Structure and superconductivity studies on ternary equiatomic silicides,MM′Si

A series of ternary equiatiomic transition metal silicidesMM′Si (M=Zr, Nb, Ta;M′=Ru, Re) and Zr_1/2 M _1/2 RuSi (M=Nb, Ta) have been synthesized and characterized. Guinier x-ray data clearly indicate that the compoundsMM′Si (M=Nb, Ta;M′=Ru, Re) crystallize with the orthorhombic TiFeSi-structure. This is contrary to one of the literature reports ascribing the hexagonal ZrRuSi structure toMReSi,M=Nb, Ta. ZrRuSi and Zr_1/2 M _1/2RuSi (M=Nb, Ta), however, crystallize with the ZrRuSi structure. All the compounds are metallic and exhibit small and negative Seebeck coefficients. Superconductivity has been discovered inMM′Si,M=Nb, Ta;M′=Ru, Re and the transition temperatures, as measured by the low frequency a.c. susceptibility technique, range from 2·7 to 5·1 K. Zr_1/2Nb_1/2RuSi is not superconducting above 2·2 K. The observed properties are explained in terms of the electronic charge transfer effects and crystal structures adopted by these metal excess ternary silicides. Dedicated to the memory of Prof. N S Satya Murthy.     

Indium segregation kinetics in InGaAs ternary compounds

A rate equation model is applied to analyze surface segregation in InGaAs and related compounds during the growth of these materials by molecular beam epitaxy (MBE). General trends in segregation are examined as a function of temperature, the V/III ratio and the type of substrate. It is suggested that the principal segregation mechanism is related to a near-equilibrium established between the volatile group III species on the growth surface and in the crystal bulk. In particular, this mechanism results in different manifestations of surface segregation for InGaAs and GaAlAs.     

A theory of superconductivity in ternary rare-earth compounds. II

In an earlier paper a theory of superconductivity in ternary rare-earth compounds which examined the effects of elastic scattering of conduction electrons by localized 4f electrons was presented. In this paper the theory is extended by treating both elastic and inelastic scattering. Expressions for the phase diagram and the upper critical field are derived and compared with expressions from other theories.This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences Division.     

Charge bag model of superconductivity in intercalated layered compounds

In certain layered compounds the superconducting transition temperature (T _c ) is enhanced on intercalation. The superconductivity in these materials arises over a charge density wave background. To explain this enhancement inT _c we propose the charge bag model analogous to the spin bag model proposed earlier by Schrieffer as a mechanism for highT _c superconductivity.     

Recent progress of applied superconductivity in China

China has been involved for many years in the development of superconducting magnets for high energy physics, fusion research, magnetohydrodynamic power generation, magnetic separator, magnetic resonance imaging and other applications. The research activity in superconducting magnets has been intensified and diversified at the Institute of Electrical Engineering, Academia Sinica and other laboratories. This paper reviews the recent progress of applied superconductivity in China. A possible future programme is also outlined in this paper.     

Research opportunities in superconductivity

Opportunities for research in the field of superconductivity are identifield in this report of a ‘Workshop on problems in superconductivity’ held at Copper Mountain, Colorado, August 22–23, 1983. Key problems in superconductivity, high payoff areas of research, barriers to progress, and the need for new facilities are outlined in the three areas of basic physics, materials, and devices.     

Superconductivity of ternary rare earth compounds. IV. Coexistence of antiferromagnetism and superconductivity

The possibility of the coexistence of antiferromagnetic order and superconductivity in ternary rare earth compounds is examined within the framework of our previous papers on the ferromagnetic case. It is demonstrated that antiferromagnetic ordering does not destroy the superconducting state, which coincides with recent experimental facts. The phase diagram and several thermodynamic properties are investigated. We calculate the upper critical fieldH _c2 in the dirty limit, and compare it with the experimental data on Gd_1.2Mo₆S₈. Some of the characteristic features ofH _c2 can be explained qualitatively.This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences Division.     

Simultaneous determination of intraparticle diffusivities from ternary component uptake curves using the shallow bed technique

In order to design and operate a fixed-bed reactor, accurate modeling is important. For a single component system, the determination of intraparticle diffusivity is rather easy. However, the calculations of multi-component systems are normally complicated and very time-consuming. Therefore, an alternative simple determination procedure using the shallow bed technique is proposed in this research to determine the intraparticle diffusivities for multi-component systems. Ternary component systems of phenol (PH), benzoic acid (BA), and p-nitro-phenol (PNP) were investigated as model components. This study illustrated that adsorption uptake curves of different components in ternary systems can be converted into one typical characteristic curve (theoretical uptake curve, TUC) by using a set of dimensionless groups. By matching the dimensionless experimental uptake curve (DEUC) with TUC, diffusivities of PH, BA and PNP were determined as 8.00 x 10(-8), 5.92 x 10(-8) and 5.05 x 10(-8)cm2 s(-1), respectively. These values are in good agreement with simulated experimental values. This study demonstrated that the shallow bed technique can be used to simultaneous determination of intraparticle diffusivities from multi-component systems.     

碳纤维作宿主的三元插层化合物研究

以高模量碳纤维作宿主，采用熔融盐法分别合成了FeCl3-ZnCl2和CuCl2一NiCl2作插层剂的三元插层化合物，由x射线衍射分析得知：前者的插层效果要优于后者。采用8mm波衰减率测试系统测试了两种产物对8mm波的衰减，结果表明：经FeCl3-ZnCl2和CuCl2-NiCl2插层的碳纤维对8mm波的衰减率分别可达8dB和6dB。     

Icosahedral quasicrystal phase in Mg-Zn-Nd ternary system

Mg-Zn-Nd master alloy containing icosahedral quasicrystal phase with an interesting macro-shape has been prepared under conventional casting conditions. The microstructures and phases of Mg-Zn-Nd ternary alloy have been investigated by using SEM, EDS and TEM. The results show that the spherical phase in Mg-Zn-Nd master alloy is a simple icosahedral quasicrystal with stoichiometric composition of Mg₄₀Zn₅₅Nd₅ and quasi-lattice a_R = 0.525 nm. In this research, when the content of Nd is 1.20 at.% and atom ratio value of Mg/Zn at the range of 2.4-2.7, the as-cast solidification microstructure mainly consists of primary I-phase and Mg₇Zn₃ single-phase matrix.     

Pd插层NbSe2化合物的制备、晶体结构和电学性质研究

通过固相反应法合成一系列插层化合物Pd_xNbSe₂ (x=0~0.17)。它们与2H-NbSe₂相同, 属于六方晶格, 空间群为P6₃/mmc。Pd占据NbSe₂层间的八面体空位。随着Pd含量的增加, 晶格常数c线性增大, 而a几乎不变。X射线单晶衍射结果表明, Pd_0.17NbSe₂的晶格常数为a=b=0.34611(2) nm, c=1.27004(11) nm。每个Pd原子与六个Se原子键合形成[PdSe₆]八面体来连接相邻的Nb-Se层, 使晶体结构变得更加稳定, 从而提高化合物的热稳定性。电学测试表明, 随着Pd含量的增加, Pd_xNbSe₂的剩余电阻比减小。此外, 超导转变温度也随着Pd含量的增加而下降, 说明Pd的引入不利于NbSe₂的超导态。     

Investigation into the synergistic effects in ternary cementitious systems containing portland cement, fly ash and silica fume

This research was primarily conducted to verify the presence of synergistic effects in ternary cementitious systems containing portland cement (OPC), class C fly ash (FA) and silica fume (SF). A subsequent objective of the study was to quantify the magnitude of the synergy and to determine its source. For a ternary mixture containing 20% FA and 5% SF by mass, the synergistic effect was observed mostly at later ages (7 days onward) and it resulted in an increased compressive strength and resistance to chloride ion penetration as well as a reduced rate of water absorption (sorptivity) compared to predictions based on individual effects of FA and SF in respective binary systems. The observed synergy was attributed to both chemical and physical effects. The chemical effect manifested itself in the form of an increased amount of hydration products. The physical effect associated with packing density was, somewhat contrary to general belief, not due to an optimized particle size distribution of the binder components of the ternary cementitious system. Instead, it was the result of smaller initial inter-particle spacing caused by lower specific gravities of both FA and SF which, in turn, led to a lower volumetric w/cm. If the mixture design was adjusted to account for these differences, the physical effect would be diminished.     

Prediction of drug solubility in ternary solvent mixture

Applicability of the combined, nearly ideal, binary solvent/Redlich-Kister equation for calculating drug solubility in ternary mixtures is presented. The advantages of the proposed model are discussed and compared with a recently published equation that calculates the solute solubility in ternary solvent mixtures based on the mixture response methodology.     

High-T c superconductivity in thed-p electron system

The relaxation time with spin flipτ _s and the parametersξ, δ, χ of superconducting phase have been calculated on the basis of the kinematical mechanism of superconductivity in strongly correlated oxide models. An inter-relation between the superconducting gap Δ₀ and the specific heat jump Δ _c allowing the experimental verification was obtained and the Ginsburg-Landau equation derived.     

Theory of superconductivity in heavy-fermion compounds

A single-order-parameter and two-gap model (a modified Suhl two-gap model) is proposed for heavy-fermion superconductors. A simple relation between two gaps is found. The thermodynamic quantities in the superconducting state are calculated in terms of this model. It is shown that the critical values of the physical quantities are quantitatively in agreement with experiment. The behavior of the specific heat, of the ultrasonic attenuation, and of the NMR rate are also in good agreement with those of CeCu₂Si₂ and UBe₁₃ at all temperatures.     

Normal zone propagation within a superconducting magnetic system and cryostabilization of superconductivity

A theoretical study of normal zone propagation along composite conductors in contact with liquid helium which accounts for the resulting rate of heat release and non-uniformity of heat conduction coefficient is described. The Maddock-James-Norris theorem is shown to be true only for a constant heat conduction coefficient. The formulae are given for the speed of the normal zone propagation. Equations have been obtained which describe the collapse dynamics or normal zone growth within the superconducting magnetic systems; time of collapse and normal zone growth being evaluated. Non-linear heat waves of a new type are assumed to exist in a composite in addition to the solution with an interface of normal and superconducting regions.     

Epitaxial growth of binary and ternary metallic strained superlattices and their magnetic properties

Since the structure at/near the interface of superlattices influences physical properties such as magnetic property, it is important to investigate details of the structure. The interface structure is characterized by the factors like atomic species, strain, mixing and roughness. The reflection high-energy electron diffraction (RHEED) system installed in our molecular-beam epitaxy (MBE) system enables us to observe, continuously, the change of the surface in-plane lattice constant, which is affected by atomic species, strain and/or mixing, on a realtime basis. Ternary superlattices consisting of three elements can clarify the effect of stacking sequence by comparison between the two types of superlattices with the reverse deposition sequences, since the effect caused by the combination of the same atomic species is cancelled out and the effect caused by the different stacking sequences remains. In the present paper, we review growth behaviors of binary and ternary metallic strained superlattices, especially magnetic ones, investigated mainly by our group, and summarize the discussion on their magnetic properties, mainly on the magnetic anisotropy, in terms of their structural characteristics. First, we introduce our RHEED system that works efficiently under a magnetic field arising from evaporation sources for low vapor-pressure materials. Then, MBE-grown binary strained superlattices, Co/Au, Co/Pt and Cu/Au, are discussed, with comparing to incoherent superlattices of Co/Ag and Cu/Ag having nearly the same lattice mismatch of constituents. Next, we review ternary strained superlattices with immiscible constituents with reverse deposition order, Au/Co/Ag and Ag/Co/Au superlattices, and Au/Co/Cu and Cu/Co/Au superlattices, in relation to the growth behaviors of binary superlattices. Finally, ternary strained superlattices containing both miscible and immiscible constituents, Pt/Co/Ag and Ag/Co/Pt superlattices, and Au/Ni/Ag and Ag/Ni/Au superlattices, are reviewed.     

Phase equilibria in ternary reciprocal systems based on IV–VI compounds

Using the experimental data obtained in this study, literature data, and a unified thermodynamic model, we have calculated the T − x − y phase diagrams of all the pseudoternary reciprocal systems formed by the Group 14 metal chalcogenides: Sn, Pb ‖ S, Se; Sn, Pb ‖ S, Te; and Sn, Pb ‖ Se, Te.     

Structural instabilities and superconductivity in La-214 compounds

In La_2–x Ba _x CuO₄ (LBCO) the transition to a low-temperature tetragonal phase and the suppression of superconductivity occur at the carrier concentration p 1/8 per copper. We will discuss the roles of various material parameters that control this instability. An unusual lattice softening has been found by ultrasonic measurement on La_2–x Sr _x CuO₄ (LSCO). This softening is present only in an in-plane shearing mode and is ascribed to the growth of structural fluctuations in the normal state.These phenomena are closely related because both the structural change in LBCO and the applied strain in LSCO lift the degeneracy of in-plane oxygen sites. They clarify the importance of strong coupling between the normal-state electronic system and the lattice by a Peierls-type mechanism.