Structure and magnetic property of potassium intercalated pentacene: observation of superconducting phase in KxC22H14

We report the results from systematic investigations on the structure and magnetic properties of potassium intercalated pentacene as a function of potassium content, K x C22H14 (1  ≤  x  ≤  3). Synchrotron radiation powder x-ray diffraction technique revealed that there are two different stable phases can be obtained via potassium intercalation, namely, K1C22H14 phase and K3C22H14 phase. Structural phase transition was induced when the potassium content was increased to the nominal value x  =  3. This phase transition is accompanied by drastic change in their magnetic property, where those samples with compositions K1C22H14 shows ferromagnetic behavior and those with near K3C22H14 lead to observation of superconductivity with transition temperature, T c, of 4.5 K. It is first time that superconductivity was observed in linear oligoacenes. Both magnetization study and synchrotron radiation powder x-ray diffraction clearly indicates that the superconducting phase belong to K3C22H14 as a result of phase transition from triclinic to monoclinic structure induced by chemical doping

The new barium compound Ba₄Al_7+x: formation and crystal structure

Combining laboratory X-ray powder diffraction with in-situ high-temperature synchrotron experiments and differential scanning calorimetry, it has been shown that Ba21Al40, Ba3Al5, Ba7Al10 and Ba4Al5 decompose peritectically at 914, 826, 756, and 732 degrees C, respectively. In addition, a new binary compound with the composition Ba4Al7+x (x = 0.17) and the formation temperature of 841 degrees C was found. The initial structural model (space group P6(3)/mmc, a = 6.0807(1), c = 39.2828(8)angstrom) with four Ba and five Al crystallographic positions was developed. It is based on the intergrowth concept involving the neighboring Ba21Al40 and Ba3Al5 phases and the derived atomic arrangement is subsequently refined using X-ray diffraction data. The crystal structures of all phases in the Ba-Al system, except BaAl4, exhibit Kagome nets of aluminum atoms resembling those observed for the B atoms in the Laves phases AB(2). In the crystal structure of Ba4Al7+x, single Kagome layers alternate with double slabs (MgZn2 motif) along [001] and are separated by Ba cations. Inter-growth features of Ba4Al7+x are discussed together with the neighboring Ba-Al compounds and Sr5Al9

Ca₃[BN₂]I₃: The First Halide-Rich Alkaline Earth Nitridoborate with Isolated [BN₂]^3- Units

The title compound Ca-3[BN2]I-3 was obtained from reactions of mixtures of the starting materials Ca-3[BN2](2) and CaI2 in a 1:4 ratio in sealed Nb tubes at 1223 K. The crystal structure was solved from powder synchrotron diffraction data. Ca-3[BN2]I-3 is the first example of a halide-rich nitridoborate crystallizing in the rhombohedral space group R32 [no. 155, Pearson code: hR96; Z = 12; a = 16.70491(2) angstrom, c = 12.41024(2) angstrom]. The crystal structure is built up by two interpenetrating networks of condensed edge-sharing [BN2]@Ca-6 and [square]@I-6 trigonal antiprisms (square = void). In Ca-3[BN2]I-3 two crystallograhically distinct [BN2](3-) anions are present with d(B1-N) = 1.393(2) angstrom and d(B2-N) = 1.369(9) angstrom. Their bond angles are practically linear, varying only slightly: N-B1-N = 179(1)degrees and N-B2-N = 180 degrees. Vibrational spectra were interpreted based on the D-infinity h symmetry of the discrete linear [N-B-N](3-) moieties, considering the site symmetry reduction and the presence of two distinct [BN2](3-) groups

Compositional evolution of the NaZn13 structure motif in the systems La-Ni-Ga and Ce-Ni-Ga

Phase relationship and structural behaviour in the substitutional series LaNi13-xGax and CeNi13-xGax have been studied by a combination of X-ray powder diffraction measurements, differential scanning calorimetry, electron diffraction tomography and metallographic analyses. The sequence of morphotropic phase transformations has been found in the series LaNi13-xGax resulting in five varieties of the NaZn13 structure: the cubic phase with aristotype structure at x = 2 (space group Fm3c, Pearson symbol cF112), two tetragonal phases at x = 2.5-4.25 (space group I4/mcm, Pearson symbol tI56-I) and 7-7.5 (space group I4/mcm, Pearson symbol tI56-II), both with an atomic arrangement of the CeNi8.5Si4.5 type and two orthorhombic phases at x = 4.5-5.75 (LaNi7In6 structure type, space group Ibam, Pearson symbol oI56) and x = 6.37-6.87 (a new derivative of the NaZn13, prototype structure, space group Fmmm, Pearson symbol oF112). The related series CeNi13-xGax shows similar behaviour. The corresponding tI56-I ↔ oI56 ↔ oF112 ↔ tI56-II phases are formed at x = 4-4.25, 4.5-6, 6.37-6.87 and 7-7.37, respectively. In contrast to the lanthanum analogues, the phase with cubic symmetry was not found for this system. Complex twinned and multiple twinned (twinning of twins) domain structures which are revealed for the tetragonal and both orthorhombic phases clearly indicate temperature-induced polymorphic phase transitions during the formation of these phases. LaNi13-xGax samples show paramagnetic behavior, whereas the CeNi13-xGax series exhibits Curie-Weiss paramagnetism

Crystal Structure and Physical Properties of Ternary Phases around the Composition Cu₅Sn₂Se₇ with Tetrahedral Coordination of Atoms

A new monoclinic selenide Cu5Sn2Se7 was synthesized, and its crystal and electronic structure as well as thermoelectric properties were studied. The crystal structure of Cu5Sn2Se7 was determined by electron diffraction tomography and refined by full-profile techniques using synchrotron X-ray powder diffraction data: space group C2, a = 12.6509(3) angstrom, b = 5.6642(2) angstrom, c = 8.9319(4) angstrom, beta = 98125(4)degrees, Z = 2; T = 295 K. Thermal analysis and high-temperature synchrotron X-ray diffraction indicated the decomposition of Cu5Sn2Se7 at 800 K with formation of the tetragonal high-temperature phase Cu4.90(4)Sn2.10(4)Se7: space group I (4) over bar 2m, a = 5.74738(1) angstrom, c = 11.45583(3) angstrom; T = 873 K. Both crystal structures are superstructures to the sphalerite type with tetrahedral coordination of the atoms. In agreement with chemical bonding analysis and band structure calculations, Cu5Sn2Se7 exhibits metal-like electronic transport behavior

Distribution of Al atoms in the clathrate-I phase Ba₈Al_xSi_46-x at x=6.9

The clathrate-I phase Ba8AlxSi46-x has been structurally characterized at the composition x = 6.9 (space group Pm (3) over barn, no. 223, a = 10.4645(2) angstrom). A crystal structure model comprising the distribution of aluminium and silicon atoms in the clathrate framework was established: 5.7 Al atoms and 0.3 Si atoms occupy the crystallographic site 6c, while 1.2 Al atoms and 22.8 Si atoms occupy site 24k. The atomic distribution was established based on a combination of Al-27 and Si-29 NMR experiments, X-ray single-crystal diffraction and wavelength-dispersive X-ray spectroscopy

Pressure effects in the isoelectronic REFe0.85Ir0.15AsO system

The effect of chemical and hydrostatic pressure has been studied systematically in a selected system belonging to the 1111 family of iron pnictide high-temperature superconductors. The results show a surprising similarity between the trend of critical temperature vs hydrostatic pressure for isoelectronic samples with different rare earths (RE) on the RE site and samples of the SmFeAsO(1-x)F(x) series with different doping levels. These results open new questions about the underlying mechanism for superconductivity in iron pnictides