Dependence of the surface topology and raman scattering spectra of Ge x Si1−x /Si films on the composition variation over the layer thickness

The surface topology and Raman scattering spectra of Ge _x Si_{1 ? x} /Si(100) films are investigated in dependence of the composition variation over the film thickness. It is shown that the character of the Ge content variation in the Ge _x Si_{1 ? x} alloy at the constant cumulative Ge fraction in the film (x _int = 0.5) affects the surface morphology of the grown Ge _x Si_{1 ? x} /Si layer. The heterostructures were grown by molecular-beam epitaxy.     

Nanostructured crystals of fluorite phases Sr1 − x R x F2 + x (R are rare-earth elements) and their ordering. I. Crystal growth of Sr1 − x R x F2 + x (R = Y,La, Ce,Pr, Nd,Sm, Gd,Tb, Dy,Ho, Er,Tm, Yb,and Lu)

Crystallography Reports - Crystals of nonstoichiometric phases Sr1 − x R x F2 + x (R are 14 rare-earth elements) and the ordered phase Sr4Lu3F17 with a trigonally distorted fluorite lattice...     

Properties of high nitrogen content mixed alkali earth oxynitride glasses (AExCa1−x)1.2(1)SiO1.9(1)N0.86(6), AE = Mg,Sr, Ba

Mixed alkali earth element containing high nitrogen content oxynitride glasses (Ca_1?xAE_x)_1.2(1)SiO_1.9(1)N_0.86(6), with AE = Mg, Sr, Ba, x ≤ 0.30 for Mg and x ≤ 0.46 for Sr and Ba, and nominally constant (Ca/AE):Si:O:N ratios were prepared in order to investigate the compositional dependencies of physical properties on alkali earth element composition. The glasses were prepared by melting mixtures of AEH₂, CaH₂, SiO₂ and Si₃N₄ powders in nitrogen atmosphere at 1600–1700 °C and characterized by X-ray powder diffraction and scanning and transmission electron microscopy. Cation and anion glass compositions were determined by respectively energy dispersive X-ray analysis and combustion analysis. The determined physical properties were density, glass transition temperature, Vickers hardness, and refractive index. The physical properties were found to vary linearly with the degree of substitution of Ca by the AE elements. The density of the glasses increases substantially upon substitution by Sr and Ba, up to 3.99 g/cm³. Glass transition temperatures are found to be higher for Mg and Sr substituted glasses, ca. 900 °C, in comparison with Ba substituted glasses, ca. 850 °C. The hardness increases upon substitution by Mg, up to 12.2 GPa at x = 0.46, and decreases upon substitution by Sr and Ba. The refractive index increases upon substitution by Sr and Ba, up to 1.97 for Ba at x = 0.46, and decreases upon substitution by Mg. The transparency of the glasses was found to increase upon increasing substitution by Mg and completely transparent glasses were obtained for x = 0.24.     

Displacements in the cationic motif of nonstoichiometric fluorite phases Ba1 − x R x F2 + x as a result of the formation of {Ba8[R 6F68–69]} clusters: I. The Ba0.78Tm0.22F2.22 crystals

The displacements of Ba²⁺ cations in the cationic motif of Ba_0.78Tm_0.22F_2.22 crystals, which are representatives of nonstoichiometric fluorite phases Ba_{1 ? x} R _x F_{2 + x} , are proved for the first time with the use of precision investigations of the fine atomic structure. It is shown that the cation displacements, like the previously revealed displacements in the anionic motif, reflect the formation of {Ba₈[R ₆F_68–69]} superclusters of structural defects with nanometer linear sizes. The Ba ²⁺ cations are displaced from the fluorite crystallographic positions 4a (space group Fm $ \bar 3 The displacements of Ba²⁺ cations in the cationic motif of Ba_0.78Tm_0.22F_2.22 crystals, which are representatives of nonstoichiometric fluorite phases Ba_{1 − x} R _x F_{2 + x} , are proved for the first time with the use of precision investigations of the fine atomic structure. It is shown that the cation displacements, like the previously revealed displacements in the anionic motif, reflect the formation of {Ba₈[R ₆F_68–69]} superclusters of structural defects with nanometer linear sizes. The Ba ²⁺ cations are displaced from the fluorite crystallographic positions 4a (space group Fm m) to the positions 32f. The static nature of the cation displacements is confirmed by the fact that these displacements are retained at a temperature of 110 K. The correctness of the interpretation of the correlation between the cation displacements and the formation of superclusters of structural defects is supported by the coincidence of the intercationic distances determined in the disordered phase Ba_0.78Tm_0.22F_2.22 with those found in the previously studied ordered phases Ba₄ R ₃F₁₇ (R = Y, Yb). The model with splitting of cationic positions is appropriate for testing in structural investigations of crystals of the fluorite phases M _{1 − x} R _x F_{2 + x} at room temperature. Original Russian Text ? A.M. Golubev, L.P. Otroshchenko, V.N. Molchanov, B.P. Sobolev, 2008, published in Kristallografiya, 2008, Vol. 53, No. 6, pp. 1023–1030.     

Crystal growth and defect crystal structure of CdF2 and nonstoichiometric phases Cd1 − x R x F2 + x (R = rare earth element or in). 5. Crystal structure of as-grown Cd0.9R0.1F2.1 (R = La-Nd) single crystals: Nanoclusters of structural defects

As-grown Cd_0.9 R _0.1F_2.1 (R = La-Nd) crystals were assigned to the CaF₂ structure type and their structure was determined by X-ray diffraction. A new octacubic cluster of structural defects in Cd_0.9 R _0.1F_2.1 phases is proposed. The changes in the anionic motif of the Cd_0.9 R _0.1F_2.1 phase can be explained as a result of the formation of tetrahedral [Cd_{4 ? n} R _n F₂₆] and inverse octacubic [Cd_{14 ? n} R _n F₆₈] clusters with, respectively, tetrahedral and cuboctahedral anionic groups as cores. It is established that fluctuations of the La concentration in the cross section of a Cd_0.9La_0.1F_2.1 crystal boule do not exceed 2.7%.     

Crystal growth,structure, crystalline perfection and characterization of zinc magnesium ammonium sulfate hexahydrate mixed crystals ZnxMg(1−x)(NH4)2(SO4)2·6H2O

Mixed crystals Zn_xMg_(1?x)(NH₄)₂(SO₄)₂·6H₂O of the two well-known Tutton's salts Zn(NH₄)₂(SO₄)₂·6H₂O and Mg(NH₄)₂(SO₄)₂·6H₂O were grown with varying molar proportions (x=0.10–0.90) by slow evaporation solution growth technique. The mixed crystal Zn_0.54Mg_0.46(NH₄)₂(SO₄)₂·6H₂O is crystallizing in monoclinic system with space group P2₁/c and cell parameters a=6.2217(4) Å, b=12.5343(7) Å, c=9.2557(6) Å, β=106.912(3)°. The coexistence of zinc and magnesium ions in the mixed crystal was confirmed by inductively coupled plasma (ICP), atomic absorption spectroscopy (AAS) and energy dispersive X-ray spectroscopy (EDS). Compositional dependence of lattice parameters follows Vegard's relations. Slight variations are observed in FT-IR and XRD of pure and mixed crystals. Comparison of crystalline perfection as evaluated by high-resolution X-ray diffraction (HRXRD) for mixed crystals of various proportions reveals a reasonably good crystalline perfection for the mixed crystal with nearly equimolar ratio of Zn and Mg. The surface morphology of the mixed crystals changing with composition was studied by scanning electron microscopy (SEM). UV–vis studies reveal that the transparency of the mixed crystals was not much affected.     

The Crystal-Chemical Features of Phases and the Nature of the Coordination Bond in the System [CuxNi(1 – x){N(CH2PO3)3}]Na4 · nH2O (x = 0–1)

Crystallography Reports - The structural features of the phases formed during crystallization of mixed copper and nickel complexes with nitrilotris(methylenephosphonic acid)...     

Intramolecular N−H...O hydrogen bonding,quinoid effect,and partial π-electron delocalization in N-aryl Schiff bases of 2-hydroxy-1-naphthaldehyde: the crystal structures of planar N-(α-naphthyl)- and N-(β-naphthyl)-2-oxy-1-naphthaldimine

The structures of N-(-naphthyl)-2-oxy-1-naphthaldimine1 and N-(-naphthyl)-2-oxy-1-naphthaldimine2 have been investigated by X-ray analysis and by spectroscopic methods. Crystals of1 are monoclinic, space groupPn, with cell dimensionsa=10.823(3),b=5.826(2),c=11.899 (3) Å, and =99.66(3)°. Compound2 crystallizes in the orthorhombic space groupPca2₁ witha=17.564(3),b=6.314(2), andc=13.663(4) Å. The IR spectra exhibited neither N–H nor O–H stretching frequencies. The existence of theintramolecular hydrogen bonding of N–H...O type was predicted by spectroscopic experiment but unequivocally established by diffraction experiment in both cases1 and2. The molecules1 and2 are significantly planar with considerable quinoid effect at the 2-oxy-naphthaldimine moiety. Although essentially planar, both molecules1 and2 show the delocalization of -electrons only in the central part of the molecules including C=N imino group with pendent ring carbon atoms.Intermolecular attractions in the crystals belong to weak van der Waals interactions-between discrete planar molecules spatially arranged into the expectedherringbone motif in the solid state.     

Synthesis,Crystal Structure and NLO Properties of a Mixed Crystal K<Subscript>1−x</Subscript>(NH<Subscript>4</Subscript>)<Subscript>x</Subscript>H<Subscript>2</Subscript>PO<Subscript>4</Subscript> (x = 0.5)

Abstract  

A new mixed crystal K_1−x(NH₄)_xH₂PO₄ (KADP) of ammonium dihydrogen phosphate (ADP) of ADP–KCl system has been synthesized with x = 0.5 by slow evaporation of the mixture of equimolar aqueous solution at room temperature. Crystal composition determined by single crystal X-ray diffraction analysis reveals that it belongs to the tetragonal system with noncentrosymmetric space group I-42d and it is structurally similar to ADP crystals with the following parameters: a = 7.418(3) ?; c = 7.2284(6) ?; v = 404.63(4) ?³; z = 4. The substitution results in defect centers which influence the physical properties. Mixed crystal has a superior NLO activity, twice that of KH₂PO₄ (KDP), a well known NLO material and the enhanced NLO activity is rationalized. The structural analysis of KADP and the influence of partial cationic substitution in ADP by K⁺ ions on the NLO properties are reported.