Dmitri O. Charkin

Lomonosov Moscow State University, Moskva, Moscow, Russia

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Publications (15)25.57 Total impact

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    ABSTRACT: Two new ternary arsenides, namely, Eu 7 Cu 44 As 23 and Sr 7 Cu 44 As 23 , were synthesized from elements at 800 °C. Their crystal structure represents a new filled version of the BaHg 11 motif with cubic voids alternately occupied by Eu(Sr) and As atoms, resulting in a 2 × 2 × 2 superstructure of the aristotype: space group Fm3̅ m, a = 16.6707(2) Å and 16.7467(2) Å, respectively. The Eu derivative exhibits ferromagnetic ordering below 17.5 K. In agreement with band structure calculations both compounds are metals, exhibiting relatively low thermopower, but high electrical and low thermal conductivity. ■ INTRODUCTION Intermetallic clathrates−binary silicides of alkali metals−are analogs of gas hydrates and have been known since 1965, 1 but their chemistry and physics attracted significant attention of the scientific community since the late nineties due to their prospective applications as mid-and high-temperature thermo-electric materials. 2−7 The frameworks are mainly based on Si, Ge, and Sn. Their cavities are usually occupied by electro-positive elements such as Eu, Ba, K, or Na, but in rare cases electronegative guest atoms such as Br, I, or Te were also observed. 8 It is shown that clathrates exhibit rather high thermoelectric figures of merit owing to a structural separation of moieties responsible for the efficient transport of charge carriers and for impeding the phonon transport. 7 This brings about a possibility of optimizing these properties almost independently. Recently, the family of clathrates has been expanded by compounds showing peculiar superstructures of various clathrate structure types and also by clathrate-like compounds. 9−16 Importantly, some of these compounds do not contain any group 14 element, for example, Ba 8 Au 16 P 30 14 and Eu 2 Ba 6 Cu 16 P 30 . 16 Although deviating from proper clathrates by composition and crystal structure, these compounds display properties that make them good candidates for creating new thermoelectric materials. In particular, Ba 8 Au 16 P 30 shows an exceptionally low thermal conductivity of 0.18 W m −1 K −1 at ambient temperature. 14 Motivated by this, we have undertaken a search for new clathrate-like compounds among complex pnictides of copper and silver. The systems alkaline earth (A)−coinage metal (T)− pnictogen (Pn) host many attractive and peculiar ternary compounds. An incomplete list includes the clathrate and clathrate-like compounds Ba 8 Cu 16 P 30 15 and Ba 2 Cu 18−x As 10 , 17 a large family of BaAl 4 -derived compounds AT 2 Pn 2 , 18−20 which are closely related to FeAs-based superconductors, and BaCu 6 Pn 2 (Pn = P, As) containing Cu in an oxidation state smaller than +1. 21 In heavier pnictides and commonly also in phosphides, europium adopts the oxidation state +2 and behaves as a structural and electronic analog of alkaline earth metals, forming isostructural compounds. The semifilled 4f level of Eu 2+ gives rise to pronounced, sometimes outstanding, magnetic phenomena. For instance, our recent studies in the A−Cu−P systems revealed two new compounds A 2 Cu 6 P 5 (A = Sr, Eu) along with a yet unique phase EuCu 4 P 3 , which exhibits three consecutive magnetic transitions below 50 K. 22 A crystal chemical peculiarity of these systems is that most structure
    Inorganic Chemistry 09/2014; 53:11173−11184. · 4.59 Impact Factor
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    ABSTRACT: A series of new rare-earth cadmium metal tellurite chlorides were synthesized by the salt flux technique and characterized by single-crystal X-ray diffraction. The new compounds CdSm2(TeO3)2Cl4 (I), CdEu2(TeO3)2Cl4 (II), and CdGd2(TeO3)2Cl4 (III), adopt layered structures corresponding to sequences of metal oxide [LnTeO3] and metal halide [Cd1–xCl3] layers. They expand the known family of 2D rare-earth selenium oxyhalides into the realm of tellurium(IV) compounds and add a new targeted structure type involving rock salt slabs formed by edge-sharing CdCl6 octahedra. The major differences in the structures of Se and Te compounds lie in the composition of the cationic slabs {[Ln11(SeO3)12]9+ vs. [Ln12(TeO3)12]12+} and symmetry (orthorhombic for selenites vs. tetragonal for tellurites).
    Berichte der deutschen chemischen Gesellschaft 06/2014; · 2.94 Impact Factor
  • Dmitri O. Charkin, Dmitri N. Lebedev, Sergey M. Kazakov
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    ABSTRACT: Simultaneous substitution of WVI by UVI and Bi3+ by La3+ in the structure of ferroelectric Bi2WO6 results in stabilization of the archetypic tetragonal I4/mmm structure which is observed for the first time among [Bi2O2][BO4] Aurivillius-type oxides. Studies at the largest U content revealed a new Aurivillius-like compound Bi1.5La0.5UO6 which exhibits a novel distorted orthorhombic version of the archetypic structure. Formation of monoclinic α-(Bi,Ln)2WO6 structure is suppressed when W is partially substituted by U. Very similar tendencies are observed when proceeding to the derived structure of PbBi3WO8Cl. Besides the tetragonal PbBi3W1−yUyO8Cl (0 ⩽ y ⩽ 0.9) and orthorhombic PbBi3−xLaxUO8Cl (0.2 ⩽ x ⩽ 0.4) solid solutions, we were able to prepare PbBi3W1−yUyO8Br (0.1 ⩽ y ⩽ 0.8) and a line phase PbBi3W0.5U0.5O8I which is a yet rare example of bismuth-based perovskitic oxyiodides. We discuss the factors governing formation of complex layered intergrowth structures, in particular from simpler layer sequences.
    ChemInform 10/2012; 536:155–160.
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    ABSTRACT: Three new ternary copper phosphides, Sr(2)Cu(6)P(5), Eu(2)Cu(6)P(5), and EuCu(4)P(3), have been synthesized from the elements in evacuated silica capsules. Eu(2)Cu(6)P(5) and Sr(2)Cu(6)P(5) adopt the Ca(2)Cu(6)P(5)-type structure, while EuCu(4)P(3) is isostructural to BaMg(4)Si(3) and still remains the only representative of this structure type among the ternary Cu pnictides. All three materials show metallic conductivity in the temperature range 2 K ≤ T ≤ 290 K, with no indication for superconductivity. For Eu(2)Cu(6)P(5) and EuCu(4)P(3), long-range magnetic order was observed, governed by 4f local moments on the Eu atoms with predominant ferromagnetic interactions. While Eu(2)Cu(6)P(5) shows a single ferromagnetic transition at T(C) = 34 K, the magnetic behavior of EuCu(4)P(3) is more complex, giving rise to three consecutive magnetic phase transitions at 70, 43, and 18 K.
    Inorganic Chemistry 07/2012; 51(16):8948-55. · 4.59 Impact Factor
  • Dmitri O. Charkin, Arthur V. Urmanov, Sergey M. Kazakov
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    ABSTRACT: Systematic studies of LaOAgS-type alkaline earth–Cu/Ag fluoride chalcogenides revealed six new compounds SrFCuTe, SrFAgS, SrFAgSe, SrFAgTe, BaFAgS, and BaFAgSe. Crystal structures have been determined for these as well as for BaFCuS. Based on trends in the bond distances within the PbO- and FeS-type layers, a semi-qualitative approach is suggested to predict new members of the LaOAgS family.
    ChemInform 04/2012; 516:134–138.
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    ABSTRACT: Polythermic studies of Bi2WO6–Bi2UO6 system revealed existence of a broad Bi2W1−xUxO6 solid solution with the Aurivillius-type structure. Below 750 °C, the homogeneity area is narrow (x ≤ 0.12) but extends significantly at higher temperatures (up to ca. 75% Bi2UO6 at 1025 °C). The solid solution retains orthorhombic symmetry over the entire compositional range, but substitution of U for W results in significant lowering of second harmonic intensity and Curie point suggesting, at high substitution degrees, a very close approach to the archetypic body-centered tetragonal centrosymmetric structure. The known Bi2WO6-based solid solutions are discussed in terms of thermal stability, and a general geometrical explanation is suggested. Incorporation of large cations into the B perovskitic positions of [Bi2O2][An−1BnO3n+1] Aurivillius structures seems yet to be restricted by the n = 1 case.Graphical abstract
    ChemInform 01/2010; 12(12):2079-2085.
  • ChemInform 07/2008; 39(31).
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    ABSTRACT: A new synthetic approach is suggested for preparation of layered rare-earth oxide compounds containing [Ln2O2] slices and molecular anion sheets (CO32-, SO42-, and CrO42-). It is based on exchange reactions of rare-earth oxychlorides, [Ln2O2]Cl2, and alkali carbonates, sulfates, or chromates. Five new rare-earth oxychromates [Ln2O2]CrO4 (Ln=Pr-Gd) have been prepared which adopt a new, probably layered, structure type. In addition, significantly easier and more efficient synthetic pathways were found to the known compounds [Ln2O2]K2(CO3)2 and [La2O2]CrO4. The structure of the latter compound has been determined from neutron powder diffraction data. Factors affecting reaction pathways and products are discussed, as well as prospects for applying the approach to more complex layered compounds.
    Inorganic Chemistry 05/2008; 47(8):3065-71. · 4.59 Impact Factor
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    ABSTRACT: Three new bismuth oxyhalides, PbxBi2−xCuxO2X2 (X=Cl, x≈0.35–0.70; X=Br, x≈0.35–0.65; X=I, x≈0.35–0.55) have been predicted and synthesized from PbO, BiOX, and CuX. All three compounds adopt a very deficient LaOAgS (stuffed PbFCl) structure. Atomic parameters have been determined for Pb0.6Bi1.4Cu0.6O2Cl2 and Pb0.6Bi1.4Cu0.6O2Br2 (P4/nmm, Z=1) as well as for a structurally and compositionally related Pb0.6Bi1.4Cs0.6O2Br2 (I4/mmm, Z=2). Comparison of these structural data with bond distances and angles in related Pb0.6Bi1.4Q0.6O2X2 oxyhalides (Q=Rb, Cs, Tl; X=Cl, Br) reveals that replacement of CsCl-like [Q0.6X2] layers by anti-fluorite-like [Cu0.6X2] has a small effect on the Pb0.6Bi1.4–O and Pb0.6Bi1.4–X distances and a larger one on bond angles. We predict existence of isostructural compounds among multinary oxyhalides of bismuth and fluorohalides of lead. It is also likely that more complicated structures involving [CuxX2] layers can be realized.
    Journal of Alloys and Compounds 06/2006; 413(1):40-45. · 2.73 Impact Factor
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    ABSTRACT: The oxyhalides Pb3TeO4X2 (X=Cl, Br, I) have been prepared from Pb3O2X2 and TeO2. All three compounds are isostructural and adopt the Nd2O2Te (PbBiO2I) structure type (I4/m, Z=1) according to single-crystal and powder X-ray and electron diffraction data. Contrary to previous results, the Pb/Te cation ordering was found to be nearly the same as Pb/I in schwartzembergite, Pb5IO4(OH)2Cl3 but not Pb/Sb in nadorite PbSbO2Cl. We discuss the factors affecting Pb/M cation ordering in layered (Sillén-type) multinary oxyhalides of lead.
    Solid State Sciences - SOLID STATE SCI. 01/2006; 8(9):1029-1034.
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    ABSTRACT: The oxyhalides Pb3TeO4X2 (X=ClX=Cl, Br, I) have been prepared from Pb3O2X2 and TeO2. All three compounds are isostructural and adopt the Nd2O2Te (PbBiO2I) structure type (I4/mI4/m, Z=1Z=1) according to single-crystal and powder X-ray and electron diffraction data. Contrary to previous results, the Pb/Te cation ordering was found to be nearly the same as Pb/I in schwartzembergite, Pb5IO4(OH)2Cl3 but not Pb/Sb in nadorite PbSbO2Cl. We discuss the factors affecting Pb/M cation ordering in layered (Sillén-type) multinary oxyhalides of lead.
    ChemInform 01/2006; 37(49).
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    ABSTRACT: Several outstanding aspects of phase behaviour in the systems (Bi,Ln)2WO6 and (Bi,Ln)2MoO6 (Ln=lanthanide) have been clarified. Detailed crystal structures, from Rietveld refinement of powder neutron diffraction data, are provided for Bi1.8La0.2WO6 (L-Bi2WO6 type) and BiLaWO6, BiNdWO6, Bi0.7Yb1.3WO6 and Bi0.7Yb1.3WO6 (all H-Bi2WO6 type). Phase evolution within the solid solution Bi2−xLaxMoO6 has been re-examined, and a crossover from γ(H)-Bi2MoO6 type to γ-R2MoO6 type is observed at x∼1.2. A preliminary X-ray Rietveld refinement of the line phase BiNdMoO6 has confirmed the α-R2MoO6 type structure, with a possible partial ordering of Bi/Nd over the three crystallographically distinct R sites.
    Journal of Solid State Chemistry 01/2006; 179(11):3437-3444. · 2.04 Impact Factor
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    ABSTRACT: The crystal structure of the Aurivillius phase Bi5TiNbWO15 has been analyzed in detail using powder X-ray and neutron diffraction. The structure can be described as a regular intergrowth of alternating single and double perovskite-like layers sandwiched between fluorite-like bismuth oxide layers, such that the layer sequence is … [WO4]–[Bi2O2]–[BiTiNbO7]–[Bi2O2] …. There is complete ordering of tungsten within the B sites of the single perovskite layer, so that the structure can be described as a direct intergrowth of the ‘component’ Aurivillius phases Bi2WO6 and Bi3TiNbO9. At 25°C the structure adopts the polar orthorhombic space group I2cm, a=5.4231(2)Å, b=5.4027(2)Å, c=41.744(1)Å.
    Journal of Solid State Chemistry 01/2005; 178(1):180-184. · 2.04 Impact Factor
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    ABSTRACT: The crystal structure of Bi0.7Yb1.3WO6 (a representative of the isomorphous series Bi2−xLnxWO6; 0.3
    Journal of Solid State Chemistry - J SOLID STATE CHEM. 01/2004; 177(7):2632-2634.
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    ABSTRACT: Using various synthetic approaches, we have prepared over 50 new multinary bismuth oxyhalides which crystallize in four layered structure types. Most of the compounds belong to the three previously reported structure types involving fluorite- and CsCl-like metal-oxygen vs. metal-halogen layers as well as single or double halide ion sheets. The majority of Bi2-xAxQ0.6O2Z2 (A=Li, Na, K, Ca, Sr, Ba, Pb; Q=Rb, Cs; Z=Cl, Br, I) compounds crystallize in the tetragonal structure of Pb0.6Bi1.4Cs0.6O2Cl2 (Y2) while both Bi1.4Ba0.6Q0.6O2I2 (Q=Rb, Cs) oxyiodides adopt its orthorhombically distorted, partially ordered version. Due to the lower degree of substitution, the fluorite-like layers in the Y2 structure accommodate more A cations than previously known for related Bi compounds. However, very large Tl+ or Rb+ give compounds with another, as yet unknown, structure. We discuss the influence of size and charge of A cations and stoichiometry of [Bi2-xAxO2] fluorite layers on structure and stability of layered oxyhalides of bismuth. Also, we predict formation of isostructural compounds with smaller Q cations like Tl+ and K+.
    Journal of Solid State Chemistry 01/2003; 173:83-90. · 2.04 Impact Factor