(Pt1–xCux)3Cu2B and Pt9Cu3B5, the first examples of copper platinum borides. Observation of superconductivity in a novel boron filled β-Mn-type compound

Abstract New ternary copper platinum borides have been synthesized by arc melting of pure elements followed by annealing at 600 °C. The structures have been studied by X-ray single crystal and powder diffraction. (Pt 1− x Cu x ) 3 Cu 2 B ( x =0.33) forms a B-filled β -Mn-type structure (space group P 4 1 32; a =0.6671(1) nm). Cu atoms are distributed preferentially on the 8 c atom sites, whereas the 12 d site is randomly occupied by Pt and Cu atoms (0.670(4) Pt±0.330(4) Cu). Boron is located in octahedral voids of the parent β -Mn-type structure. Pt 9 Cu 3 B 5 (space group P -62 m ; a =0.9048(3) nm, c =0.2908(1) nm) adopts the Pt 9 Zn 3 B 5– δ -type structure. It has a columnar architecture along the short translation vector exhibiting three kinds of [Pt 6 ] trigonal prism columns (boron filled, boron semi-filled and empty) and Pt channels with a pentagonal cross section filled with Cu atoms. The striking structural feature is a [Pt 6 ] cluster in form of an empty trigonal prism at the origin of the unit cell, which is surrounded by coupled [BPt 6 ] and [Pt 6 ] trigonal prisms, rotated perpendicularly to the central one. There is no B–B contact as well as Cu–B contact in the structure. The relationships of Pt 9 Cu 3 B 5 structure with the structure of Ti 1+ x Os 2− x RuB 2 as well as with the structure families of metal sulfides and aluminides have been elucidated. (Pt 1– x Cu x ) 3 Cu 2 B ( x =0.3) (B-filled β -Mn-type structure) is a bulk superconductor with a transition temperature of about 2.06 K and an upper critical field μ 0 H C2 (0) WHH of 1.2 T, whereas no superconducting transition has been observed up to 0.3 K in Pt 9 Cu 3 B 5 (Pt 9 Zn 3 B 5– δ -type structure) from electrical resistivity measurements.