Göran Svensson

Large thermoelectric figure of merit at high temperature in Czochralski-grown clathrate Ba8Ga16Ge30

The Czochralski method was used to grow a 46-mm-long crystal of the Ba8Ga16Ge30 clathrate, which was cut into disks that were evaluated for thermoelectric performance. The Seebeck coefficient and electrical and thermal conductivities all showed evidence of a transition from extrinsic to intrinsic behavior in the range of 600–900K. The corresponding figure of merit (ZT) was found to be a record high of 1.35 at 900K and with an extrapolated maximum of 1.63 at 1100K. This makes the Ba8Ga16Ge30 clathrate an exceptionally strong candidate for medium and high-temperature thermoelectric applications.

Excitonic and recombination processes in CaWO4 and CdWO4 scintillators under synchrotron irradiation

Excitation spectra of intrinsic (IL) and extrinsic luminescence (EL) from CaWO 4 and CdWO 4 crystals, measured using synchrotron radiation (4-30 eV) at 8 K, have been analysed. In CaWO 4 the IL (2.9 eV) is efficiently excited by photons of 5.5-7.0 eV at the creation of molecular excitons. The EL is efficiently excited in interband transitions (hv>6.8 eV). The energy threshold for the multiplication of electronic excitations is E t 15 eV in CaWO 4 and E t 10 eV CdWO 4 . In CdWO 4 , a fraction of the molecular excitons undergoes autoionization due to an overlap with the continuum of the interband transitions. Fast emission (<2 ns) is found at 80 K under the pulse excitation by electrons with an energy of 300 keV. The continuous temperature-independent emission of CaWO 4 crystals in the region of 2-5 eV is interpreted as an intraband luminescence. The emission at 5.5 eV is ascribed to a metastable molecular excitons.

On the structures and properties of Cr(DMSO)(6)(3+) and the coordination polymer cis-Cr(III)(oxalate)(2)(DMSO)(2) K(DMSO)(2) (n)

cis-Cr(III)(oxalate)(2)(DMSO)(2)K(DMSO)(2) was formed by K3Cr(oxalate), in dimethylsulfoxide-THF mixtures. The structure is ribbon-like with cis-Cr(oxalate)(2)(DMSO)(2)(-) complex ions bridged by oxalates to (DMSO)K(DMSO)(2)K(DMSO) units forming interconnected rings of six metal complexes. In the same type of solutions Cr(DMSO)(6)(NO3)(3) was also formed. In this structure Cr(III) is six-coordinated by oxygens from DMSO. Cr(DMSO)(6)(NO3)(3) is isostructural with Fe(DMSO)(6)(NO3)(3) (J.R. Tzou et al., Acta Crystallogr., Sect. C, 51 (1995) 2249). The Cr(III)-O distance shows an expected shortening of about 0.04 Angstrom compared to the Fe(III)-O bond in Fe(DMSO)(6)(NO3)(3)

Lead(II) oxydiacetate hydrate

The coordination polyhedron around the Pb atom in the title compound, poly[aqualead(II)-mu(5)-oxydiacetato], [Pb(mu(5)-C4H4O5)(H2O)](n), is a distorted square antiprism formed by three O atoms from one oxydiacetate ligand, four O atoms from four other identical ligands and one water O atom, resulting in a three-dimensional network structure. The almost planar oxydiacetate ligand is disordered over two positions. The Pb lone-pair 6s(2) electrons show stereochemical activity in the coordination sphere.

The langbeinite type Rb2TiY(PO4)(3)

Dirubidium titanium yttrium triphosphate belongs to the langbeinite structure type with a framework of Mo-6 octahedra (M = Ti, Y) sharing corners with PO4 tetrahedra and vice versa, creating cages in which the Rb+ cations are located. The compound exhibits mixed Ti/Y populations in the two crystallographically independent octahedral sites of symmetry 3. More than two-thirds of the yttrium is found in one site and the remaining amount in the other; this is caused by the difference in coordination for the two sites.

Top seeded solution growth of [Rb,Cs]TiOAsO4

Large single crystals of KTiOPO4 (KTP) isomorphs RbTiOAsO4 (RTA), CsTiOAsO4 (CTA) and RbxCs1−xTiOAsO4 (RCTA), x=0.93, have been grown using the top seeded solution growth technique in a temperature controlled four-zone furnace. The seed was situated at the top end of the crystal, which minimized the part of the crystal that is strongly affected by the seed. The combination of Rb and Cs in RCTA is more favorable for crystal growth, in comparison with the end members RTA and CTA. Mixed crystals are Rb-enriched and contain only 20–30% of the Cs content of the flux composition. The IR transmission is slightly higher for CTA than for RTA. Various etching solutions have been used to study the domain patterns revealing that these crystals grown above the transition temperature consist of a few large domains.

A single-crystal neutron diffraction study of RbTiOAsO4

A rubidium titanyl arsenate single-crystal has been studied by neutron diffraction (lambda = 1.207 A). The polished sample used was 5 x 3 x 2 mm and was cut from a crystal made by top-seeded solution growth. The crystal showed severe extinction. It was, however, possible to obtain a structural model with well defined oxygen sites and reasonable anisotropic displacement parameters.

The Structure of Na2W2O7·H2O Synthesized under High Pressure and Temperature

A new compound, Na 2 W 2 O 7 .1/2H 2 O, has been found in the Na 2 O-WO 3 -H 2 O system. It is the fourth compound in the Na 2 W 2 O 7 .xH 2 O system and the second phase containing water. The crystals were prepared at a pressure of 1.5 GPa and a temperature of 900°C. Na 2 W 2 O 7 .1/2H 2 O crystallizes in the triclinic space group, P1, Z=2, with lattice constants of a = 8.4902(6) A, b = 7.6636(6) A, c = 5.1501(3) A, α = 91.959(7)°, β=96.521(8)° and γ=111.678(7)°. The structure is built up from double chains of WO 6 octahedra running along c, interconnected by two-dimensional nets of NaO 6 polyhedra. Sodium coordinates to six oxygens forming both octahedra and trigonal prisms.