Metal Borocarbides Research Articles

Electronic structure and superconductivity of nonmagnetic transition metal borocarbides

The electronic structure of tetragonal (RC(N))m(TB)2, m=1−3, compounds, with R= Y,Lu,La, T=Ni,Pt is studied. Total and partial densities of states N(E) are calculated and compared with orbital resolved x-ray absorption data. Special attention is paid to the structure of N(E) near the Fermi-level and its consequences for thermodynamic properties in the superconducting and the normal states. A medium el-ph coupling constant 0.5≤λ≤ 1.2 is found. There is no simple correlation between N(0) and Tc. The analysis of the upper critical field reveals the presence of at least two groups of electrons with quite different Fermi velocities vFin accord with dHvA data, and with calculated distributions of vFaround the Fermi surface

Rare earth metal borocarbides: Examples of coordination compounds in solid-state chemistry

A variety of structural types of solid-state rare earth metal borocarbide materials containing infinite two-dimensional layers, infinite one-dimensional chains, or finite groups of boron and carbon are reviewed. Although the solid-state language of Zintl–Klemm concept, band structures, and density of states is necessary to rationalize this kind of compound, they are governed by the laws that guide most molecular and solid-state structural chemistry: the relationship between the electron count and the structural arrangement. More precisely, one could think of these materials as solid-state coordination compounds in which the classical bonding scheme of σ-donation, sometimes supplemented by some π-backdonation, is present.

ChemInform Abstract: Superconductivity and Magnetism in Quaternary F (F: Y or f Elements) Transition Metal Borocarbides and Magnetic Properties of LnNi4B (R: Y or Rare Earth)

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Superconductivity and magnetism in quaternary F (F  Y or f elements) transition metal borocarbides and magnetic properties of RNi 4B (R  Y or rare earth)

Our recent pioneering discovery of bulk superconductivity (SC) in YNiBC at an elevated temperature ( T c ≈ 12 K) has triggered intense research activity in borocarbide materials containing 4f and 5f elements. This was an offshoot of our studies of RNi 4B (R  Y or rare earth) series of materials. Replacing Ni by Pd produces a superconducting phase in YPdBC with record T c (≈ 23 K) in bulk intermetallics. Here we present the results of some of our investigations in borocarbide materials. Our specific heat studies suggest that YNi 2B 2C is a strong-coupling type II superconductor. The temperature dependence of H c2( T) is rather unusual. μ-SR measurements indicate the possibility that Ni atoms carry a magnetic moment. SC and magnetism coexist in RNi 2B 2C (R  Ho, Er or Tm). CeNi 2B 2C is found to be a mixed-valence material. NdNi 2B 2C and GdNi 2B 2C, which we have been able to synthesize as a single phase, do not superconduct but order magnetically at T m ≈ 4.5 K and T m ≈ 19 K respectively. We have observed SC in ThNiBC and ThPdBC systems. There are at least two superconducting transitions in the Pd-containing systems ThPdBC and YPdBC. YT 2B 2C (T  Co, Ir, Rh or Os) crystallize in a YNi 2B 2C-type structure but do not superconduct down to 4.2 K. Substitution studies show that Th (non-magnetic) and Gd (magnetic) suppress T c by nearly the same extent. We also summarize our results on RNi 4B series of materials which show remarkable physical properties.

Superconductivity at an elevated temperature in a new class of quaternary rare earth-transition metal boro-carbides

Our discovery of superconductivity at an elevated temperature (∼ 12 K) in the system YNiBC has opened up an entirely new area of research in superconductivity of intermetallics. We briefly present the results of our recent studies on magnetic history effects in YNi 2B 2C, the coexistence of superconductivity and magnetism in ErNi 2B 2C, the effect of substituents on superconductivity in YNi 2B 2C, the mixed valence of Ce in CeNi 2B 2C and superconductivity in Th-based borocarbides.

Superconductivity and magnetism in quaternary borocarbides

We present a status report of the new rare earth transition metal borocarbides and discuss in particular the magnetic properties, results of heat capacity measurements in connection with pressure experiments together with band structure calculations and properties of the superconducting state.

EPR and microwave-absorption studies in a new class of superconductors. Quarternary rare-earth transition metal borocarbides YPd 5B 3C 0.35 and YNi 2B 2C

Microwave-absorption techniques have been used for investigating the superconducting behaviour of the recently discovered quarternary rare-earth transition metal borocarbide superconductors. The direct microwave absorption shows a steep drop at 23 K in YPd 5B 3C 0.35. Besides the expected drop in microwave absorption observed in YNi 2B 2C at 15.5 K, there is another drop at ∼ 23 K, the origin of which is not understood at present. We have estimated the value of the lower critical field H c1 (∼ 20 G at 10 K) in the two cases from magnetic-field-modulated low-field microwave-absorption measurements.