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

Cage compound Sc5Pt24B12: a Pt-stuffed variant of filled skutterudite structure. Electronic and structural properties

The title compound was obtained from elements via arc melting and its crystal structure was determined from single-crystal X-ray diffraction data (space group Im3̄, a = 10.2042(6) Å). The refinement indicated the occupancy of icosahedral 2a and cubooctahedral 8c sites solely by Sc atoms which leads to the composition Sc5Pt24B12 in contrast to the previously reported ternary stannides of Gd3Ni8Sn16 type (RE5-xM12Sn24(+x) compounds). The compound is the first representative of borides crystallizing with a site exchange variant of this stannide structure type. The structural relationships of the boride structure and filled skutterudite LaFe4P12vs. the Remeika phase of Yb3Rh4Sn13-type are discussed. Analysis of chemical bonding classifies Sc5Pt24B12 as a cage compound exhibiting the ionic interaction of cationic scandium species in the cages of anionic framework, formed by covalently bonded B and Pt atoms. Electronic structure calculations show that the electronic states of atoms centered around the cubooctahedral 8c site, i.e. Sc2 3d-, Pt2 5d- and B 2p-states dominate the density of states (DOS) at the Fermi level EF. Strong effect of spin-orbit coupling on the band structure at the gamma point has been found from density functional theory calculations. Sc5Pt24B12 exhibits superconductivity with a transition temperature of TC = 2.45 K.

Assignment of enantiomorphs for the chiral allotrope β-Mn by diffraction methods

The assignment of enantiomorphs by diffraction methods shows fundamental differences for x-rays and electrons. This is particularly evident for the chiral allotrope of β-Mn. While it is not possible to determine the sense of chirality of β-Mn with established x-ray diffraction methods, Kikuchi pattern simulation of the enantiomorphs reveals differences, if dynamical electron diffraction is considered. Quantitative comparison between experimental and simulated Kikuchi patterns allows the spatially resolved assignment of the enantiomorph in polycrystalline materials of β-Mn, as well as the structurally strongly related phase Pt₂Cu₃B. On the basis of enantiomorph distribution maps, crystals were extracted from enantiopure domains by micropreparation techniques. The x-ray diffraction analyses confirm the assignment of the Kikuchi pattern evaluations for Pt₂Cu₃B and do not allow to distinguish between the enantiomorphs of β-Mn.

Th7 Fe3 -Type Related Structures in Pd(Pt)-Cu-B Systems: Pd6 CuB3 -A New Structure Type for Borides

A new member of the series of Th₇ Fe₃ -type derivative structures, h-(Pd_0.86 Cu_0.14 )₇ B₃ (≡Pd_6.02 Cu_0.98 B₃ , unique structure type Pd₆ CuB₃ , space group P6₃ cm, 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 Mn₇ C₃ -type structure, o-(Pd_0.93 Cu_0.07 )₇ B₃ (≡Pd_6.51 Cu_0.49 B₃ , space group Pnma, a=4.8971(2) Å, b=7.5353(3) Å, c=12.9743(6) Å, single-crystal XRD). Isotypic LT h-(Pt_0.70 Cu_0.30 )₇ B₃ (≡Pt_4.90 Cu_2.10 B₃ ) was observed in the Pt-Cu-B system as a low-temperature (LT) phase (T≤600 °C) (powder XRD), whereas the Th₇ Fe₃ -type (high-temperature (HT) h-(Pt_0.73 Cu_0.27 )₇ B₃ ≡Pt_5.11 Cu_1.89 B₃ , space group P6₃ mc, 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 Th₇ Fe₃ -type derivative borides relate as 1:2:3. Superconductivity was discovered for Pt_4.9 Cu_2.1 B₃ (Pd₆ CuB₃ -type) and Pt_5.1 Cu_1.9 B₃ (Th₇ Fe₃ -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.

Boron induced structure modifications in Pd-Cu-B system: new Ti2Ni-type derivative borides Pd3Cu3B and Pd5Cu5B2

The formation of two distinct derivative structures of Ti2Ni-type, interstitial Pd3Cu3B and substitutive Pd5Cu5B2, has been elucidated in Pd-Cu-B alloys from analysis of X-ray single crystal and powder diffraction data and supported by SEM. The metal atom arrangement in the new boride Pd3Cu3B (space group Fd3m, W3Fe3C-type structure, a = 1.1136(3) nm) follows the pattern of atom distribution in the CdNi-type structure. Pd5Cu5B2 (space group F(4)3m, a = 1.05273(5) nm) exhibits a non-centrosymmetric substitutive derivative of the Ti2Ni-type structure. The reduction of symmetry on passing from Ti2Ni-type structure to Pd5Cu5B2 corresponds to the loss of an inversion centre delivered by an ordered occupation of the Ni position (32e) by dissimilar atoms, Cu and B. In both structures, the boron atom centers Pd forming [BPd6] octahedra in Pd3Cu3B and [BPd6] trigonal prisms in Pd5Cu5B2. Neither a perceptible homogeneity range nor mutual solid solubility was observed for two compounds at 600 °C, while in as cast conditions Pd5Cu5B2 exhibits an extended homogeneity range formed by a partial substitution of Cu atoms (in 24f) by Pd (Pd5+xCu5-xB2, 0 ≤x≤ 1). Electrical resistivity measurements performed on Pd3Cu3B as well as on Pd-poor and Pd-rich termini of Pd5+xCu5-xB2 annealed at 600 °C and in as cast conditions respectively demonstrated the absence of any phase transitions for this compounds in the temperature region from 0.3 K to 300 K.