Electrical Conductivity and Thermoelectrical Parameters of Argyrodite-Type Cu7 – xPS6 – xIx Mixed Crystals

Cu7−xPS6−xIx mixed crystals were grown by the direct crystallization from a melt. The electrical conductivity is measured in the frequency range from 10 Hz to 300 kHz and in the temperature interval 293–383 K. The frequency, temperature, and compositional dependences of the electrical conductivity for Cu7−xPS6−xIx mixed crystals are studied. The measurements of thermoelectric parameters of Cu7−xPS6−xIx mixed crystals are carried out in the temperature interval 293–383 K. The compositional behaviors of the electrical conductivity, activation energy, Seebeck coefficient, and power factor are investigated. The interrelation between the structural, electrical, and thermoelectrical properties is analyzed.

Zircon in mantle eclogite xenoliths: a review

Very few zircon-bearing, kimberlite-hosted mantle eclogite xenoliths have been identified to date; however, the zircon they contain is crucial for our understanding of subcratonic lithospheric mantle evolution and eclogite genesis. In this study, we constrain the characteristics of zircon from mantle eclogite xenoliths based on existing mineralogical and geochemical data from zircons from different geological settings, and on the inferred origin of mantle eclogites. Given the likely origin and subsequent evolution of mantle eclogites, we infer that the xenoliths can contain zircons with magmatic, metamorphic and xenogenic (i.e. kimberlitic zircon) origins. Magmatic zircon can be inherited from low-pressure mafic oceanic crust precursors, or might form during direct crystallization of eclogites from primary mantle-derived melts at mantle pressures. Metamorphic zircon within mantle eclogites has a number of possible origins, ranging from low-pressure hydrothermal alteration of oceanic crustal protoliths to metasomatism related to kimberlite magmatism. This study outlines a possible approach for the identification of inherited magmatic zircon within subduction-related mantle eclogites as well as xenogenic kimberlitic zircon within all types of mantle eclogites. We demonstrate this approach using zircon grains from kimberlite-hosted eclogite xenoliths from the Kasai Craton, which reveals that most, if not all, of these zircons were most likely incorporated as a result of laboratory-based contamination.

Эффективная масса, подвижность носителей заряда и решеточная теплопроводность в нанокомпозитных термоэлектриках на основе халькогенидов висмута и сурьмы

In the p-type thermoelectrics based on bismuth chalcogenides and antimony with an excess bismuth, the density of states effective mass m/m0 increases in nanocomposite and nanostructured solid solutions compared with the base material obtained by the direct crystallization method. It is shown that an increase in m/m0 is associated with an increase in the effective scattering parameter reff and amplifying the relaxation time of energy, which is typical for topological insulators. The material parameter beta, proportional to the thermoelectric efficiency of ZT, at temperatures below room increases stronger in nanostructured composition than in a nanocomposite with the inclusions of SiO2 due to the growth of m/m0 and decrease the lattice thermal conductivity κL. At high temperatures in the range of 300-500 to the greatest growth of the parameter beta in the base material associated with higher mobility.

Origin of noble-metal nuggets in sulfide-saturated arc magmas: A case study of olivine-hosted sulfide melt inclusions from the Tolbachik volcano (Kamchatka, Russia)

Minerals that contain platinum-group elements (PGEs) and occur in some magmatic Cu-Ni sulfide deposits have been ascribed to crystallization from an originally PGE-rich sulfide liquid. The occurrence of PGE-bearing minerals (PGMs) in some sulfide-undersaturated primitive melts has been envisaged and recently reported, whereas direct crystallization of PGMs in sulfide-saturated silicate magmas is seemingly hindered by strong partitioning of PGE into immiscible sulfide melts. In this study, we discovered abundant nanoparticles containing noble metals in association with sulfide melt inclusions entrapped inside primitive olivine phenocrysts (Fo85–92) from the recent basaltic magma of the Tolbachik volcano (Kamchatka arc, Russia). These nuggets occur in swarms on the surface of the sulfide globules and are represented by native metals, sulfides, and alloys of Pd, Pt, Au, Pb, and Bi. The nuggets on different globules can be either Pd- or Pt-rich nuggets, and the compositions are highly variable, even among adjacent nuggets. We argue that the diffusive supply of Pd from the external nuggets can be responsible for significant uptake of Pd (up to 2 wt%) in the sulfide melt. We consider direct crystallization of PGMs in a primitive basaltic melt undergoing sulfide unmixing, and possibly sulfide breakdown due to oxidation, as another mechanism additional to their “classic” origin from the PGE-rich sulfide melt in response to solidification.