Low-temperature heat capacity and ac magnetic susceptivility of the re-entrant ferromagnetic superconductor Ho1.2Mo6S8

Thermal hysteresis in the ac magnetic susceptibility and a spike-shaped anomaly in the heat capacity, superimposed on a feature due to ferromagnetic ordering, have been observed at the coupled superconducting to normal-ferromagnetic transition in Ho_1.2Mo₆S₈.     

Low temperature magnetization measurements on heavy rare earth molybdenum sulfides, (RE)1.2Mo6S8

Magnetization measurements on the heavy rare earth molybdenum sulfides, (RE)_1.2Mo₆S₈ (RE = Gd, Tb, Dy and Ho) were performed to further clarify the natures of their magnetic orders found in our recent resistivity and ac susceptibility measurements below 1 K. The variations of their magnetic and superconducting transition temperatures along the series of the rare earth ions in the Periodic Table are interpreted by means of available theories.     

Chevrel相MxMo6S8化合物电荷转移和Mo原子上4d轨道能级的分裂

本文用配位场方法导出了Chevrel相M_xMo₆S₈化合物中M和Mo₆S₈原子簇间电荷转移和Mo原子上4d轨道能级分裂的解析关系。结合PbMo₆S₈的反射光谱,求得Mo₆S₈原子簇至Pb的电子转移数为1.18,和以前一般文献上认为的两个电子从Pb转移至Mo₆S₈不同。Mo₆上的4d电子数为18.8。 关键词：     

Electron spin resonance on GdxMo6Se8 (x = 1.0 and 1.2)

Electron spin resonance of Gd³⁺ in Gd_xMo₆Se₈ (x = 1.0 and 1.2) has been measured in X-band and in K-band between 1.4 and 290 K. The results indicate that the conduction electron - Gd³⁺ spin exchange coupling constant is positive and equal to +0.011 eV, in agreement with previous determinations based on superconductivity and static magnetic susceptibility measurements.     

Salting-out in intercalation compounds: Removing copper from Cu3Mo6S8 by intercalating lithium

We study the removal of the copper in Cu₃Mo₆S₈ by the intercalation of lithium. For 0<×<1, Li_xCu₃Mo₆S₈ is a single phase compound. For x?1, the copper atoms are forced out of the Mo₆S₈ host. We present a lattice-gas model which shows how the intercalation of Li can force the Cu out of the host.     

Coulometric titration of copper in CuxMo6S8−y(0⩽y⩽0.4) with solid Cu-electrolyte Rb4Cu16I7Cl13

In order to determine the copper content x of copper Chevrel compound Cu_xMo₆S_8?y(0?y?0.4) as a function of copper activity a_Cu and sulfur deficit y, a solid state electrochemical cell, Cu/Rb₄Cu₁₆I₇Cl₁₃/Cu_xMo₆S_8?y/Pt, was constructed and coulometric titration studies were made at 400 K. For the evaluation of the coulometric titration data, measurements were made on the electronic conductivity of copper-ion conductor Rb₄Cu₁₆I₇Cl₁₃. Also, a brief investigation was made on the condition of formation of single phase Chevrel Cu_xMo₆S_8?y with varying x and y at 1000°C. The structural change of Cu_xMo₆S_8?y with a change in x and y was studied by the X-ray diffraction method. It was found that x for constant a_Cu decreases with increasing y. The maximum value x_max of x in Cu_xMo₆S_8?y in equilibrium with metallic copper was found to be expressed by $\text{x}{}_{\mathrm{<mtext>max</mtext>}}\text{=-(}\text{10}\text{3}\text{)y+5}$. In the region of y<0.3, x_max exceeded 4, contrary to a presupposition that x_max is less than 4. X-ray analysis revealed that most of the copper Chevrel compounds denoted by Cu_xMo₆S₈ so far were sulfur deficient ones with y?0.4. The importance of sulfur deficit on the properties of the copper Chevrel compound was emphasized.     

Synthesis and physical properties of new superconducting Chevrel phases HgxMo6S8

New ternary molybdenum chalcogenides Hg_xMo₆S₈ (0 < x < 1) have been synthesized and investigated for their structural, magnetic, and superconducting behavior. These new phases prepared at low temperature by reaction of mercury with Mo₆S₈ (obtained from oxidation of Cu₂Mo₆S₈ by iodine) have been characterized by x-ray diffraction, static Faraday susceptibility, and superconducting transition temperature studies. HgMo₆S₈ crystallizes in the rhombohedral space group $\text{R}\text{3 (}\text{a}{}_{\mathrm{r}}\text{= 6.51}\text{A}\text{?}\text{, α}{}_{\mathrm{<mtext>r</mtext>}}\text{= 92.53°)}$, has a paramagnetic, temperature dependent susceptibility, and superconducts at 8.1K. As the mercury content decreases, a continuous decrease in T_c from 8.1K to 1.7K for x=0 (Mo₆S₈) is observed.     

Superconductivity in the RexMo6S8

The rare earth molybdenum sulfides RE_xMo₆S₈ (RE = rare earth) have been synthesized and are found to be superconducting with a few exceptions. This result, which is surprising in view of the high concentration of magnetic ions, is correlated with the particular structure of these compounds based on on units of Mo₆S₈.     

Preparation and mass transport properties of Li2.3Mo6S7.7

Unsuccessful attempts were made to prepare Li_xMo₆S_7.7 by direct ionic exchange of Cu₂Mo₆S_7.7 using aqueous, acetontrille, and molten salt solvents. Li_2.3Mo₆S_7.7 was eventually prepared by lithiation of Mo₆S₈ using n-butyl lithium reagent. The mass transport properties of hot-pressed samples were measured using a four-point dc technique and the following values at 415°C for the lithium ionic conductivity, .4×10⁻⁴ (ohms cm⁻¹) and lithium chemical diffusion coefficient 3.5×10⁻⁷ cm²/s, were derived. A possible explanation for the relatively low lithium ion mobility in Li_2.3Mo₆S_7.7 is discussed.     

Low temperature structural distortion in the high Tc Chevrel-phase superconductors PbMo6S8 and SnMo6S8

High-resolution powder neutron diffraction data reveal that, at temperatures below 100 K, oxygen-free, high-T_c samples of PbMo₆S₈ and SnMo₆S₈ exhibit a small structural distortion from the R$\text{3}$ rhombohedral space group. The data cannot be refined in a simple P$\text{1}$ triclinic space group as previously reported for EuMo₆S₈ and BaMo₆S₈. Thus, a supercell ordering is suggested.     

Phase transition in the superconducting state in Gd-rich pseudoternary compounds (La1-xGdx)1.0Mo6Se8

A pronounced lambda-type specific heat anomaly in the superconducting state is reported for Gd-rich pseudoternary compounds (La_1-xGd_x)_1.0Mo₆Se₈. The anomaly is very similar to that previously reported for the compound Gd_1.2Mo₆Se₈. Both the temperature of the lambda anomaly (≈ 3.5 K) and the Curie-Weiss temperature were found to be nearly independent of x. In addition, evidence for the occurence of magnetic ordering at 0.8 K in Gd_1.2Mo₆Se₈ is presented. These observations support our earlier conjecture that the lambda anomaly at 3.5 K does not arise from magnetic ordering of the Gd³⁺ ions. The anomaly appears instead to be due to a different type of phase transition which is associated with the presence of the localized 4f electrons of the Gd³⁺ ions, but the exact nature of the transition remains to be established.     

Low temperature heat capacity of rare earth molybdenum sulfides

Pronounced anomalies in the heat capacity of Gd_1.2Mo₆S₈, and probably Dy_1.2Mo₆S₈ are associated with the previously reported antiferromagnetic transition which occurs in the superconducting state in each of these compounds.     

Physical properties of several M2Mo6X6 compounds (M = GROUP IA METAL; X = Se,Te)

We report the physical properties of the pseudo one dimensional ternary molybdenum chalcogenides M₂Mo₆X₆ (M = K, Rb,Cs,Tl;X = Se, Te) measured on single crystals grown at high temperature. For Group IA metals (Rb,..,Cs) the transport properties evolve from a metallic to a semiconducting-like behavior on decreasing the temperature. Over the same temperature range the Group IIIA compound (Tl₂Mo₆Se₆) remains metallic and even superconducts at 5.1K. The susceptibility of these materials is weakly diamagnetic and does not reveal anomalied correlated to the onset of the broad metal-nonmetal transition, except perhaps for Cs₂Mo₆Te₆. A variation of the electronic interchain coupling is proposed to explain the difference between the Group IA and IIIA metal compounds. In the absence of evidence of three dimensional ordering at low temperature, we suggest that the broad metal-nonmetal transition is due to a fluctuating Pierls gap that is uncorrelated from one Mo chain to the next.     

Coexistence of superconductivity and long-range antiferromagnetic order in Gd1.2Mo6Se8

Neutron diffraction experiments confirm that the ternary rare earth compound Gd_1.2Mo₆Se₈ orders antiferromagnetically in the superconducting state at a Neél temperature T_N=0.75 K.     

A triple potential model for the structural transition in Cu2Mo6S8

A simple model for the structural phase transition in Cu₂Mo₆S₈ is proposed. The model uses a triple well potential for copper atoms. In the molecular field approximation a first order transition of the order—disorder type involving the rearrangement of the copper atoms is obtained.     

反应扩散法制备的PbMo6S8超导带的超导特性

本文报道反应扩散法制备Chevrel相PbMo₆S₈超导带材的过程以及带材的超导特性。Mo带与H₂S气体反应生成单相的Mo-S化合物(MoS₂或Mo₂S₃,根据反应温度而定),再与Pb的蒸汽反应生成单相的PbMo₆S₈薄层。PbMo₆S₈超导层的临界温度T_c=13.0 关键词：     

Lattice instability in the non-superconducting compound EuMo6S8

We have performed electrical resistivity and specific heat measurements on bulk Eu_1.1Mo₆S₈ together with low-temperature X-ray powder diffractometry. These investigations revealed a structural phase transition (occuring at 109 K) from the room-temperature rhombohedral structure to a low-temperature triclinic distorted structure in which the compound exhibits a non-metallic behavior.     

Superconducting thin films of MxMo6S8 type

Thin films of M_xMo₆S₈, where M=Pb, Sn, Sn-Al and Cu, known as the Chevrel phases have been prepared by d.c. getter sputtering method and the optimal conditions of their preparation have been determined. The transition temperatures reached: 10.16, 13.66, 11.74 and 12.86 K for thin films with M=Cu, Sn, Sn-Al and Pb respectively. The highest critical fields H_c²(0) of 428 kG were obtained for Pb compounds.     

Superconductivity and magnetic order in the pseudoternary system Ho1−xEuxMo6S8

Ac susceptibility, resistance and magnetization experiments on the pseudoternary system, Ho_1?xEu_xMo₆S₈ confirm that there exist three distinct domains of concentration between x=0 and 1 with respect to the interplay of superconductivity and magnetism.     

Absence of hydrogen in superconducting molybdenum sulfide,Mo3S4

Superconducting Mo₃S₄(T_c=1.8 K) was prepared from the ternary sulfides MMo₃S₄ (M=Cu, Ni) by the acid extraction method, and was studied by neutron diffraction and NMR spectroscopy. In contrast to earlier reports no significant amounts of hydrogen could be found in the rhombohedral structure. However, large proton concentrations were found in samples which had been exposed to moist air.