Superconductivity in the Th0.93Zr0.07B12 compound with UB12 prototype structure

Abstract

In this work, we report superconductivity at 5.5 K in the new pseudo-ternary Th 0.93 Zr 0.07 B 12 compound. We show clearly evidence that appropriate amounts of Zr substitution at the Th site induce the stabilization of the UB 12 prototype structure at ambient pressure. The superconducting bulk properties of Th 0.93 Zr 0.07 B 12 are confirmed by means of magnetization, electronic transport properties and specific heat measurements. The H-T phase diagrams based on magnetization and magnetoresistance measurements yield μ 0 H c1 (0) = 6 mT and μ 0 H c2 (0) = 98 mT and allow us to estimate the coherence length ξ o ∼ 57.9 nm and the penetration depth λ L ∼ 234 nm at zero kelvin.

Rediscovering the Crystal Chemistry of Borides

“…The primary requirement for the formation of the cubic-UB 12 structure is the radius of the metal in a 12 coordinate environment, with yttrium and zirconium being the largest and smallest metals, respectively, capable of accommodating a boron cuboctahedron cage, with slight size deviation rendering the metal dodecaboride unstable under ambient pressure. [102,133,134,306] Notable exceptions are HfB 12 , ThB 12 , and GdB 12 all of which in pure form can only be synthesized under high pressure, [96,134] or stabilized as a solid solution under ambient pressure: Y 1−x Hf x B 12 , [60] Th 1−x Zr x B 12 , [307] and Zr 1−x Gd x B 12.…”

Synthesis and Characterization of Single-Phase Metal Dodecaboride Solid Solutions: Zr1–xYxB12 and Zr1–xUxB12

“…The baseline run of the sample holder was subtracted from the sample signal. All runs were done under an applied field of 10 –3 Tesla (10 Oersted) …”

Superhard Mixed Transition Metal Dodecaborides

“…The cages are usually arranged in a face-centered cubic close packed arrangement, forming the cubic-UB 12 ( Fm 3̅ m ) structure; however, ScB 12 forms its own structural type, tetragonal-ScB 12 ( I4/mmm ), where the cuboctahedra are arranged in a body-centered tetragonal close-packed structure (Figure ). Dodecaborides are known to exist for a number of metals: transition metals (Zr, Hf, Y, and Sc), lanthanides (Tb, Dy, Ho, Er, Tm, Yb, and Lu), and actinides (U and Th). , For the most part, the aforementioned dodecaborides have been prepared via arc melting from the elements or by borothermal reduction of the metal oxide under vacuum to yield fully dense ingots or compacts, respectively. ,− HfB 12 and ThB 12 are especially interesting because in pure form they can only be formed under high pressure (6.5 GPa) and high temperature (1660 °C); however, they can be stabilized under ambient pressure in the matrices of ZrB 12 (Zr 1– x Th x B 12 ) and YB 12 (Y 1– x Hf x B 12 )…”

“…20,21 For the most part, the aforementioned dodecaborides have been prepared via arc melting from the elements or by borothermal reduction of the metal oxide under vacuum to yield fully dense ingots or compacts, respectively. 17,22−28 HfB 12 and ThB 12 are especially interesting because in pure form they can only be formed under high pressure (6.5 GPa) and high temperature (1660 °C); 29 however, they can be stabilized under ambient pressure in the matrices of ZrB 12 (Zr 1−x Th x B 12 ) 24 and YB 12 (Y 1−x Hf x B 12 ). 25 Pure dodecaborides are superhard, which can be attributed to their high isotropy and stiff metal−boron bonds as well as boron−boron bonds forming the cuboctahedra.…”