Band 238, Heft 9-10

To gain insight into the applicability as building blocks for optoelectronic device development, alkaline earth metal sulfides are investigated. MgS, CaS, SrS, and BaS have been systematically synthesized as colloidal particles in olelyamine. The particle sizes range from around 819 nm for MgS to 12.8 nm for CaS, 25.0 nm for SrS, and 21.6 nm for BaS. The heat-up synthesis uses commerically available precursors without complicated procedures. The structural and optical properties are investigated with X-ray diffraction, spectroscopic ellipsometry, UV–vis spectrophotometry, scanning electron microscopy, and energy dispersive X-ray spectroscopy.

Large-scale single crystals of Ca 9 Mg(PO 4 ) 6 (PO 3 OH), Ca 9 Zn(PO 4 ) 6 (PO 3 OH), and Ca 9 Co(PO 4 ) 6 (PO 3 OH) were synthesized using hydrothermal technique, and turned out to be similar to natural bone whitlockite. The hexagonal single crystals about 1 mm with high-quality were obtained with this method for the first time. The crystals were of sufficiently good quality for the precision X-ray structural investigation. The compounds crystallize in usual for this structural type trigonal space group R 3 c . Presence of hydrogen atom in the structure was confirmed by means of infra-red (IR) spectroscopy, differential scanning calorimetry (DSC) and differential thermogravimetry (DTG) methods. Based on the analysis of the local bond valence sum (BVS), a conclusion on the localization of H atoms was made. The formation of O–H groups and hydrogen bonds H⋯O in vicinity of PO 4 tetrahedra was shown and similar to bone whitlockite. This research provides new data on possibility of using hydrothermal technique for obtaining doped bone whitlockites. Hydrogen-containing doped whitlockites can combine bioactive properties and improve biocompatibility due to similarity to natural bond. New structural data are useful for finding the ways to better biocompatibility of whitlockite-based materials.

The intermetallic compounds (Ca 0.95 Cd 0.10 )Pd 2 Cd 3 , SrPd 2 Cd 3 and (Eu 0.95 Cd 0.10 )Pd 2 Cd 3 were synthesized from the elements in sealed niobium ampoules in an induction furnace. The polycrystalline samples were characterized through their Guinier powder patterns. The structures were refined from single crystal X-ray diffractometer data: YNi 2 Al 3 type, P 6/ mmm , a = 984.61(5), c = 455.33(3) pm, w R 2 = 0.0216, 376 F 2 values, 21 variables for (Ca 0.95 Cd 0.10 )Pd 2 Cd 3 , a = 998.55(8), c = 453.65(3) pm, w R 2 = 0.0296, 341 F 2 values, 17 variables for SrPd 2 Cd 3 and a = 992.57(4), c = 457.34(2) pm, w R 2 = 0.0300, 384 F 2 values, 21 variables for (Eu 0.95 Cd 0.10 )Pd 2 Cd 3 . The striking crystal chemical motif in the three structures is a planar [PdCd 2 ] Kagome-type layer. The two crystallographically independent Ca (Sr, Eu) atoms have a coordination number of 18 by 6 Pd and 12 Cd atoms. The calcium and europium compound show a small degree of Ca (Eu) substitution by Cd 2 dumb-bells with 281 pm Cd–Cd in (Eu 0.95 Cd 0.10 )Pd 2 Cd 3 . Temperature dependent magnetic susceptibility measurements show Curie–Weiss behaviour (7.63(1) µ B /Eu atom) for the europium compound and the onset of ferromagnetic ordering at T C = 14.9(2) K. The divalent character of europium is corroborated by 151 Eu Mössbauer spectroscpy.

Systematization of the vast number of known crystal structures of intermetallic phases is a challenge. One previously proposed group is referred to here as vacancy variants of the W-type structure. Members of this group, may, however, not be easily recognized because of the structural irregularity introduced by the vacancies. Descriptions of the experimentally observed crystal structures of Ni 3 Sn 4 and FeAl 2 in terms of vacancy variants of the W-type structure are, respectively, derived by establishing a lattice correspondence with the W-type structure, allowing, in particular, identification of the vacant sites. In both cases only small deviatoric strains are required to obtain the experimentally encountered lattice parameters, and generally small atomic displacements occur from the ideal positions, thus demonstrating significance of the lattice correspondence. The lattice correspondences allow, for both Ni 3 Sn 4 and FeAl 2 , relating reported microstructure evidence (directions/planes occurring in orientation relationships and crystal habits but also on twinning and slip) with such typical for metals and solid solutions with W-type (“bcc”) structures. This demonstrates that the established lattice correspondences have a significance going beyond a descriptive one, but the underlying W-type structures reveal themselves in the materials’ behavior.

A new compound, K 5 [(Mo 3.2 W 1.8 )O 11 ](PO 4 ) 3 [(P 0.5 Mo 0.5 )O 4 ], was synthesized via solid-state reaction and its crystal structure was determined by single-crystal X-ray diffraction. This compound crystallizes in the space group Pnma , with a  = 9.0360(4) Å, b  = 10.1603(4) Å, c  = 26.1538(12) Å and V  = 2401.14(18) Å 3 . The structure consists of a corner-sharing MO 6 –TO 4 (M = Mo, W; T = P, Mo) polyhedral connection arranged to form an ordered packing of ∼14.9 Å-thick layers parallel to (001). The stacking of the layers forms trigonal, tetragonal and hexagonal channels. XPS study reveals the presence of W at the hexavalent state only, whereas Mo appears as a mixed-valent species (Mo 6+ , Mo 5+ and Mo 4+ ). Magnetic susceptibility reveals the occurrence of a relevant antiferromagnetic coupling and is consistent with the presence of reduced metal species as indicated by the XPS results.

The copper borate of CuB 2 O 4 in tetragonal form was successfully synthesized as a single-phase by using a solid-state method without using any modifying agent. For the designed experimental procedure, the optimized reaction conditions were estimated as a reaction temperature of 950 °C, reaction time of 240 min, argon atmosphere and Cu:B ratio of 1:5. The possible reaction mechanism estimated for both boron sources of boric acid and boron oxide. In both sets, the lower ratios of Cu:B supported CuB 2 O 4 formation. In the use of boric acid as a boron source, higher reaction yield percentages (98 %) and lower particle sizes were determined. The micron-scale rounded particles were observed in morphological analyses and the particles were shaped in homogeneity in the use of boron oxide as a boron source. The specific FT-IR peaks were observed at the band values of 1190, 1035, 988, 945, 890, 695, 631, 540 and 479 cm −1 . The experimental results highlighted the probable use of solid-state in the copper borate synthesis.

A new rubidium uranyl silicate, Rb 2 (UO 2 ) 2 O(Si 3 O 8 ) ( 1 ), was obtained using high-temperature approach from the melt in silica tubes. Its crystal structure was solved by direct methods: hexagonal, P 6/ m , a  = 27.7992(7), c  = 7.2346(2) Å, V  = 4841.8(3) Å 3 , R 1  = 0.033. The structure of 1  represents a new structure type with unprecedented topology not observed before among U(VI) oxides and oxysalts. It is comprised of layers with large voids derived from the U 3 O 8 structure formed exclusively by pentagonal Ur O 5 bipyramids. The low-occupied Rb sites are located in the interlayer space. The SiO 4 silicate tetrahedra in the structure of 1 share vertices to form rolled [Si 6 O 16 ] 8− chains. The nanotubules [(UO 2 )(Si 6 O 16 )] 6− penetrate through both U 3 O 8 -derived layers and Rb interlayer. These tubules are attached to the U 3 O 8 derived sheets via uranyl-uranyl interactions and edge-sharing between silicate tetrahedra and Ur O 5 bipyramids.