Anisotropic Physical Properties of the Kondo Semimetal CeCu1.11_{1.11}As2_2

The recently proposed novel materials class called Weyl-Kondo semimetal (WKSM) is a time reversal invariant but inversion symmetry broken Kondo semimetal in which Weyl nodes are pushed to the Fermi level by the Kondo interaction. Here we explore whether CeCu$_{1+x}$As$_2$ may be a new WKSM candidate. We report on its single-crystal growth, structure determination and physical properties investigation. Previously published studies on polycrystalline samples suggest that it is indeed a Kondo semimetal, which is confirmed by our investigations on single crystals. X-ray diffraction reveals that CeCu$_{1+x}$As$_2$ crystallizes in a tetragonal centrosymmetric structure, although the inversion symmetry could still be broken locally due to partially occupied Cu sites. Chemical analysis results in an average occupation $x$ = 0.11(1). The electrical resistivity increases logarithmically with decreasing temperature, and saturates below 10 K. A Kondo temperature $T_{\mathrm{K}}$ $\approx$ 4 K is extracted from entropy, estimated from the specific heat measurements. From Hall effect experiments, a charge carrier density of $8.8 \times 10^{20}$ cm$^{-3}$ is extracted, a value characteristic of a semimetal. The magnetization shows pronounced anisotropy, with no evidence of magnetic ordering down to 0.4 K. We thus classify CeCu$_{1.11}$As$_2$ as a tetragonal Kondo semimetal with anisotropic magnetic properties, with a possibly broken inversion symmetry, thus fulfilling the necessary conditions for a WKSM state.Comment: 6 pages, 4 figures, Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2019

Lexical access and lexical diversity in first language attrition

This paper presents an investigation of lexical first language (L1) attrition, asking how a decrease in lexical accessibility manifests itself in long-term residents in a second language (L2) environment. We question the measures typically used in attrition studies (formal tasks and type?token ratios) and argue for an in-depth analysis of free spoken data, including factors such as lexical frequency and distributional measures. The study is based on controlled, elicited and free data from two populations of attriters of L1 German (L2 Dutch and English) and a control population (n = 53 in each group). Group comparisons and a Discriminant Analysis show that lexical diversity, sophistication and the distribution of items across the text in free speech are better predictors of group membership than formal tasks or elicited narratives. Extralinguistic factors, such as frequency of exposure and use or length of residence, have no predictive power for our results

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

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

Mechanism of Rare Earth Incorporation and Crystal Growth of Rare Earth Containing Type‑I Clathrates

Type-I clathrates possess extremely low thermal conductivities, a property that makes them promising materials for thermoelectric applications. The incorporation of cerium into one such clathrate has recently been shown to lead to a drastic enhancement of the thermopower, another property determining the thermoelectric efficiency. Here we explore the mechanism of the incorporation of rare earth elements into type-I clathrates. Our investigation of the crystal growth and the composition of the phase Ba_8–<i>x</i>RE_<i>x</i>TM_<i>y</i>Si_{46–<i>y</i>} (RE = rare earth element; TM = Au, Pd, Pt) reveals that the RE content <i>x</i> is mainly governed by two factors, the free cage space and the electron balance

ScRu₂B₃ and Sc₂RuB₆: Borides Featuring a 2D Infinite Boron Clustering

Two borides, ScRu₂B₃ and Sc₂RuB₆, were obtained by argon-arc melting of the elements followed by annealing at 800 °C. ScRu₂B₃ exhibits a new structure type with the space group <i>Cmcm</i> (<i>a</i> = 3.0195(2) Å, <i>b</i> = 15.4056(8) Å, <i>c</i> = 5.4492(3) Å; single crystal X-ray data; <i>R</i>_F² = 0.0105). Sc₂RuB₆ adopts the Y₂ReB₆-type structure (space group <i>Pbam</i>; <i>a</i> = 8.8545(2) Å, <i>b</i> = 11.1620(3) Å, <i>c</i> = 3.4760(1) Å; single crystal X-ray data; <i>R</i>_F² = 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 graphite like boron layers (6³ 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 °C 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 <i>I</i>4₁/<i>acd</i> (No. 142), <i>a</i> = 7.3543(2) Å, <i>c</i> = 14.92137(8) Å). Cell parameters and atomic coordinates have been refined for ScRu₂B₃, Sc₂RuB₆, and ScRu₄B₄ in the scope of the 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

Pt–B System Revisited: Pt₂B, a New Structure Type of Binary Borides. Ternary WAl₁₂-Type Derivative Borides

On the basis of a detailed study applying X-ray single-crystal and powder diffraction, differential scanning calorimetry, and scanning electron microscopy analysis, it was possible to resolve existing uncertainties in the Pt-rich section (≥65 atom % Pt) of the binary Pt–B phase diagram above 600 °C. The formation of a unique structure has been observed for Pt₂B [X-ray single-crystal data: space group <i>C</i>2/<i>m</i>, <i>a</i> = 1.62717(11) nm, <i>b</i> = 0.32788(2) nm, <i>c</i> = 0.44200(3) nm, β = 104.401(4)°, <i>R</i>_F2 = 0.030]. Within the homogeneity range of “Pt₃B”, X-ray powder diffraction phase analysis prompted two structural modifications as a function of temperature. The crystal structure of “<i>h</i>T-Pt₃B” complies with the hitherto reported structure of anti-MoS₂ [space group <i>P</i>6₃/<i>mmc</i>, <i>a</i> = 0.279377(2) nm, <i>c</i> = 1.04895(1) nm, <i>R</i>_F = 0.075, <i>R</i>_I = 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 the Pt–Cu–B system at 600 °C revealed a new ternary compound, Pt₁₂CuB_6–<i>y</i> [X-ray single-crystal data: space group <i>Im</i>3̅, <i>a</i> = 0.75790(2) nm, <i>y</i> = 3, <i>R</i>_F2 = 0.0129], which exhibits the filled WAl₁₂-type structure accommodating boron in the interstitial trigonal-prismatic site 12<i>e</i>. The isotypic platinum–aluminum–boride was synthesized and studied. The solubility of copper in binary platinum borides has been found to attain ∼7 atom % 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 <i>x</i> axis with a double 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 (space group <i>R</i>3), the Pt₁₂CuB_6–<i>y</i> structure exhibits serpentine-like columns of edge-connected boron-filled [Pt₆] trigonal prisms running infinitely along the <i>z</i> axis and embedding the icosahedrally coordinated Cu atom. Pt₂B, (Pt_1–<i>y</i>Cu_<i>y</i>)₂B (<i>y</i> = 0.045), and Pt₁₂CuB_6–<i>y</i> (<i>y</i> = 3) behave metallically, as revealed by temperature-dependent electrical resistivity measurements