Electrical resistivities of the uranium carbides

Matsui, H.; Tamaki, Masayoshi; Nasu, Shōichi; Kurasawa, T.

doi:10.1016/0022-3697(80)90209-7

Cited by 25 publications

(8 citation statements)

References 12 publications

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“…9 This transformation has been studied for a number of metal dicarbides, and the transition temperature varies from 100 °C for BaC 2 to 1765 °C for UC 2 . 12,13 A third, high pressure polymorph of UC 2 also exists, which requires 17.6 GPa to transition from the low temperature tetragonal structure to a high pressure hexagonal structure. 10 We originally attempted to grow heteroepitaxial thin films of uranium carbides on substrate materials such as c-cut sapphire and lanthanum aluminum oxide (LAO).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…An enlargement of the near E F region in the inset of Figure 2 shows a metallic 5f feature cut by E F , consistent with previously measured conductivity in UC 2 . 13 The data in the Figure 2a inset was taken at 21.2 eV photon energy and 8 K so that the details of the Fermi energy are apparent. In this inset, one can see that the tail of the spectral weight extends through the Fermi energy but is mostly attributed to U 5f intensity which is consistent with the metallic but limited conductivity of the UC 2 material.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Preparation of Epitaxial Uranium Dicarbide Thin Films by Polymer-Assisted Deposition

et al. 2013

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High quality epitaxial thin films of cubic UC 2 were synthesized using a solution based technique. The films were characterized using XRD, UPS, Raman, and resistivity. The substrate lattice is yttrium stabilized zirconia and serves to stabilize the high temperature cubic phaseof UC 2 (>1765°C) at room temperature. The resistivity and UPS data indicate that UC 2 has relatively low electrical conductivity consistent with HSE hybrid DFT calculations showing a narrow band gap. In situ XRD measurements show that the UC 2 films oxidize to U 3 O 8 above 200°C. KEYWORDS: actinide carbide, epitaxial thin film, nuclear energy ■ INTRODUCTIONThe carbides of uranium have received much attention in recent years as potential fuel sources for Generation IV nuclear reactors. While at least six different Generation IV reactor concepts are currently being explored, the consensus is that new nuclear fuels must be developed for these advanced systems to maintain reasonable operating temperatures. 1 Two such possibilities are uranium carbide (UC) and uranium dicarbide (UC 2 ), which have much higher thermal conductivities than conventional nuclear fuels such as UO 2 , mixed-metal oxides, and ThO 2 . This would have the effect of lowering fuel centerline temperatures, which would increase operational safety, fuel lifetime, and efficiency. In addition to their potential as nuclear fuels, uranium carbide has been used for many years as a target material in the production of neutron-rich isotopes. 2 In order to gain a more in-depth understanding of the properties of uranium carbide materials, we have synthesized and characterized epitaxial thin films of UC 2 . These thin films are of high purity and are nearly single crystal in quality and thus facilitate high quality measurements to validate computational models. Herein, we report the synthesis and characterization of these thin films including valence band photoemission, Raman spectroscopy, electrical conductivity, and in situ XRD studies of oxidation.Uranium carbides have been known for quite some time, with U 2 C 3 and UC 2 first mentioned over a century ago. 3 These bulk materials were originally prepared by treating U 3 O 8 with graphite in an electric arc furnace. 3a,c,4 While carbothermic methods are still used to prepare uranium carbides, 5 other strategies such as the reaction of uranium metal with methane have been used to prepare UC at much lower temperature. 3b In spite of the wealth of knowledge on these materials, little is known about uranium carbide thin films. In 2004, researchers used sputter codeposition to generate films that were found to have compositions UC 1.2 and UC 1.6 . X-ray diffraction studies revealed the presence of polycrystalline UC and UC 2 in these films; however, the diffraction peaks were broadened possibly due to stress, inhomogeneities, or the presence of amorphous material. 6 Herein, we report the first preparation of singlecrystal quality UC 2 by polymer-assisted deposition (PAD). In this process, metal polymer solutions are used as film precursor...

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

Preparation of Epitaxial Uranium Dicarbide Thin Films by Polymer-Assisted Deposition

et al. 2013

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“…The U-U distance for UC is just ∼3.5Å, and indeed this compound is a Pauli paramagnet at the edge of a magnetic instability, 18 with no localized moment and a Sommerfeld coefficient γ ∼ 20 mJ mol −1 K −2 . 19,20 The tetragonal α-UC 2 is also metallic, 21 with the 5f electrons contributing in part to the metallic bonding and in part being transferred to the C 2p states. 22 The U-U distances in α-UC 2 are ∼3.54 and ∼3.90Å, larger than the Hill limit.…”

Section: Introductionmentioning

confidence: 99%

“…The other U-U distances imposed by the U 2 C 3 structure are 3.38 and 3.68Å, slightly below and above the Hill limit. The magnetic susceptibility has been reported down to 4 K. A broad maximum observed at T * ∼ 59 K, 25 accompanied by a kink in the electrical resistivity, 21 was initially interpreted to signal the onset of antiferromagnetic order. 26,27 Below T * , the electrical resistivity ρ(T ) increases as T 2 , whereas above T * it increases up to about 1100 K where it saturates, 21 with an overall behavior similar to the one observed for the itinerant antiferromagnet UGa 3 .…”

Section: Introductionmentioning

confidence: 99%

“…The magnetic susceptibility has been reported down to 4 K. A broad maximum observed at T * ∼ 59 K, 25 accompanied by a kink in the electrical resistivity, 21 was initially interpreted to signal the onset of antiferromagnetic order. 26,27 Below T * , the electrical resistivity ρ(T ) increases as T 2 , whereas above T * it increases up to about 1100 K where it saturates, 21 with an overall behavior similar to the one observed for the itinerant antiferromagnet UGa 3 . 28 However, no anomaly in the temperature dependence of the specific heat was observed at T * , 29 and both neutron-diffraction 27 and 13 C Knight-shift measurements 30 failed to provide evidence for long-range magnetic order or for structural distortions down to 4 K. On the other hand, the broad maximum and the overall susceptibility curve at intermediate temperatures can be reproduced by a logarithmic term of the form (T 2 + cT 4 )ln(T /T ).…”

Section: Introductionmentioning

confidence: 99%

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Evidence for persistent spin fluctuations in uranium sesquicarbide

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The low-temperature magnetic susceptibility, heat capacity, and electrical resistivity of uranium sesquicarbide have been determined down to 2 K by combining measurements carried out on samples of U 2 C 3 , containing UC as minority phase, and on pure UC specimens. The presence of spin fluctuations with characteristic temperature T SF = 7 K is revealed by a nonanalytic contribution to the specific heat behaving (well below T SF ) as T 3 ln(T /T SF ), and confirmed by a T 2 increase of the electrical resistivity and a 1 − κT 2 decrease of the low-temperature magnetic susceptibility. The analysis of the specific-heat data above T SF provides a Debye temperature D ≈ 256 K and a moderate high value of the Sommerfeld coefficient, γ ≈ 42 mJ mol −1 U K −2 . The zero-temperature many-body enhancement of the electron mass is found to be m * /m ≈ 2.7. Our data rule out the occurrence of magnetic ordering in U 2 C 3 . First-principles electronic structure calculations support the absence of a magnetically ordered ground state but suggest that dynamical spin fluctuations are responsible for the electron mass enhancement.

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Nonoxide Ceramic Nuclear Fuels

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2006

Materials Science and Technology

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Electrical resistivities of the uranium carbides

Cited by 25 publications

References 12 publications

Preparation of Epitaxial Uranium Dicarbide Thin Films by Polymer-Assisted Deposition

Preparation of Epitaxial Uranium Dicarbide Thin Films by Polymer-Assisted Deposition

Evidence for persistent spin fluctuations in uranium sesquicarbide

Nonoxide Ceramic Nuclear Fuels

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