Neutron diffraction investigation of the evolution of the crystal structure of oxygen-conducting solid solutions (Yb1 ? x Ca x )2Ti2O7 ( x = 0, 0.05, 0.10)

The crystal structure of pyrochlore-like solid solutions (Yb_{1 − x} Ca _x )₂Ti₂O₇ (x = 0, 0.05, 0.10) synthesized by high-temperature annealing of mechanically activated initial oxides at temperatures of 1300–1500°C is studied using neutron diffraction. It is found that the Ca²⁺ cations are located in the ytterbium sublattice, which apparently favors the splitting of one of the oxygen sublattices [O(2) (48f)] of the pyrochlore structure: the decrease in the occupancy of this sublattice is accompanied by the formation of a new sublattice O(3) (8b), whereas the other oxygen sublattice O(1) (8a) remains unchanged. This rearrangement of the anions in the oxygen subsystem due to the incorporation of an alkaline-earth cation explains the high ionic conductance (∼0.2 S/cm at 1000°C) for (Yb_0.9Ca_0.1)₂Ti₂O₇ ∼ 0.2, which is the maximum value observed to date for pyrochlores of the A ₂ B ₂O₇ type, where A = Ln and B is a Subgroup IVA element of the periodic system. The bulk and grain-boundary components of the conductivity of (Yb_0.95Ca_0.05)₂Ti₂O₇ synthesized at temperatures of 1300, 1400, and 1500°C are studied using impedance spectroscopy. It is found that the (Yb_0.95Ca_0.05)₂Ti₂O₇ sample synthesized at 1500°C has the highest total conductivity due to the increased grain-boundary component. The bulk component of the ionic conductivity of (Yb_0.95Ca_0.05)₂Ti₂O₇ is hardly affected by the synthesis temperature and depends mainly on the degree of heterovalent substitution. Original Russian Text ? A.V. Shlyakhtina, A.E. Sokolov, V.A. Ul’yanov, V.A. Trunov, M.V. Boguslavskiĭ, A.V. Levchenko, L.G. Shcherbakova, 2009, published in Kristallografiya, 2009, Vol. 54, No. 1, pp. 31–36.     

N,N′-Dihydrogenpiperazonium dichloridobis(dimethylglyoximato-k2N,N′)cobaltate(III) Dihydrate

Abstract  

The title complex: C₄H₁₂N₂[Co(C₄H₇N₂O₂)₂Cl₂]₂·2H₂O, viz., PpH₂[Co(dmgH)₂Cl₂]₂·2H₂O, where, dmgH⁻ = dimethylglyoximate and Pp = piperazine was synthesized and analyzed by single crystal XRD studies. The complex was grown as brown crystals by the slow evaporation method in ethanol. The complex crystallizes as triclinic with the space group p[`1] p\overline{1} and unit cell parameters a = 8.4521 (10) Å, b = 10.0999 (11) Å, c = 10.8952(13) Å; α = 94.066(6)°, β = 106.047(6)° and γ = 100.901(6)°. There are two complex molecules present in the unit cell. The short intra molecular O–H···O hydrogen bonds link the glyoximate moieties in the crystal.     

Study of the relationship between the crystal structure of nanolayers and electrical properties in Al x Ga1? x As/In y Ga1? y As pseudobinary heterostructures by double-crystal X-ray diffraction

The structural parameters of individual layers of samples of a Al _x Ga_1−x As/In _y Ga_1−y As/GaAs pseudomorphic heterostructure have been determined by double-crystal X-ray diffraction. A relationship of the technological parameters of fabrication of heterostructures with their structural and electrical properties is established. The increase in the mobility of the 2D electron gas in the samples under study, caused by the increase in the growth temperature of the Al _x Ga_1−x As spacer layer and the decrease in the time of silicon δ doping from the two sides of the quantum well, correlates well with the degree of the sample structural quality. Original Russian Text ? R.M. Imamov, I.A. Subbotin, G.B. Galiev, 2008, published in Kristallografiya, 2008, Vol. 53, No. 2, pp. 210–213.     

The X-Ray Structure and Spectroscopic Characterization of [Zn(H2O)6][{Zn(H2O)}2(ttha)]·4H2O (ttha?=?Triethylenetetraamine-N,N,N′,N″,N?,N?-hexaacetate)

Abstract  

[Zn(H₂O)₆][{Zn(H₂O)}₂(ttha)]·4H₂O (ttha = triethylenetetraamine-N,N,N′,N″,N‴,N‴-hexaacetate) has been structurally characterized (triclinic, P-1, a = 7.4014(4) ?, b = 8.5521(4) ?, c = 15.0309(7) ?, α = 73.582(1)°, β = 85.173(1)°, γ = 69.935(1)°; V = 857.15(7) ?³; Z = 1). The two Zn²⁺ ions bound by the [ttha]⁻⁶ ligand are in distorted octahedral environments. While there exists a center of symmetry in the [{Zn(H₂O)}₂(ttha)]²⁻ anion in the crystalline state, ¹³C{¹H} NMR spectroscopy demonstrates the absence of a center of symmetry in aqueous solution. Furthermore, electronic absorption spectroscopy reveals that [Zn(H₂O)₆][{Zn(H₂O)}₂(ttha)]·4H₂O reacts with vanadyl(IV) acetate in aqueous solution at room temperature to yield [(VO)₂(ttha)]²⁻. This reaction implies that Zn²⁺ can dissociate from [{Zn(H₂O)}₂(ttha)]²⁻ in aqueous solution.     

Synthesis and Structure of cis-Dioxo(3-Methoxysalicylaldehyde 4-Methylthiosemicarbazonato-N,O,S)(γ-Picoline-N)Molybdenum(VI)

Abstract  Red crystals of cis-dioxo(3-methoxysalicylaldehyde 4-methylthiosemicarbazonato-N,O,S)(γ-picoline-N)molybdenum(VI), [MoO₂L(γ-pic)], [L²⁻=CH₃OC₆H₄(O)CH=NN=C(S)NHCH₃, 3-methoxysalicylaldehyde 4-methylthiosemicarbazonato] were prepared by the reaction of [MoO₂L] _n with γ-picoline in dry methanol. The title compound crystallized in the monoclinic space group P2₁/n, a = 6.7984(7) ?, b = 15.9760(12) ?, c = 17.1466(14) ?, β = 93.613(8)°, V = 1858.6(3) ?³, Z = 4. The coordination geometry around the molybdenum center is distorted octahedral with the tridentate thiosemicarbazonato ligand (L²⁻) bonded meridionally to the [MoO₂]²⁺ core. The sixth coordination site is occupied by a weakly bound γ-picoline molecule. The adjacent molecules are joined by the N–H···O hydrogen bonds between their amino and methoxy groups thus forming infinite molecular chains. The three-dimensional solid-state structure is achieved by the additional C–H···O, C–H···π and van der Waals interactions. Graphical Abstract  In the title compound, [MoO₂L(γ-pic)], the tridentate thiosemicarbazonato ligand (L²⁻) is meridionally bound to the [MoO₂]²⁺ core, while a molecule of γ-picoline completes the distorted octahedral coordination around the metal atom.      

Synthesis and Crystal Structure a Two-Dimensional Coordination Polymer: [Cd( μ -N3)( μ -HL)(H2O)]n [HL?=?Monodeprotonated 2,2′-bypyridine-3,3′-diol]

Abstract  Hydrated cadmium perchlorate reacted with sodium azide and 2,2′-bypyridine-3,3′-diol (H₂L) in ethanol solution and resulted in the formation of a two-dimensional coordination polymer: [Cd(μ-N₃)(μ-HL)(H₂O)]_n. The complex has been characterized by elemental analysis and IR spectrum, and its crystal structure determined by X-ray crystallography and the complex crystallizes in the monoclinic system with space group P2₁/c and a = 7.2849(14), b = 9.9568(19), c = 17.058(3) Ǻ, β = 102.254(2)°. In the complex both azide anion and monodepronated 2,2′-bypyridine-3,3′-diol anion (HL) act as bridge ligands and led to the formation of a two-dimensional sheet structure on (100) plane, and the O–H⋯N hydrogen bond made the sheets pile up along [100] direction, which forms a supramolecular three-dimensional structure. Graphical Abstract  The title two-dimensional Cd(II) coordination polymer was synthesized by cadmium perchlorate, sodium azide and 2,2′-bypyridine-3,3′-diol and its crystal structure determined. Single crystal X-ray diffraction analysis reveals that the two-dimensional coordination polymer was fabricated with azide anion and monodeprotonated 2,2′-bypyridine-3,3′-diol as mixed bridge ligands.      

Synthesis and the crystal and molecular structures of (H3L · Cl)[CoCl4] and H2L[CuBr4] (L is 2,4,6-Tri(N,N-dimethylamino)methylphenol)

The complex compounds (H₃ L · Cl)[CoCl₄] (I) and H₂ L[CuBr₄] (II), where L is 2,4,6-tri(N,N-dimethylamino)methylphenol, were isolated in the crystalline state and studied by X-ray diffraction. The organic cations were found to be outer-sphere ligands. All three nitrogen atoms of the tertiary amino groups are protonated. In compound I, the H₃ L ³⁺ cation exists as the cis tautomer. In compound II, the H₂ L ²⁺ dication exists as the trans isomer. In the crystal structure, the dications are arranged in layers via hydrogen bonds.     

Synthesis, Characterization and X-Ray Structure of Bis(O-propyldithiocarbonato-κ2S,S′)bis(4-cyanopyridine-κN)nickel(II)

Abstract  

The [Ni(S₂COCH₂CH₂CH₃)₂(C₆H₄N₂)₂] adduct of 4-cyanopyridine with [Ni(S₂COCH₂CH₂CH₃)₂] was synthesized and characterized by elemental analysis, magnetic susceptibility measurement, IR, electronic spectral data, Thermogravimetric analysis/DTA techniques and X-ray diffraction analysis. The Ni atom in the title complex is octahedrally coordinated within a trans-N₂S₄ donor set, with the Ni atom located on a centre of inversion. The title complex crystallizes in the monoclinic space group P2 ₁ /c with unit cell parameters a = 11.75(4), b = 11.62(3), c = 9.20(2) ?, β = 104.99(3)°. Crystal structure was solved by direct methods and refined by full matrix least squares procedures to a final R-value of 0.0294 for 1895 observed reflections. The packing of layers of molecules is stabilized by weak C–H···N and C–H···π interactions.     

Synthesis and Crystal Structures of α-Phenyl- and α-Trifluoromethyl-α-(2-pyridyl-N-oxide)ethanols and α-Phenyl-α-(2-pyridyl-N-oxide)ethylene

Abstract  

The X-ray structures of two α-substituted α-(2-pyridyl-N-oxide)ethanols, the α-phenyl- (3a) and α-trifluoromethyl- (3b) derivatives, were determined. On dehydration of 3a, compound 4a was obtained. This study brought a clear proof that the α-(2-pyridyl-N-oxide)ethanols are formed following oxidation with peroxides of their corresponding pyridines. A different molecular packing was observed for the α-trifluoromethyl derivative due to an additional hydrogen bonding. Compound 3a crystallized in the monoclinic space group P 2₁/n with unit cell parameters a = 5.7416(1) ?, b = 14.3841(4) ?, c = 13.2821(3) ?, β = 94.918(2)°, V = 1092.90(4) ?³, Z = 4, D = 1.308 Mg/m³. Compound 3b crystallized in the triclinic space group P −1 with unit cell parameters a = 6.1209(2) ?, b = 8.1938(4) ?, c = 9.4675(4) ?, α = 73.363(3)°, β = 73.166(3)°, γ = 71.659(3)°, V = 421.32(3) ?³, Z = 2, D = 1.633 Mg/m³. Compound 4a crystallized in the monoclinic space group P 2₁/n with unit cell parameters a = 9.3579(3) ?, b = 12.7340(3) ?, c = 9.8579(3) ?, β = 117.3249(15)°, V = 1043.63(5) ?³, Z = 4, D = 1.255 Mg/m³.     

Synthesis, Crystal Structure of catena-poly [[4,4′-bipyridine-N,N′-bis[(triphenylphosphine)-copper(I)]-pyridine-2-carbaldehyde azine-N,N′:N″,N′″] bis(tetrafluoroboride)]

Abstract  

The title complex [Cu₂(C₁₀H₈N₂)(C₁₂H₁₀N₄)(C₁₈H₁₅)₂(BF₄)₂] _n has been synthesized and characterized by single crystal X-ray analysis. The compound crystallizes in the monoclinic space group P2₁/c with a = 10.450(4) Å, b = 14.027(5) Å, c = 18.950(6) Å, β = 100.459(5)°, V = 2,731.7(16) ų. In the title complex, the cation forms a linear chain, which is bridged by 4,4′-bipyridine and pyridine-2-carbaldehyde azine. The crystallographic asymmetry unit could be expanded polymeric structure using symmetry code: x, 1 + y, z; 1 − x, −y, 1 − z. The Cu(I) atom is coordinated by one P atom of PPh₃ ligand, two N atoms of pyridine-2-carbaldehyde azine ligand and one N atom of 4,4′-bipyridine ligand. There is a crystallographic centre of symmetry at the mid-point of the C–C bond between two pyridine rings of 4,4′-bipyridine.     

Single Crystal XRD Structure Determination and Analysis of Bis(2,9-Dimethyl-1,10-Phenanthroline-κ2N,N′)(Sulfato-κ2O,O′)Nickel(II), Hydrate (NiNeo2SO4·H2O; Neo: 2,9-Dimethyl-1,10-Phenanthroline)

Abstract  

The title compound is monomeric with a Ni(II) hexacoordinated center. The coordination sphere is formed with four nitrogens from two neocuproine molecules and two oxygens from a sulfate ion that acts as a bidentate ligand. A water molecule completes the formula with an important role in the stabilization of the structure through the formation of O_W–H···O_S bridges, in which it acts as a donor and interactions of the type C_ar–H···O_W and C_Met–H···O_W, where it is an acceptor group (W: water; S: sulfate; ar: arene; Met: methyl). The compound is monoclinic, space group P2₁ /c with a = 14.4829(4) ?, b = 14.4563(4) ?, c = 12.1559(3) ?, β = 94.407(1)°, V = 2,537.55(12) ?³ and Z = 4. The structure was solved by direct methods with a conventional R (on F) = 0.0359 for 4841 reflexions with Fo > 4σ(Fo). Three levels of super-structural hierarchy can be identified in the crystal construction: (1) the primary structure corresponding to the molecular skeletons of their building blocks, the isolated complex itself and the water molecule, (2) an 1D supramolecular array that form chains through a non-covalent polymerization via interactions O_W–H···O_S, C_ar–H···O_W, C_ar–H···O_S and C_Met–H···O_W and (3) finally the 3D macroscopic conglomerate formed through inter-chains interactions C_ar–H···O_W, C_ar–H···O_S, C_Met–H···ar and offset stacked arene–arene.     

Stereospecific Ligands and Their Complexes. III. Oxalato and Malonato-(ethylenediamine- N , N ′-di- S , S -2-propionato)-Chromate(III) Complexes. Crystal Structure of the Δ-(–)589- s - cis -K[Cr( S , S -eddp)(ox)]?·?0.5H2O

Abstract  The s-cis-[Cr(S,S-eddp)L]⁻ complexes (S,S-eddp = S,S-ethylenediamine-N,N′-di-2-propionate ion; L = oxalate or malonate ions) were prepared. The complexes were purified by ion-exchange chromatography. The geometry of the complexes has been supposed on the basis of the electronic absorption spectra, and the absolute configurations of the isolated s-cis-[Cr(S,S-eddp)L]⁻ complexes have been predicted on the basis of their circular dichroism (CD) spectra and confirmed by X-ray analysis of the crystal structure of the Δ-(–)₅₈₉-s-cis-K[Cr(S,S-eddp)(ox)] 0.5H₂O complex. Index Abstract  The title compound, s-cis-potassium-(ethylenediamine-N,N’-di-S,S-2-propionato) (oxalato)chromate(III) semihydrate was synthesized by passing the corresponding sodium salt through cation exchange-resin Merck I in potassium form and its crystal structure determined. Single crystal X-ray diffraction analysis reveals s-cis geometry of the complex cation. For Part II see Glodjović VV, Trifunović SR (2008) J Serb Chem Soc 73:541.     

Crystal and molecular structure of Sr2( Edta ) · 5H2O, Sr2(H2 Edta )(HCO3)2 · 4H2O, and Sr2(H2 Edta )Cl2 · 5H2O strontium ethylenediaminetetraacetates

Three Sr²⁺ compounds with the Edta ⁴⁻ and H₂ Edta ²⁻ ligands—Sr₂(Edta) · 5H₂O (I), Sr₂(H₂ Edta)(HCO₃)₂ · 4H₂O (II), and Sr₂(H₂ Edta)Cl₂ · 5H₂O (III)—are synthesized, and their crystal structures are studied. In I, the Sr(1) atom is coordinated by the hexadentate Edta ⁴⁻ ligand following the 2N + 4O pattern and by two O atoms of the neighboring ligands, which affords the formation of zigzag chains. The Sr(2) atom forms bonds with O atoms of five water molecules and attaches itself to a chain via bonds with three O atoms of the Edta ⁴⁻ ligands. The Sr(1)-O and Sr(2)-O bond lengths fall in the ranges 2.520(2)–2.656(3) and 2.527(3)–2.683(2) ?, respectively. The Sr(1)-N bonds are 2.702(3) and 2.743(3) ? long. In II and III, the H₂ Edta ²⁻ anions have a centrosymmetric structure with the trans configuration of the planar ethylenediamine fragment. The N atoms are blocked by acid protons. In II, the environment of the Sr atom is formed by six O atoms of three H₂ Edta ligands, two O atoms of water molecules, and an O atom of the bicarbonate ion, which is disordered over two positions. In III, the environment of the Sr atom includes six O atoms of four H₂ Edta ²⁻ ligands and three O atoms of water molecules. The coordination number of the Sr atoms is equal to 8 + 1. In II and III, the main bonds fall in the ranges 2.534(3)–2.732(2) and 2.482(2)–2.746(3) ?, whereas the ninth bond is elongated to 2.937(3) and 3.055(3) ?, respectively. In II, all the structural elements are linked into wavy layers. The O-H…O interactions contribute to the stabilization of the layer and link neighboring layers. In III, hydrated Sr²⁺ cations and H₂ Edta ^– anions form a three-dimensional [Sr₂(H₂ Edta)(H₂O)₃] _n ²ⁿ⁺ framework. The Cl⁻ anions are fixed in channels of the framework by hydrogen bonds with four water molecules. In II and III, the N-H groups form four-center N-H…O₃ hydrogen bonds, which include one intermolecular and two intramolecular components. PACS numbers: 61.66.Hq Original Russian Text ? I.N. Polyakova, A.L. Poznyak, V.S. Sergienko, 2009, published in Kristallografiya, 2009, Vol. 54, No. 2, pp. 262–267.     

Synthesis and Crystal Structure of a Carboxylate Bridged Binuclear Copper Complex of Schiff Base Derived from β-amino acid and Salicylaldehyde

Abstract  

The tridentate ligand H₂L (H₂L = β-phenylalanine, N-[1-(2-hydroxyphenyl)propylidene] reacts with copper(II) nitrate and imidazole to give binuclear compound [Cu₂L₂(imi)₂] (1). The coordination geometry of each copper(II) ion is best described as a square-pyramided with one nitrogen atom, two oxygen atoms of the ligand one nitrogen atom of imidazole and one carboxylate oxygen atom belong to another ligand. It crystallizes in the monoclinic system P−1 with a = 7.8439(12) ?, b = 10.2717(16) ?, c = 11.6885(18) ?, α = 76.672(2)°, β = 85.397(2)°, γ = 71.412(2)°, V = 868.6(2) ?³, Z = 1.     

High Temperature Flux Crystal Growth of Uranium-Containing Perovskites: Sr3UO6 and Ba2MUO6 (M?=?Cu, Ni, Zn)

Abstract  

Single crystals of four uranates, Sr₃UO₆ and Ba₂ MUO₆ (M = Cu, Ni, Zn), were grown out of reactive carbonate melts. The compounds crystallize in the perovskite structure type as determined by single crystal X-ray diffraction. Ba₂ZnUO₆ and Ba₂NiUO₆ crystallize in the cubic double perovskite structure, the Cu analog is tetragonal and the Sr₃UO₆ compound is monoclinic. The crystal growth conditions and single crystal structures of these complex uranium-containing double perovskites are reported.     

Crystal Structures of Dipeptides Derived from the β-Amino Acids (1R,2S)-2-Aminocyclopentanecarboxylic Acid and (1S,2R,3S)-2-Amino-3-methylcyclopentanecarboxylic Acid

Abstract  

Crystals of the dimeric β-peptides 13 and 20, derived from (1R,2S)-2-aminocyclopentanecarboxylic acid and (1S,2R,3S)-2-amino-3-methylcyclopentanecarboxylic acid, respectively, were synthesised and studied by X-ray diffraction in order to establish their solid state secondary structural characteristics. Compound 13 crystallises in the monoclinic space group P 2 ₁ with cell parameters of a = 5.2682(1) ?, b = 9.1211(2) ?, c = 22.4467(6) ?, β = 91.3855(9)°, V = 1078.29(4) ?³ and Z = 2. Compound 20 crystallizes in the orthorhombic space group P 2 ₁ 2 ₁ 2 ₁ with cell parameters of a = 5.0968(1) ?, b = 11.5546(2) ?, c = 43.5414(8) ?, V = 2564.22(8) ?³ and Z = 4. In both cases adjacent molecules are linked by a series of N–H···O=C hydrogen bonds to form β-sheet like structures.     

Investigations of 2-Thiazoline-2-thiol as a Ligand: Synthesis and X-ray Structures of [Mn2(CO)7(μ-NS2C3H4)2] and [Mn(CO)3(PPh3)(κ2-NS2C3H4)]

Abstract  Treatment of Mn₂(CO)₁₀ with 2-thiazoline-2-thiol in the presence of Me₃NO at room temperature afforded the dimanganese complexes [Mn₂(CO)₇(μ-NS₂C₃H₄)₂] (1) and [Mn₂(CO)₆(μ-NS₂C₃H₄)₂] (2) in 51 and 34% yields, respectively. Compound 1 was quantitatively converted into 2 when reacted with one equiv of Me₃NO. Reaction of 1 with triphenylphosphine at room temperature furnished the mononuclear complex [Mn(CO)₃(PPh₃)(κ ²-NS₂C₃H₄)] (3) in 66% yield. All three new complexes have been characterized by elemental analyzes and spectroscopic data together with single crystal X-ray diffraction studies for 1 and 3. Compound 1 crystallizes in the orthorhombic space group Pbca with a = 12.4147(2), b = 16.2416(3), c = 19.0841(4) ?, β = 90°, Z = 8 and V = 3848.01(12) ?³ and 3 crystallizes in the monoclinic space group P 2₁/n with a = 10.41730(10), b = 14.7710(2), c = 14.9209(2) ?, β = 91.1760(10)°, Z = 4 and V = 2295.45(5) ?³. Graphical Abstract  Two new dimanganese complexes [Mn₂(CO)₇(μ-NS₂C₃H₄)₂] (1) and [Mn₂(CO)₆(μ-NS₂C₃H₄)₂] (2) were formed when [Mn₂(CO)₁₀] was treated with 2-thiazoline-2-thiol in the presence of Me₃NO. Compound 2 reacts with PPh₃ to give the monomeric complex [Mn(CO)₃(PPh₃ )(κ ²-NS₂C₃H₄)]. The structures of 1 and 3 were established by crystallography. Shishir Ghosh, Faruque Ahmed, Rafique Al-Mamun, Daniel T. Haworth, Sergey V. Lindeman, Tasneem A. Siddiquee, Dennis W. Bennett, Shariff E. Kabir Investigations of 2-thiazoline-2-thiol as a ligand: Synthesis and X-ray structures of [Mn₂(CO)₇(μ-NS₂C₃H₄)₂] and [Mn(CO)₃ (PPh3)(κ ²-NS₂C₃H₄)].      

Ionic conductivity of congruently melting Ca0.6Sr0.4F2 and Ca1 ? x ? ySryRxF2 + x (R = La, Ce, Pr, Nd) single crystals with fluorite structure

Single crystals of congruently melting compositions of the Ca_0.6Sr_0.4F₂ and Ca_{1 − x − y} Sr _y R _x F_{2 + 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 Ca_0.6Sr_0.4F₂ 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 Ca_0.77Sr_0.07La_0.16F_2.16, Ca_0.70Sr_0.11Ce_0.19F_2.19, Ca_0.65Sr_0.15Pr_0.20F_2.20, and Ca_0.58Sr_0.21Nd_0.21F_2.21 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 Ca_{1 − x − y} Sr _y R _x F_{2 + 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.     

Refinement of the crystal structure of [Rb x (NH4)1? x ]3H(SO4)2( x = 0.11) by single-crystal X-ray and neutron diffraction: I. Phase II at 300 K

The crystal structure of a mixed [Rb_0.11(NH₄)_0.89]₃H(SO₄)₂ crystal was refined using single-crystal X-ray and neutron diffraction at 300 K. The refinement confirmed that the phase II of the crystal belongs to the monoclinic crystal system (space group C2/c). It was shown that, according to the single-crystal neutron diffraction data, ammonium ions can be represented as regular tetrahedra. The analysis of the constructed difference Fourier maps of the electron and nuclear densities of ammonium ions revealed the presence of additional peaks, which can indicate the dynamic disorder of ammonium ions in the phase II. The results obtained con-firmed that the phase transition to the orientational-glass state can occur in the mixed [Rb_0.11(NH₄)_0.89]₃H(SO₄)₂ crystal with a decrease in the temperature. Original Russian Text ? L.S. Smirnov, K. Wozniak, P. Dominiak, A. Loose, I. Natkaniec, M.V. Frontasyeva, E.V. Pomyakushina, A.I. Baranov, V.V. Dolbinina, 2008, published in Kristallografiya, 2008, Vol. 53, No. 3, pp. 450–459.