb²⁺ and La³⁺.     

Phase relations and stoichiometry of superconducting Pbx Mo6 S8−y

The composition of Pb_xMo₆S_8?y can vary between 0.85 < x < 1.05 and 0.6 < y < 1.2 at 1100 °C and is shifted to lower Pb content at higher temperatures. The phase decomposes peritectically at about 1530 °C. At the approximate composition line Pb_xMo₆S₇, the rhombohedral lattice constant and the transition temperature T_c for superconductivity show maxima while the rhombohedral angle has a minimum. Small single crystals (～0.2 mm) of Pb_xMo₆S_8?y and larger crystals (～3 mm) of Cu_xMo₆S_8?y, Sn_xMo₆Se_8?y can be obtained in sealed Mo-crucibles     

Structural and electrical properties of cadmium-sulpho-selenide solid solutions

Complete solid solutions of CdS _x Se_1–x (0x1) were synthesized by vacuum fusion of stoichiometric proportions of CdS and CdSe. X-ray diffraction data revealed that they possess the hexagonal wurtzite structure. The unit cell lattice constants vary linearly with the composition parameter,x, following Vegard's law.Thin films of CdS _x Se_1–x (0x1) solid solutions could be deposited onto glass substrates by thermal evaporation of the bulk material in 10^–4 Pa vacuum. Structural investigation showed that the films are polycrystalline with predominant appearance of the (002) reflecting plane. On annealing at 250°C in 10^–2 Pa vacuum atmosphere, aggregation and rearrangement of the as-deposited tiny crystallite occurred, preserving the same crystal structure.The dark electrical resistivity of the films is independent on the film thickness, but it varies appreciably with the composition parameter,x, showing a minimum resistivity of 0.02 cm atx=0.55. The temperature dependence of the resistivity follows the semiconducting behaviour with an extrinsic and an intrinsic conduction below and above 70°C, respectively. The determined activation energies 0.2 eV and 0.8 eV, respectively, correspond to shallow and deep trap levels, respectively.     

Phase Relations in the Systems Ln1 – x Ba x CoO3 – δ(0 < x ≤ 0.66; Ln = Nd, Sm)

Data are presented on the structural and magnetic properties of Ln_{1 – x} Ba _x CoO_{3 –} (Ln = Nd, Sm; 0 < x 0.66) samples slowly cooled in air after synthesis. The composition stability limits of the intermediate phases Ln_{1 – y} Ba_{1 + y} Co₂O_{5 +} and solid solutions are determined. The magnetic phase diagram of the Nd_{1 – x} Ba _x CoO_{3 –} system is constructed.     

Growth and Properties of CuAlS2x Se2(1 – x) Single Crystals

CuAlS₂, CuAlSe₂, and CuAlS_2x Se_{2(1 – x)} (0 < x < 1) single crystals were grown by chemical vapor transport in a close-spaced geometry and characterized by x-ray diffraction and differential thermal analysis. The results were used to map out the CuAlSe₂–CuAlS₂ phase diagram. The density of the crystals was found to vary linearly with x, while microhardness shows a maximum. The transmission and reflection data obtained near the intrinsic edge were used to determine the band gap E _g of CuAlS₂, CuAlSe₂, and the solid solutions. E _g was found to vary nonlinearly with composition.     

Influence of Soaking in the Molten (Li0.62K0.38)2CO3Eutectic on the Structure and Conductivity of LiMnxFe1 – xO2and Li1 – yMnyFeO2 + δ

The phase composition, structure, and 920-K electrical conductivity of LiMn _x Fe_{1 – x} O₂(0 < x 1) and Li_{1 – y} Mn _y FeO_{2 +} (0 < y 1) materials prepared by solid-state reactions in air at 1270 K were studied before and after soaking in molten (Li_0.62K_0.38)₂CO₃. The highest conductivity of 32 S/m was found in the spinel solid solution Li_0.2Mn_0.8FeO_{2 +} ( = 2/3). Soaking in the carbonate melt converted all Li_{1 – y} Mn _y FeO_{2 +} samples into rocksalt solid solutions and reduced their conductivity.     

Magnetic structure and spin-glass state of Fe1-x Zn x Cr2S4 spinels

Fe_1-x Zn _x Cr₂S₄ (0 <x < 1) solid solutions were synthesized and their magnetic properties and structure were investigated. The magnetic phase diagram of the solid-solution system was constructed. The results reveal a ferrimagnetic-spin glass-antiferromagnetic compositional transition in the FeCr₂S₄-ZnCr₂S₄ system.     

Phase Equilibria and Crystal Structures of Mixed Oxides in the La-Mn-Ni-O System

The phase equilibria and crystal structures of mixed oxides in the ternary system La₂O₃-Mn₃O₄-NiO are studied at 1100°C in air. The projection of the La-Mn-Ni-O phase diagram at 1100°C and = 0.21 × 10⁵ Pa onto the metal-composition triangle is found to comprise 12 phase fields. The lattice parameters of La₂NiO₄ (sp. gr. I4/mmm), La₃Ni₂O₇ (sp. gr. Cmcm), La₄Ni₃O₁₀ (sp. gr. Cmca), and La_{1 + x} Mn_{1 − x − y} Ni_yO₃ solid solutions (sp. gr. Pnma, −0.04 ≤ x ≤ 0.05, 0 ≤ y ≤ 0.4) are determined. The composition stability limits of La₄Ni_{3 − y} Mn_yO₁₀ solid solutions are 0 < y ≤ 0.05. With increasing Ni concentration in La_{1 + x} Mn_{1 − x − y} Ni_yO₃, the metal nonstoichiometry decreases from −0.04 ≤ x ≤ 0.05 at y = 0 to x = 0 at y = 0.4.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 7, 2005, pp. 841–848.Original Russian Text Copyright © 2005 by Demina, Cherepanov, Petrov, Klokova.     

Phase equilibria in PbTe/CdTe alloys

The Pb/Cd/Te phase diagram in the range Pb_1–x Cd _x Te_1+y where 0x0.15 and y±0.05 was examined by differential thermal analysis. The congruent melting point for PbTe was found to be unique. Annealing of alloys in Te-rich and deficient atmospheres showed that the phase width of the system increased and moved more towards the n-side with increasing cadmium content. The energy of formation of a divacancy for a 3 mole % CdTe alloy was found to be 0.16 eV less than that in PbTe.     

Phase Diagram and Luminescent Properties of CdTe–MnTe Solid Solutions

The T–x phase diagram of the CdTe–MnTe system is mapped out. The CdTe–MnTe join is shown to be nonpseudobinary. The system contains an extended series of CdTe-based solid solutions (0–71.4 mol % MnTe at 1070 K). At 1070 K, -MnTe dissolves up to 0.3 mol % CdTe. Data are presented on the composition dependences of lattice parameters for the solid solutions studied and the luminescent properties of Cd_{1 – x} Mn _x Te single crystals annealed in cadmium or tellurium vapor.     

Freestanding 1T‐MnxMo1–xS2–ySey and MoFe2S4–zSez Ultrathin Nanosheet‐Structured Electrodes for Highly Efficient Flexible Solid‐State Asymmetric Supercapacitors

Fabrication of hierarchical nanosheet arrays of 1T phase of transition‐metal dichalcogenides is indeed a critical task, but it holds immense potential for energy storage. A single‐step strategy is employed for the fabrication of stable 1T‐Mn_xMo_1–xS_2–ySe_y and MoFe₂S_4–zSe_z hierarchical nanosheet arrays on carbon cloth as positive and negative electrodes, respectively. The flexible asymmetric supercapacitor constructed with these two electrodes exhibits an excellent electrochemical performance (energy density of ≈69 Wh kg^?1 at a power density of 0.985 kW kg^?1) with ultralong cyclic stability of ≈83.5% capacity retention, after 10 000 consecutive cycles. Co‐doping of the metal and nonmetal boosts the charge storage ability of the transition‐metal chalcogenides following enrichment in the metallic 1T phase, improvement in the surface area, and expansion in the interlayer spacing in tandem, which is the key focus of the present study. This study explicitly demonstrates the exponential enhancement of specific capacity of MoS₂ following intercalation and doping of Mn and Se, and Fe₂S₃ following doping of Mo and Se could be an ideal direction for the fabrication of novel energy‐storage materials with high‐energy storage ability.     

Phase equilibria and decomposition of solid solutions in the YbTe–SnTe–PbTe system

Phase equilibria in the YbTe–SnTe–PbTe system have been studied using differential thermal analysis, X-ray diffraction, scanning electron microscopy, and emf measurements on YbTe concentration cells. We have mapped out a number of vertical sections, the 400-K isothermal section of the YbTe–SnTe–PbTe phase diagram, and projections of its liquidus and solidus surfaces. The results demonstrate that the system is characterized by the formation of a continuous series of high-temperature solid solutions with a cubic structure (NaCl type), which undergo decomposition below ~1050 K. At room temperature, the YbTe solubility in the Sn_1–x Pb _x Te solid solution system is ~33–35 mol %, whereas the extent of the YbTe-based solid solution series does not exceed 3 mol %.     

Composition range and physicochemical properties of La1 − x Ba x Mn1 − y Fe y O3 solid solutions

We have determined the extent of La_{1 ? x} Ba _x Mn_{1 ? y} Fe _y O₃ solid solutions with orthorhombically and rhombohedrally distorted perovskite structures. A partial phase diagram of the LaMnO_{3 + δ}-BaMnO₃-BaFeO_2.5-LaFeO₃ system in air at a temperature of 1373 K has been proposed for the first time. We have measured the relative length change of La_{1 ? x} Ba _x Mn_{1 ? y} Fe _y O₃ samples and calculated their thermal expansion coefficients.     

High-field superconductivity in Al-O-Pb and Al-O-Pb-Bi sputtered films

The sputter-quenched Al _x O _y alloys containing lead and bismuth elements, which are insoluble to aluminium; have been found to exhibit a remarkably enhanced upper critical field,H _c2, which is higher by about 6 to 66 times than those of pure lead metal and Pb₆₀Bi₄₀ alloy. The sputtered structure consists of amorphous Al _x O _y and f c c lead or h c p (lead-bismuth) phases. The lead and phases disperse homogeneously in the amorphous matrix and their particle sizes and interparticle distances are about 10 to 20 nm and 5 to 20 nm, respectively, for lead and particles. The superconducting transition temperature,T _c, upper critical magnetic field,H _c2, at 4.3 K, and residual resistivity at 10 K are 7.74 K, 3.3 T and 2.09 × 105cm, respectively, for (Al-O)_92.8 Pb_7.2 and 7.45 K, 8.2 T and 1.70 × 106 cm, respectively, for (Al-O)_86.2(Pb_0.6 Bi_0.4)_13.8. The remarkable enhancement ofH _c2 is interpreted as being mainly due to a remarkable decrease of the coherence length resulting from a large reduction of the effective mean free path of electrons. Additionally, the fluxoid pinning force under applied field has also been markedly enhanced for the duplex structure films than for sputtered lead film, probably because of the change of the dispersed lead phase into a type-II superconductor and an effective fluxoid pinning action at the interface between Al _x O _y and fine lead particles.     

Tuning Pb Content in High-T c Bi2Sr2CaCu2O y Superconductors Studied By X-ray Absorption Near-Edge Structure Spectroscopy

The variation of hole concentration within the CuO₂ planes via tuning Pb content in (Bi_2–x Pb _x )Sr₂CaCu₂O _y (0.2x0.6) has been investigated by X-ray absorption near-edge structure (XANES) spectroscopy using synchrotron radiation. The profile of XANES spectra indicated that Pb can be incorporated into Bi-2212 phase under nitrogen atmosphere around x=0.6. However, after annealing the nitrogen-sintered samples in oxygen, Pb solubility is found to be decreased only up to x=0.2 in (Bi_2–x Pb _x )Sr₂CaCu₂O _y , showing that compounds with high Pb content are more stable under oxygen-free atmosphere.