Electrical resistivity and superconductivity in the chevrel phase compounds of the type Cu1.8Mo6S8—ySey (0 ⩽ y ⩽ 8) and Cu1.8Mo6S8—y Tey, (0 ⩽ y ⩽ 4)
TL;DR: In this paper, the superconducting transition temperatures and normal state residual electrical resistivities of the ternary Chevrel phase compounds Cu 1.8 Mo 6 S 8-Y Se y (0 ⩽ y ©� 8) and Cu 2.4 Mo 6S 8-y Te y (1.4 ) were investigated for possible correlations with structural parameters of the rhombohedral unit call and residual resistivity values.
Abstract: The superconducting transition temperatures and normal state residual electrical resistivities of the ternary Chevrel phase compounds Cu 1.8 Mo 6 S 8-Y Se y (0 ⩽ y ⩽ 8) and Cu 1.8 Mo 6 S 8-y Te y (0 ⩽ y ⩽4) are reported. The data are examined for possible correlations with structural parameters of the rhombohedral unit call and the residual resistivity values. It is found that T c decreases as the c/a ratio increases and as the rhombohedral angle approaches 90°. There is also an inverse correlation between T c and the normal residual resistivity of the samples.
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TL;DR: In this article, low-temperature specific heat measurements were performed on a series of binary, pseudobinary, ternary, and pseudoternary molybdenum chalcogenides M/sub x/Mo/sub 6/X/sub 8.
Abstract: Low-temperature specific heat measurements wee performed on a series of binary, pseudobinary, ternary, and pseudoternary molybdenum chalcogenides M/sub x/Mo/sub 6/X/sub 8/. The measurements covered a sufficiently wide temperature range to yield the relevant moments of the phonon spectra in addition to the electronic term. From the data in the superconduting state strong coupling parameters were also obtained, particularly the gap ratios 2..delta..(0)/kT/sub c/. The superconducting transition temperature of the Chevrel-type phases essentially depends on the bare electronic density of states as the Fermi level and, moreover, on the atomic order pertaining to the Mo/sub 6/ and certain chalcogen sites. For the ordered compounds, the relation lambdaapprox. =an/sub b/s(E/sub F/) holds on the average. The factor aapprox. =1.25 eV Mo atom spin is practically equal to that found for Nb-based A15-type compounds.
18 citations
TL;DR: A survey of the known highT − c ternary systems of compounds is presented in this paper, with a special emphasis on the part played by the crystal structure and bonding in the exhibition of high T − c superconductivity.
Abstract: A survey of the known highT
c ternary systems of compounds is presented. Special emphasis has been placed on the part played by the crystal structure and bonding in the exhibition of highT
c superconductivity. The superconducting and other physical properties of the ternary borides have been discussed in relatively more detail. Finally, the available guidelines from crystal and solid state chemistry points of view, have been reiterated for a search for new highT
c materials.
13 citations
TL;DR: In this paper, the effects of incorporating a small amount of oxygen into Cu1.8Mo6S8 have been studied, where lattice parameters, superconducting transition temperature, and the temperature dependence of both the upper critical field and the magnetic susceptibility x.
Abstract: The Chevrel compounds Cu1.8Mo6S8−x
O
x
have been studied, wherex=0.00, 0.05, and 0.10. In order to establish the effects of incorporating a small amount of oxygen into Cu1.8Mo6S8, we have measured lattice parameters, superconducting transition temperatureT
c, and the temperature dependence of both the upper critical fieldH
c2 and the magnetic susceptibility x. We show that the usual method of making this compound incorporates oxygen, and that this impurity may be removed by gettering the material with Y2S3. We observe that the substitution of oxygen for sulfur in Cu1.8Mo6S8 increasesT
c and decreases the ratioc/a of the hexagonal lattice constants and x. A breakdown in the rigid-band approximation is indicated by a comparison of the relative signs of the effect onT
c and that on x. In addition to these observations, we report on a correlation between hardness andT
c of Cu1.8Mo6S8 and on the temperature dependence of the magnetic susceptibility of Cu3.2Mo6S8.
3 citations
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TL;DR: In this paper, a rectangular prism with edges in principal crystal directions is prepared with electrodes on the corners of one face, and voltage-current ratios for opposite pairs of electrodes permit calculation of components of the resistivity tensor.
Abstract: A rectangular prism with edges in principal crystal directions is prepared with electrodes on the corners of one face. Voltage‐current ratios for opposite pairs of electrodes permit calculation of components of the resistivity tensor. The method can use small samples, and is best suited to materials describable by two or three tensor components. Examples are given of measurements of V2O3–Cr and oriented amorphous graphite.
574 citations
TL;DR: In this article, many unusual properties of the ternary molybdenum chalcogenides of the type MMo6X8 (M=Metal, X = Chalcogen) are reviewed and special emphasis is put on the superconducting properties like critical temperature, critical field and the problem of coexistence of magnetism and superconductivity.
Abstract: The many unusual properties of the ternary molybdenum chalcogenides of the type MMo6X8 (M=Metal, X=Chalcogen) are reviewed. Special emphasis is put on the superconducting properties like critical temperature, critical field and the problem of coexistence of magnetism and superconductivity.
395 citations
TL;DR: In this paper, the solid solutions PbyMo6X8−xX′x and Mo6X 8−x X′x (X, X′ = S, Se, Te) are studied and it is shown that there are correlations between Tc and certain structural parameters.
Abstract: The solid solutions PbyMo6X8−xX′x and Mo6X8−xX′x (X, X′ = S, Se, Te) are studied and it is shown that there are correlations between Tc and certain structural parameters.
67 citations
TL;DR: In this paper, a simple valence bond model based on the electron requirement of the Mo 6 octahedron to form 12 covalent bonds is proposed to stabilize the structure and have a strong influence on the superconducting transition temperature.
Abstract: Single crystal X-ray diffraction measurements on M x Mo 3 S 4 compounds ( M = Cu, Ag, Sn, In) yield evidence for the existence of a charge transfer from the interstitial element M to the Mo 6 S 8 building blocks. The importance of this transfer was estimated from the contraction of the Mo 6 octahedron as a function of the valency and the concentration of the cations. It is suggested that this effect stabilises the structure and has a strong influence on the superconducting transition temperature. Bonding is discussed using a simple valence bond model which is based on the electron requirement of the Mo 6 octahedron to form 12 covalent bonds.
66 citations
TL;DR: In this article, the decrease in the superconducting transition temperature after fast-neutron irradiation has been measured in V2Hf (C•15 Laves phase), Nb3Al (A•15 phase), PbMo6S7 (Chevrel phase), and SnMo5S8 (Chase phase).
Abstract: The decrease in the superconducting transition temperature Tc after fast‐neutron irradiation has been measured in V2Hf (C‐15 Laves phase), Nb3Al (A‐15 phase), PbMo6S7 (Chevrel phase), and SnMo5S8 (Chevrel phase). The samples were irradiated at 6 K and warmed to 300 K during transfer to the measuring cryostat. The Tc of the samples was measured as a function of dose up to 3.0×1019 n/cm2 (E≳0.1 MeV). The different crystal structures showed a marked difference in the sensitivity of the Tc depression with irradiation. The total decrease in Tc of V2Hf was 5%, while ΔTc(Nb3Al) =23%, ΔTc(PbMo6S7) =61%, and ΔTc(SnMo5S8) =51%. Log(ΔTc) was linear with dose for all samples as expected for radiation saturation, i.e., the damage rate was proportional to the undamaged fraction. The recovery of Tc after a series of 5‐min isochronal anneals up to 1200 °C has been measured, and the annealing stages observed are discussed in terms of the radiation‐induced defects.
57 citations