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  • 1
    ISSN: 1434-6036
    Keywords: 75.30M ; 61.60 ; 78.70D ; 76.80
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report on measurements of the lattice constants, magnetic susceptibility, LIII X-ray absorption and Mössbauer-effect on EuNiP and EuPdP, which crystallize in the hexagonal layered Ni2In structure. In both compounds the Eu valence above 510 K is 2.33. With decreasing temperature they show one (EuPdP) or two (EuNiP) first order phase transitions with a valence increase of about 0.16. At the same time thec-axis shrinks while the a-axis even increases. From Mössbauer measurements we show that the nature of the valence mixing is static. In contrast, the valence mixing in isostructural EuPtP is static at low temperatures, too, but it becomes homogeneous valent above a first order phase transition at 235 K. The behaviour of these compounds (as well as that of EuPdAs) is explained in a new model of electrostatically charged layers. In this model we can explain the temperature dependence of the lattice constants, the static valence mixing and the occurrence of preferred valences of the order 2 6/n. Together with the compression shift model of Hirst we can also understand the mechanism of the phase transitions. A comparison with EuT2Si2 compounds in ThCr2Si2 structure shows that in EuTX compounds only the electronic structure of the transition elements is relevant for the occurrence of mixed valency.
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  • 2
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The intermetallic alloy EuPdAs exhibits a first order phase transition at 180 K. The transition is seen by anomalies in lattice parameters, susceptibility, resistivity, Moessbauer effect and X-ray absorption. It is accompanied by an increase of the Eu valence from 2.15 to 2.40 between 300 K and 4 K. The nature of the non-integral valence and the phase transition are discussed.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 620 (1994), S. 561-565 
    ISSN: 0044-2313
    Keywords: Ternary palladium phosphide ; erbium ; crystal structure ; band calculations ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Er3Pd7P4  -  Crystal Structure Determination and Extended Hückel CalculationsEr3Pd7P4 was prepared by heating the elements (1050°C) and investigated by means of single-crystal X-ray methods. The compound crystallizes in a new structure (C2/m; a = 15.180(3) Å, b = 3.955(1) Å, c = 9.320(1) Å, β = 125,65(1)°; Z = 2) with a three-dimensional framework of Pd and P atoms and with Er atoms in the holes. The Pd atoms are surrounded tetrahedrally, trigonally or linearly by P atoms, which are coordinated by nine metal atoms in the form of a tricapped trigonal prism. Therefore the atomic arrangement of Er3Pd7P4 is related to the structures of ternary transition metal phosphides with a metal: phosphorus ratio of 2:1. Band calculations using the Extended Hückel method show strong covalent Pd—P bonds and weak bonding interactions between Pd atoms with Pd—Pd distances shorter than 2.9 Å.
    Notes: Er3Pd7P4 wurde durch Erhitzen der Elemente auf 1050°C dargestellt und röntgenographisch mit Einkristallmethoden untersucht. Die Verbindung kristallisiert monoklin (C2/m; a = 15,180(3) Å, b = 3,955(1) Å, c = 9,320(1) Å, β = 125,65(1)°; Z = 2) in einer neuen Struktur mit einem dreidimensionalen Gerüst aus Pd- und P-Atomen, in dessen Lücken sich die Er-Atome befinden. Die P-Umgebung der Pd-Atome ist tetraedrisch, trigonal oder linear. Die P-Atome ihrerseits werden von 9 Metallatomen in Form eines dreifach überkappten trigonalen Prismas koordiniert. Der Aufbau von Er3Pd7P4 ist dementsprechend verwandt mit den Strukturen ternärer Übergangsmetall-Phosphide mit einem Metall: Nichtmetallverhältnis von 2:1. Extended Hückel Rechnungen zeigen u. a. neben starken kovalenten Pd—P-Bindungen schwache bindende Wechselwirkungen zwischen denjenigen Pd-Atomen, deren Abstände voneinander kürzer als 2,9 Å sind.
    Additional Material: 5 Ill.
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  • 4
    ISSN: 0044-2313
    Keywords: ternary aluminium germanides ; yttrium ; rare earth ; crystal structure ; band calculations ; electron localization ; superconductivity ; zintl-compounds ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Y2AlGe3 - a Superconductive Metallic Zintl CompoundY2AlGe3 was prepared by heating the elements (950°C) and investigated by means of single-crystal X-ray methods. The compound crystallizes in a new structure (Pnma; a = 6.785(1) Å, b = 4.189(1) Å, c = 17.676(2) Å; Z = 4) with a three-dimensional framework of Al and Ge atoms and with Y in the cavities. The Al atoms are surrounded tetrahedrally by Ge atoms, which are arranged in the form of planar (Ge2-)∞ chains and isolated from each other respectively. Although Y2AlGe3 is a metallic conductor and no valence compound, it achieves the structural requirements of Zintl's concept. This picture is supported by electrondensity and ELF calculations, which reveals covalent Al—Ge and Ge—Ge bondings, therefore Y2AlGe3 is interpreted as a metallic Zintl-Compound, down-playing the metallic propertys. Y2AlGe3 becomes superconductively at 4.5 K. Isotypic compounds are found for Ln2AlGe3 with Ln = Dy, Ho, Er, and Tm (For lattice constants see “Inhaltsübersicht”).
    Notes: Y2AlGe3 wurde durch Erhitzen der Elemente auf 950°C dargestellt und röntgenographisch mit Einkristallmethoden untersucht. Die Verbindung kristallisiert in einer neuen Struktur (Pnma; a = 6,785(1) Å, b = 4,189(1) Å, c = 17,676(2) Å; Z = 4) mit einem dreidimensionalen Gerüst aus Al- und Ge-Atomen, in dessen Lücken sich die Y-Atome befinden. Al ist tetraedrisch von Ge-Atomen umgeben, die ihrerseits ebene (Ge2-)∞-Ketten bilden bzw. voneinander isoliert vorliegen. Trotz nicht valenzmäßiger Zusammensetzung gemäß Y3+ Y3+ Al3+ (Ge2)4- Ge4- und metallischer Leitfähigkeit weist Y2AlGe3 die Strukturmerkmale einer Zintl-Verbindung auf. Diese Interpretation wird gestützt durch Berechnungen der Elektronendichte und Elektronenlokalisierungsfunktion (ELF), die kovalente Ge—Ge- und Al—Ge-Bindungen zeigen. Die Verbindung wird demnach als metallische Zintl-Verbindung angesehen. Y2AlGe3 wird bei 4,5 K supraleitend. Isotyp kristallisieren die Verbindungen Ln2AlGe3 (Ln = Dy—Tm) mit den Gitterkonstanten: Dy2AlGe3: a = 6,785(3) Å, b = 4,171(1) Å, c = 17,665(7) Å Ho2AlGe3: a = 6,753(2) Å, b = 4,158(1) Å, c = 17,580(4) Å Er2AlGe3: a = 6,732(1) Å, b = 4,147(3) Å, c = 17,517(3) Å Tm2AlGe3: a = 6,706(3) Å, b = 4,061(5) Å, c = 17,550(9) Å.
    Additional Material: 3 Ill.
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  • 5
    ISSN: 0044-2313
    Keywords: Ternary nickel phosphides ; strontium ; barium ; crystal structure ; phase transition ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: About Polymorphism of SrNi2P2 and Crystal Structure of BaNi2P2SrNi2P2 and BaNi2P2 were prepared by heating mixtures of the elements and investigated by single crystal X-ray methods. The Sr compound at room temperature crystallizes in a superstructure of the ThCr2Si2 type (NT-phase; Immm; Z = 6; a = 3.951(2), b = 11.853(2), c = 10.432(2) Å), which is caused by displacements of the atoms from the ideal positions; the P—P distances are 2.45 and 3.28 Å. With increasing temperature at 45°C (ambient pressure) and increasing pressure at 4 kbar (room temperature) respectively the compound undergoes first order phase transitions and crystallizes after that in the undistorted ThCr2Si2 type (I4/mmm; Z = 2). While the P atoms of the high temperature phase (HT-SrNi2P2: a = 3.948(1), c = 10.677(3) Å; 100°C) are isolated from each other (dp p: 3.12 Å) they most probably form pairs in the high pressure phase (HD-SrNi2P2: a = 4.003(1), c = 9.761(2) Å; ca. 4 kbar). This will be discussed on the basis of band structure calculations. BaNi2P2 (a = 3.947(1), c = 11.820(1) Å) also crystallizes in the ThCr2Si2 type structure, the P—P distance is extended to 3.71 Å.
    Notes: SrNi2P2 und BaNi2P2 wurden durch Erhitzen entsprechender Elementgemenge dargestellt und röntgenographisch mit Einkristallmethoden untersucht. Die Sr-Verbindung kristallisiert bei Normaltemperatur in einer Überstruktur des ThCr2Si2-Typs (NT-SrNi2P2: Immm; Z = 6; a = 3,951(2), b = 11,853(2), c = 10,432(2) Å), die durch Auslenkung der Atome aus den idealen Positionen verursacht wird. Die P—P-Abstände längs [001] betragen 2,45 und 3,28 Å. Die Verbindung durchläuft mit steigender Temperatur bei 45°C (Normaldruck) sowie mit zunehmendem Druck bei ca. 4 kbar (Normaltemperatur) jeweils eine Phasenumwandlung 1. Ordnung und kristallisiert dann im unverzerrten ThCr2Si2-Strukturtyp (I4/mmm; Z = 2). Während bei der Hochtemperaturphase (HT-SrNi2P2: a = 3,948(1), c = 10,677(3) Å; 100°C) der P—P-Abstand längs [001] 3,12 Å beträgt, liegt er bei der Hochdruckphase (HD-SrNi2P2: a = 4,003(1), c = 9,761(2) Å; ca. 4 kbar) dem c/a-Verhältnis zufolge vermutlich bei 2,45 Å. Die Gründe für die Phasenumwandlungen werden an Hand der elektronischen Struktur diskutiert, BaNi2P2 (a = 3,947(1), c = 11,820(1) Å) kristallisiert ebenfalls im ThCr2Si2-Typ, der P—P-Abstand längs [001] ist hier auf 3,71 Å aufgeweitet.
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  • 6
    ISSN: 0044-2313
    Keywords: Strontium palladium phosphides ; Sr4Pd5P5, Sr2Pd3P3 ; preparation ; crystal structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Structures with AIB2- and BaAl4-type Units. I The Compounds Sr4Pd5P5 and Sr2Pd3P3Sr4Pd5P5 (Cmcm, a = 4.177(1) Å, b = 31.377(5) Å, c = 8.581(2) Å, Z = 4) und Sr2 Pd3P3(Pmmm, a = 4.199(1) Å, b = 4.212(1) Å, c = 34.227(4) Å, Z = 4) have been prepared by heating the elements. Both structures contain exclusively units characteristic for the AIB2- and BaAl4-type. The ratio between isolated P-atoms and P2-pairs is interpreted with an ionic splitting of the formulas.
    Notes: Sr4Pd5P5 (Cmcm, a = 4,177(1) Å, b = 31,377(5) Å, c = 8,581(2) Å, Z = 4) und Sr2 Pd3P3(Pmmm, a = 4,199(1) Å, b = 4,212(1) Å, c = 34,227(4) Å, Z = 4) wurden durch Erhitzen der Elemente dargestellt. Beide Strukturen setzen sich ausschließlich aus Baueinheiten zusammen, die für AlB2- und BaAl4-Varianten charakteristisch sind. Das jeweils vorliegende Verhältnis von ,isolierten′ P-Atomen zu P2-Hanteln wird anhand einer ionischen Aufspaltung der Formel interpretiert.
    Additional Material: 2 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 618 (1992), S. 30-34 
    ISSN: 0044-2313
    Keywords: Calcium palladium pnictides ; Preparation ; crystal structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Preparation and Crystal Structures of the Compounds CaPdAs, CaPdSb, and CaPdBiThe new compounds CaPdAs, CaPdSb, and CaPdBi were prepared by heating appropriate mixtures of the elements. X-ray structure determinations carried out with single crystals (space group and lattice constants see “Inhaltsübersicht”) showed, that the arsenide crystallizes in a distorted stacking variant of the AlB2, type structure, where the Pd atoms have a planar environment of As atoms. CaPdSb and CaPdBi are isotypic and form the TiNiSi type structure, where the Pd-Atoms are surrounded tetrahedrally (strongly distorted) by Sb or Bi atoms.
    Notes: CaPdAs (Pnma; a = 7,137(1) Å, b = 8,646(2) Å, c = 16,590(3) Å; Z = 16) kristallisiert in einer verzerrten Stapelvariante des AlB2-Typs, bei der die Pd-Atome planar von drei As-Atomen umgeben sind. CaPdSb (a = 7,354(2) Å, b = 4,617(1) Å, c = 7,903(2) Å) und CaPdBi (a = 7,422(2) Å, b = 4,753(1) Å, c = 8,085(2) Å) sind isotyp und bilden die TiNiSi-Struktur (Pnma; Z = 4) mit einer stark verzerrten Tetraederkoordination um die Pd-Atome. Die Verbindungen wurden durch Erhitzen der entsprechenden Elementgemenge dargestellt, die Strukturen röntgenographisch mit Einkristallmethoden bestimmt.
    Additional Material: 3 Ill.
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  • 8
    ISSN: 0044-2313
    Keywords: ternary palladium pnictides ; europium ; calcium ; preparation ; crystal structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Structures with AlB2- and CeMg2Si2-Type Units. The Compounds Eu3Pd4As4, Ca4Pd5P5, and Ca5Pd6P6The new compounds Eu3Pd4As4, Ca4Pd5P5, and Ca5Pd6P6 (space groups and lattice constants see „Inhaltsübersicht“) have been prepared by heating mixtures of the elements. Their structures were determined by means of single-crystal X-ray methods and contain exclusively units, which are characteristic for the AlB2- and CeMg2Si2-type. The non-metal atoms are isolated from each other or connected to pairs; the ratio between these two kinds can be interpreted by ionic splittings of the formulas.
    Notes: Eu3Pd4As4 (Pmmm; a = 4,205(2) Å, b = 4,308(1) Å, c = 12,640(7) Å; Z = 1), Ca4Pd5P5 (Cmcm; a = 4,094(1) Å, b = 31,061(4) Å, c = 8,168(1) Å; Z = 4) und Ca5Pd6P6 (Pmma; a = 8,172(2) Å, b = 4,088(1) Å, c = 19,077(6) Å; Z = 2) wurden durch Erhitzen der jeweiligen Elemente dargestellt. Die mit Röntgen-Einkristallmethoden bestimmten Kristallstrukturen setzen sich ausschließlich aus AlB2- und CeMg2Si2-analogen Einheiten zusammen. Die Nichtmetallatome sind teils voneinander isoliert und teils zu Hanteln miteinander verknüpft; das jeweilige Verhältnis läßt sich mit Hilfe einer ionischen Formelaufspaltung interpretieren.
    Additional Material: 3 Ill.
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  • 9
    ISSN: 0044-2313
    Keywords: Ternary Rhodium phosphides ; crystal structure ; phase transition ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: About the Effect of Temperature, Pressure, and Substitution on the Crystal Structure of ARh2P2 (A = Ca, Sr, Eu, Ba)Four compounds ARh2P2 (A = Ca, Sr, Eu, Ba) were prepared by heating mixtures of the elements and investigated by means of single crystal X-ray methods. They crystallize in the ThCr2Si2 type structure (I4/mmm; Z = 2) with P—P distances along [001] reaching from 2.26 Å (CaRh2P2) to 3.74 Å (BaRh2P2). With increasing temperature (EuRh2P2) or increasing pressure (SrRh2P2) a first order phase transition occurs with strong changes of the P—P distances. Substitution of the atoms changes the bond lengths of the compounds too.
    Notes: Vier Verbindungen ARh2P2 (A = Ca, Sr, Eu, Ba) wurden durch Erhitzen entsprechender Elementgemenge dargestellt und hinsichtlich ihrer Kristallstruktur mit Hilfe von Einkristallmethoden charakterisiert. Sie kristallisieren in der tetragonalen ThCr2Si2-Struktur (I4/mmm; Z = 2) und unterscheiden sich im wesentlichen durch ihre P—P-Abstände längs [001]. Diese reichen von 2,26 Å bei CaRh2P2 bis 3,74 Å bei BaRh2P2 und verändern sich drastisch im Zuge von Phasenumwandlungen 1. Ordnung durch Temperaturerhöhung bei EuRh2P2 sowie unter erhöhtem Druck bei SrRh2P2. Substitution übt ebenfalls einen großen Einfluß auf den Strukturfeinbau der Verbindungen aus.
    Additional Material: 7 Ill.
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  • 10
    ISSN: 0921-4526
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
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