다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

BoltzTraP. A code for calculating band-structure dependent quantities

日本物理学会誌及びJournal of the Physical Society of Japanの月刊について

Physical Review B

Herein we cover the key concepts in the field of thermoelectric materials research, present the current understanding, and show the latest developments. Current research is aimed at increasing the thermoelectric figure of merit (ZT) by maximizing the power factor and/or minimizing the thermal conductivity. Attempts at maximizing the power factor include the development of new materials, optimization of existing materials by doping, and the exploration of nanoscale materials. The minimization of the thermal conductivity can come through solid-solution alloying, use of materials with intrinsically low thermal conductivity, and nanostructuring. Herein we describe the most promising bulk materials with emphasis on results from the last decade. Single-phase bulk materials are discussed in terms of chemistry, crystal structure, physical properties, and optimization of thermoelectric performance. The new opportunities for enhanced performance bulk nanostructured composite materials are examined and a look into the not so distant future is attempted.

New and Old Concepts in Thermoelectric Materials

Crystal structure of Ba8Ga4.44Ge39.14square2.42, Ba8Ga8.62Ge36square1.38, and Ba8Ga12.35Ge33.27square0.38, three clathrate-I variants

We investigate the low temperature properties of the recently discovered clathrates Ba 6 Ge 25 and Na 2 Ba 4 Ge 25 by tuning both materials with hydrostatic pressure. At ambient pressure, Ba 6 Ge 25 undergoes a two-step structural phase transition between 230 K and 180 K from metallic behavior to a high-resistivity state. A superconducting transition occurs at T_{C}\approx 0.24\,\hbox{K} out of the resulting bad metal ( \rho_{0}\approx 1.5\,\hbox{m}\Omega\;\hbox{cm} ). With increasing pressure, the structural phase transition is shifted to lower temperature but T C increases drastically. T C reaches a maximum value of 3.85 K at the critical pressure p_{C}\approx 2.8\,\hbox{GPa} , where the structural distortion is completely suppressed and the system exhibits metallic behavior. On replacing 1/3 of the Ba atoms with Na (Na 2 Ba 4 Ge 25 ), no structural transformation is observed below room temperature, and the superconducting transition temperature is higher (T_{C}(p = 0) \approx 1.05\,\hbox{K}) than in th...

Pressure study on new superconducting germanium clathrates

The title compound was prepared from a mixture of the elements by melting in a glassy carbon crucible (HF furnace, argon atmosphere). EuGa2±xGe4∓x crystallizes in a new structure type (orthorhombic symmetry, space group Cmcm (no. 63), a=4.1571(3) A, b=11.268(1) A, c=13.155(1) A, V=616.2(2) A3, Z=4, Pearson symbol oC28) and is characterized by a 3D framework of 4-fold bonded (4b) E atoms (E=Ga,Ge) with channels parallel to the short a-axis. The europium atoms lie in the E18 holes of those channels. The structure can also be described as an intergrowth of segments from BaAl2Si2 and from a reconstructed diamond type of structure. The (Ga,Ge)24 framework of the title compound is equivalent to that of the Si(Al) atoms in the zeolite structure of CsAlSi5O12. Magnetic susceptibility measurements show that EuGa2±xGe4∓x undergoes a transition from a paramagnetic to an antiferromagnetic ordered state at about 9 K. In the paramagnetic region, an oxidation state of 2+ for europium (μeff≈8 μB/Eu) was obtained. The crystal chemical formula of EuGa2Ge4 is Eu2+[(4b)Ga1−]2[(4b)Ge0]4 according to a charge balanced Zintl phase. This was confirmed by quantum chemical calculations (TB-LMTO, ELF). However, like several other similar compounds, e.g. alkaline earth metal clathrates, EuGa2±xGe4∓x has a metal-like temperature dependence of the electrical resistivity with a low charge-carrier concentration in agreement with the low value of the calculated density of states.

EuGa2.+‐.xGe4.+‐.x: Preparation, Crystal Chemistry and Properties.

Bulk sensitive hard x-ray photoelectron spectroscopy data of the Ce 3p core level of CeRu4Sn6 are presented. Using a combination of full multiplet and configuration iteration model we were able to obtain an accurate lineshape analysis of the data, thereby taking into account correlations for the strong plasmon intensities. We conclude that CeRu4Sn6 is a moderately mixed valence compound with a weight of 8% for the Ce f0 configuration in the ground state.

Ce 3p hard x-ray photoelectron spectroscopy study of the topological Kondo insulator CeRu4Sn6

We study the evolution of the magnetic ground state close to the putative quantum critical point in CeCoGe2.2Si0.8 by using electrical resistivity and specific heat measurements under the same high hydrostatic pressure conditions. The electrical resistivity shows that the antiferromagnetic ordering temperature, TN, is suppressed above PC = 5.9 kbar, with the emergence of non-Fermi liquid behavior. On the other hand, the specific heat shows two different magnetic transitions at 0 kbar, one at TN and another one at Tl ≈ 0.3 K. Both transition temperatures are reduced by pressure but remain finite up to at least 7.2 kbar. The height of the specific heat anomaly at TN, ΔCN, is strongly reduced above PC. These features suggest that the quantum criticality in CeCoGe2.2Si0.8 is governed by disorder.

Silke Paschen

Papers

Crystal structure of Ba8Ga4.44Ge39.14square2.42, Ba8Ga8.62Ge36square1.38, and Ba8Ga12.35Ge33.27square0.38, three clathrate-I variants

Pressure study on new superconducting germanium clathrates

EuGa2.+‐.xGe4.+‐.x: Preparation, Crystal Chemistry and Properties.

Ce 3p hard x-ray photoelectron spectroscopy study of the topological Kondo insulator CeRu4Sn6

High pressure electrical resistivity and specific heat of the heavy fermion compound CeCoGe2.2Si0.8