bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diffusion lengths in GaN obtained from steady state photocarrier gratings (SSPG)
Authors: Niehus M. , Schwarz R. 
Published: May 2006

AbstractWe present diffusion length measurements in gallium nitride (GaN) and AlXGa1–XN/GaN multilayers with aluminium contents up to Xmax = 37 at.%. The opto‐electrical method employed is the steady‐state photocarrier grating (SSPG), which uses two interfering laser beams to induce a periodic resistivity modulation normal to the sense current lines. We experimentally refined the SSPG, using a double beamsplitter technique and introducing a variable ND filter. We measured diffusion lengths of single GaN and AlXGa1–XN/GaN double layers, and analysed the obtained diffusion lengths as function of the aluminium concentration, comparing them with the respective drift lengths. Finally, we critically discuss the common interpretation in terms of ambipolar transport. We suggest a new model in which minority carriers are rapidly trapped in acceptor‐like valence band tails and participate in the grating blurring passively, as spatially localized recombination centres. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Recent results on AlN growth by HVPE and fabrication of free standing AlN wafers
Authors: Soukhoveev V. , Kovalenkov O. , Ivantsov V. , Syrkin A. , Usikov A. , Maslennikov V. , Dmitriev V. 
Published: May 2006

AbstractProperties of thick crack‐free AlN layers grown by hydride vapor phase epitaxy (HVPE) on 2‐inch and 3‐inch silicon carbide (SiC) and sapphire substrates are described. The maximum thickness of crack free layer was 75 μm and 15 μm for AlN grown on SiC and sapphire, respectively. Wafer bow was contolled below 50 μm for AlN/SiC wafers. Surface for as‐grown and polished AlN surface was studied. X‐ray diffraction and wet chemical etching was used for crystal quality evaluation showing defect density in high 107 to low 108 cm–2 range. Initial experiments on AlN growth on patterened SiC wafers resulted in local etch pit density of about 2x107 cm–2 for 35 μm thick AlN layer. Electrical resistivity of AlN layers exceeded 1011 and 106 Ω cm at 300 K and 600 K, respectively. Free‐standing 2‐inch AlN wafers were fabricated by removal of SiC substrate using reactive ion etching. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
[Sb11]3− and [As11]3−: Synthesis and Crystal Structure of Two New Ammoniates containing Trishomocubane‐like Polyanions
Authors: Hanauer Tobias , Korber Nikolaus 
Published: May 2006

AbstractThe ammoniates [K(18‐crown‐6)(NH3)2]3Sb11 · 5.5NH3 (1) and [Cs(18‐crown‐6)]2CsAs11 · 8NH3 (2) (18‐crown‐6 = 18C6: 1,4,7,10,13,16‐Hexaoxacyclooctadecan) were synthesized by either the reaction of K3Sb7 with SbPh3 in liquid ammonia or by extraction of Cs3As11 with liquid ammonia. Single crystals were isolated and characterized by low temperature X‐ray structure analysis. [K(18‐crown‐6)(NH3)2]3Sb11 · 5.5NH3 crystallizes in the space group $P{\bar 1}$ with a = 13.31(2) Å, b = 15.161(2) Å, c = 22.521(3) Å, α = 99.23(1)°, β = 100.99(1)° and γ = 105.03(1)°. [Cs(18‐crown‐6)]2CsAs11 · 8NH3 crystallizes in the monoclinic space group C2/c with a = 20.009(3) Å, b = 17.024(1) Å, c = 19.838(2) Å and β = 119.732(9)°. While 1 contains isolated [Sb11]3− anions and [K(18‐crown‐6)(NH3)2]+ complexes, cesium–arsenic contacts lead to one–dimensionally infinite $^{1}_{\infty}\rm [CsAs_{11}]^{2-}$ chains in 2.
Structure Motifs of Sodium Stannides on the Tin‐rich Side of the Phase Diagram
Authors: Fässler Thomas F. 
Published: May 2006

AbstractThe flexibility of the Sn‐Sn bond is acknowledged by the structural variety of compounds which are formed between tin and electropositive metals as minority components. As demonstrated for Na/Sn, already in the case of simple, binary systems a plethora of different structural motifs becomes obvious. Although the phase diagram of sodium and tin has been studied extensively for many years, the series of sodium stannides could be complemented by several new representatives during the last few years.
Structure and Stability of TaON Polymorphs
Authors: Bredow Thomas , Lumey Marck‐Willem , Dronskowski Richard , Schilling Heikko , Pickardt Joachim , Lerch Martin 
Published: May 2006

AbstractThe stabilities and electronic structures of several polymorphs of tantalum oxynitride, TaON, were studied quantum‐chemically at density‐functional level. Results obtained by complementary quantum‐chemical techniques with wave‐functions either expanded in atom‐centered functions or in plane waves were compared. Close agreement was obtained for the relative stabilities of the baddeleyite, anatase, rutile, and fluorite phases of TaON. The effect of anion distribution on the structural parameters and the lattice energies of the anatase and rutile polymorphs was investigated. The calculated band structure of the polymorphs is compared with available experimental information.
Synthesis and Characterization of Na5[VO4][O] and Na4[VO4][OH]
Authors: Kerp Oliver , Möller Angela 
Published: May 2006

AbstractNa5[VO4][O] and Na4[VO4][OH] were obtained from reactions of V2O5 with Na2O and additional NaOH in the latter case, respectively, at 600‐700 °C in sealed Ag containers under Ar atmosphere. The crystal structures have been determined from X‐ray single crystal data. The structures contain isolated [VO4]3− complexes and non‐coordinating oxide and hydroxide anions, respectively. Raman and infrared data is compared for both compounds and hydrogen bonding is discussed for Na4[VO4][OH].
Verbindungen A3M5 (A = Erdalkalimetall, M = Triel/Tetrel): Eine Fallstudie zur strukturellen und elektronischen Stabilität polarer intermetallischer Phasen
Authors: Rhode Michael , Wendorff Marco , Röhr Caroline 
Published: May 2006

AbstractCompounds A3M5 (A = alkaline earth, M = triel/tetrel): A Case Study on Structural and Electronic Factors Stabilizing Polar IntermetallicsStarting from the non electron precise binary compounds Ca3Ga5/Sr3In5 (Hf3Ni2Si3 type) and Ba3Al5 at one hand and Ba3Pb5 (Pu3Pd5 type) at the other hand, a series of new ternary intermetallics of the general formula A3M5 (A: alkaline earth, M: triel/tetrel) has been synthesized, structurally characterized and studied by band structure calculations. The chemical substitution of M in A3M5 allows, via the continous variation of the radius ratio (rA:rM) and the valence electron number (VE/M) the detection of the geometrically and electronically determined stability ranges of the three structure types formed by the binary compounds. At values of rA:rM between 1.30 and 1.52 in the triel rich region of A3M′xM″5−x the Hf3Ni2Si3 type (orthorhombic, space group Cmcm) is formed: In Ca3Ga5 up to 1.8 Ga can be substituted by Al, in Sr3In5 similar amount of In can be replaced by either Al or Ga. The mixed trielide Sr3Al2.6Ga2.4 (a = 468.4(1), b = 1132.5(1), c = 1570.0(2) pm, R1 = 0.0261) can be obtained, although both corresponding binary phases are not known. At larger values of the ratio rA/rM as in Ba3Al3Ga2 (Ba3Al5 type, hexagonal, space group P63/mmc, a = 598.9(1), c = 1456.0(3) pm, R1 = 0.0353) layers of condensed M5 building blocks with Al‐Al partial bonds are formed. Substituting one In position in Sr3In5 against Pb results in the isotypic, but electron precise Zintl compound Sr3In4Pb (a = 506.1(1), b = 1191.8(3), c = 1650.2(4) pm, R1 = 0.0286), where the Fermi level in shifted into a distinct minimum of the density of states. Conversely, at the tetrele rich end of the series A3InxPb5−x, characterized by compounds of the Pu3Pd5 type (orthorhombic, space group Cmcm) with almost isolated nido clusters M5, a minimum of the DOS can be reached, if Pb is partially substituted by In (A3InxPb5−x with A = Sr/Ba: x = 0.7/0.6; a = 1084.6(2)/1118.6(2), b = 867.1(2)/904.4(1), c = 1104.8(2)/1133.9(2) pm, R1 = 0.0394/0.0434).
Characterization of Mixed Crystals in the System Cu2MnxCo1−xGeS4 and Investigations of the Tetrahedra Volumes
Authors: Bernert Thomas , Pfitzner Arno 
Published: May 2006

AbstractIn a series of investigations on normal tetrahedral compounds we present mixed crystals in the system Cu2MnxCo1−xGeS4 (0 < x < 1) and an inspection of their tetrahedra volumes. Cu2CoGeS4 crystallizes tetragonal in a stannite type structure, Cu2MnGeS4 crystallizes orthorhombic in the wurtzstannite structure type. The crystal structures of Cu2CoGeS4 and Cu2Mn0.68Co0.32GeS4 were refined from single crystal diffraction data. The refinement of Cu2CoGeS4 converged to R = 0.0547 and wR2 = 0.0847 for 299 unique reflections. The refinement of Cu2Mn0.68Co0.32GeS4 converged to R = 0.0481 and wR2 = 0.0877 for 1556 unique reflections. From these data the tetrahedra volumes of the end members and of Cu2Mn0.68Co0.32GeS4 are calculated. In Cu2CoGeS4 tetrahedra [MS4] are similar in size. In contrast, the differences of the volumes of the polyhedra [MS4] in the orthorhombic wurtzite superstructure type compounds Cu2MnGeS4 and Cu2Mn0.68Co0.32GeS4 are significant (M = Cu, Mn, (Mn0.68Co0.32), Co, Ge). From x = 0 to x = 0.5 the tetragonal structure type dominates while from x = 0.7 to the Cu2MnGeS4 end member the products crystallize in the orthorhombic structure type. Melting points of the mixed crystals decrease linearly with increasing manganese content.
PdAs2O6, das erste paramagnetische Palladiumoxid
Authors: Orosel Denis , Jansen Martin 
Published: May 2006

AbstractPdAs2O6, the First Paramagnetic Palladium OxideSsolid state reaction of palladium(II) oxide (PdO) and arsenic(V) oxide (As2O5) yielded an auburn colored microcrystalline powder of palladium(II) metaarsenate(V), PdAs2O6. The crystal structure of the compound belongs to the PbSb2O6 structure type, $P{\bar 3}{\rm 1}m$ (no. 162), a = 4.8196(0) Å, c = 4.6646(1) Å, V = 93.84(0) Å3 and Z = 1. The structure consists of layers of edge sharing AsO6 octahedra and PdO6 octahedra connecting them. This is one of the rare structures with divalent palladium in octahedral coordination by oxygen. The compound is paramagnetic and shows antiferromagnetic ordering at about 150 K, which is 5 times higher than that of the isotypic NiAs2O6 compound.
The Structural Systematics of Protonation of Some Important Nitrogen‐base Ligands. IV. Some Ethane‐1,2‐diaminium Univalent Anion Salt/1,10‐Phenanthroline (Hydrate) Arrays
Authors: Buttery Jarrod H. , Effendy  , Junk Peter C. , Mutrofin Siti , Skelton Brian W. , Whitaker Claire R. , White Allan H. 
Published: May 2006

AbstractSyntheses and single crystal X‐ray structure characterisations are recorded for some novel series of crystalline complexes formed between salts of univalent anions of the ethane‐1,2‐diaminium cation, [enH2]X2, and 1,10‐phenanthroline (‘phen’), variously hydrated, thus: [enH2]X2·mphen(·nH2O), for m = 2, 4 and 10 (one example), n various. In all cases, the motifs constituting the arrays comprise columns of [enH2]2+ cations, carrying the protonic array but linked in a second dimension by hydrogen‐bonding to associated anions and water molecules (where present), expanding the column in some cases to form a sheet, different degrees of hydration compensating for changing anion bulk. In a third dimension the protonic hydrogen complement also links to the nitrogenous component of phen stacks which surround the column. Thus, for the m = 2 array, in a triclinic $P{\bar 1}$ cell, a, b, c broadly 10‐11 (x2), 7Å, α, β, γ 80, 70° (x2), the cation and phen columns lie parallel to c; in the unsolvated trichloroacetate compound, the cation column is associated with anions to either side, these linking into a sheet with water molecules in the more highly hydrated trifluoroacetate (‘tfa’) and nitrate (n = 2), and chloride and bromide (n = 4) arrays (the tfa adduct a superlattice doubled in c). In the m = 4 arrays, an additional phen stack is inserted, forming a sheet with the first in the second dimension for the perchlorate tetrahydrate array, the iodide pentahydrate counterpart being a 2 x c superlattice. A second nitrate salt, m = 10, n = 4, is also described, a complex array of multiple networks of the above type. Single crystal X‐ray structure determinations are also recorded for salts [phenH](PF6)·phen and [2,9‐Me2phenH](PF6). In the phen adduct, the protonic hydrogen atom is closely associated (N···H 0.90(4) Å) with one of the two independent phen moieties, these disposed alternately in a stack up b close to the 21 screw axis, so that the hydrogen bridges to the unprotonated moiety (H···N′ 2.36(4) Å) pitched at an angle of 47° to it in the screw‐related stack. In the Me2phen salt, the phen moieties lie in crystallographic mirror planes, normal to and stacked up b, with the protonic hydrogen atom contacting a PF6 fluorine atom (H···F 1.96(3) Å). The structure of unsolvated Me2phen is also recorded.
Solvothermal Synthesis and Crystal Structure of Mn2(C5H14N2)Sb2S5: A New Member of the Mn2(L)Sb2S5 Family (L is an Organic Structure Director)
Authors: Puls A. , Näther C. , Bensch W. 
Published: May 2006

AbstractThe new compound Mn2(C5H14N2)Sb2S5 (C5H14N2 = 1,3‐diaminopentane, DAPE) was prepared under solvothermal conditions using the elements as starting materials. The compound crystallizes in the orthorhombic space group Pbca with the lattice parameters a = 12.620(3), b = 11.877(2) and c = 21.814(4) Å. The primary building units are trigonal SbS3 pyramids and distorted MnS6 and MnS4N2 octahedra. These primary building blocks are joined to form Mn2Sb2S4 hetero‐cubane units which are then connected via common corners, edges and faces thus forming a second type of hetero‐cubane. The hetero‐cubanes are condensed into layers within the (001) plane. The connection mode yields ellipsoidal pores within the layers with dimensions of about 9·7.5Å. The N atoms of the structure directing amines are exclusively bound to one of the two crystallographically independent Mn2+ cations and they point into the pores and between the layers separating the layers from each other. The interlayer separation measures about 6.7Å. Whereas the MnS6 octahedron shows only a moderate distortion the MnS4N2 octahedron is severely distorted with a remarkable long Mn‐S bond length of 2.968Å.
Syntheses of Phosphoryl Chloro‐ and Bromofluorides and Crystal Structures of POFCl2 and POF2Cl
Authors: Rovnaník Pavel , Žák Zdirad , Černík Miloš 
Published: May 2006

AbstractA simple procedure for the preparation of phosphoryl chlorofluorides, POFCl2 and POF2Cl, by chlorination of the appropriate potassium fluorophosphates, K2PO3F and KPO2F2, respectively, with PCl5 is described. The analogous bromination with PBr5 gives POFBr2 and POF2Br. However, due to low yields and high content of impurities, this method is not suitable for the synthesis of the former compound. Both chlorofluorides were crystallized from the melt at low temperatures and their crystal structures were determined by X‐ray diffraction at −153 °C. Distorted tetrahedral molecules of POFCl2 are only weakly associated through intermolecular O···Cl contacts forming infinite chains similarly as in crystalline POCl3. In POF2Cl, however, the chains are formed by the O···P contacts, and an additional P–O···Cl bridging leads to their linkage into a double‐chain structure.
Synthese und Kristallstruktur von Blei(II)‐oxidhalogenid‐Alkoholaten mit unterschiedlichen Verknüpfungsvarianten von Pb4O4‐Heterokubaneinheiten
Authors: Oldag Thorsten , Keller Hans‐Lothar 
Published: May 2006

AbstractSynthesis and Crystal Structure Determination of Lead(II) Oxide Halide Alcoholates with Different Connectivity of Pb4O4 Heterocubane‐like SubunitsThe reaction of red lead(II) oxide (Litharge) and lead(II) halide (Cl− and Br−) with diethylene glycole at a temperature of 180 °C leads to the isotypic compounds [Pb6(C4H8O3)O2Cl6] (1) and [Pb6(C4H8O3)O2Br6] (2). In a similar synthesis with PbI2 as educt at temperature of 160 °C the two modifications β‐[Pb6(C4H8O3)O2I6] (3) and α‐[Pb6(C4H8O3)O2I6] (4) were found, whereas at a reaction temperature of 180 °C [Pb9(C2H4O2)(C4H8O3)O3I8] (5) was surprisingly obtained as product. The X‐ray diffraction data show that at a temperature of 180 °C a splitting of the ether took place. The cited compounds show cubane like subunits built by lead and oxygen atoms. These fragments are connected by alkoholate molecules. In 5 additionally an I6 octahedra centered by lead is observed.
Trichloroberyllat‐Komplexe von Dimethylcyanamid, Morpholin und 4,4′‐Bipyridin
Authors: Neumüller Bernhard , Dehnicke Kurt 
Published: May 2006

AbstractTrichloroberyllate Complexes of Dimethyl Cyanamide, Morpholine, and 4,4′‐BipyridineThe trichloroberyllate complexes (Ph4P)[BeCl3(NCNMe2)] (1), (Ph4P)[BeCl3{HN(CH2)4O}] (2), and (Ph4P)2[(BeCl3)2(4,4′‐bipy)] (3) were prepared by reactions of (Ph4P)2[Be2Cl6] with dimethyl cyanamide, trimethylsilylmorpholinate, and 4,4′‐bipyridine, respectively, in dichloromethane solutions. 1‐3 were characterized by X‐ray crystallography and by IR‐spectroscopy.1·CH2Cl2: Space group P1, Z = 1, lattice dimensions at 173 K: a = 714.2(1), b = 919.5(2), c = 1233.4(2) pm, α = 94.97(1)°, β = 90.86(1)°, γ = 111.90(1)°, R1 = 0.0310. In the complex anion [BeCl3(NCNMe2)]− the dimethyl cyanamide ligand is coordinated via a linear Be–N≡C‐NMe2 arrangement, the CH2Cl2 molecules forming linear chains by hydrogen bridges ···HCH···Cl··· with the chlorine atoms of the {BeCl3−} groups.2: Space group $P{\bar 1}$, Z = 2, lattice dimensions at 173 K: a = 1050.9(1), b = 1099.7(1), c = 1308.3(2) pm, α = 87.57(1)°, β = 70.97(1)°, γ = 74.58(1)°, R1 = 0.0397. The complex anions are dimerized by centrosymmetric puckered eight‐membered [Be–N–H···Cl]2 rings.3·2CH2Cl2: Space group $P{\bar 1}$, Z = 2, lattice dimensions at 173 K: a = 1095.4(1), b = 1559.6(2), c = 1869.8(3) pm, α = 79.12(1)°, β = 73.83(1)°, γ = 78.76(1)°, R1 = 0.0548. The complex contains dianions [Cl3Be(μ‐bipy)BeCl3]2− with Be–N distances of 177.0(6) and 178.5(6) pm. Both {BeCl3}− groups form C–H···Cl hydrogen bridges with the dichloromethane molecules.
The effects of saprobic conditions on some ciliated Protozoa in the benthos and hypolimnion of a eutrophic pond
Authors: GOULDER R. 
Published: May 2006

SummarySeasonal fluctuations in numbers of some mesosaprobic ciliated Protozoa were followed from May 1969 to December 1970 in a eutrophic pond in north‐west England. The most common species were Loxodes magnus and Loxodcs striatus; some counts of Frontonia leucas, Spirostomum teres, Stentor coeruleus and Paramecium caudatum were also made.From about October to May, when the pond was mixed and the bottom water was well oxygenated, dense benthic populations of these ciliates were found (maxima 221 L. magnus and 293 L. striatus in 0·1 ml of sediment). They were absent from the plankton.In summer, stratification occurred, conditions in the hypolimnion became saprobic (i.e. low oxygen and high levels of potentially toxic substances such as sulphide, ammonia, and carbon dioxide), and very few benthic ciliates were present. Some planktonic Loxodes (up to 34 L. magnus and 137 L. striatus/ml) were, however, found in the hypolimnion. Possibly conditions in the water column were less severe than in the sediment, or perhaps the planktonic ciliates migrated vertically, from time to time, to an oxygen supply at the boundary with the epilimnion.Experimental exposure of the Loxodes species (also S. teres) to saprobic conditions in closed bottles caused the death of most ciliates within 50–150 h of closing the bottles.Deoxygenation of Loxodes was also carried out in a stream of argon, when there was no build‐up of the potential toxins associated with anoxia. Almost all Loxodes were lost between 20 and 70 h, hence, oxygen deficiency alone is probably sufficient to explain the low populations in the summer benthos.
The recent diatom history of Loch Leven, Kinross
Authors: HAWORTH ELIZABETH Y. 
Published: May 2006

SummaryDiatoms in the top metre of lake sediment have been studied for indications or recent changes in the environment of Loch Leven. The diatoms indicate a eutrophic, alkaline lake with Melosira italica ssp. subarctica, Tabellaria Flocculosa and Stephanodiscus astraea the dominant taxa at the base of the 1‐m section. There is then an appeance of Melosira ambigua and Stephanodiscus hantzschii suggesting a richer environment. Post A.D. 1816 changes in taxa suggest possible correlation with the lowering of lake level in 1830 and the dominance of Diatoma elongatum, Cyclotella pseudostelligera, Stephanodiscus astraea var. minutula, S. tenuis, S. hantzschii, and Synedra rumpens and var. soctica in zone 4 agrees with present‐day plankton records.
Lakes of south‐western Uganda
Authors: DENNY PATRICK 
Published: May 2006

SummaryLake Bunyonyi was formed about 18,000 years B.P. by a volcanic eruption which blocked a steep‐sided valley. Earlier this century fish were introduced into the lake but recently there have been mass fish deaths. Although the thermocline was inconspicuous, density profiles showed the lake to the stratified and chemical evidence suggested stratification was for many years. The water was clear with little plankton and the epilimnioncontained low concentrations of dissolved mineral ions. The hypolimnion was anoxic and had a relatively high mineral ion concentration. The mass fish deaths were attributed to a violent shallow mixing, probably caused by wind, but mixing was insufficient to remineralize the epilimnion.
Rates of gastric evacuation in brown trout, Salmo trutta L.
Authors: ELLIOTT J. M. 
Published: May 2006

SUMMARYBrown trout of similar length and weight were fed a standard meal which contained a known number of food organisms of the same size‐group and taxon (seven taxa were used). The weight of digestible organic matter in a trout stomach decreased exponentially with time. i.e. at a constant relative rate. At a particular water temperature, the food organisms were either evacuated from the stomach at similar rates (Group 1: Gammarus pulex, Baetis rhodani, Chironomidae, Oligochaetes) or at progressively slower rates (Group 2: Protonemura meyeri, Hydropsyche spp., Tenebrio molitor). Rates of gastric evacuation were not significantly different for food organisms of different size groups of the same taxon, or for different sized meals, or for different sizes of trout (range 20–30 cm), or for mixed and multiple meals (three meals over 16 h). Times are given for the gastric evacuation of 50%, 75%, 90% and 99% of the digestible organic matter in a meal. Starvation periods of 1, 2, 3,4 and 5 days prior to feeding did not affect evacuation rates. The rates were slightly, but not significantly, slower for starvation periods of 6 and 7 days, and were often significantly slower for starvation periods of 10, 15 and 20 days. Evacuation rates increased exponentially with increasing water temperature. It was possible to estimate both the rate and time for the gastric evacuation of different meals at water temperatures between 3–8°C and 19·1°C.
Actinomycete virus in fresh water
Authors: WILLOUGHBY L. G. , SMITH SUSAN M. , BRADSHAW R. M. 
Published: May 2006

SUMMARYAn ecological study was made of the freshwater distribution of Actinomycete virus. One component of this, the virus of Actinoplanes, is highly specific and its pattern of occurrence mirrors that of its host. The occurrence of Streptomyces virus is more difficult to explain in ecological terms, but this is attempted. Micromonospora virus was not obtained and the significance of this is discussed. The Actinoplanes virus is characterized at the fine‐structure level by a polyhedral‐shaped head with a tail bearing a contractile sheath, the latter feature being previously undescribed for actinophage.