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L. Salamakha, O. Sologub, B. Stöger, P. Rogl, M. Waas, H. Michor, E. Bauer:
"Th₇Fe₃-Type Related Structures in Pd(Pt)-Cu-B Systems: Pd₆CuB₃- A New Structure Type for Borides";
Chemistry - A European Journal, 23 (2017), 4810 - 4817.

A new member of the series of Th7Fe3-type derivative structures, h-(Pd0.86Cu0.14)7B3 (≡Pd6.02Cu0.98B3, unique structure type Pd6CuB3, space group P63cm, a=12.9426(9) Å, c=4.8697(4) Å, single-crystal X-ray diffraction (XRD) data) was obtained from as cast alloys and alloys annealed at 600-650 °C. Further substitution of Cu by Pd led to formation of a Mn7C3-type structure, o-(Pd0.93Cu0.07)7B3 (≡Pd6.51Cu0.49B3, space group Pnma, a=4.8971(2) Å, b=7.5353(3) Å, c=12.9743(6) Å, single-crystal XRD). Isotypic LT h-(Pt0.70Cu0.30)7B3 (≡Pt4.90Cu2.10B3) was observed in the Pt-Cu-B system as a low-temperature (LT) phase (T≤600 °C) (powder XRD), whereas the Th7Fe3-type (high-temperature (HT) h-(Pt0.73Cu0.27)7B3≡Pt5.11Cu1.89B3, space group P63mc, a=7.4671(1) Å, c=4.9039(1) Å, powder XRD) proved to be stable at high temperature. The three structures are built of columns of face connected metal octahedra and columns of metal tetrahedra alternatingly fused by common faces and vertices. Boron atoms are found in trigonal prisms formed by metal atoms. The volumes of the three new Th7Fe3-type derivative borides relate as 1:2:3. Superconductivity was discovered for Pt4.9Cu2.1B3 (Pd6CuB3-type) and Pt5.1Cu1.9B3 (Th7Fe3-type) below 0.67 and 0.66 K, respectively. Despite the close value of the transition temperature the values of the upper critical field at 0 K differ as 0.37 T and 0.27 T for the two compounds.

boride intermetallics, crystal structures

http://dx.doi.org/10.1002/chem.201602767