Pressure-induced Oxidation State Change of Ytterbium in YbGa2

On the Ytterbium Valence and the Physical Properties in Selected Intermetallic Phases

The present review summarizes important aspects of the crystal chemistry of ytterbium-based intermetallic compounds along with a selection of their outstanding physical properties. These originate in many cases from the ytterbium valence. Different valence states are possible here, divalent (4f14), intermediate-valent, or trivalent (4f13) ytterbium, resulting in simple diamagnetic, Pauli or Curie-Weiss paramagnetic, or valence fluctuating behavior. Especially, some of the Yb3+ intermetallics have gained deep interest due to their Kondo or heavy Fermion ground states. We have summarized their property investigations using magnetic and transport measurements, specific heat data, NMR, ESR, and Mössbauer spectroscopy, elastic and inelastic neutron scattering, and XAS data as well as detailed thermoelectric measurements.

First ternary tungsten tellurate(IV) WTe2O7 with unique crystal structure type

At multianvil high-pressure/high-temperature conditions of 10 GPa and 1273 K, the first ternary tungsten tellurate WTe₂O₇ is formed, starting from a stoichiometric mixture of WO₃ and TeO₂. The compound crystallizes triclinic in a hitherto unknown crystal structure type with the space group P1̄; (no. 2), and was refined from single-crystal X-ray diffractometer data: a = 538.3(1), b = 687.5(1), c = 802.3(1) pm, α = 72.4(1)°, β = 85.7(1)°, γ = 68.1(1)°, wR₂ = 0.0323, GooF = 1.048, 3157 F² values, and 106 variables. The main motifs of the crystal structure are pairs of edge-linked [WO₆]^6- octahedra and fourfold oxygen-coordinated Te⁴⁺ atoms. The oxidation state of W⁶⁺ and Te⁴⁺ was further verified by measuring the characteristic binding energy values for the W 4f and the Te 3d core levels via X-ray photoelectron spectroscopy (XPS). In addition, DFT calculations of the structure, the associated electron localisation functions (ELF) and vibrational spectra have been carried out. The theoretical data clearly demonstrates the impact of the residual electron density located at the Te⁴⁺ ions, which can be directly interpreted as the presence of lone electron pairs within the solid structure.

Structural phase transition of CeAuGe at high pressure

Structural properties of the ternary intermetallic compound CeAuGe were investigated at hydrostatic pressures up to 15 GPa with high-resolution angle dispersive X-ray powder diffraction using synchrotron radiation and the diamond anvil cell technique. At 8.7(7) GPa a first order phase transition is observed from a hexagonal NdPtSb-type arrangement into an orthorhombic high-pressure modification with a TiNiSi-type crystal structure. The transformation is associated with a 3% shortening of the lattice parameter perpendicular to the puckered layers [AuGe]n and an elongation of one of the lattice parameters within the plane of the layers. The changes of interatomic distances are more pronounced than the metrical alterations and indicate that a transition from layer-type poly anions into a 3D network [AuGe]n is associated with the structural transformation.