Filled skutterudite superconductor CaOs4P12 prepared by high-pressure synthesis

In this paper, we report the transport, thermodynamic, and superconducting properties of a new filled skutterudite CaOs4P12 synthesized under high pressure and high temperature. The electrical resistivity of 3.4–4.8 mΩcm, carrier concentration of 3.8–6.1 × 1020cm−3 , and positive Hall coefficient suggest that CaOs4P12 is a semimetal with hole carriers. An anomaly due to low-energy optical modes corresponding to an Einstein temperature of 150 K was observed in the specific heat. Resistivity, dc magnetic susceptibility, and specific heat measurements indicate bulk superconductivity below 2.5 K. The specific heat anomaly at Tc, ∆C/γTc ≈ 1.4, is in agreement with the BardeenCooper-Schrieffer (BCS) value of 1.43. The electron-phonon coupling constant λep is estimated to be 0.47. CaOs4P12 is classified as a BCS-type, weakly coupled type-II superconductor with an upper critical field of Hc2 ≈ 22 kOe and Ginzburg-Landau coherence length of ξ ≈ 12 nm

Zr doped β-rhombohedral boron: widely variable Seebeck coefficient and structural properties

The final publication is available via https://doi.org/10.1016/j.actamat.2016.10.014.The doping effect of zirconium on the structure, Seebeck coefficient and electrical resistivity of β-rhombohedral B was studied for the metal rich concentration range ZrxB100-x, 1.88x2.75. Structural studies proved the Zr atoms mainly in E and D voids for the metal rich compositions, and also elucidated the minor Zr occupancies of the N, F and A1 holes. Seebeck coefficients were effectively shifted within a wide range of positive and negative values by varying the Zr content (p-type: Smax ~ +420 µVK-1 at 673 K for x=1.88; n-type: Smax ~ -670 VK-1 at 473 K for x=2.74). Electrical resistivities generally followed the Mott’s relation for the variable-range hopping. Excellent compositional agreement has been observed between structural and thermoelectric properties discontinuities.Austrian Science Funds (FWF

Incorporation of platinum atoms in a silicon-free boride of the YB50-type structure

The final publication is available via https://doi.org/10.1016/j.jallcom.2016.03.015.A new Pt-doped yttrium boride of the YB50 family, YB45-xPty, x=2.12, y=0.21 (space group Pbam, a=16.6246(4) Å, b=17.6453(4) Å, c=9.4167(2) Å), has been synthesized by arc-melting pure elements and subsequent annealing at 1123 K. A single crystal has been studied in order to assess the Pt-doping effect on the crystal structure. Insertion of Pt in two 4h interstitial sites of the boron atom framework leads to the transformation of -[B12]-[B12]- icosahedral chain into -[B11]-Pt-[B11]- for 38.6% of them as well as, to a lesser extent, induces the disorder into the [B15] polyhedron and neighboring interstitial B site (97.3% vs 2.7%).Austrian Science Funds (FWF

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

The final publication is available via https://doi.org/10.1039/C5DT05058H.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 , W3Fe3C-type structure, a=1.1136(3) nm) follows the pattern of atom distribution in the CdNi-type structure. Pd5Cu5B2 (space group , 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 the axis delivered by an ordered occupation of the Ni position (32e) by dissimilar atoms, Cu and B. In both structures, the boron atom has only contact to 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 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.Austrian Science Funds (FWF

Pd6CuB3 - a new structure type of borides. Th7Fe3-type derivative structures in Pd(Pt)-Cu-B systems

The final publication is available via https://doi.org/10.1002/chem.201602767.A missing member of the series of Th7Fe3-type derivative structures, h-(Pd0.864Cu0.136)7B3 (unique structure type Pd6CuB3, space group P63cm, a=12.9426(9) Å, c=4.8697(4) Å) was obtained from as cast alloys and alloys annealed at 600 °C - 650 °C. Further substitution of Cu by Pd led to formation of a Mn7C3-type structure, o-(Pd0.93Cu0.07)7B3 (space group Pnma, a=4.8971(2) Å, b=7.5353(3) Å, c=12.9743(6) Å). Isotypic h-(Pt0.70Cu0.30)7B3 was observed in the Pt-Cu-B system as a low temperature phase (T≤600 °C), whereas the B-filled Th7Fe3-type (HT h-(Pt0.717Cu0.283)7B3+x, space group P63mc, a=7.4424(12) Å, c=4.8549(8) Å) 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; additionally octahedral boron coordination was encountered in HT h-(Pt0.717Cu0.283)7B3+x. A superconductivity was discovered for Pt4.9Cu2.1B3 (Pd6CuB3-type) and Pt5.04Cu1.96B3.3 (B-filled 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.Austrian Science Funds (FWF

ScRu2B3 and Sc2RuB6, new borides featuring a 2D infinite boron clustering

The final publication is available via https://doi.org/10.1021/acs.inorgchem.7b01512.Two borides, ScRu2B3 and Sc2RuB6 were obtained by argon-arc melting of the elements followed by annealing at 800 ºC. ScRu2B3 exhibits a new structure type with the space group Cmcm (a=3.0195(2) Å, b=15.4056(8) Å, c=5.4492(3) Å; single crystal X-ray data; RF2=0.0105). Sc2RuB6 adopts the Y2ReB6-type structure (space group Pbam; a=8.8545(2) Å, b=11.1620(3) Å, c=3.4760(1) Å; single crystal X-ray data; RF2=0.0185). ScRu2B3 displays an unusual intergrowth of CeCo3B2- and AlB2- related slabs; a striking feature is a boat configuration of puckered boron hexagons within infinite B63 nets. Sc2RuB6 presents two-dimensional planar nets of condensed boron pentagons, hexagons and heptagons sandwiched between metal layers. In Sc/Y substituted Y2ReB6-type, Y atoms are distributed exclusively inside the boron heptagons. Exploration of the Sc-Ru-B system at 800 ºC including binary boundaries employing EPMA and powder X-ray diffraction technique furthermore rules out the existence of previously reported "ScRuB4" but confirms the formation and crystal structure of Sc2Ru5B4. ScRu4B4 forms in cast alloys (LuRu4B4-type structure; space group I41/acd (no. 142), a=7.3543(2) Å, c=14.92137(8) Å). Cell parameters and atomic coordinates have been refined for ScRu2B3, Sc2RuB6 and ScRu4B4 in the scope of generalized gradient approximation. Ab initio electronic structure calculations indicate a moderate electronic density of states at the Fermi level situated near the upper edge of essentially filled d-bands. Electrical resistivity measurements characterize ScRu2B3 and Sc2RuB6 as metals in concord with electronic band structure calculations.Austrian Science Funds (FWF

Crystal structure and physical properties of UMo3B7

The final publication is available via https://doi.org/10.1016/j.intermet.2017.02.009.A novel ternary compound, UMo3B7, has been synthesized by arc melting and annealing at 900 °C. Its crystal structure was determined from X-ray single crystal diffraction data (YMo3B7-type structure, space group Pnma; a=1.10310(8) nm, b=0.30995(2) nm, c=1.2792(1) nm, RF2=0.0205). The structure is composed of boron filled trigonal prisms as well as unfilled tetrahedra and tetragonal pyramids formed by metal atoms. With respect to boron atoms aggregation, it exhibits a well-developed two-dimensional boron network revealing infinite bands of edge linked boron hexagons. The relationship with the members of the structural series within the V-B system: VnBn+1= (n-1)VB (CrB-type) + VB2 (AlB2-type) (n=1, 2, 3, 5) is discussed. Specific heat, magnetic susceptibility and electrical resistivity measurements characterizes UMo3B7 as a spin fluctuating system.Austrian Science Funds (FWF

Elucidating the lack of magnetic order in the heavy fermion CeCu2Mg

The final publication is available via https://doi.org/10.1103/PhysRevB.95.115146.Magnetic, transport, and thermal properties of CeCu2Mg are investigated to elucidate the lack of magnetic order in this heavy-fermion compound with a specific heat value, Cmag/T|T0 ≈ 1.2 J/mol K² and robust effective magnetic moments (μeff ≈ 2.46 μB). The lack of magnetic order is attributed to magnetic frustration favored by the hexagonal configuration of the Ce sublattice. In fact, the effect of magnetic field on Cmag/T and residual resistivity ρ0 does not correspond to that of a Fermi liquid (FL) because a broad anomaly appears at Tmax ≈ 1.2 K in Cmag(T)/T, without changing its position up to μoH=7.5 T. However, the flattening of Cmag/T|T0 and its magnetic susceptibility χ(T0), together with the T² dependence of ρ(T), reveal a FL behavior for T ≤ 2 K which is also supported by Wilson and Kadowaki-Woods ratios. The unusual coexistence of FL and frustration phenomena can be understood by placing paramagnetic CeCu2Mg in an intermediate section of a frustration-Kondo model. The entropy, Smag, reaches 0.87 Rln6 at T ≃ 100 K, with a tendency to approach the expected value Smag = Rln6 of the J=5/2 ground state of Ce3+

Pt-B system re-visited: Pt2B, a new structure type of binary borides. Ternary WAl12-type derivative borides

The final publication is available via https://doi.org/10.1021/acs.inorgchem.5b01998.Based on a detailed study applying X-ray single crystal and powder diffraction, DSC and SEM analysis it was possible to resolve existing uncertainties in the Pt-rich section (65 at.% Pt) of the binary Pt-B phase diagram above 600C. The formation of a unique structure has been observed for Pt2B (X-ray single crystal data: SG C2/m, a=1.62717(11) nm, b=0.32788(2) nm, c=0.44200(3) nm, =104.401(4)º, RF2=0.030). Within the homogeneity range of "Pt3B", X-ray powder diffraction phase analysis prompted two structure modifications as a function of temperature. The crystal structure of "hT-Pt3B" complies with the hitherto reported structure of anti-MoS2 (SG P63/mmc, a=0.279377(2) nm, c=1.04895(1) nm; RF=0.075, RI=0.090). The structure of the new "ℓT-Pt3B" is still unknown. The formation of previously reported Pt~4B has not been confirmed from binary samples. Exploration of the Pt-rich section of Pt-Cu-B system at 600C revealed a new ternary compound Pt12CuB6-y (X-ray single crystal data: SG Im , a=0.75790(2), y=3; RF2=0.0129) which exhibits the filled WAl12-type structure accommodating boron in the interstitial trigonal-prismatic site 12e. The isotypic platinum-aluminium-boride was synthesized and studied. Solubility of copper in binary platinum borides has been found to attain about 7 at.% Cu for Pt2B but to be insignificant for "ℓT-Pt3B". The architecture of the new Pt2B structure combines puckered layers of boron filled and empty [Pt6] octahedra (anti-CaCl2-type fragment) alternating along the x axis with a doubled layer of boron-semifilled [Pt6] trigonal prisms interbedded with a layer of empty tetrahedra and tetragonal pyramids (B-deficient α-TℓI fragment). Assuming boron vacancies ordering (SG R3), the Pt12CuB6-y structure exhibits the serpentine-like columns of edge-connected boron filled [Pt6] trigonal prisms running infinitively along z axis and embedding the icosahedrally coordinated Cu atom. Pt2B, (Pt1-yCuy)2B (y=0.045) and Pt12CuB6-y (y=3) behave metallic, as revealed from temperature dependent electrical resistivity measurements.Austrian Science Funds (FWF

Structural and Physical Properties Diversity of New CaCu₅‑Type Related Europium Platinum Borides

Three novel europium platinum borides have been synthesized by arc melting of constituent elements and subsequent annealing. They were characterized by X-ray powder and single-crystal diffraction: EuPt₄B, CeCo₄B type, <i>P</i>6/<i>mmm</i>, <i>a</i> = 0.56167(2) nm, <i>c</i> = 0.74399(3) nm; Eu₃Pt₇B₂, Ca₃Al₇Cu₂ type as an ordered variant of PuNi₃, <i>R</i>3̅<i>m</i>, <i>a</i> = 0.55477(2) nm, <i>c</i> = 2.2896(1) nm; and Eu₅Pt₁₈B_6–<i>x</i>, a new unique structure type, <i>Fmmm</i>, <i>a</i> = 0.55813(3) nm, <i>b</i> = 0.95476(5) nm, <i>c</i> = 3.51578(2) nm. These compounds belong to the CaCu₅ family of structures, revealing a stacking sequence of CaCu₅-type slabs with different structural units: CaCu₅ and CeCo₃B₂ type in EuPt₄B; CeCo₃B₂ and Laves MgCu₂ type in Eu₃Pt₇B₂; and CaCu₅-, CeCo₃B₂-, and site-exchange ThCr₂Si₂-type slabs in Eu₅Pt₁₈B_6–<i>x</i>. The striking motif in the Eu₅Pt₁₈B_6–<i>x</i> structure is the boron-centered Pt tetrahedron [BPt₄], which build chains running along the <i>a</i> axis and plays a decisive role in the structure arrangement by linking the terminal fragments of repeating blocks of fused Eu polyhedra. Physical properties of two compounds, EuPt₄B and Eu₃Pt₇B₂, were studied. Both compounds were found to order magnetically at 36 and 57 K, respectively. For EuPt₄B a mixed-valence state of the Eu atom was confirmed via magnetic and specific heat measurements. Moreover, the Sommerfeld value of the specific heat of Eu₃Pt₇B₂ was found to be extraordinarily large, on the order of 0.2 J/mol K²