Elastic properties of KGd(WO4)2:Ho3+ single crystals studied by Brillouin spectroscopy

The analysis some of the acoustic phonons propagating in pure and Ho³⁺‐doped KGd(WO₄)₂ single crystals in the GHz frequency range by Brillouin scattering method has been presented. For investigated crystals the velocities of the longitudinal and transverse acoustic phonons [100], [010], [001], [101], [101] and [110] have been determined. Moreover, the value of elastic constants C₂₂, C₄₄ and C₆₆ of pure and Ho³⁺‐doped KGd(WO₄)₂ single crystals have been estimated. It was revealed that the presence of the Ho³⁺‐ions in KGd(WO₄)₂ crystals, for the used doping concentration 1 at% and 8 at%, does not influence their elastic properties. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Contribution to the study of elastic properties of KGd(WO4)2:Er3+ single crystals by Brillouin spectroscopy

In this paper we present the study of the acoustic phonons propagating in Er³⁺‐doped KGd(WO₄)₂ single crystals by Brillouin spectroscopy. For the investigated crystals the velocities of the longitudinal and transverse acoustic phonons [100], [010], [001], [101] and [110] have been determined. Moreover, the values of the elastic constants: C₂₂, C₄₄ and C₆₆ of Er³⁺‐doped KGd(WO₄)₂ single crystals have been estimated. It was revealed that the presence of the Er³⁺‐ions in KGd(WO₄)₂ crystals, for the used doping concentration 1 at% does not influence their elastic properties. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microhardness studies on as‐grown (111) faces of some alkaline earth nitrates

Single crystals of Sr(NO₃)₂, Ba(NO₃)₂ and Pb(NO₃)₂ are grown from their aqueous solutions at a constant temperature of 35 °C by slow evaporation technique. Crystals of size 8 to 10 mm along one edge are obtained in a period of 10 days. Chemical etching technique has been employed to study the dislocations in these crystals. The dislocations are randomly distributed and the dislocation density is about 10⁴ to 10⁵ /cm². Microhardness studies are made on as–grown (111) faces of these crystals upto a load of 100 g. The hardness of the crystals increases with an increase in load and thereafter it becomes independent of the applied load. These results are discussed on the basis of reverse indentation size effect. Meyer index number n for these crystals is estimated at both low and high load regions. An analysis of hardness data of these crystals as well as some other cubic crystals like alums and alkali halates are discussed using Gilman–Chin parameter H_v/C₄₄, where H_v is the microhardness and C₄₄ is the shear constant. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Acoustical properties of single crystals of mercurous halides

Velocities of propagation of elastic waves along principal crystallographic directions in Hg₂Br₂ and Hg₂J₂ single crystals were measured using the pulse and phase-pulse techniques. The values obtained were used to calculate the components of the elastic tensors c_ik and s_ik, as well as the phase and group velocities of propagation of longitudinal and transverse waves in the (100) and (001) planes, and the angular deviation of acoustic energy flux from the direction of the corresponding wave normal. Knowledge of the anisotropy of the elastic properties of Hg₂X₂ crystals and of their change with the anion (X = Cl, Br, J) leads to deeper understanding of the character of bonds in the crystal lattice and points the way to a better utilization of technical properties of the crystals. — Minimum velocity of propagation of an elastic wave falls in the case of Hg₂J₂ to a value v [100] [11 10] = 0,25 · 10⁵ cm/s, what is the lowest value known among all crystals. Maximum angular deviation of acoustic energy flux — nearly 50° — is exhibited by the quasi-longitudinal wave in Hg₂J₂ crystals. On substituting the Cl⁻ ions with Br⁻ and J⁻ ions, the anisotropy of elastic moduli C₃₃/C₁₁ increases by nearly 80%. Different mechanisms contribute to vectorial dependence of the elastic properties along different crystallographic directions.     

Effect of change of state of aggregation of impurity on tl and microhardness of KClxBr1–x mixed crystals doped with Ca2+

Microhardness and Thermoluminescence (TL) measurements have been made in KCl_xBr_1–x mixed crystals doped with Ca²⁺ impurity. The variation of hardness in undoped and Ca²⁺ doped KCl_xBr_1–x crystals with quenching temperature is investigated. TL studied of KCl_xBr_1–x crystals doped with Ca²⁺, both in as-grown state and after quenching them from various elevated temperatures indicate that the positions of the glow peak which has been attributed to F-centers is found to depend upon the state of dispersion of impurity.     

EPR spectra of irradiated Na2Cr2O7 · 2 H2O crystals

The EPR spectra of X-irradiated Na₂Cr₂O₇ · 2 H₂O crystals grown from the aqueous solution at room temperature are studied. Three groups of lines are detected, which marked conventionally as C₁, C₂ and C₃. Each of the C₁ and C₂ line groups is a superposition of two doublets. The lines are interpreted as due to the Cr⁵⁺ ions in the distorted (stretched) oxygenous tetrahedron. The doublet structure is due to hyperfine interaction with nuclei of 1/2 spin which are protons of water. It is shown that the C₁ and C₂ line groups are due to the centers of the same type with different orientations in the lattice. The principal g-tensor values for these centres were as follows: g_z = 1.916, g_y = 1.978, g_x = 1.986.     

Crystal structure of Zn[Cl2Ti(C5H5)2]2·2C6H6

The structure of crystals of the composition Zn[Cl₂Ti(C₅H₅)₂]₂·2C₆H₆ has been determined from Patterson and Fourier syntheses of two projections, and refined toR = 0·117 by full-matrix three-dimensional least-squares methods. The crystals are orthorhombic:Pbcn,a = 18·45(5),b = 15·40(6),c = 11·35(3) Å,Z= 4. The complex consists of a central distorted ZnCl ₄ ^2– tetrahedron linked along the Cl—Cl edges to two distorted TiCl₂(C₅H₅)₂ ⁺ tetrahedra in such a way that their centres are nearly collinear The two C₆H₆ molecules in the formulae unit may be regarded as benzene of crystallization.     

Solubility of CaO in CaF2 crystals

By means of conductivity investigations the solubility of CaO in CaF₂ crystals was estimated to be C_L(CaO) ≈︁ 3.7 exp (-0.68 eV/kT) = 3.7 exp (-7900 K/T) and the diffusion constant of O⁻ ions in CaF₂ D(O⁻) ≈︁ 3 exp (-2.2 eV/kT) cm²/s = 3 exp (-25 500 K/T) cm²/s.     

Microscopic calculations of displacive (Elpasolite family) and order-disorder (Potassium selenate family) structural phase transitions

The critical temperatures and thermodynamic characteristics for the displacive phase transition O ⁷_h → O ⁵_4h in crystals of the elpasolite family Rb₂ K BF₆ (B = Sc, In, Lu) and for the successive phase transitions O ⁴_6h → D ¹⁶_2h → I → C ^2h/5 (I is the incommensurate phase) in crystals of the selenate potassium family have been calculated. The calculations were carried out using the effective Hamiltonian method. The Hamiltonian parameters for the elpasolite-like crystals were determined from ab initio calculations, and those for the crystals of the selenate potassium family were found using a small number of fitting parameters.

     

The crystal and molecular structure of the Nematogenic Compound 5,8-Dihydro-5,8-methano-1,4-naphthalenediyl Bis(4-ethoxybenzoate)

Single crystals of the title compound with the formula (C₂H₅O C₆H₄ COO)₂C₁₁H₈ have been investigated by X-ray analysis. The compound crystallizes in the monoclinic space group P2₁/n with a = 8.555(1), b = 15.280(2), c = 19.093(3) Å, β = 94.17(1)⁰, V = 2489.2(5) ų, and Z = 4. The structure was solved by direct methods and refined to a final R value of 0.062 The molecule adopts an almost stretched form. The norbornene skeleton within the central part of the molecule is disordered and occurs in two different conformations. The molecular packing is characterized by different lattice regions: the molecules in one region are parallel but their long axes are inclined by 49.5° to the molecules of the other region.     

X-ray and Raman studies of single crystals of CsSbF6

Crystals of CsSbF₆ belong to the rhombohedral space groupR¯3-C _3i ² witha=7.904(1)andc=8.261(1) Å,V=446.95 ų,Z=3,D _c=4.11 gcm^–3. The antimony atom is surrounded by six fluorine atoms in a nearly perfect octahedral configuration with Sb-F 1.875(9) Å, while 12 fluorine atoms surround the cesium atom with closest contact 3.116 Å. Polarized Raman spectra of single crystals of CsSbF₆ have been obtained, and it is shown that these results can be interpreted in terms of a unimolecular rhombohedral structure. The small distortion from an octahedral arrangement for the SbF ₆ ^– group is clearly reflected in the spectra. The Raman results are in better agreement with the space groupR¯3m-D _3d ⁵ than withR¯3-C _3i ² , but this conclusion must be regarded with caution since the two features in the vibrational spectra of CsSbF₆ which can be used to distinguish between the two structures are weak and ill-defined.     

Molecular and crystal structure of 3-(4-chlorophenylthio)-1-(2,4-dinitrophenylamino)-pyrrolidine-2,5-dione

3-(4-Chlorophenylthio)-1-(2,4-dinitrophenylamino)-pyrrolidine-2,5-dione, C₁₆H₁₁N₄C10₆S, was obtained in the addition reaction of 4-chlorobenzenethiol and 2,4-dinitrophenyl-aminomaleimide. It forms orthorhombic crystals; the finalR=0.048 for 1083 unique observed reflections. The molecule consists of three rigid rings connected by single bonds. A synclinal conformation of the terminal phenyl rings (A andC) with respect to the central pyrrolidine ring (B) is observed in the crystal, with ringsA andC close to one another. An intramolecular hydrogen bond N(2)O(4) of 2.593(7) Å is observed. The structure of the title compound was also investigated by IR,¹H-NMR and M.S.     

Specific heat of vitreous systems: Temperature dependence near absolute zero

Unlike the low temperature heat capacities (L.T. C_V) of crystals, those of vitreous substances near T = 0 K require the formula C_V/3R = C₁T+C₂T²+C₃T³+C₅T⁵+…, where the constants C₁ and C₂ represent the anomalous excess characteristic of vitreous systems. The C₃ and C₅ represent, respectively, Debye and dispersion terms as for crystals. Recent literature confirms C₁ ≠ 0 for various glasses and offers diverse theoretical justifications for this. The C₂T² term has been proposed but not evaluated by Leadbetter. As shown here, it is required to represent the experimental C_V of vitreous silica at T < 2 K, is inferred from its Raman spectrum and is supported by theoretical calculations.     

Synthesis and thermal,phase transition and FTIR spectral characterization of tetraethylammonium tetrachlorocuprate (II) crystals

Single crystals of tetraethylammonium tetrachlorocuprate (II), [N(C₂H₅)₄]₂CuCl₄, were grown by slow evaporation method at room temperature. The crystals were characterized through powder XRD, thermogravimetric (TG‐DTA), low temperature differential scanning calorimetric (DSC) studies and FTIR spectroscopy. While the powder XRD pattern of the compound shows sharp Bragg peaks confirming the crystallinity of the compound, the TG‐DTA studies confirm formation of the compound in the stoichiometric ratio. The thermal anomalies observed in DSC curve at ‐120°C in the heating cycle and around ‐30°C in the cooling cycle indicate a first order phase transition. The phase transition was predicted to be associated with the ordering of CuCl₄^2‐ and successive long range orientation of [N(C₂H₅)₄]⁺ ions which are disordered at high temperatures. The cationic [N(C₂H₅)₄]⁺ plays a role in phase transitions at low temperatures. The sharp exothermic peak observed in high temperature DSC indicates a structural phase transition when [N(C₂H₅)₄]CuCl₃ is formed on heating the compound. The FTIR spectra of the compound characterize the various chemical bonding and water molecules adsorbed in the compound. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of Optical Properties of YAlO3Pr3+ Single Crystals

Colour centers in YAlO₃:Pr³⁺ crystals originating under xenon lamp or y–radiation and oxidizing annealing are considered. The nature of colour centers under these treatments is similar in nominally pure and Pr³⁺ containing crystals but the intensity of induced absorption lines is higher in activated crystals which assumably is associated with valent transitions of Pr ions.     

Formation and crystal structure of 1-methyl-2-phenylindolizine-3-acetonitrile

1-Methyl-2-phenylindolizine-3-acetonitrile was unexpectedly obtained in the reaction of 1-methyl-2-phenylindolizine-3-thioaldehyde with cyanide ions. Its structure was determined by IR, ¹H NMR, MS, elemental analyses, and X-ray crystallography. Colorless regular prism shaped crystals of C₁₇H₁₄N₂ crystallize in the space group C2/c with cell dimensions a = 12.956(3) Å, b =10.516(2) Å, c = 20.429(4) Å, and = 90°, = 104.98(3)°, = 90°, V =2688.7(9) ų, D _calc =1.217 Mg/m³, and Z = 8.     

Mesomorphism in chloro substituted isomeric series including chalconyl central bridge

A novel homologous series of thermotropic liquid crystals α-4-(4′-n-alkoxy benzoyloxy phenyl) β-2″-chloro benzoyl ethylenes have been synthesized and studied with a view to understand and establish the effect of molecular structure on liquid crystal (LC) properties with reference to molecular flexibility in isomeric series with differing positional status of same functional group. Novel homologues series consist of 12 homologues C₁ to C_16. C₁, C₂, and C₃ homologues are nonliquid crystals (NLC) and rest of the homologues are liquid crystals. C₁₀ to C₁₆ homologues are enantiotropically smectogenic plus nematogenic and C₄ to C₈ homologues are enantiotropic nematic. The texture of nematogenic derivatives is threaded or schlieren and that of the smectic mesophase are focal conic of the type smectic A or C. Analytical, thermal and spectral data supported molecular structures of novel homologues. Transition temperatures as determine by a hot stage polarizing optical microscopy (POM) were plotted against number of carbon atom present in n-alkyl chain ‘R’ of left n-alkoxy (-OR) group and the phase transition curves Cr–I/M, Sm–N, N–I were obtained on linking like or related points. The odd–even effect is observed for the N–I transition curve and thus transition curves behaved in normal manner. The even-membered nematic transition curve occupied higher position than the odd-membered transition curve. Present series is predominantly nematogenic and partly smectogenic with middle-ordered melting type.     

The precipitation of transition metal oxalate powders from aqueous solution. Crystal numbers and final sizes

The precipitation of manganous, ferrous, cobalt, nickel and copper oxalate hydrates was studied from equivalent solutions of concentrations from 0.001 to 0.3 M at pHs 7 to 6, by optical microscopy and other methods. Crystals growth started after induction periods: the precipitations were heterogeneously nucleated at low supersaturations and homogeneously nucleated at medium to high supersaturations. The crystal numbers of the final precipitates depended on the number of nuclei (and crystallites) formed during the induction periods. At medium to high supersaturations, crystal numbers increased with increasing initial metal oxalate complex ion concentrations according to the relation. N = N₁C_mox^β, where β was 5. The N values increased in the order Mn ≪ Fe < Co < < Ni < Cu. The final crystal lengths, in this range, then decreased with increasing metal oxalate complex ion concentrations according to the relation l_fin = l₁/C_mox^γ, where γ was 1.3. For precipitations from solution of any concentration, smaller crystals were generally obtained in the precipitates of the metal oxalate of lower solubility; nickel oxalate precipitations were the exception to this.     

Structural and spectral studies of N-trans-cinnamylidene-m-toluidine and N-trans-cinnamylidene-m-chloroaniline

N-trans-cinnamylidene-m-toluidine (1) C₁₆H₁₅N, and N-trans-cinnamylidene-m-chloroaniline (2) C₁₅H₁₂NCl form isomorphous crystals which are monoclinic, space group P2_l/c, with unit cell dimensionsa=5.967(2),b=13.793(3),c=15.048(5) Å, =91.97(3)° anda=5.868(2),b=13.788(4),c=15.191(4) Å, =91.87(3)°, respectively. The single-crystal X-ray structure determinations of the title compounds revealtrans structures. Ring (A) C_10–15 and ring (B) C_1–6, are practically planar in both structures with dihedral angels of 61.3(3) and 63.6(2)°, respectively.¹H nmr, u.v. and i.r. spectra are also reported.     

Structure and IR,UV spectroscopic behavior of azabicyclo[2.2.2]octane pentachlorophenolate

The structure of C₆Cl₅O^–·C₇H₁₃NH⁺ has been determined by X-ray diffraction. The crystals are orthorhombic:Pcab,a=10.706(1),b=11.966(2),c=24.913(5)Å,Z=8. The structure was solved by direct methods, and refined to R=0.042 for 1523 nonzero reflections. The N⁺-HO^– hydrogen bond is shortened (2.553(5)Å) and deformed (相似文献