The ternary iron arsenide BaFe2As2 with the tetragonal ThCr2Si2-type structure exhibits a spin density wave (SDW) anomaly at 140 K, very similar to LaFeAsO, the parent compound of the iron arsenide superconductors. BaFe2As2 is a poor Pauli-paramagnetic metal and undergoes a structural and magnetic phase transition at 140 K, accompanied by strong anomalies in the specific heat, electrical resistance and magnetic susceptibility. In the course of this transition, the space group symmetry changes from tetragonal (I4/mmm) to orthorhombic (F mmm). 57 Fe Mössbauer spectroscopy experiments show a single signal at room temperature and full hyperfine field splitting below the phase transition temperature (5.2 T at 77 K). Our results suggest that BaFe2As2 can serve as a parent compound for oxygen-free iron arsenide superconductors.

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The new quaternary iron arsenide-fluoride SrFeAsF with the tetragonal ZrCuSiAstype structure was synthesized and the crystal structure was determined by X-ray powder diffraction (P 4/nmm, a = 399.30(1), c = 895.46(1) pm). SrFeAsF undergoes a structural and magnetic phase transition at 175 K, accompanied by strong anomalies in the specific heat, electrical resistance and magnetic susceptibility. In the course of this transition, the space group symmetry changes from tetragonal (P 4/nmm) to orthorhombic (Cmme). 57 Fe Mössbauer spectroscopy experiments show a single signal at room temperature at an isomer shift of 0.30(1) mm/s and magnetic hyperfine-field splitting below the phase transition temperature. Our results clearly show that SrFeAsF exhibits a spin density wave (SDW) anomaly at 175 K very similar to LaFeAsO, the parent compound of the iron arsenide-oxide superconductors and thus SrFeAsF may serve as a further parent compound for oxygen-free iron arsenide superconductors.

We report a combined experimental and theoretical investigation of the layered antimonide PrMnSbO which is isostructural to the parent phase of the iron pnictide superconductors. We find linear resistivity near room temperature and Fermi liquid-like T^{2} behaviour below 150 K. Neutron powder diffraction shows that unfrustrated C-type Mn magnetic order develops below \sim 230 K, followed by a spin-flop coupled to induced Pr order. At T \sim 35 K, we find a tetragonal to orthorhombic (T-O) transition. First principles calculations show that the large magnetic moments observed in this metallic compound are of local origin. Our results are thus inconsistent with either the itinerant or frustrated models proposed for symmetry breaking in the iron pnictides. We show that PrMnSbO is instead a rare example of a metal where structural distortions are driven by f-electron degrees of freedom

One decade after the first characterization of Zintl ions by Kummer and Diehl [1a] and Corbett, [1b, c]

Two K([2.2.2]crypt) salts of lanthanide-doped semimetal clusters were prepared, both of which contain at the same time two types of ternary intermetalloid anions, [Ln@Sn(7)Bi(7)](4-) and [Ln@Sn(4)Bi(9)](4-), in 0.70:0.30 (Ln = La) or 0.39:0.61 (Ln = Ce) ratios. The cluster shells represent nondeltahedral, fullerane-type arrangements of 14 or 13 main group metal atoms that embed the Ln(3+) cations. The assignment of formal +III oxidation states for the Ln sites was confirmed by means of magnetic measurements that reveal a diamagnetic La(III) compound and a paramagnetic Ce(III) analogue. Whereas the cluster anions with a 14-atomic main-group metal cage represent the second examples in addition to a related Eu(II) cluster published just recently, the 13-atomic cages exhibit a yet unprecedented enneahedral topology. In contrast to the larger cages, which accord to the Zintl-Klemm-Busmann electron number-structure correlation, the smaller clusters require a more profound interpretation of the bonding situation. Quantum chemical investigations served to shed light on these unusual complexes and showed significant narrowing of the HOMO-LUMO gap upon incorporation of Ce(3+) within the semimetal cages.

In this contribution the preparation and structural characterization of nanoscale fluorine doped tin-oxide (SnO2:F, FTO) is described. By using a microwave assisted polyol approach, nanoparticles with different doping levels are prepared, which show narrow size distribution as measured by X-ray diffraction, electron microscopy and dynamic light scattering. They were converted into electrically conductive optically transparent films at 500 °C by a specific thermal treatment (500 °C in air followed by 250 °C in forming gas), exhibiting a specific resistivity of (1.9 × 10−1 Ω cm). Solid-state MAS NMR and 119Sn Mössbauer spectroscopy were used to study how F atoms are incorporated into the SnO2:F nanoparticles. Distance constraints were determined by 119Sn{19F} REDOR, fluorine-doping homogeneity by homonuclear dipolar recoupling experiments (SR66 2). Cross-polarization was used to investigate the immediate environment of the dopant. The experiments were supplemented by first-principles quantum-chemical calculations for possible defect site models. The combined data strongly indicate that F doping is not directly related to an increase in charge-carrier concentration, even though F atoms do occupy O vacancy sites in SnO2:F. For this study we have implemented background compensated NMR 2D pulse-sequences which reliably suppress the fluorine background originating from the NMR probe. Moreover we show that cluster calculations on the basis of the extended embedded ion method (EEIM) can be used to study the structure of diluted defects in crystalline host structures and predict NMR properties.

Eu Moessbauer spectroscopy. The structure of EuCd2As2 is determined by single crystal XRD (space group P3m1, Z = 1; CaAl2Si2 type structure). The two-dimensional [Cd2X2] (X: P, As, Sb) networks of the title compounds consist of edge-sharing CdX 4 tetrahedra. The networks are separated and charge-balanced by europium and ytterbium atoms. Redetermination of the magnetic properties revealed divalent europium and ytterbium. YbCd2Sb2 is diamagnetic. The europium compounds exhibit only one magnetic phase transition.