Thermal conductivity and diffusivity of Cu-Y alloys produced by different powder metallurgy routes

Full density Cu-1%Y and Cu-0.8%Y alloys have been produced by different powder metallurgy routes and subsequent hot isostatic pressing. Some of the alloys have been subjected to equal channel angular pressing (ECAP) via BC route up to 8 passes. ECAP deformation homogenizes and refines the microstructure up to attaining a sub-micron grain structure. Thermal properties have been characterized by the laser flash method in the temperature range 373–773 K. The ECAP process, irrespective of the production route, enhanced the thermal conductivity to values similar to those for CuCrZr (ITER grade). The linear thermal expansion coefficient was temperature independent for all materials

Variational Mote Carlo Study of Flat Band Ferromagnetism -- Application to CeRh_3 B_2

A new mechanism for ferromagnetism in CeRh_3B_2 is proposed on the basis of variational Monte Carlo results. In a one-dimensional Anderson lattice where each 4f electron hybridizes with a ligand orbital between neighboring Ce sites, ferromagnetism is stabilized due to a nearly flat band which is a mixture of conduction and 4f electron states. Because of the strong spin-orbit interaction in 4f electron states, and of considerable amount of hybridization in the nearly flat band, the magnetic moments from 4f and conduction electrons tend to cancel each other. The resultant ferromagnetic moment becomes smaller as compared with the local 4f moment, and the Fermi surface in the ferromagnetic ground state is hardly affected by the presence of 4f electrons. These theoretical results are consistent with experimental observations in CeRh_3B_2 by neutron scattering and dHvA effects.Comment: to be published in J.Phys.Soc.Jp

Damage threshold of CuCrFeTiV high entropy alloys for nuclear fusion reactors

A CuCrFeTiV high entropy alloy was prepared and irradiated with swift heavy ions in order to check its adequacy for use as a thermal barrier in future nuclear fusion reactors. The alloy was prepared from the elemental powders by ball milling, followed by consolidation by spark plasma sintering at 1178 K and 65 MPa. The samples were then irradiated at room temperature with 300 keV Ar+ ions with fluences in the 3 × 1015 to 3 × 1018 Ar+/cm2 range to mimic neutron-induced damage accumulation during a duty cycle of a fusion reactor. Structural changes were investigated by X-ray diffraction, and scanning electron microscopy and scanning transmission electron microscopy, both coupled with X-ray energy dispersive spectroscopy. Surface irradiation damage was detected for high fluences (3 × 1018 Ar+/cm2) with formation of blisters of up to 1 μm in diameter. Cross-sectional scanning transmission electron microscopy showed the presence of intergranular cavities only in the sample irradiated with 3 × 1018 Ar+/cm2, while all irradiation experiments produced intragranular nanometric-sized bubbles with increased density for higher Ar+ fluence. The Williamson-Hall method revealed a decrease in the average crystallite size and an increase in residual strain with increasing fluence, consistent with the formation of Ar+ bubbles at the irradiated surface.publishedVersio

Behavior of Cu-Y2O3 and CuCrZr-Y2O3 composites before and after irradiation

ABSTRACT: The Cu-Y2O3 and CuCrZr-Y2O3 materials have been devised as thermal barriers in nuclear fusion reactors. It is expected that in the nuclear environments, the materials should be working on extreme conditions of irradiation. In this work the Cu-Y2O3 and CuCrZr-Y2O3 were prepared and then irradiated in order to understand the surface irradiation resistance of the material. The composites were prepared in a glove box and consolidated with spark plasma sintering. The microstructures revealed regions of Y2O3 dispersion and Y2O3 agglomerates both in the Cu matrix and in the CuCrZr. The irradiated samples did not show any surface modification indicating that the materials seem to be irradiation resistant in the present situation. The thermal conductivity values for all the samples measured are lower than pure Cu and higher than pure W, however are higher than those expected, and therefore, the application of these materials as thermal barriers is compromised.info:eu-repo/semantics/publishedVersio

Fabrication and properties of the SITE-SiCf/SiC composite

Continuous SiC-fiber-reinforced SiC composite (SiCf/SiC) is an attractive candidate structural material for advanced concepts of future fusion power plants, mainly due to the favourable intrinsic properties of the SiC ceramics, i.e. high temperature- and chemical stability, low neutron activation and afterheat levels as well as due to the fact that it is the only nonmagnetic material proposed. Fabrication of such composites is a very challenging task due to limitations and requirements set for fusion-relevant structural materials

Thermodynamic Studies on Non Centrosymmetric Superconductors by AC Calorimetry under High Pressures

We investigated the non centrosymmetric superconductors CePt$_3$Si and UIr by the ac heat capacity measurement under pressures. We determined the pressure phase diagrams of these compounds. In CePt$_3$Si, the N\'{e}el temperature $T_{\rm N}$ = 2.2 K decreases with increasing pressure and becomes zero at the critical pressure $P_{\rm AF}$ $\simeq$ 0.6 GPa. On the other hand, the superconducting phase exists in a wider pressure region from ambient pressure to $P_{\rm AF}$ $\simeq$ 1.5 GPa. The phase diagram of CePt$_3$Si is very unique and has never been reported before for other heavy fermion superconductors. In UIr, the heat capacity shows an anomaly at the Curie temperature $T_{\rm C1}$ = 46 K at ambient pressure, and the heat capacity anomaly shifts to lower temperatures with increasing pressure. The present pressure dependence of $T_{\rm C1}$ was consistent with the previous studies by the resistivity and magnetization measurements. Previous ac magnetic susceptibility and resistivity measurements suggested the existence of three ferromagnetic phases, FM1-3. $C_{\rm ac}$ shows a bending structure at 1.98, 2.21, and 2.40 GPa .The temperatures where these anomalies are observed are close to the phase boundary of the FM3 phase.Comment: This paper was presented at the international workshop ``Novel Pressure-induced Phenomena in Condensed Matter Systems(NP2CMS)" August 26-29 2006, Fukuoka Japa

Non-Centrosymmetric Heavy-Fermion Superconductors

In this chapter we discuss the physical properties of a particular family of non-centrosymmetric superconductors belonging to the class heavy-fermion compounds. This group includes the ferromagnet UIr and the antiferromagnets CeRhSi3, CeIrSi3, CeCoGe3, CeIrGe3 and CePt3Si, of which all but CePt3Si become superconducting only under pressure. Each of these superconductors has intriguing and interesting properties. We first analyze CePt3Si, then review CeRhSi3, CeIrSi3, CeCoGe3 and CeIrGe3, which are very similar to each other in their magnetic and electrical properties, and finally discuss UIr. For each material we discuss the crystal structure, magnetic order, occurrence of superconductivity, phase diagram, characteristic parameters, superconducting properties and pairing states. We present an overview of the similarities and differences between all these six compounds at the end.Comment: To appear in "Non-Centrosymmetric Superconductors: Introduction and Overview", Lecture Notes in Physics 847, edited by E. Bauer and M. Sigrist (Springer-Verlag, Berlin Heidelberg, 2012) Chap. 2, pp. 35-7

Critical Scaling of the Magnetization and Magnetostriction in the Weak Itinerant Ferromagnet UIr

The weak itinerant ferromagnet UIr is studied by magnetization and magnetostriction measurements. Critical behavior, which surprisingly extends up to several Tesla, is observed at the Curie temperature $T_C\simeq45$ K and is analyzed using Arrott and Maxwell relations. Critical exponents are found that do not match with any of the well-known universality classes. The low-temperature magnetization $M_s\simeq0.5$ $\mu_B \cong const.$ below 3 T rises towards higher fields and converges asymptotically around 50 T with the magnetization at $T_C$. From the magnetostriction and magnetization data, we extract the uniaxial pressure dependences of $T_C$, using a new method presented here, and of $M_s$. These results should serve as a basis for understanding spin fluctuations in anisotropic itinerant ferromagnets.Comment: 4 pages, 3 figure

Field-induced phase transitions and giant magnetoresistance in Dy Dy3CoD{y_3}Co Co single crystals

PACS. 72.15.Eb Electrical and thermal conduction in crystalline metals and alloys, 75.30.Kz Magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.), 75.40.-s Critical-point effects, specific heats, short-range order,