共查询到20条相似文献,搜索用时 15 毫秒
1.
B. P. Sobolev T. M. Turkina N. I. Sorokin D. N. Karimov O. N. Komar’kova E. A. Sulyanova 《Crystallography Reports》2010,55(4):657-661
The nonstoichiometric phase EuF2+x
has been obtained via the partial reduction of EuF3 by elementary Si at 900–1100°C. Eu0.9162+Eu0.0843+F2.084 (EuF2.084) single crystals have been grown from melt by the Bridgman method in a fluorinating atmosphere. These crystals belong to
the CaF2 structure type (sp. gr. Fm
$
\bar 3
$
\bar 3
m) with the cubic lattice parameter a = 5.8287(2) ?, are transparent in the spectral range of 0.5–11.3 μm, and have microhardness H
μ = 3.12 ± 0.13 GPa and ionic conductivity σ = 1.4 × 10−5 S/cm at 400°C with the ion transport activation energy E
a = 1.10 ± 0.05 eV. The physicochemical characteristics of the fluorite phases in the EuF2 − EuF3 systems are similar to those of the phases in the SrF2 − EuF3 and SrF2 − GdF3 systems due to the similar lattice parameters of the EuF2 and SrF2 components. Europium difluoride supplements the list of fluorite components MF2 (M = Ca, Sr, Ba, Cd, Pb), which are crystal matrices for nonstoichiometric (nanostructured) fluoride materials M
1 − x
R
x
F2 + x
(R are rare earth elements). 相似文献
2.
A combinatorial and topological analysis of Li19Na8Ba15 (hP842, a = 20 ?, c = 93 ?, V = 33552 ?3, P
$
\bar 3
$
\bar 3
) has been performed using computer methods (the TOPOS program package). Two types of crystal-forming quasi-spherical nanoclusters
about 20 ? in diameter with internal Friauf polyhedra (A-172) and icosahedra (B-137) have been established by the complete
decomposition of the 3D factor graph of the structure into cluster substructures. Each type of nanoclusters forms close-packed
2D layers 36, which alternate along the c axis. The B-137 and A-172 nanoclusters are composed of three layers and have shell compositions (1 + 12 + 32 + 92) and (1
+ 16 + 59 + 103) with local symmetries 3 and $
\bar 3
$
\bar 3
, respectively; they were revealed for the first time in crystal structures as cluster precursors. The icosahedral B-137 nanocluster
contains a 104-atom quasicrystal approximant (Samson cluster). 相似文献
3.
An X-ray diffraction study of the scandium iodide complex with antipyrine [Sc(AP)6]I3 (AP is antipyrine, i.e., 2,3-dimethyl-1-phenyl-3-pyrazolin-5-one) (I), which is not isostructural to the analogous compounds of Y, La, and Eu (II), is performed. Crystals I are trigonal; a = 24.911 ? and c = 10.140 ?; Z = 3, space group P
$
\bar 3
$
\bar 3
. Crystal I is built of [Sc(AP)6]3+ complex cations of two types and I− anions. In both cations, the Sc atom is octahedrally coordinated by six O atoms of six AP ligands (Sc-O, 2.054–2.078 ?).
Complexes I differ from II by the absence of π-π stacking interactions between AP molecules, resulting in a supramolecular cation. Complex cations I of both types form combined layers. All I− anions are located in the interlayer space, being statistically disordered within a flat area limited by eight complex cations
of Sc1 and Sc2. 相似文献
4.
N. I. Sorokin D. N. Karimov E. A. Krivandina Z. I. Zhmurova O. N. Komarkova 《Crystallography Reports》2008,53(2):271-277
Single crystals of congruently melting compositions of the Ca0.6Sr0.4F2 and Ca1 − x − y
Sr
y
R
x
F2 + x
(R = La, Ce, Pr, Nd; x = 0.16–0.21; y = 0.07–0.16) solid solutions with fluorite structure have been grown by the Bridgman-Stockbarger method. Their electrical
properties have been investigated in the range from 473 to 823 K, and it is shown that they are ionic conductors. For Ca0.6Sr0.4F2 crystals, the ionic conductivity σ = 2 × 10−6 S/cm at 673 K, and the ion transport activation energy E
a
= 1.1 eV. For Ca0.77Sr0.07La0.16F2.16, Ca0.70Sr0.11Ce0.19F2.19, Ca0.65Sr0.15Pr0.20F2.20, and Ca0.58Sr0.21Nd0.21F2.21 crystals, the values of σ lie in the range from 9 × 10−7 to 2 × 10−6 S/cm at 500 K, and the activation energy E
a
is 0.88–0.93 eV. The concentration and mobility of ionic charge carriers in Ca1 − x − y
Sr
y
R
x
F2 + x
crystals have been calculated.
Original Russian Text ? N.I. Sorokin, D.N. Karimov, E.A. Krivandina, Z.I. Zhmurova, O.N. Komar’kova, 2008, published in Kristallografiya,
2008, Vol. 53, No. 2, pp. 297–303. 相似文献
5.
V. A. Fedorov D. N. Karimov O. N. Komar’kova E. A. Krivandina Z. I. Zhmurova B. P. Sobolev 《Crystallography Reports》2010,55(1):122-126
Transmission spectra of two-component crystals of Sr1−x
R
x
F2+x
(R = Y, La-Lu; 0 ≤ x ≤ 0.5) in the 1–17-μm wavelength range were studied. The spectral characteristics of these crystals and of single-component
crystals of MF2 (M = Ca, Sr, or Ba) and RF3 (R = La-Nd) were compared. The transmission cutoff of Sr1−x
R
x
F2+x
crystals is shifted to shorter wavelengths with increasing x. The same tendency is observed with the increasing atomic number R of rare-earth elements for two isoconcentration series of Sr1−x
R
x
F2+x
(x ∼ 0.10 and 0.28). This tendency is pronounced at large x. The transmission cutoff of Sr1−x
R
x
F2+x
crystals can be varied in the range of from 10.7 to 12.2 μm by changing their qualitative (R) and quantitative (x) composition. Hence, these crystals can be assigned to multicomponent fluoride optical materials with controlled optical
characteristics. The Sr1−x
R
x
F2+x
crystals, where R = Ce-Sm, were shown to be promising materials for the design of selective optical filters in the 2–10-μm spectral range. 相似文献
6.
E. A. Sulyanova V. N. Molchanov N. I. Sorokin D. N. Karimov S. N. Sulyanov B. P. Sobolev 《Crystallography Reports》2009,54(4):572-583
Single crystals of the Ca1 − x
Sc
x
F2 + x
(x = 0.106, 0.132, 0.156) solid solutions (CaF2 structure type, space group Fm
m) are investigated using X-ray diffraction. It is revealed that the crystals under investigation contain vacancies in the
8c positions and interstitial fluorine ions in the 48i positions. The coordination number of Sc3+ ions in the structure of the Ca1 −x
Sc
x
F2 + x
solid solutions is equal to eight. The specific features of the concentration dependences of the ionic conductivity and the
activation energy of ion transfer for the Ca1 − x
Sc
x
F2 + x
(0.02 ≤ x ≤ 0.15) solid solutions are explained in the framework of the percolation model of conducting “defect regions.” The percolation
threshold equal to 3–5 mol % ScF3 corresponds to the model of [Ca14 − n
Sc
n
F68] octacubic clusters containing fluorine ions in the 48i positions. The ionic conductivity of the Ca1 − x
Sc
x
F2 + x
solid solutions is analyzed in comparison with the change in this characteristic for the series of Ca0.8
R
0.2F2.2 crystals with rare-earth elements.
Original Russian Text ? E.A. Sulyanova, V.N. Molchanov, N.I. Sorokin, D.N. Karimov, S.N. Sulyanov, B.P. Sobolev, 2009, published
in Kristallografiya, 2009, Vol. 54, No. 4, pp. 612–622. 相似文献
7.
L. B. Serezhkina A. V. Vologzhanina V. V. Klepov V. N. Serezhkin 《Crystallography Reports》2011,56(2):265-269
Uranyl triacetate complexes (Cs0.5Ba0.25)[UO2(CH3COO)3] (I) and Ba0.5[UO2(CH3COO)3] (II) are synthesized for the first time and their structures are determined by X-ray diffraction. Both compounds crystallize
in the cubic crystal system. The crystal data are as follows: a = 17.3289(7) ?, V = 5203.7(4) ?3, space group I213 and Z = 16 (I); a = 17.0515(8)?, V = 4957.8(4) ?3, space group I
$
\bar 4
$
\bar 4
3d, and Z = 16 (II). In I and II, as in all uranyl triacetates studied earlier, the coordination polyhedron of the uranium atom is a hexagonal bipyramid whose
vertices are occupied by the oxygen atoms of the uranyl and three acetate groups. The uranium-containing group belongs to
the AB
301 (A = UO22+, B
01 = CH3COO−) crystal chemical group of uranyl complexes. It was found that compound II is isostructural to the (Rb0.50Ba0.25)[UO2(CH3COO)3] studied earlier. 相似文献
8.
A. F. Konstantinova T. M. Glushkova I. I. Buchinskaya E. A. Krivandina B. P. Sobolev 《Crystallography Reports》2009,54(4):609-612
The optical properties of the isoconcentration series of Cd0.9
R
0.1F2.1 crystals (R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu) grown from a melt by the Bridgman method have been investigated.
The crystals have an anomalous birefringence (∼10−6) nonuniformly distributed over the sample diameter; the dichroism in them does not exceed 10−9. Scanning using a spectral modulator showed the nonuniform distribution of rare earth elements over the crystal diameter.
The refractive indices n have been measured at wave-lengths of 0.436, 0.546, and 0.589 μm. The character of change in n along the rare-earth series is nonuniform and similar to the change in n in Sr0.9
R
0.1F2.1 crystals. It is shown that the refractive indices in Cd1 − x
R
x
F2 + x
crystals, depending on the RF3 content, can be estimated using the method of molecular refraction additivity.
Original Russian Text ? A.F. Konstantinova, T.M. Glushkova, I.I. Buchinskaya, E.A. Krivandina, B.P. Sobolev, 2009, published
in Kristallografiya, 2009, Vol. 54, No. 4, pp. 648–651. 相似文献
9.
E. A. Sulyanova A. P. Shcherbakov V. N. Molchanov V. I. Simonov B. P. Sobolev 《Crystallography Reports》2005,50(2):203-216
The structures of as-grown Cd0.90
R
0.10F2.10 (R = Sm-Lu and Y) crystals are determined and related to the CaF2 structure type. It is assumed that in all the crystals R
3+ and Cd2+ ions form clusters with the tetrahedral configuration of the [Cd2
R
2F26] and [CdR
3F26] cations. The concentration of [Cd2
R
2F26] cations in crystals with R = Er-Lu and Y is considerably higher that in crystals with R = Sm-Ho. The tendency to a decrease in the coordination number of R
3+ toward the end of the rare earth series manifests itself in the fact that the Yb3+ ions in Cd0.90Yb0.10F2.10 occupy both tetrahedral (c.n. 10) and octahedral (c.n. 8) clusters. The Yb3+ ions in tetrahedral clusters are displaced from their basic positions by 0.15 Å along the 〈100〉 directions. In Cd1−x
R
x
F2+x
the relaxation of the anion sublattice of the fluorite matrix around clusters is much more pronounced than in the Ca1−x
R
x
F2+x
phases having similar geometry.
__________
Translated from Kristallografiya, Vol. 50, No. 2, 2005, pp. 235–248.
Original Russian Text Copyright ? 2005 by Sul’yanova, Shcherbakov, Molchanov, Simonov, Sobolev. 相似文献
10.
11.
B. P. Sobolev I. A. Sviridov V. I. Fadeeva S. N. Sulyanov N. I. Sorokin Z. I. Zhmurova P. Herrero A. Landa-Canovas R. M. Rojas 《Crystallography Reports》2005,50(3):478-485
The nonstoichiometric Ca1−x
LaxF2+x
phase (x ≥ 0.1) is obtained by mechanochemical synthesis from CaF2 and LaF3 single crystals. This phase is the first representative of fluorite fluorides obtained by mechanochemical synthesis in the
MFm-RFn systems (m < n ≤ 4). The average grain size ranges within 10–30 nm. The temperature dependence of ionic conductivity of the mechanochemically
synthesized phase pressurized at 600 MPa (at its high-temperature portion at temperatures exceeding 200–250°C) coincides with
the conductivity of the single crystals of the same composition (Ca0.8La0.2F2.2). The activation energy of ionic conductivity (0.95 eV) corresponds to migration of interstitial fluoride ions in the crystal
bulk. Mechanochemical synthesis of a multicomponent fluoride material with nanometer grains opens a new chapter in the chemistry
of inorganic fluorides. A decrease of the sintering temperature of the powders with nanometer grains is very important for
preparing dense fluoride ceramics of complicated compositions and other polycrystalline forms of fluoride materials.
__________
Translated from Kristallografiya, Vol. 50, No. 3, 2005, pp. 524–531.
Original Russian Text Copyright ? 2005 by Sobolev, Sviridov, Fadeeva, Sul’yanov, Sorokin, Zhmurova, Herrero, Landa-Canovas,
Rojas. 相似文献
12.
A new lead-sodium borosilicate (Pb4.8Na1.2)[Si8(Si1.2B0.8)O25] (a = 9.5752 and c = 42.565 ?; space group R
$
\bar 3
$
\bar 3
c) is synthesized under hydrothermal conditions, and its crystal structure is determined without preliminary knowledge of the
chemical formula. The anionic radical of a new type is a double layer in which one of the three independent Si-tetrahedra
contains an isomorphous boron admixture. Its topological relationship with the radicals in the structures of benitoite and
langasite, as well as in the structures of lead silicates barisilite and hyttsjoeite, is found based on the block consisting
of an octahedron and six tetrahedra. This allows one to consider that the new layer is derived from the hyttsjoeite layer
by the replacement of the octahedron with two tetrahedra and the increase of the silicon fraction. Although lead atoms are
located between the layers in the intersheet space, they form relatively strong bonds with silicon-oxygen layers. This structural
type is a collector of heavy metals. 相似文献
13.
D. V. Pushkin E. V. Peresypkina L. B. Serezhkina A. V. Marukhnov A. V. Virovets 《Crystallography Reports》2011,56(3):451-455
The synthesis and X-ray diffraction analysis of K2(H5O2)[UO2(C2O4)2(HSeO3)] single crystals have been performed. This compound crystallizes in the triclinic system with the unit-cell parameters a = 6.7665(4) ?, b = 8.8850(4) ?, c = 12.3147(7) ?, α = 94.73°, β = 90.16°, γ = 92.11°, sp. gr. P[`1]P\bar 1, Z = 2, and R = 0.019. The basic structural units are island [UO2(C2O4)2(HSeO3)]3− groups, which belong to the AB
201
M
1 crystallochemical group of uranyl complexes (A = UO22+, B
01 = C2O42−, and M
1 = HSeO3−). Uraniumcontaining complexes are linked through K+ and H5O2+ ions and via a system of hydrogen bonds with the participation of oxonium hydrogen atoms in this structure. 相似文献
14.
I. P. Makarova T. S. Chernaya A. A. Filaretov A. L. Vasil’ev I. A. Verin V. V. Grebenev V. V. Dolbinina 《Crystallography Reports》2010,55(3):393-403
With the aim of elucidating the nature of anomalies in the physical properties of K3H(SO4)2 crystals that arise as the temperature grows, the dielectric and optical properties of the crystals are studied, an X-ray
diffraction analysis of single-crystal and polycrystalline specimens are performed, and the morphology and chemical composition
are studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy. As a result of the studies performed,
a phase transition from the phase with the monoclinic symmetry (space group C2/c) to the phase with the trigonal symmetry (space group R
$
\bar 3
$
\bar 3
m) is found in a number of K3H(SO4)2 specimens at a temperature of ≈457 K, the responsibility of the dynamically disordered hydrogen-bond system for the rise
of high proton conductivity in the high-temperature phases of the crystals of this family is confirmed, and data on the solid-phase
reactions proceeding at high temperatures are obtained. 相似文献
15.
V. I. Nikolaichik B. P. Sobolev M. A. Zaporozhets A. S. Avilov 《Crystallography Reports》2012,57(2):299-307
The effect of high-energy (150 eV) electron irradiation in an electron microscope column on crystals of fluorides of alkaline
earth elements CaF2, SrF2, and BaF2 is studied. During structural investigations by electron diffraction and electron microscopy, the electron irradiation causes
chemical changes in MF2 crystals such as the desorption of fluorine and the accumulation of oxygen in the irradiated area with the formation of oxide
MO. The fluorine desorption rate increases significantly when the electron-beam density exceeds the threshold value of ∼2 ×
103 pA/cm2). In BaF2 samples, the transformation of BaO into Ba(OH)2 was observed when irradiation stopped. The renewal of irradiation is accompanied by the inverse transformation of Ba(OH)2 into BaO. In the initial stage of irradiation of all MF2 compounds, the oxide phase is in the single-crystal state with a lattice highly matched with the MF2 matrix. When the irradiation dose is increased, the oxide phase passes to the polycrystalline phase. Gaseous products of
MF2 destruction (in the form of bubbles several nanometers in diameter) form a rectangular array with a period of ∼20 nm in the
sample. 相似文献
16.
B. P. Sobolev I. A. Sviridov V. I. Fadeeva S. N. Sulyanov N. I. Sorokin Z. I. Zhmurova I. I. Khodos A. S. Avilov M. A. Zaporozhets 《Crystallography Reports》2008,53(5):868-880
The nonstoichiometric phases La1 − y
Ca
y
F3 − y
(y = 0.15, 0.20) with a tysonite (LaF3) structure have been prepared for the first time by the mechanochemical synthesis from CaF2 and LaF3 crystals. The average size of coherent scattering regions is approximately equal to 10–30 nm. It has been shown that the
compositions of the phases prepared by the mechanochemical synthesis are inconsistent with the phase diagram of the CaF2-LaF3 system. The “mechanohydrolysis” of the La1 − y
Ca
y
F3 − y
phase has been observed for the first time. Under these conditions, the La1 − y
Ca
y
F3 − y
phase partially transforms into lanthanum calcium oxyfluoride for a milling time of 180 min with intermediate sampling. The
La1 − y
Ca
y
F3 − y
nanoceramic materials have been prepared from a powder of the mechanochemical synthesis product by pressing under a pressure
of (2–6) × 108 Pa at room temperature. The electrical conductivity of the synthesized materials at a temperature of 200°C is equal to 4.9(6)
× 10−4 S/cm, and the activation energy of electrical conduction is 0.46(2) eV. These data for the nanoceramic materials coincide
with those obtained for migration of fluorine vacancies in single-crystal tysonite fluoride materials.
Original Russian Text ? B.P. Sobolev, I.A. Sviridov, V.I. Fadeeva, S.N. Sul’yanov, N.I. Sorokin, Z.I. Zhmurova, I.I. Khodos,
A.S. Avilov, M.A. Zaporozhets, 2008, published in Kristallografiya, 2008, Vol. 53, No. 5, pp. 919–929. 相似文献
17.
L. B. Serezhkina E. V. Peresypkina A. V. Virovets M. O. Karasev 《Crystallography Reports》2010,55(1):19-23
Single crystals of the compound (NH4)3[UO2(CH3COO)3]2[UO2(CH3COO)(NCS)2(H2O)] (I) are synthesized, and their structure is investigated using X-ray diffraction. Compound I crystallizes in the monoclinic system with the unit cell parameters a = 18.3414(6) ?, b = 16.3858(7) ?, c = 12.4183(5) ?, β = 92.992(1)°, space group C2/c, Z = 4, V = 3727.1(3) ?3, and R = 0.0253. The uranium-containing structural units of crystals I are mononuclear complexes of two types with an island structure, i.e., the [UO2(CH3COO)3]− anionic complexes belonging to the crystal-chemical group (AB
301 = UO22+, B
01 = CH3COO−) of the uranyl complexes and the [UO2(CH3COO)(NCS)2(H2O)]− anionic complexes belonging to the crystal-chemical group AB
01M31 (A = UO22+, B
01 = CH3COO−, M
1 = NCS− or H2O). 相似文献
18.
M. Yu. Gryaznov S. V. Shotin V. N. Chuvil’deev M. O. Marychev E. A. Sul’yanova S. N. Sul’yanov B. P. Sobolev 《Crystallography Reports》2012,57(1):144-150
Hardness, crack resistance, brittleness, and effective fracture energy have been studied for crystals of 24 fluorite phases
Sr1 − x
R
x
F2 + x
(R are 14 rare earth elements (REEs); 0 < x ≤ 0.5) and SrF2 grown by the Bridgman method from a melt. These characteristics change nonlinearly with an increase in the
REE content for Sr1 − x
R
x
F2 + x
(0 < x ≤ 0.5) with R = La, Nd, Sm, Gd, and Lu; it is maximum in the range x < 0.1 for all REEs. The changes in a number of REEs have been traced for an isoconcentration series of Sr0.90
R
0.10F2.10 crystals (R = La, Nd, Sm, Gd, Ho, Er-Lu, or Y) and crystals (similar in composition) with R = Tb and Dy. The hardness of Sr1 − x
R
x
F2 + x
crystals is higher by a factor of ∼2–3 than that of SrF2. The effect of decrease in microstresses in SrF2 crystals is confirmed by the isomorphic introduction of R
3+ ions into this crystalline matrix. 相似文献
19.
I. I. Buchinskaya E. A. Ryzhova M. O. Marychev B. P. Sobolev 《Crystallography Reports》2004,49(3):500-508
This article begins a series of publications on growth of single crystals of nonstoichiometric Cd1− x
R
x
F2 + x
phases (R = La-Lu, Y, In) with the defect CaF2-type structure, their crystal structures, and some properties. The present article is dedicated to the phase diagrams of
the CdF2-RF3 systems in the region of Cd1−x
R
x
F2 + x
formation. Their analysis shows that it is possible to synthesize homogeneous Cd0.9
R
0.1F2.1 crystals. The dependence of the defect structure of the crystals on the type and concentration of rare earth elements is
studied on specially grown Cd0.9
R
0.1F2.1 (R = La-Lu) and Cd1−x
YxF2 + x
(x = 0.1, 0.15, 0.20) crystals. It is shown that, despite the fact that all the Cd0.9
R
0.1F2.1 crystals melted congruently, irrespectively of the rare earth elements used, they were rather homogeneous. The chemical compositions
of the Cd1−x
R
x
F2 + x
phases (R = Sm, Gd, Tb, Ho, and Lu) determined by the method of inductively coupled plasma atomic emission spectroscopy (ICP-AES) turned
out to be close to Cd0.9
R
0.1F2.1.
__________
Translated from Kristallografiya, Vol. 49, No. 3, 2004, pp. 566–574.
Original Russian Text Copyright ? 2004 by Buchinskaya, Ryzhova, Marychev, Sobolev. 相似文献
20.
E. Kh. Mukhamedzhanov M. V. Kovalchuk M. M. Borisov E. N. Ovchinnikova E. V. Troshkov V. E. Dmitrienko 《Crystallography Reports》2010,55(2):174-181
Purely resonant Bragg reflections 006, 5$
\bar 5
$
\bar 5
0, and 666 in a rubidium dihydrophosphate (RbH2PO4) crystal at the K edge of rubidium have been experimentally and theoretically investigated. These reflections remain forbidden when the resonant
dipole-dipole (E1E1) contribution to the resonant atomic factor is taken into account; they may be due to the dipole-quadrupole (E1E2) transitions as well as to the anisotropy atomic factor, which is caused by thermal atomic displacements (thermally induced
contribution) and/or local jumps of hydrogen atoms. A numerical simulation showed that, at room temperature (experimental
conditions), the thermally induced contribution to the “forbidden” reflections is dominant. 相似文献