Structural mechanisms of superionic conductivity in M 1−x R x F2+x single crystals

The relationship between the superionic transport in fluorite phases M _{1 ? x} R _x F_{2 + x} (M = Ca, Sr, or Ba; R are rare earth elements) and their defect structure has been analyzed. The superionic conductivity of M _{1 ? x} R _x F_{2 + x} crystals is provided by the high concentration of charge carriers. However, the carrier concentration is several tens of times lower than the concentration of anionic defects, which is explained by the presence of defect regions (DRs), which partially block carriers. The dependence of the superionic conductivity of M _{1 ? x} R _x F_{2 + x} phases on the RF₃(x) content has a percolation nature. Crystals of these phases are divided into two groups with respect to the percolation threshold: x _{p, 1} = 2–3 mol % RF₃ and x _{p, 2} = 7–8 mol % RF₃. The corresponding DR volumes are 3000–4000 ų (x _{p, 1}) and 500–700 ų (x _{p, 2}). The x _{p, 1}, and x _{p, 2} values correlate, respectively, with the octahedral cubic {M _{14 ? p} R _p F_{68 ? 69}} and tetrahedral {M _{4 ? p} R _p F₂₆} clusters, which are DR cores. The DR model and cluster structure are indicative of the heterogeneity of nonstoichiometric M _{1 ? x} R _x F_{2 + x} crystals at the nanoscale level with respect to the chemical composition and the electrical and crystallochemical (coordinations of M and R) characteristics.     

Nanostructured crystals of fluorite phases Sr1 − x R x F2 + x and their ordering: 9. The defect crystal and real structure of quenched fluorite phases Sr1 − x Ce x F2 + x (x = 0–0.5)

A Sr_0.7Ce_0.3F_2.3 crystal (CaF₂ type, sp. gr. $Fm\bar 3m$ ), obtained by quenching from melt, has been studied for the first time by X-ray diffraction. Fluorine vacancies and interstitial anions are found in the 8c and 32f sites, respectively. The defect ratio in the Sr_0.7Ce_0.3F_2.3 structure corresponds to the tetrahedral cluster configuration of defects {Sr_{4 ? n} Ce _n F₂₆}. The defect structure of quenched (at a rate of ～25 K/min) crystal differs from that of a crystal grown from melt (cooling at a rate of ～3 K/min) by the displacement of some cations (presumably Ce³⁺) along the threefold axis to the 32f site and the anisotropy of thermal vibrations of ions in the cluster core (F _int(32f)3). The concentration dependence of the lattice parameters of quenched Sr_{1 ? x} Ce _x F_{2 + x} phases (x = 0–0.5) is described by a third-order polynomial: a = 5.80009 + 1.166518 × 10^?3 x ? 1.124969 × 10^?5 x ² + 8.258155 × 10^?8 x ³. The compositional dependence of microdistortions is also nonlinear; maximum microdistortions are observed in the SrF₂ crystal. They decrease with an increase in the cerium concentration x to ～ 0.35. The minimum in the range x = 0.30–0.35 correlates with a composition corresponding to the peak (at x ～ 0.29) in the melting curves of the fluorite phase estimated from the phase diagram of the SrF₂-CeF₃ system (the method of thermal analysis).     

The crystallization kinetics of nanothin amorphous TlGa1 − x Ge x Se2 films

Crystallography Reports - The kinetics of phase transformations of amorphous Ge-doped TlGaSe2 films has been investigated by kinematic electron diffraction. It is shown that the crystallization of...     

Nanostructured crystals of fluorite phases Sr1 − x R x F2 + x (R are rare earth elements) and their ordering: 5. A study of the ionic conductivity of as-grown Sr1 − x R x F2 + x crystals

Crystallography Reports - The ionic conductivity σ of Sr1 ? x R x F2 + x crystals (R = Y, La-Lu) has been measured in the temperature range of 324–933 K. The isomorphic...     

Growth of faces of K2Co x Ni1 – x(SO4)2 · 6H2O mixed crystals

Data on the morphology and normal growth rate of the (110) and (001) faces, velocities of step motion, and slopes of dislocation hillocks on the (001) face of K₂Co _x Ni₁– _x (SO₄)₂ · 6H₂O crystals at different supersaturations of solutions with a Co/Ni ratio equal to 1: 1 or 1: 2 have been obtained using a Michelson interferometer. The morphology of the (110) faces is found to be the same for solutions of both compositions. Powerful dislocation sources with large Burgers vectors dominate on the (001) face. The morphology of the (001) surface is rougher than that of (110), especially in a 1: 2 solution at high supersaturation. The (110) faces grow more slowly as compared with (001). The kinetic coefficients of steps on the (001) face are identical in the 1: 1 and 1: 2 solutions. The influence of the kinetic and morphological characteristics of (001) faces on the single-crystal quality is analyzed.

     

Crystal structure of α‴-(Zn1−x Cd x )3As2 (x = 0.26)

Single crystals of the α?-phase of (Zn_{1 ? x} Cd _x )₃As₂ solid solution (x = 0.26) have been prepared and investigated by X-ray diffraction analysis. The tetragonal unit-cell parameters are found to be a = b = 8.5377(2) Å, c = 24.0666(9) Å, sp. gr. I4₁/amd, Z = 16. Zn and Cd atoms in the crystal statistically occupy three symmetrically independent positions in the mirror planes and are tetrahedrally coordinated by arsenic atoms. (Zn,Cd) tetrahedra share edges to form a three-dimensional structure framework. The α?-phase is geometrically related to the fluorite structure. The character of arrangement of tetrahedral vacancies in fluorite-like unit cells is revealed. Chains of tetrahedral vacancies form microchannels oriented parallel the a and b axes, which pierce the three-dimensional structure framework at different levels along the c axis. The structure of α″-Cd₃As₂ crystals is found to be similar to that of α?-(Zn_0.74Cd_0.26)₃As₂.     

X-ray diffraction study of the crystallographic characteristics of TlInS x Se2 − x solid solutions

Crystallographic parameters of TlInS _x Se_{2 ? x} solid solutions have been measured by X-ray diffraction. Dependences of the unit-cell parameters on the composition are determined. It is established that the values of parameters a, b, and c and the angle β decrease with an increase in x. It is shown that the TlInS _x Se_{2 ? x} system includes a continuous series of solid solutions based on the TlInSe₂ compound with tetragonal symmetry at x values ≤ 0.4, while at x ≥ 0.6 solid solutions based on the TlInS₂ compound with a monoclinic structure are formed.     

Concentration dependences of the unit-cell parameters of nonstoichiometric fluorite-type Na0.5 − x R 0.5 + x F2 + 2x phases (R = rare-earth elements)

Unit-cell parameter a of the cubic phases with a varying composition Na_{0.5 ? x} R _{0.5 + x} F_{2 + 2x} (R = Gd-Lu and Y) and with a fluorite-type structure, is described within an accuracy of ±0.003 Å, by the formula a = 4.454 + 0.874r ₃ + x(6.7238r ₃ ? 7.259) where r ₃ is the Shannon “crystal ionic radius” R ³⁺ at c.n. = 8.     

Synthesis and Structure Refinement of Polycrystalline Solid Solution: Na1 + x Zr2 − x Sb x P3O12 (x = 0.1)

Abstract  The solid solution of Na_1 + x Zr_2 − x Sb _x P₃O₁₂ (x = 0.1) was prepared at 1,000 °C by ceramic route. The ceramic material belonging to sodium zirconium phosphate (hereafter NZP) family crystallizes in space group R-3c with unit cell parameters: a = b = 8.77283(16) ?, c = 22.8375(7) ?, α = β = 90.0° γ = 120.0° and Z = 6. The structure of the title phase has been determined by Rietveld refinement of the powder diffraction data on GSAS software. The refinement converges to a satisfactory structure fit with R _p = 0.0764, R _wp = 0.1099 and RF ² = 0.0450. The interatomic distances and bond angles are in good agreement with their standard values. The particle size along prominent reflecting planes ranges between 13 and 50 nm. The polyhedral (ZrO₆ and PO₄ and NaO₈) distortions and valence calculations from bond strength data are also reported. The investigations show that the Sb⁺³ cation occupies the zirconium (A^VI) site of NZP structural framework and resultant charge compensation takes place through partial occupation of M₂ site by Na⁺ ions. Index Abstract  Synthesis and Structure Refinement of Polycrystalline Solid Solution: Na_1 + x Zr _2 −  x Sb _x P ₃ O ₁₂ ( x  = 0.1) O. P. Shrivastava and Rashmi Chourasia Antimony enters crystallochemically in the framework of nano ceramic sodium zirconium phosphate at the Zr site of the ZrO₆ octahedra which are inter linked by PO₄ tetrahedra through corner sharing of the vertical columns. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Crystallochemical model of ion-transport percolation in nonstoichiometric M 1−x RxF2+x phases with the defect CaF2-type structure

A crystallochemical model of ion-transport percolation in M _1?x R_xF_2+x (M = Ca, Sr, Ba; R = RE) solid solutions with the “defect” CaF₂-type structure has been suggested. Within this model, the percolation thresholds in M _1?x R_xF_2+x crystals with tetrahedral R ₄F_26? and octahedral R ₆F_37? clusters are considered, whose existence is highly probable in these disordered fluorite phases. It is established that the calculated percolation thresholds x _c = 2.8 mol % for nnn (next nearest neighbors) [(R ₆F₃₇) _M6F32 ?F_i] and x _c = 4.7 mol % for nn (nearest neighbor) [(R ₄F₂₆) _M6F32 ?F_i] are in satisfactory accord with the experimental percolation thresholds determined from the conductometric data.     

Crystal structure of new synthetic Ca,Na carbonate-borate Ca2Na(Na x Ca0.5 ? x )[B 3 t B 2 δ O8(OH)(O1 ? x OH x )](CO3)

New Ca,Na carbonate-borate Ca₂Na(Na _x Ca_{0.5 ? x} ) [B ₃ ^t B ₂ ^?? O₈(OH)(O_{1 ? x} OH _x )](CO₃) crystals (x ?? 0.4) have been synthesized by the hydrothermal method in the Ca(OH)₂-H₃BO₃-Na₂CO₃-NaCl-system at t = 250°C and P = 70?C80 atm; the structure parameters are found to be a = 11.1848(3) ?, b = 6.4727(2) ?, c = 25.8181(7) ?, ?? = 96.364(3)°, V = 1857.60(9) ?³, sp. gr. C2/c, Z = 8, and ??_calcd = 2.801 g/cm³ (Xcalibur S autodiffractometer (CCD), 2663 reflections with I > 2?? (I), direct solution, refinement by the least-squares method in the anisotropic approximation of thermal atomic vibrations, hydrogen localization, R ₁ = 0.0387). The structure is based on boron-oxygen layers of pentaborate radicals 5(2?? + 3T). Ca and Na polyhedra and CO₃ triangles are located between the layers. A crystallochemical analysis of the new Ca,Na carbonate-borate has established its similarity to natural Na,Ca pentaborates (heidornite and tuzlaite) and synthetic Na,Ba-decaborate.     

CaCu_3Ti_(4+x)O_(12+2x)陶瓷的电学性能

采用传统的固相合成方法在1100℃,保温3 h制备了不同Ti含量的CaCu3Ti4+xO12+2x陶瓷(x=-0.5,-0.2,0,0.2,0.5)。通过XRD分析了CCTO的相组成;在-20~100℃温度范围内、500 Hz~1 MHz的频率范围测量了CaCu3Ti4+xO12+2x陶瓷的介电特性和阻抗特性。Ti的化学计量变化明显的影响了CCTO陶瓷的电学性能,系统对比发现Ti的含量偏离CaCu3Ti4O12的化学计量比,会显著的降低CCTO陶瓷的介电常数,同时增加介电损耗。     

Optical band gap and Raman spectra in some (Bi2O3)x(WO3)y(TeO2)100−x−y and (PbO)x(WO3)y(TeO2)100−x−y glasses

The glasses representing (Bi₂O₃)_x(WO₃)_y(TeO₂)_100?x?y and (PbO)_x(WO₃)_y(TeO₂)_100?x?y systems were prepared. The dilatometric glass-transition temperatures of examined glass samples were found in the region 383–434 °C, the coefficient of thermal expansion varied from 12 to 16 ppm/°C and the density ranged from 6.30₂ to 6.80₈ g/cm³. From the optical transmission measurements of thin glassy bulk samples prepared by a glass blowing, the optical gap values were found in the narrow region 3.21–3.36 eV. For the temperature interval 300–480 K, the values of the temperature coefficient of the optical band gap varied from 3.7 × 10^?4 to 5.24 × 10^?4 eV/K. It is suggested that Raman feature observed at around 350 cm^?1 can be assigned to an overlap of Raman bands attributed to WO₆ corner shared octahedra and to the following three atomic linkages: Bi–O–Te, Pb–O–Te and W–O–Te.     

Crystal structure of cesium sodium hexathiocyanatobismuthate Cs2Na[Bi(SCN)6] and characterization of Cs2Na[Bi(SCN)6−x Cl x ] and Cs2Na[Bi2(SCN)9−x Cl x ] complexes by X-ray powder diffraction

Cs₂Na[Bi(SCN)₆] crystallizes in the trigonal space group with one formal molecule per unit cell.M=846.25,a=7.189(1),c=10.580(2) ,V=473.5(1) ,D _x =2.967 g cm^–3, (MoK)=13.70 mm^–1,F(000)=378. FinalR=0.029 for 917 absorption-corrected reflections. The structure consists of infinite[Bi(SCN)₆Na] ^2– anionic chains along thec axis with slightly distorted octahedral Bi–6S and Na–6N coordination and Cs⁺ ions surrounded by three anionic chains with irregular coordination by six N and three S atoms. X-ray powder diffractograms of three complexes, Cs₂Na[Bi(SCN)_6–x Cl _x ] withx=2, 3 and 4, indicate that the mixed complexes are not isostructural and can be indexed in different orthorombic unit cells witha=14.617(8),b=12.32(1),c=10.769(6) forx=2;a=15.37(1),b=10.81(1),c=10.287(6) forx=3 anda=14.662(7),b=14.366(7),c=7.932(4) forx=4. The two dinuclear complexes Cs₂Na[Bi₂(SCN)_9–x Cl _x ] withx=2 and 3, despite the large similarity of their diffractograms, are not isostructural and can be indexed in different orthorombic unit cells witha=14.79(1),b=13.72(1),c=10.591(5) forx=2 anda=18.423(8),b=15.657(7),c=7.410(7) forx=3.     

Magnetic susceptibility of sodium rare-earth fluorites Na0.5 − x R 0.5 + x F2 + 2x (R = Dy, Ho, Er, Tm, Yb) and some ordered phases

Magnetic properties of the nonstoichiometric phases with the fluorite-type “defect” structure Na_0.4 R _0.6F_2.2 (R = Ho, Er, Tm, Yb) and Na_0.35Dy_0.65F_2.3 have been studied as well as some ordered phases with different distortions of the initial fluorite lattice (NaHo₂F₇, Na₇Tm₁₃F₄₆, NaYb₂F₇, and Na₇Yb₁₃F₄₆) and Na_1.5Dy_1.5F₆ with the gagarinite-type structure (NaCaYF₆). Magnetic susceptibility χ was measured with the aid of the Faraday balance in the temperature range from 20 to 300 K. The crystals with R= Dy, Ho, Er, Tm are paramagnetic; their temperature dependence χ is described by the Curie-Weiss law. It is shown that in the temperature range studied, magnetic susceptibility does not depend on the degree of order of Dy, Ho, Er, and Tm ions in the structure. Below 80 K, the temperature dependence of magnetic susceptibility of the the Yb³⁺-containing phases differs from the analogous dependence χ of an ideal paramagnetic crystal, which is assumed to be caused by the interaction of the crystalline field with Yb³⁺ ions.     

Thermal conductivity of single crystals of Ba1–x R x F2 + x (R = La,Ce, Nd,or Gd) solid solutions

The thermal conductivity of single crystals of Ba_1–х R _х F_{2 + х} (R = La, Ce, Nd, or Gd) solid solutions has been experimentally investigated in the temperature range of 50–300 K. With an increase in the content of rare-earth elements, the thermal-conductivity behavior in these series changes from that characteristic of defect single crystals to the behavior typical of glasslike materials. The thermal-conductivity concentration dependences are almost identical, which can be explained by the same type of defect clusters arising upon heterovalent ion substitution.

     

Nanostructured crystals of fluorite phases Sr1−x R x F2+x and their ordering: VIII. Imperfect crystal structure of Sr0.71Ce0.29F2.29

A congruently melting single crystal of nonstoichiometric phase Sr_0.71Ce_0.29F_2.29 crystallizing into the CaF₂ structural type (sp. gr Fm $\bar 3$ m) has been studied by X-ray diffraction analysis. Vacancies in the main fluorine position 8c and interstitial anions in two 32f positions have been found. The ratio of the structural defects in the Sr_0.71Ce_0.29F_2.29 solid solution corresponds to the tetrahedral configuration of the defect cluster {Sr_{4 ? n} Ce _n F₂₆}.     

The preparation and structural studies in the (80 − x)TeO2–20ZnO–(x)Er2O3 glass system

Er³⁺-doped tellurite glasses of the (80 ? x)TeO₂–20ZnO–(x)Er₂O₃ system (0.5 mol% ? x ? 2.5 mol%) have successfully been made by melt-quenching technique and their structure has been investigated by means of DTA and Raman spectroscopy. The DTA results show the thermal parameters; such as the glass transition temperature (T_g) and crystallization temperature (T_c) were determined. It is found that this system provides a stable and wide glass formation range in which the glass stability around 99–140 °C may be obtained. The Raman spectroscopy used the structural studies in the glass system. Two Raman shift peaks were observed around 640–670 cm^?1 and 720–740 cm^?1, which correspond to the stretching vibration mode of TeO₄ tbp and TeO₃ tp, respectively. It is found that the spectral shift in Raman spectra is depending on the Er₂O₃ content. This evolution is an indication of the changes in the basic unit of the glass structure.     

Characterization of an asymmetric M(chelate)2(μ-Cl)2MCl2 dimer and isolation of corresponding DMSO adducts: X-ray crystal structures of Co(phen)2(μ-Cl)2CoCl2⋅C4H8O and M(chelate)Cl2(DMSO) x (Co, x = 1; Ni, x = 2) complexes

In aqueous solution, [M(chelate)Cl₂]x (chelate = 2,2-bipyridine, 1,10-phenanthroline) complexes can disproportionate to produce M(chelate)₂ ⁿ⁺ species that contain two chelating ligands. After extraction with organic solvent,Co(phen)₂(-Cl)₂CoCl₂(1) has been characterized by X-ray diffraction (monoclinic, C2/c, a = 10.278(2)Å, b = 22.026(5)Å, c = 12.941(3)Å, = 103.959(4)°, Z = 4, 2414 reflections [I 2 (I)], R ₁ = 0.0321, wR ₂ = 0.0864). However, addition of [M(chelate)Cl₂]x starting materials to dimethyl sulfoxide produces complexes that retain a single chelate ligand. The pentacoordinate complex Co(bpy)Cl₂DMSO (2) has been structurally characterized (triclinic, P , a = 7.824(2)Å, b = 9.570(4)Å, c = 10.025(2)Å, = 83.24(3)°, = 87.14(2)°, = 83.35(3)°, Z = 2, 2455 reflections [I 2 (I)], R ₁ = 0.0278, wR ₂ = 0.0747). In the case of nickel, two different geometric isomers are observed, depending on the chelate identity: trans-(DMSO)₂Ni(bpy)Cl₂ DMSO (3) (monoclinic, P21/c, a = 10.9149(8)Å, b = 12.1287(9)Å, c = 17.0044(13)Å, = 98.610(1)°, Z = 4,3519 reflections [I 2 (I)], R ₁ = 0.0209, wR ₂ = 0.0560) and cis-(DMSO)₂Ni(phen)Cl₂ (4) (monoclinic, P21/c, a = 8.404(2)Å, b = 14.051(4)Å, c = 16.710(4)Å, = 92.44(3)°, Z = 4, 3069 reflections [I 2 (I)], R ₁ = 0.0691, wR ₂ = 0.1782).