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.     

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.     

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...     

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.     

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).     

Growth and properties of mixed K2Ni x Co1−x (SO4)2 · 6H2O crystals

Optically homogeneous mixed K₂Ni _x Co_{(1 ? x)}(SO₄)₂ · 6H₂O crystals are grown from solutions of different compositions by the temperature-reduction technique in static and dynamic regimes. The optical characteristics of the grown crystals are measured: transmittance reaches 80% in the wavelength range of 240–290 nm and no more than 9% in the visible spectral range. The thermal stability of the crystals is studied. It is established that the thermal stability of mixed K₂Ni _x Co_{1 ? x} (SO₄)₂ · 6H₂O crystals is higher than that of K₂Co(SO₄)₂ · 6H₂O crystal. The defects of the mixed crystals grown in static and dynamic regimes are investigated by X-ray topography.     

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.     

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.     

Electrical properties of glass and liquid semiconductor system (As2Te3)x(Tl2Se)1−x

We have measured the electrical conductivity and thermoelectric power of the pseudobinary system (As₂Te₃)_x(Tl₂Se)_1−x both in the glass and liquid states. The effect of the addition of excess Tl has also been examined. It has been found that the activation energy of electronic conduction is closely related to the average atomization energy of these materials.     

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.     

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}.     

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.     

Investigation of the structure and properties of (K x (NH4)1 − x )3H(SO4)2 single crystals

The influence of isomorphous replacement in the cation sublattice on the kinetics of the phase transition in single crystals of the solid solutions (K _x (NH₄)_{1 ? x} ) _m H _n (SO₄)_{(m + n)/2} · yH₂O belonging to the K₃H(SO₄)₂-(NH₄)₃H(SO₄)₂-H₂O salt system was studied. Superproton phase transitions for the end compositions of this system have been found earlier. The optical and thermal properties of crystals with the composition (K,NH₄)₃H(SO₄)₂ in the temperature range from 295 to 500 K were investigated, and the crystal structure was determined at 295 K. The results of the study and the comparison with the literature data show that the replacement of potassium atoms with ammonia leads to a fundamental change in the kinetics of the phase transition, the phase-transition temperature remaining virtually unchanged.     

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.     

Photo-acoustic spectroscopy of SixSe1−x glasses

The optical properties near the fundamental absorption edge has been studied for a series of Si_xSe_1−x glasses using photoacoustic spectroscopy. The compositional dependence of the bandgap E_O, derived from these measurements, is presented and contrasted with the GeSe and the SiS systems. This data is qualitatively explained with a model which accounts for differing numbers of homopolar and heteropolar and heteropolar bonds as the composition is varied. Additional support for this interpretation is found in the compositional behavior of the glass transitions of these alloys.     

Growth and Study of Properties of Mixed Crystals (NH4)2NixCo1 –x(SO4)2 · 6H2O

Crystallography Reports - Mixed crystals (NH4)2NixCo1 –x(SO4)2 · 6H2O have been grown from aqueous solutions of different compositions by reducing the solution temperature in two growth...     

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).