Properties of HxTaS2

The preparation of Hx TaS2 (0 \u3c x \u3c 0.87) is described. The compounds are only marginally stable at room temperature, slowly evolving H2S and H2 (and possibly Hp in air). Magnetic susceptibility data show that a low temperature transformation in 2H ... TaS2 (at so•K) is suppressed with the addition of hydrogen, and· at the same time the superconducting transition temperature T c rises from 0.8 to ~4.2•K at x = 0.11. Heat capacity measurements near this concentration show the superconductivity to be a bulk effect. Finally, by correlation of this data with susceptibility and T c measurements in other intercalation compounds, we suggest that the rise of T c (at low electron transfer) is due to suppression of the low temperature transformation and not due to an excitonic mechanism of superconductivity

Observation of Substitutional Site Preference in a Quasicrystal and Implication on Local Structure

A combination of magnetic susceptibility and Mössbauer measurements on quasicrystalline i-Al74Mn20-xFexSi6 (0.02≤x≤7.5) establishes that Mn atoms in i-Al74Mn20Si6 occupy two distinct classes of sites, and that Fe substitutes for only one of them. The two classes are distinguished by the possession or otherwise of a localized magnetic moment. The data are consistent with a structure of interconnecting Mackay icosahedra (MI) in which localized moments are possessed only by Mn atoms adjacent to broken MI connections. The implied connectivity of the resulting MI network is close to that anticipated for a packing of MI on a three-dimensional Penrose-tile lattice

The Main Belt Comets and ice in the Solar System

We review the evidence for buried ice in the asteroid belt; specifically the questions around the so-called Main Belt Comets (MBCs). We summarise the evidence for water throughout the Solar System, and describe the various methods for detecting it, including remote sensing from ultraviolet to radio wavelengths. We review progress in the first decade of study of MBCs, including observations, modelling of ice survival, and discussion on their origins. We then look at which methods will likely be most effective for further progress, including the key challenge of direct detection of (escaping) water in these bodies

Dramatic Impurity Effects On the Charge-Density Wave in Potassium Molybdenum Bronze

Potassium molybdenum bronze, K0.30MoO3, undergoes a charge-density-wave (CDW-) driven phase transition at 180 K, below which nonlinear current-voltage characteristics are observed. Behavior is similar to that observed in NbSe3 and is currently understood based on models which involve charge transport by the CDW. The effects of impurities on CDW phenomena has been a subject of considerable interest. Two types of substitutional doping are possible in the K0.30MoO3 structure. In the alloy system, K0.30-xRbxMoO3, disorder is introduced on the alkali sublattice while in the alloy system, K0.30Mo1-xWxO3, the isoelectronic element tungsten is substituted for molybdenum. We show that the effects of tungsten substitution are very large, larger than such doping effects in other CDW systems, whereas alkali substitution produces only small effects. The data obtained on the K0.30Mo1-xWxO3 system suggest that the low-temperature CDW coherence length becomes very short at low tungsten concentrations

Magnetic Studies of Strontium Lanthanum Copper Oxides

We report measurements of static magnetic susceptibilities for a series of stronium-substituted lanthanum copper oxides prepared under identical conditions. These materials have recently been shown to exhibit bulk superconductivity with high critical temperatures. Measurements of the end member La2CuO4 provie evidence for a phase transition of unknown origin at 260 K. This phase transition is suppressed by the substitution of small amounts of strontium for lanthanum. Understanding the normal-state properties of SrxLa2-xCuO4- may provide important clues to the superconducting behavior of these materials

Heat-Capacity Investigations Near the Normal-Superconducting Transition of YBa2Cu3O7

A high-resolution ac quasiadiabatic calorimeter has been employed to measure the heat-capacity anomaly associated with the normal-superconducting transition of several slightly twinned YBa2Cu3O7 single-crystal samples. The heat-capacity anomaly from one of the samples displays a very sharp 1090% jump on the high-temperature side of anomaly and can be described by a mean-field model based on the BCS theory

New Transition Metal Substituted Cadmium Tellurides

While crystal growth and physical phenomena in the MnxCd-xTe system have been extensively investigated, little is known about the substitution of other transition metals in cadmium telluride. We have examined the substitution of Fe, Co, and Ni for Cd in CdTe. We find that Co and Ni have very low solubilities in CdTe less than a percent while Fe can be substituted to ≈ 10%. Magnetic susceptibility shows that the iron sites couple antiferromagnetically and gives evidence for clustering at higher Fe concentrations. The lattice constant is observed to decrease with increasing iron concentration, behavior similar to that observed in MnxCd1-xTe. Manganese cadmium tellurides have shown interesting magneto-optical properties. Investigations of this newly formed analog. FexCd1-xTe, may reveal interesting behavior in this system as well

Anomalous Pinning Behavior in Slightly-Oxygen-Deficient Ba2YCu3O7-Δ

Single crystals of Ba2YCu3O7-δ were equilibrated at ∼400-500°C to obtain δ∼0.05-0.15, with Tc87-83 K, respectively. Despite the consequent increase in point defects, the field-broadened resistive transition (B|c) ofhe crystal with Tc∼83 K indicates a marked reduction in the pinning energy compared with the fully oxidized case. The c-axis coherence length, inferred from the fluctuation conductivity, does not change. We speculate that the pinning energy decrease is due to a decrease in coupling between superconducting CuO planes due to proximity-effect reduction of the order parameter on CuO chains