About: This article is published in Physical Review Letters.The article was published on 1964-08-17 and is currently open access. It has received 22 citation(s) till now. The article focuses on the topic(s): Germanium telluride & Superconductivity.
Abstract: Publisher Summary This chapter discusses rare earth pnictides. The rare earth elements are transitional in their chemical properties between the alkaline-earth elements, especially Ba, and the 5d transition elements Hf, Ta. With certain exceptions they behave like transition elements of the Sc group with additional f electrons in discrete levels. The exceptions are mainly because of the high stability of the empty, half- or completely-filled 4f shell. Certain compounds formed by Eu and Yb, in some cases also Sm and Tm, therefore, show close similarities with the corresponding alkaline-earth compounds whereas Ce and Tb in fluorides and oxides resemble Hf4+ and Th4+ compounds. The chapter discusses the preparation of the rare earth pnictides. All lanthanide elements react in the solid state with pnigogen vapors. Except for nitrogen, the chemical reaction takes place at temperatures below the melting point of the elementary pnigogen; therefore, they can be performed in fused-silica tubes. The reaction products are microcrystalline powders, which usually serve only as starting materials for single-crystal growth.
Abstract: The discoveries of superconductivity in the heavily-boron doped semiconductors diamond (C:B) in 2004 [Ekimov et al., Nature (London) 428, 542 (2004)] and silicon (Si:B) in 2006 [Bustarret et al., Nature (London) 444, 465 (2006)] have renewed the interest in the physics of the superconducting state of doped semiconductors. Recently, we discovered superconductivity in the closely related ``mixed'' system heavily boron-doped silcon carbide (SiC:B) [Ren et al., J. Phys. Soc. Jpn. 76, 103710 (2007)]. Interestingly, the latter compound is a type-I superconductor whereas the two aforementioned materials are type II. In this paper, we present an extensive analysis of our recent specific-heat study, as well as the band structure and expected Fermi surfaces. We observe an apparent quadratic temperature dependence of the electronic specific heat in the superconducting state. Possible reasons are a nodal gap structure or a residual density of states due to nonsuperconducting parts of the sample. The basic superconducting parameters are estimated in a Ginzburg-Landau framework. We compare and discuss our results with those reported for C:B and Si:B. Finally, we comment on possible origins of the difference in the superconductivity of SiC:B compared to the two ``parent'' materials C:B and Si:B.
Abstract: In order to optimize the binary Ge-Te system available experimental data were critically compiled from the literature. The cubic high-temperature β-phase and the rhomboedric room-temperature α-phase were described by a two-sublattice model with one kind of defect (vacancies on germanium sites). The room-temperature orthorhombic γ-phase was treated as a stoichiometric compound, as there is a lack of information about its solubility. The liquid phase was modelled by the the associate model with one kind of associate, namely ‘GeTe’. A set of thermodynamic parameters was obtained and the calculated phase diagram is presented.
Abstract: The measured transport properties of non-stoichiometric GeTe have been satisfactorily analysed on the basis of a two-carrier model and the various band parameters have been evaluated. In particular the variation of the carrier density of the system with composition has been obtained and then compared to the total number of excess atoms in the non-stoichiometric lattice. It is found that the defects occurring in GeTe due to these excess atoms are of a complex nature, except for compositions close to stoichiometry where singly ionized vacancies are the dominant defect.