Volume 238, Issue 5-6

Single crystals of five (Al,Ge)-mullites incorporating Pb, and four of which also incorporating foreign cations (Fe,Cr,Nd,Sm) were grown by flux techniques in a PbO-MoO 3 flux. They were characterized by scanning electron microscopy, electron microprobe analyses, single-crystal X-ray diffraction. In addition, the refractive indices of mullite containing Nd were determined by spindle-stage optical investigations. Careful inspection of the single-crystal X-ray diffraction data revealed that weak superstructure reflections observed in all doped crystals violating the reflection conditions can be attributed to λ/2 contributions in the primary X-ray beam. Consequently, all crystal structures were refined in space group Pbam , thus avoiding a symmetry lowering to a noncentrosymmetric subgroup as done in earlier work on a (Al,Ge)-mullite doped with Pb and Nd (Saalfeld & Klaska, Z. Kristallogr. 1985, 172, 129–133). The following phases with chemical compositions used in the refinements were obtained: undoped mullite (Al 4.50 Ge 1.50 O 9.75 ; a = 7.6559(4) Å, b = 7.7763(4) Å, c = 2.9233(2) Å, V = 174.04(2) Å 3 ); (Pb,Fe)-doped mullite (Pb 0.02 Fe 0.68 Al 3.95 Ge 1.37 O 9.70 ; a = 7.7125(7) Å, b = 7.8527(7) Å, c = 2.9528(2) Å, V = 178.83(3) Å 3 ); (Pb,Cr)-doped mullite (Pb 0.01 Cr 0.63 Al 3.90 Ge 1.47 O 9.75 ; a = 7.6917(6) Å, b = 7.8168(6) Å, c = 2.9522(2) Å, V = 177.50(2) Å 3 ); (Pb,Nd)-doped mullite (Pb 0.06 Nd 0.02 Al 4.82 Ge 1.18 O 9.69 ; a = 7.6585(7) Å, b = 7.7666(7) Å, c = 2.9164(3) Å, V = 173.47(3) Å 3 ); (Pb,Sm)-doped mullite (Pb 0.06 Sm 0.02 Al 4.55 Ge 1.45 O 9.79 ; a = 7.6563(3) Å, b = 7.7873(3) Å, c = 2.9236(1) Å, V = 174.31(1) Å 3 ); Pb is only incorporated into the crystal structure when a co-dopant element is present. Then it resides together with Nd or Sm in the oxygen-vacancy sites created by the formation of triclusters of AlO 4 and GeO 4 tetrahedra. In the case of (Pb,Fe)-doped mullite, Fe shares the same position as Al and Ge. In contrast to the (Al,Si)-mullites, Ge is located in both tetrahedral sites T and T*. The occupancies follow a substitution scheme according to Pb q (Nd,Sm) r (Cr,Fe) z Al 4+2 v − z Ge 2−2 v O 10− v + q +3/2 r . With v = number of vacancies, such a mullite can be understood as a “stuffed mullite” derived from a related “open mullite” (no vacancies filled with large cations) of composition (Cr,Fe) z Al 4+2 v − z Ge 2−2 v O 10− v and then “stuffed” with q Pb 2+ + r (Nd 3+ ,Sm 3+ ) formula units where concurrently the number of available O3-vacancies is reduced by q + 3/2 r units of extra oxygen. Thus, charge compensation upon incorporation of Pb 2+ and (Nd,Sm) 3+ is achieved by adding the amount of oxygen corresponding to the oxidation state of divalent Pb 2+ and trivalent rare-earth elements. Based on this description, the maximum number of large cations which can be stuffed into the mullite structure can directly be calculated from the v -value of the related “open mullite”. In contrast, the smaller cations Fe 3+ and Cr 3+ are directly substituting Al 3+ . In the stuffed mullites, Pb and (Nd,Sm) could not be distinguished and were refined with a mixed occupancy on the same site. In addition to structure analysis, refractive indices of (Pb,Nd)-mullite were determined by immersion methods using a micro-refractometer spindle stage yielding n x = 1.697(3), n y = 1.708(3), and n z = 1.710(3) and 2 V z = 122(4)°. The mean refractive index corresponds closely to the corresponding parameter calculated from the chemical composition whereas it would be significantly off if the extra cations were ignored, thus representing an independent evidence for the incorporation of Pb and Nd into the crystal structure.

Dolomite-type MSn(BO 3 ) 2 phases for M = Mn, Fe, Co and Ni have been synthesized using solid-state synthesis carried out in sealed quartz tubes. X-ray powder diffraction data Rietveld refinements confirm the rhombohedral space group R 3 ‾ $R\overline{3}$ for all compositions. The change in unit-cell parameters follows the increasing nature of the radius of the M-cations. Both the MO 6 and SnO 6 octahedra are found to be quite regular. 119 Sn Mössbauer spectroscopy investigations complement the almost undistorted nature of the SnO 6 octahedra and the tetra-valent charge of the tin-atoms. Detailed vibrational features are described from the Raman and the FTIR spectral data collected at ambient conditions. The frequency shifts of some selective Raman and IR bands are explained in terms of the change of cationic sizes and the respective M–O bond distances. The UV/Vis diffuse reflectance data are analyzed using the RATD method, leading to direct bandgaps for all the investigated samples. The wide bandgap semiconductors (3 – 4 eV) show increasing transition energies with increasing cation sizes of the high-spin M-cations in the dolomite types.

Crystals of two new polymorphic forms of the known compound (NaCl)[Cu(HSeO 3 ) 2 ], which we term polymorphs II and III , were formed after a ca . one-year dwelling of a crystalline precipitate under mother liquor and upon crystallization in the presence of K + , respectively. Both structures belong to the “layered copper hydroselenite” family. The polymorph II is a structural analog of (KCl)[Cu(HSeO 3 ) 2 ] with a fully ordered Na + site; the main difference concerns the environment of Cu 2+ which is more regular in (NaCl)[Cu(HSeO 3 ) 2 ] -II . In contrast to some expectations, crystallization from solutions containing KCl. NaCl, CuCl 2 , and H 2 SeO 3 upon evaporation does not result in formation of mixed (Na 1− x K x Cl)[Cu(HSeO 3 ) 2 ] crystals, but rather in a separate crystallization of (KCl)[Cu(HSeO 3 ) 2 ] and (NaCl)[Cu(HSeO 3 ) 2 ]- III which exhibits a complex structure with four ordered and one disordered Na + sites. It is possible that longer crystallization times enhance formation of ordered structures.

In intermetallic chemistry, the Gd 14 Ag 51 structure type is rather common and has many amalgam representatives. Up to today, binary amalgams of this type have been described for M  = Na, Ca, Sr, Eu, Yb, and the structure family still is growing. Yb 11 Hg 54 is the only representative with a fully ordered crystal structure, and all other representatives exhibit individual disorder phenomena or patterns. The diversity of disorder phenomena in this structural family is unique. In order to shed a light on the underlying reasons for this unexpected structural complexity, we compare the available literature structure models with three new ternary variants, Yb 10.7 Sr 0.3 Hg 54 , Ca 4.5 Eu 6.5 Hg 54 and Ca 6.9 Na 4.1 Hg 54 (all in space group type P 6 ‾ $P\overline{6}$ , a  = 13.5379(12), 13.5406(8) and 13.564(5) Å, c  = 9.7488(14), 9.7149 and 9.810(7) Å for Yb 10.7 Sr 0.3 Hg 54 , Ca 4.5 Eu 6.5 Hg 54 and Ca 6.9 Na 4.1 Hg 54 , respectively). Their crystal structures have been examined in detail on the basis of both single crystal and powder X-ray diffraction data. Each of the three new amalgams exhibits its own set of disorder phenomena that is again different from those of the respective binary variants. The synopsis of the crystal structures and their individual disorder phenomena indicates that the reason for the disorder phenomena cannot be found only by analyzing geometric details such as atomic radii quotients or coordination polyhedral volumina, and additional electronic reasons must be assumed.

The ternary Laves phases Sr 2 Pd 3 Sn, Eu 2 Pd 3 Sn and Eu 2 Pd 3 In were synthesized by induction melting of the elements in sealed tantalum ampoules. The polycrystalline products were characterized through their powder X-ray diffraction patterns. The structure of Eu 2 Pd 3 Sn was refined from single crystal X-ray diffractometer data: Mg 2 MnGa 3 type, Cmcm , a = 583.36(5), b = 908.31(7), c = 958.06(8) pm, w R 2 = 0.0366, 557  F 2 values, 23 variables. The palladium and tin atoms show the inverse coloring on the network of condensed tetrahedra of Mg 2 MnGa 3 , i.e., MnGa 3 versus Pd 3 Sn. Refinement of the occupancy parameters revealed small defects for the europium site, leading to composition Eu 1.962(6) Pd 3 Sn for the studied crystal. Sr 2 Pd 3 Sn is a Pauli paramagnet and Eu 2 Pd 3 Sn shows Curie-Weiss paramagnetism (7.86(1) µ B  Eu atom −1 and Θ P = 48.1(1) K). Ferromagnetic ordering is observed below T C = 46.1(1) K. The 119 Sn and 151 Eu Mössbauer spectra of Sr 2 Pd 3 Sn and Eu 2 Pd 3 Sn are discussed with respect to electron density changes as a function of the tin content and the ionicity in the sequence of the stannides Sr 2 Pd 3 Sn/Eu 2 Pd 3 Sn → Sr 2 Pd 2 Sn/Eu 2 Pd 2 Sn → EuPdSn → EuPdSn 2 .

Yellow needles-like single crystals of Li 4 P 2 S 6 were obtained serendipitously during the preparation of Li 7 P 3 S 10 O. The twinned crystal structure of Li 4 P 2 S 6 was determined from single-crystal X-ray diffraction data [w R ( F 2 ) = 0.069, 716 reflections, 40 variables]. Li 4 P 2 S 6 crystallizes in the trigonal system, space group P 3 ‾ m 1 $P\overline{3}m1$ (N° 164), a  = 10.5042(8) Å, c  = 6.5837(6) Å, V  = 629.11(9) Å 3 and Z  = 2. The lithium octahedra form a [Li 4 S 6 ] 8− honeycomb-like structure within which diphosphate units are located. The comparison of our crystal structure to those of P 6 3 / mcm -, P 3 ‾ 1 m $P\overline{3}1m$ -, and P 321-Li 4 P 2 S 6 demonstrated group-subgroup relationships and associated the disorder or order of the phosphorus atoms within the identical [Li 4 S 6 ] 8− 3d-frameworks to the choice of the unit cell (the subcell with a  ∼ 6.07 Å vs. the supercell with a  ∼ 10.5 Å).

The crystal structure of the β-phase of Pigment Yellow 110 was determined from X-ray Powder Diffraction (XRPD) data. The crystal structure of the α-phase (Erk et al., CrystEngComm 2004, 6 , 474) is re-refined against the original XRPD data to modern-day standards. Dispersion-corrected density functional theory calculations are used to complement the powder data. The α- and β-form crystallise in P 1 ‾ $P\overline{1}$ and P 2 1 / c , respectively, with the P.Y. 110 molecule occupying a centre of symmetry in both forms. Both polymorphs are layered structures consisting of infinite chains of hydrogen-bonded molecules.