Browsing by Author "Nalbandyan, VB"

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    Alkali metal cation and proton conductors: relationships between composition, crystal structure, and properties
    (Wiley, 2009-07-15) Avdeev, M; Nalbandyan, VB; Shukaev, IL
    This chapter contains sections titled: Principles of Classification, and General Comments; Crystal‐Chemistry Factors Affecting Cationic Conductivity; Crystal Structural Screening and Studies of Conduction Paths; Conductors with Large Alkali Ions; Lithium Ion Conductors; Proton Conductors; References. © 2009 Wiley‐VCH Verlag GmbH & Co. KGaA
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    Crystal structure of Li4ZnTeO6 and revision of Li3Cu2SbO6
    (Elsevier, 2013-03-01) Nalbandyan, VB; Avdeev, M; Evstigneeva, MA
    Li4ZnTeO6 has been prepared by solid-state reactions and characterized by powder X-ray and neutron diffraction. It is monoclinic, C2/m, a=5.2114(3), b=8.9288(4), c=5.1768(3)Å, β=110.783(3)°. The material is structurally analogous to Li3Zn2SbO6 with LiTe substitution for ZnSb. The structure is based on honeycomb [(Li,Zn)2TeO6]3− layers interleaved with Li+ layers. Minor substitution of Zn in Li layers was detected. It is shown that Li3Cu2SbO6 known as C2/c actually belongs to the same C2/m type with halved unit cell volume. © 2012 Elsevier Inc.
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    First observation of the reversible O3↔P2 phase transition: crystal structure of the quenched high-temperature phase Na0.74Ni0.58Sb0.42O2
    (Elsevier, 2006-06-15) Smirnova, OA; Avdeev, M; Nalbandyan, VB; Kharton, VV; Marques, FMB
    According to thermal expansion data, O3-type phase NaxNi(1+x)/3Sb(2−x)/3O2 (x ≈ 0.8) undergoes at ca. 1270 K a reversible transition to a less dense form. The high-temperature phase quenched to liquid nitrogen belongs to P2 type, space group P63/mmc (no. 194), a = 3.0123 Å(2), c = 11.2264 Å(7) for x ≈ 0.74 at 298 K. The stabilisation of P2 versus O3-type structure at high temperatures seems to be due to alkali distribution over greater number of sites thus increasing entropy and decreasing Na+–Na+ repulsion. © 2005 Elsevier Ltd.
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    Ion exchange reactions of NaSbO3 and morphotropic series MSbO3
    (Elsevier, 2006-10-17) Nalbandyan, VB; Avdeev, M; Pospelov, AA
    By reactions of ilmenite-type NaSbO3 with molten nitrates at ca. 300 °C, ilmenite forms of AgSbO3 and TlSbO3 have been obtained and characterized by chemical analysis and X-ray diffraction (rhombohedral, a=5.3272(9) and 5.3149(7) Å, c=16.6923(2) and 21.5136(4) Å, respectively). Unexpectedly, a new form of LiSbO3, prepared in a similar way, is not rhombohedral. Its XRD pattern has been indexed on a monoclinic C-centred pseudo-orthorhombic cell with a=5.2948(7), b=9.0082(7), c=5.2923(6) Å, β=113.790(5). This cell may be derived from the ilmenite structure by gliding SbO6/2 layers. Diffuse nature of the XRD pattern is due to stacking faults. TlSbO3 also contains faults, which have been modelled by ∼10% 2H stacking analogous to known P-31c polytype. On heating, layered AgSbO3 and LiSbO3 transform to stable phases (pyrochlore and Pncn, respectively), but TlSbO3 remains unchanged at least to 850 °C. Attempts to substitute Cs for Na have been unsuccessful. Previously reported X-ray data for ilmenite-type CsSbO3 are discredited. Volume relations in the MSbO3 series are discussed. © 2006 Elsevier SAS.
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    New cubic perovskite Na(Cu2.5Ti0.5)Ti4O12 with square planar coordination of Ti4+
    (American Chemical Society, 2006-02-08) Avdeev, M; Nalbandyan, VB
    A new perovskite, Na[Cu2.5Ti0.5]Ti4O12, has been synthesized using a conventional solid-state technique. Neutron and synchrotron X-ray powder diffraction studies in combination with density measurements and bond-valence calculations have revealed that the material crystallizes in the cubic Im3̄ space group (a = 7.38472(2) Å, Z = 2) with the square-plane site accommodating 16.7% of Ti4+. This is the highest level of non-Jahn−Teller cation substitution for Cu2+ reported to date for CaCu3Ti4O12-type perovskites prepared at ambient pressure. © 2006 American Chemical Society