R.N. Shelton

Pressure dependence of the super conducting transition temperature for ternary molybdenum sulfides

The variation of the superconducting transition temperature for some ternary molybdenum sulfides (Chevrel phase) has been investigated as a function of hydrostatic pressure up to 22 kbar. The effects of pressure on T/sub c/ are the largest yet reported for any set of compounds. 12 references.

The effect of pressure on the superconducting and crystallographic transitions of La3S4, La3Se4 and La3Te4

The superconducting transition temperatures (Tcs) for La3S4 and La3Se4 vary in a non-linear fashion under hydrostatic compression to 22 kbar. Both Tc and the crystallographic transformation temperature rise with pressure for La3S4 and show a maximum near 10 kbar for La3Se4. Non-transforming isostructural La3Te4 exhibits a linear pressure dependence of Tc. However, the telluride undergoes a pressure induced phase transformation at ∼70 kbar. In this case the sign of the pressure dependence is different from the sulfide and selenide. Variation of Tc with the crystallographic transformation temperature shows a new and unexpected behavior.

Superconductivity of transition metal sulfides, selenides, and phosphides with the NaCl structure

The superconducting properties of transition metal sulfides, selenides, and phosphides having the cubic NaCl structure are described. Binary compounds found to be superconducting are ThS, ScSe, ThSe, HfP, and ThP. More detailed information about the known superconductors Zr1−xS, LuS, Sc1−xS, YS, and ZrP is presented. Transition temperature was established as a function of composition for Zr-S, Sc-S, and Y-S NaCl-structure systems. Superconductivity at high pressure was determined in several systems. Some low-temperature specific heat capacity results, room-temperature magnetic susceptibility, and electrical resistance measurements between 2 K and room temperature are reported. Some information is presented about the rhombohedrally distorted compounds ZrSe and HfS. Results of NaCl-structure solid solution (metal replacement) synthesis (including superconductivity data) are reported for (Zr, Sc)-S, (Zr, Y)-S, (Zr, Ti)-S, (Zr, Hf)-S, (La, Y)-S and (Y, Th)-S. We find that superconductivity occurs generally in these materials, and that these compounds have much in common with the better known NaCl defect structure carbides and nitrides.

Structural transformation in some chevrel phase compounds: ZnMo5S6, ZnMo5Se6 and Cu0.7Mo3Se4

Abstract Low temperature x-ray powder diffraction and electrical resistivity experiments show that the Chevrel phase compounds ZnMo5S6, ZnMo5Se6 and Cu0.7Mo3Se4 are structurally unstable near or below room temperature. The binary compounds Mo3S4, Mo3Se4 and Mo3Te4 are stable to 6 K.

Kondo Anomalies due to Rare Earth Impurity Ions

Rare earth (RE) ions are capable of producing “Kondo-like” anomalies in the physical properties of both concentrated and dilute RE metallic systems which are qualitatively similar. These temperature dependent anomalies scale with a characteristic temperature T0, above which the RE metallic system behaves magnetically and below which it behaves nonmagnetically. The physical properties in which Kondo-like anomalies are found include the electrical resistivity, magnetic susceptibility, thermoelectric power, specific heat, and, in systems where appropriate, superconducting properties such as the critical temperature Tc and the jump in specific heat which occurs at Tc. The anomalies can be viewed as originating from admixture of the localized 4f electron states with the extended states of the conduction band, which can be traced to the unstable valence of certain RE ions.

Anomalous pressure dependences of the superconducting transition temperature of dilute alloys of LaSn3 containing light rare earth impurities

The initial depressions of the superconducting transition temperature Tc of LaSn3 by rare earth (RE) impurities are known to be anomalous. In an attempt to clarify this behavior, we have measured the pressure dependence of the Tc of (LaRE)Sn3 alloys (RE = Y, Ce, Pr, Nd, Sm, Eu, Gd, and Lu) to pressures up to 25 kbar. The magnitude of the pressure dependence of the Tc of (LaRE)Sn3 alloys containing RE impurities with partially filled 4f electron shells decreases monotonically with increasing RE atomic number. A general discussion of existing zero- and high-pressure data for various physical properties of (LaRE)Sn3 alloys demonstrates that the association of large pressure dependences of Tc with the occurrence of unstable impurity 4f shells (the Kondo effect) should be made with caution. The experimental high-pressure results are analyzed in terms of appropriate theoretical models for magnetic and nonmagnetic localized impurity states in superconductors.

Pressure dependence of Tc and phase stability for V3Si

Abstract Measurements of the superconducting transition temperature T c for a transforming polycrystalline sample of V 3 Si have been made as a function of hydrostatic pressure up to ≈29 kbar. T c increases over the entire pressure range with no evidence of the maximum at ≈24 kbar predicted by Chu and Testardi. A distinct break in the slope dT c /dP does occur near 16 kbar which is coincident with the discontinuity in the pressure dependence of the lattice parameter reported by Blaugher et al .

Pressure dependence of Tc for the shear-stress-induced tetragonal phase of V3Si

Abstract The effect of hydrostatic pressure on the superconducting transition temperature (T c ) of the shear-stress-induced tetragonal phase of V 3 Si (T c ≈ 10 K, c/a ≈ 1.05) is reported for the first time. The T c of this phase increases linearly with pressure at a rate of (1.0 ± 0.1) × 10 −5 K bar −1 , substantially lower than values of dT c /dp previously reported for the other two phases of V 3 Si.