B. I. Lazoryak

Lomonosov Moscow State University, Moskva, Moscow, Russia

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Publications (144)238.87 Total impact

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    ABSTRACT: Structural changes in Sr9In(PO4)7 during the antiferroelectric (AFE) phase transition are studied by X-ray powder diffraction, electron microscopy, second-harmonic-generation, and dielectric measurements. Sr9In(PO4)7 complements a group of Ca3(VO4)2-type ferroelectric (FE) phosphates and vanadates and is the first example of an AFE material in this family. Antiparallel shifts of Sr atoms from their average positions and ordering of the P1O4 tetrahedra form two contributions in the structural mechanism of the AFE phase transition: a displacive contribution and an order-disorder constituent, respectively. The displacive and order-disorder type of structural changes may account for the obtained value of the Curie–Weiss constant (C ~ 104 K) which is in between the value usually observed for pure displacive (C ~ 105 K) and that for orderdisorder phase transitions (C ~ 103 K). The structural mechanism of the AFE phase transition in Sr9In(PO4)7 is very similar to that of the FE phase transition in Ca9R(PO4)7 and Ca9R(VO4)7. Both displacive and orderdisorder contributions are responsible for the physical properties of the Ca3(VO4)2-type materials.
    Full-text · Article · Feb 2016 · Inorganic Materials
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    ABSTRACT: K2Sr(MoO4)2 crystals were synthesized and their properties examined. The distortive polymorphic transformations at 421 K (α (LT)→ β(MT)) and 744 K (β(MT)→γ (HT)) of K2Sr(MoO4)2 were studied. It has been shown that the transitions go in sequence from the high-temperature palmierite K2Pb(SO4)2-type γ-phase (R m) to an intermediate β-phase with a probable incommensurate structure and then to a low-temperature α-phase. Domain structures peculiarities in ferroelastic α-K2Sr(MoO4)2 have been investigated. The electrical conductivity of K2Sr(MoO4)2 rises tenfold in the vicinity of the phase transition at 744 K that may be associated with a change conductivity path from quasi-one-dimensional to two-dimensional. The crystal structure of the α-phase (sp. gr. С2/c, а=14.318(3) Å, b=5.9337(12) Å, с=10.422(2) Å, β=105.83(3)о, Z=4, R=0.0219) is similar to that of α-Pb3(PO4)2. Sr-atoms are mainly located at site with the coordination number CN=8 (a tetragonal antiprism with bond lengths of 2.578(2)–2.789(2) Å) and K atoms are located at site with CN=9+1).
    Full-text · Article · Jan 2016
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    ABSTRACT: Deferrized glass was produced by the reduction smelting of basalt batch in a graphite crucible at a high temperature. The deferrized continuous fiber has higher glass transition and drawing temperatures, lower crystallization ability and enhanced thermal stability in comparison with those of the original basalt fiber.
    No preview · Article · Sep 2015 · Mendeleev Communications
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    Full-text · Dataset · Aug 2015
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    ABSTRACT: Subsolidus phase relations in the Cs2MoO4–ZnMoO4–Zr(MoO4)2 system were determined and two new compounds, Cs2ZnZr(MoO4)4 and Cs2ZnZr2(MoO4)6, were obtained. The structure of Cs2ZnZr(MoO4)4 (a=5.7919(1) Å, c=8.0490(3) Å; space group P m1; Z=0.5; R=0.0149) belongs to the layered glaserite-like KAl(MoO4)2 structure type where the octahedral Al3+ positions are statistically occupied by 0.5 Zn2++0.5 Zr4+. The second triple molybdate, Cs2ZnZr2(MoO4)6 (a=13.366(1) Å, c=12.253(3) Å, space group R , Z=3, R=0.0324), is isostructural to Cs2MnZr2(MoO4)6 and Cs2M2Zr(MoO4)6 (M=Al, Fe) and contains a mixed 3D framework built of МоO4 tetrahedra and (Zn, Zr)O6 octahedra sharing common vertices. Cesium cations are located in large channels of the framework. The latter compound undergoes a first-order phase transition at 723 K with considerable increasing its ionic conductivity.
    Full-text · Article · Jun 2015 · Journal of Physics and Chemistry of Solids
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    DESCRIPTION: We have prepared solid solutions based on whitlockite-structure ferroelectrics, Ca9 – xPbxR(PO4)7 (R = Sc, Cr, Fe, Ga, In), through Pb substitution for Ca. Single-phase Ca9 – xPbxR(PO4)7 materials with a polar whitlockite-like structure (sp. gr. R3c) exist in the range 0 ≤ x ≤ 1.5 for all of the R metals studied. X-ray powder diffraction profile analysis results for R = In (x = 0.5, 0.8, and 1.0) demonstrate that the trivalent cations reside on the octahedral site M5 of the whitlockite structure, the calcium cation occupy the M1–M3 sites, and the lead cations are located predominantly on the M3 site. Differential scanning calorimetry, dielectric permittivity, and second-harmonic generation data attest to a ferroelectric phase transition, whose temperature is 580–610°C in Ca9R(PO4)7 and decreases monotonically to 480–520°C as x increases to 1.5.
    Full-text · Research · Jun 2015
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    Dina Deyneko · Sergey Stefanovich · Bogdan Lazoryak
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    ABSTRACT: New phosphates Ca9– x Pb x Eu(PO4)7 were obtained by solid state reaction techniques at 1213–1253 K in air atmosphere and were found to be isotypic with whitlockite-type β-Ca3(PO4)2. The unit cell parameters were determinate using Le Bail decomposition. Rietveld method structural refining showed that Eu3+ ions are located statistically with calcium in M1, M2, and M3 sites, whereas Pb2+-ions are preferentially located in the M3. Examination of optical second harmonic generation evidences nonlinear optical activity and confirms polar space group R3c.
    Full-text · Article · Jun 2015 · Powder Diffraction
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    ABSTRACT: Ca 9ex Pb x Eu(PO 4) 7 (0 x 1) solid solutions with a whitlockite-type (or b-Ca 3 (PO 4) 2-type) structure (sp.gr. R3c) were prepared by a standard solid-state method in air. Their luminescent properties under near-ultraviolet (n-UV) light were investigated. Excitation spectra of Ca 9ex Pb x Eu(PO 4) 7 showed the strongest absorption at about 395 nm, which matches well with commercially available n-UV-emitting GaN-based LED chips. Emission spectra indicated an intense red emission due to the 5 D 0 / 7 F 2 transition of Eu 3þ , with a maximum in the intensity for Ca 8.5 Pb 0.5 Eu(PO 4) 7. The emission intensity of Ca 8.5 P-b 0.5 Eu(PO 4) 7 was about 1.8 times higher than that of a Ca 9 Eu(PO 4) 7 phosphor. We suggest that the introduction of Pb 2þ is an efficient approach to enhance luminescence properties of such phosphors. We clarified the influence of the Ca 2þ / Pb 2þ substitution on intensities of three bands for the 5 D 0 / 7 F 0 transition in excitation spectra of Ca 9ex Pb x Eu(PO 4) 7. In addition, we found a reversible first-order phase transition from R3с to R3с symmetry by second-harmonic generation in the range from 753 K (x < 1) to 846 K (x = 0).
    Full-text · Article · May 2015 · Journal of Alloys and Compounds
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    ABSTRACT: Basalt glasses and fibers with zirconia content in the range from 0 to 7 wt% were obtained using ZrSiO4 as a zirconium source. Weight loss and tensile strength loss of fibers after refluxing in alkali solution were determined. Basalt fiber with 5.7 wt% ZrO2 had the best alkali resistance properties. Alkali treatment results in formation of protective surface layer on fibers. Morphology and chemical composition of surface layer were investigated. It was shown that alkali resistance of zirconia doped basalt fibers is caused by insoluble compounds of Zr4+, Fe3+ and Mg2+ in corrosion layer. Mechanical properties of initial and leached fibers were evaluated by a Weibull distribution. The properties of basalt fibers with ZrSiO4 were compared with AR-glass fibers. The performance of concrete with obtained fibers was investigated.
    No preview · Article · May 2015 · Materials and Design
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    ABSTRACT: Basaltic glass fibers with different lithium oxide (6–14 mol%) and sodium oxide (2–14 mol%) contents were prepared. The influence of Li2O and Na2O content on the process of fiber manufacturing was investigated. Addition of alkali oxides reduced the forming temperature and substantially expanded the fiber-forming temperature ranges. The obtained thermal data from differential thermal analysis revealed a decline in glass transition temperature (Tg) of fibers against the compositional changes. The inclusion of Li2O and Na2O in the glass network led to a reduction in its thermal stability. The obtained X-ray diffraction patterns and IR spectra of Li-rich and Na-rich basaltic glass fibers confirmed the formation of highly polymerized structures such as LiAl(Si2O6) and (Na,K)(AlSiO4), respectively, and relatively depolymerized silicate anions. The effects of potassium–lithium and potassium–sodium ion exchange on the mechanical properties of basaltic glass fibers were investigated. As-received Li-rich and Na-rich basaltic glass fibers were ion-exchanged in potassium nitrate for different exchange times, and their mechanical properties were measured before and after chemical tempering. The measured tensile strength and Young's modulus values of the fibers showed an increase after treatment in molten salt.
    No preview · Article · May 2015 · International Journal of Applied Glass Science
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    ABSTRACT: Solid solutions Sm2 − x Eux (MoO4)3 (0 ≤ x ≤ 2) have been prepared in two modifications: monoclinic α modification with distorted scheelite structure and orthorhombic β′ modification with non-scheelite structure. The α → β′ phase transition is accompanied by a considerable increase in the unit cell volume (∼24%). For all solid solutions, the transition with the strongest luminescence is 5D 0→7F 2 of Eu3+ cations that determines red luminescence of the samples (λmax ∼ 616 nm). Whatever the type of Sm2 − x Eux (MoO4)3 structure, the luminescence maximum is in the concentration range 1.75 < x ≤ 2; for the α-and β′-modifications, different luminescence excitation mechanisms have been found.
    Full-text · Article · Jan 2015 · Russian Journal of Inorganic Chemistry
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    ABSTRACT: A new hydrogen-containing whitlockite-type phosphate Ca 9 (Fe 0.63 Mg 0.37)H 0.37 (PO 4) 7 : hydrothermal synthesis and structure Abstract: A new hydrogen-containing Ca 9 (Fe 0.63 Mg 0.37) H 0.37 (PO 4) 7 phosphate with the whitlockite-type structure has been synthesized by a hydrothermal method and its structure has been studied by the single-crystal X-ray dif-fraction. The compound crystallizes in the trigonal space group R3c (traditional for compounds with the whitlockite-type structure) with unit-cell parameters: a = 10.3533(1) Å, c = 37.1097(4) Å. The structure has been determined using the "charge flipping" method. Ca 9 (Fe 0.63 Mg 0.37)H 0.37 (PO 4) 7 structure is similar to that of other members of the whit-lockite-type family. The presence of hydrogen in the struc-ture leads to the formation of OH-group with one of the oxygen of PO 4 -tetrahedra. Based on an analysis of the bond valence sums (BVS) a conclusion has been made about localization of H atoms in the structure. Smaller values of BVS for O1 and O10 atoms than ones for other oxygen atoms indicate localization of H atoms between them in a position with site symmetry 18b.
    Full-text · Article · Dec 2014 · Zeitschrift für Kristallographie
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    ABSTRACT: A new triple molybdate Na25Cs8Fe5(MoO4)24 was synthesized using solid state reactions and studied with X-ray powder diffraction, second harmonic generation (SHG) technique, differential scanning calorimetry, Mössbauer and dielectric impedance spectroscopy. Single crystals of Na25Cs8Fe5(MoO4)24 were obtained and its structure was solved (the space group P , a=12.5814(5), b=13.8989(5), c=28.4386(9) Å, α=90.108(2), β=90.064(2), γ=90.020(2)°, V=4973.0(3) Å3, Z=2, R=0.0440). Characteristic features of the structure are polyhedral layers composed of pairs of edge-shared FeO6 and (Fe, Na)O6 octahedra, which are connected by bridging МоО4 tetrahedra. The layers share common vertices with bridging МоО4 tetrahedra to form an open 3D framework with the cavities occupied by the Cs+ and Na+ cations. The compound undergoes first-order phase transformation at 642 K and above this phase transition, electrical conductivity reaches 10−3-10−2 S cm−1. Thus, Na25Cs8Fe5(MoO4)24 may be considered as a promising compound for developing new materials with high ionic conductivity.
    Full-text · Article · Nov 2014 · ChemInform
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    ABSTRACT: The R2(MoO4)3 (R = rare earth elements) molybdates doped with Eu3+ cations are interesting red-emitting materials for display and solid state lighting applications. The structure and luminescent properties of the R2−xEux(MoO4)3 (R=Gd, Sm) solid solutions have been investigated as a function of chemical composition and preparation conditions. Monoclinic (α-) and orthorhombic (β´-) R2−xEux(MoO4)3 (R=Gd, Sm, 0≤x≤2) modifications were prepared by solid-state reaction and their structures were investigated using synchrotron powder X-ray diffraction and transmission electron microscopy. The pure orthorhombic β´-phases could be synthesized only by quenching from high temperature to room temperature for Gd2−xEux(MoO4)3 in the Eu3+-rich part (x > 1) and for all Sm2−xEux(MoO4)3 solid solutions. The transformation from the α-phase to the β´-phase results in a notable increase (~24%) of the unit cell volume for all R2−xEux(MoO4)3 (R = Sm, Gd) solid solutions. The luminescent properties of all R2−xEux(MoO4)3 (R = Gd, Sm; 0≤x≤2) solid solutions were measured, and their optical properties were related to their structural properties. All R2−xEux(MoO4)3 (R= Gd, Sm; 0≤x≤2) phosphors emit intense red light dominated by the 5D0 – 7F2 transition at ~616 nm. However, a change in the multiplet splitting is observed when switching from the monoclinic to the orthorhombic structure, as a consequence of the change in coordination polyhedron of the luminescent ion from RO8 to RO7 for the α- and β´-modification, respectively. The Gd2−xEux(MoO4)3 solid solutions are the most efficient emitters in the range of 0<x<1.5, but have a comparable or even significantly lower emission intensity than Sm2−xEux(MoO4)3 for higher Eu3+ concentrations (1.5≤x≤1.75). Electron energy loss spectroscopy (EELS) measurements revealed the influence of the structure and element content on the number and positions of bands in the UV-visible-infrared regions of the EELS spectrum.
    Full-text · Article · Nov 2014 · Chemistry of Materials
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    Full-text · Dataset · Oct 2014
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    ABSTRACT: a b s t r a c t A new triple molybdate Na 25 Cs 8 Fe 5 (MoO 4) 24 was synthesized using solid state reactions and studied with X-ray powder diffraction, second harmonic generation (SHG) technique, differential scanning calorimetry, Mössbauer and dielectric impedance spectroscopy. Single crystals of Na 25 Cs 8 Fe 5 (MoO 4) 24 were obtained and its structure was solved (the space group P1, a ¼12.5814(5), b¼ 13.8989(5), c ¼28.4386(9) Å, α¼90.108(2), β¼90.064(2), γ¼90.020(2)1, V¼ 4973.0(3) Å 3 , Z¼ 2, R¼ 0.0440). Char-acteristic features of the structure are polyhedral layers composed of pairs of edge-shared FeO 6 and (Fe, Na)O 6 octahedra, which are connected by bridging МоО 4 tetrahedra. The layers share common vertices with bridging МоО 4 tetrahedra to form an open 3D framework with the cavities occupied by the Cs þ and Na þ cations. The compound undergoes first-order phase transformation at 642 K and above this phase transition, electrical conductivity reaches 10 À 3 –10 À 2 S cm À 1 . Thus, Na 25 Cs 8 Fe 5 (MoO 4) 24 may be considered as a promising compound for developing new materials with high ionic conductivity.
    Full-text · Article · Sep 2014 · Journal of Solid State Chemistry
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    ABSTRACT: Scheelite related compounds (A′,A″)n[(B′,B″)O4]m with B′, B″ = W and/or Mo are promising new materials for red phosphors in pc-WLEDs (phosphor-converted white-light-emitting-diode) and solid-state lasers. Cation substitution in CaMoO4 of Ca2+ by the combination of Na+ and Eu3+, with the creation of A cation vacancies, has been investigated as a factor for controlling the scheelite-type structure and the luminescent properties. Na5Eu(MoO4)4 and NaxEu3+(2–x)/3□(1–2x)/3MoO4 (0.138 ≤ x ≤ 0.5) phases with a scheelite-type structure were synthesized by the solid state method; their structural characteristics were investigated using transmission electron microscopy. Contrary to powder synchrotron X-ray diffraction before, the study by electron diffraction and high resolution transmission electron microscopy in this paper revealed that Na0.286Eu0.571MoO4 has a (3 + 2)D incommensurately modulated structure and that (3 + 2)D incommensurately modulated domains are present in Na0.200Eu0.600MoO4. It also confirmed the (3 + 1)D incommensurately modulated character of Na0.138Eu0.621MoO4. The luminescent properties of all phases under near-ultraviolet (n-UV) light have been investigated. The excitation spectra of these phosphors show the strongest absorption at about 395 nm, which matches well with the commercially available n-UV-emitting GaN-based LED chip. The emission spectra indicate an intense red emission due to the 5D0 → 7F2 transition of Eu3+, with local minima in the intensity at Na0.286Eu0.571MoO4 and Na0.200Eu0.600MoO4 for 613 nm and 616 nm bands. The phosphor Na5Eu(MoO4)4 shows the brightest red light emission among the phosphors in the Na2MoO4–Eu2/3MoO4 system and the maximum luminescence intensity of Na5Eu(MoO4)4 (λex = 395 nm) in the 5D0 → 7F2 transition region is close to that of the commercially used red phosphor YVO4:Eu3+ (λex = 326 nm). Electron energy loss spectroscopy measurements revealed the influence of the structure and Na/Eu cation distribution on the number and positions of bands in the UV-optical-infrared regions of the EELS spectrum.
    Full-text · Article · May 2014 · Chemistry of Materials
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    ABSTRACT: Crystallization of basalt fibers containing 0–7 wt% ZrO2 was studied. Fibers were drawn from basalt glasses and annealed in air at different temperatures. Phase composition of obtained samples was determined by XRD. Kinetics of crystallization processes was investigated by DSC. Kinetic models and parameters were estimated for crystallization of spinel-like phase, pyroxene and plagioclase using model-free analysis. It was found that doping of fibers with 1–3 wt% ZrO2 increased Arrhenius parameters of aluminosilicate crystallization. When the zirconia content was 5–7 wt% the crystallization mechanism significantly changed. This phenomenon resulted in increasing of fiber thermal stability.
    No preview · Article · Jan 2014 · Thermochimica Acta
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    ABSTRACT: In the present research, the effect of contents network formers and modifiers oxides on mechanical properties of basalt continuous fibers (BCF) was investigated. The influence of surface modification basalt fibers on mechanical behavior of a basalt fiber reinforced plastics (BFRP) was explored experimentally. The basalt/epoxy laminates were fabricated by impregnating woven basalt fibers into epoxy resin via vacuum assisted resin transfer molding (VARTM). The results showed significant improvement in tensile strength after surface modification. The tensile strength and Young's modulus of BCF under study were amounted to 3700±250 MPa and 79±3 GPa respectively. Also BRFP with tensile strength 500±20 MPa, interlaminar shear strength 55±1 MPa and E-modulus not less than 25±1 GPa were obtained.
    No preview · Article · Jan 2014
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    ABSTRACT: Na9Sc(MoO4)6 {nonasodium scandium hexakis[tetraoxidomolybdate(II)]} was synthesised by a solid-state method. The basic structure units are polyhedral clusters composed of an ScO6 octahedron and three NaO6 octahedra sharing total edges. The clusters are connected by sharing vertices with bridging MoO4 tetrahedra, forming a three-dimensional framework where the cavities are occupied by the other two crystallographically independent Na atoms.
    Full-text · Article · Nov 2013 · Acta Crystallographica Section C Crystal Structure Communications

Publication Stats

1k Citations
238.87 Total Impact Points

Institutions

  • 1990-2015
    • Lomonosov Moscow State University
      • Division of Chemistry
      Moskva, Moscow, Russia
  • 1995-2014
    • Moscow State Forest University
      Mytishi, Moskovskaya, Russia
  • 2010
    • Wake Forest University
      • Department of Chemistry
      Winston-Salem, North Carolina, United States
  • 2006
    • University of Antwerp
      • Department of Physics
      Antwerpen, Flanders, Belgium
  • 2004-2005
    • Kyoto University
      • Institute for Chemical Research
      Kioto, Kyōto, Japan