Linear optical properties of BaNaB9O15, BaLiB9O15 and SrLiB9O15 glasses

Transparent BaNaB₉O₁₅ (BNBO), BaLiB₉O₁₅ (BLBO) and SrLiB₉O₁₅ (SLBO) glasses were fabricated via the conventional melt-quenching technique. X-ray diffraction (XRD) and Differential thermal analysis (DTA) studies carried out on the as-quenched glasses confirmed their amorphous and glassy nature, respectively. The optical properties for these as-quenched glasses were investigated. The refractive index, optical band gap, Urbach energy and Fermi energy were determined. The average electronic polarizability calculated from the refractive index expression.     

A new nonlinear optical material Sr2TiSi2O8

Fresnoite type compound Sr₂TiSi₂O₈ was found as a new nonlinear optical material. This compound was synthesized by substituting Sr²⁺ for Ba²⁺ in fresnoite Ba₂TiSi₂O₈. X- ray diffraction data showed Sr₂TiSi₂O₈ and fresnoite are isostructural. The second harmonic generation (SHG) effect of Sr₂TiSi₂O₈ is about 8 times larger than that of KH₂PO₄ (KDP). The ultraviolet absorption edge of Sr₂TiSi₂O₈ is around 270nm.     

Crystal growth and characterization of two-leg spin ladder compounds: Sr14Cu24O41 and Sr2Ca12Cu24O41

Single crystals of Sr_14−xCa_xCu₂₄O₄₁ (x=0 and 12) are grown by the travelling solvent floating zone technique using an image furnace. The grown crystals are characterized for their single crystallinity by the X-ray and Neutron Laue method. The magnetic susceptibility measurements in Sr₁₄Cu₂₄O₄₁ show considerable anisotropy along the main crystallographic axes. Low-temperature specific heat measurement and DC susceptibility measurement in Ca-doped crystal showed antiferromagnetic ordering at 2.8 K at ambient pressure. High-pressure AC susceptibility measurement on Ca-doped crystal showed a sharp superconducting transition at 2 K under 40 kbars. T_c onset reached a maximum value of 9.9 K at 54 kbars. The bulk superconductivity of the sample is confirmed by the high-pressure AC calorimetry with T_c max=9.4 K and T_N=5 K at 56 kbars.     

Atomic structure of (Sr0.50Ba0.50)Nb2O6 single crystals in the series of (SrxBa1 ? x)Nb2O6 compounds

Czochralski grown (Sr_0.50Ba_0.50)Nb₂O₆ single crystals have been studied by the method of precision X-ray diffraction analysis. The structural characteristics of (Sr_xBa_{1 − x} )Nb₂O₆ compounds with x = 0.33, 0.50, 0.61, and 0.75 were analyzed. The distributions of the Sr and Ba atoms over the crystallographic positions are considered depending on their concentration. The establishment of the mechanisms of isomorphous replacements in these solid solutions allows the variation, within certain limits, of crystal properties by changing the Ba/Sr ratio. __________ Translated from Kristallografiya, Vol. 47, No. 2, 2002, pp. 249–252. Original Russian Text Copyright ? 2002 by Chernaya, Volk, Verin, Ivleva, Simonov.     

Growth, dielectric, ferroelectric and optical properties of Ca0.28Ba0.72Nb2O6 single crystals

Calcium barium niobate Ca_0.28Ba_0.72Nb₂O₆ (CBN-28) crystals were grown by the Czochralski method. The effective segregation coefficients of Ca, Ba, Na elements in CBN-28 crystal growth were measured, and the rocking curve from 0 0 2 reflection of CBN-28 wafer was also measured by the high-resolution X-ray diffractometer D5005, and the full-width at half-maximum value was measured to be 70.6″. The measured dependence of dielectric constants on temperature showed the Curie temperature of the CBN-28 crystals is between 246.8 and 260 °C. Typical polarization–electric field (P–E) hysteresis loops were measured at room temperature. Ferroelectric 180° domains were observed by scanning electron microscopy (SEM) on the etched (0 0 1) surface of the CBN-28 crystals. The transmittance of [0 0 1]-oriented CBN-28 crystals was measured and the result shows that optical properties of CBN-28 crystal are almost the same as those of SBN for wavelengths between 2500 and 7500 nm.     

Stability and formation of pyrochlore phase in doped Sr0.8Bi2.3Ta2O9 thin films

Ferroelectric thin films of bismuth-containing layered perovskite Sr_0.8Bi_2.3Ta_2−xM_xO₉ (SBTM), where M is V, Ti, W, and Zr, have been prepared on Pt/Ti/SiO₂/Si substrates using the metal-organic decomposition method. The effect of the incorporated B-site cations on pyrochlore phase formation and microstructure evolution of SBTM films was investigated. The pyrochlore phase formation has been identified due to out-diffusion of titanium from underneath platinum layer to participate in the reaction with the films. Furthermore, the formation of pyrochlore phase in the SBTM films has been observed strongly dependent on the characteristics of incorporated M cation. The substitution of both W and V for Ta leads to the formation of pyrochlore phase at lower annealing temperature (750–800 °C). On the other hand, the addition of Zr can retard the formation of pyrochlore phase from 850 to 900 °C. A model based on the binding energy of octahedral structure is used to elucidate the formation and stability of the pyrochlore phase present in the SBT film.     

Atomic layer deposition of Al2O3, ZrO2, Ta2O5, and Nb2O5 based nanolayered dielectrics

Ta₂O₅, Ta-Nb-O, Zr-Al-Nb-O, and Zr-Al-O mixture films or solid solutions were grown on Si(1 0 0) substrates at 300 °C by atomic layer deposition. The equivalent oxide thickness of Ta₂O₅ based capacitors was between 1 and 3 nm. In Zr-Al-O films, the high permittivity of ZrO₂ was combined with high resistivity of Al₂O₃ layers. The permittivity, surface roughness and interface charge density increased with the Zr content and the equivalent oxide thickness was between 2.0 and 2.5 nm. In the Zr-Al-Nb-O films the equivalent oxide thickness remained at 1.8-2.0 nm.     

Enantiomorphism of the Ca3Ga2Ge4O14 compound and comparison of the Ca3Ga2Ge4O14 and Sr3Ga2Ge4O14 structures

The absolute crystal structures of two enantiomorphic forms of the Ca₃Ga₂Ge₄O₁₄ crystals (a = 8.075(1) ?, c = 4.9723(6) ?, space group P321) with the positive and negative senses of the optical activity are determined using X-ray diffraction analysis. The final R factors are as follows: R = 1.75% and R _w = 2.57% for the crystal with the positive sense of the optical activity and R = 1.86% and R _w = 2.78% for the crystal with the negative sense of the optical activity. The replacement of the Ca²⁺ ions by larger Sr²⁺ ions (with the formation of the Sr₃Ga₂Ge₄O₁₄ compound) leads to an anisotropic expansion of the crystal lattice (with a more considerable increase in the lattice parameter a as compared to the lattice parameter c), a change in the occupation of the 1a and 3f positions by the Ga³⁺ and Ge⁴⁺ ions, and symmetrization of the octahedra and tetrahedra forming the structural framework. The shape of the dodecahedron changes so that its size along the polar electric axis 2 increases significantly. This change is the main factor responsible for the increase in the piezoelectric activity of the Sr₃Ga₂Ge₄O₁₄ compound as compared to the piezoelectric activity of the Ca₃Ga₂Ge₄O₁₄ compound. Original Russian Text ? B.V. Mill, A.A. Klimenkova, B.A. Maximov, V.N. Molchanov, D.Yu. Pushcharovsky, 2007, published in Kristallografiya, 2007, Vol. 52, No. 5, pp. 816–823.     

Elastic constants and structure of the vitreous system Co3O4P2O5

The elastic moduli of the entire vitreous range of the system CoPO that can be prepared by melting together Co₃O₄ and P₂O₅ oxides in open crucibles, have been measured by ultrasonic techniques at 15 MHz. The bulk, shear, longitudinal and Young's moduli and the Poisson ratio are found to be rather sensitive to the glass composition. It is found from this ultrasonic data, that the glass system can be divided into “three compositional regions”. This behaviour is qualitatively interpreted in terms of the cobalt co-ordination, crosslink densities, interatomic force constants and atomic ring sizes. Also presented is a full discussion of effects of annealing on elastic properties.     

Local structure of liquids Al2O3 and GeO2 under densification

Molecular dynamic simulation has been conducted to study the local structure of liquid Al₂O₃ and GeO₂ under densification. Those liquids are found to be a mixture of species of TO_x. Here T is Ge or Al and x = 4, 5 and 6. This result is supported by the fact that the density, fraction of oxygen connectivity and volume of different void kinds are a linear function of TO_x fraction. The microscopic mechanism of liquid densification is quantified and interpreted in term of the change in TO_x fraction.     

Growth,thermal and optical properties of a new nonlinear optical crystal: ZnBi2B2O7

Single crystals of ZnBi₂B₂O₇ (ZBBO) have been successfully grown by the top-seeded growth method from a high-temperature melt. The crystal was colorless and transparent with size of 15×10×5 mm³. The orientation of ZBBO crystal has been discussed. The melting point, molar enthalpy of fusion, and molar entropy of fusion of the crystal were determined to be 964.02 K, 110680.36 J mol⁻¹, and 113.92 J K⁻¹ mol⁻¹, respectively. The transparency range of the crystal extends from 370 to 2100 nm.     

Synthesis and characterization of monolithic Gd2O3 aerogels

In this thesis, we will elaborate on the synthesis and characterization of monolithic Gd₂O₃ aerogel. We conducted the experiment in the following procedure. Use gadolinium nitrate or gadolinium chloride, a kind of inorganic gadolinium salt as raw material, and polymerize it in ethanol with propylene oxide as gelation initiator in the way of sol-gel. After this step, we can obtain the wet gel. Then, dry the wet gel by supercritical CO₂, at last we will get aerogel. The product has strong transparency and also shows some thermal stability. XRD characterization shows that it is amorphous. Nitrogen adsorption/desorption analysis tells clearly its surface area (223 m²/g), average pore diameters (42 nm) and large pore volume (1.83 ml/g). It is also characterized by transmission electron microscopy and high-resolution transmission electron microscopy.     

Quenched glasses in the systems of Li2O with Al2O3, Ga2O3 and Bi2O3

By rapid quenching in a twin roller apparatus, glass was found to occur widely in the systems of Li₂O with Al₂O₃, Ga₂O₃, Bi₂O₃ and in mixed systems. Examination of the resulting flakes by X-ray powder diffraction, differential thermal analysis, and capacitance data revealed the occurrence of glass, glass transitions, crystallization exotherms and the nature of some of the crystallization paths.The log ionic conductivity of the glasses was found to follow a linear relationship with the Li concentration. Evidence was observed for three new metastable crystalline phases, one in the Li₂OAl₂O₃ system and two in the Li₂OBi₂O₃ system. The latter system also showed evidence for the occurrence of two glasses at almost all compositions.     

Synthesis,characterization and growing mechanism of monodisperse Fe3O4 microspheres

Monodisperse Fe₃O₄ microspheres assembled by a number of nanosize tetrahedron subunits have been selectively synthesized through the hydrothermal process. The synthesized Fe₃O₄ microspheres have good dispersibility. The subunits made up of microspheres were uniform in size and like-tetrahedron in shape. The average diameter of each Fe₃O₄ microsphere is about 50–55 μm. The length of each edge of tetrahedron is about 100 nm. A series of experiments had been carried out to investigate the effect of reductant, precipitator and reaction time on the formation of Fe₃O₄ microsphere and tetrahedron subunits. The results show that ascorbic acid as reductant and urea as precipitator supplied a relatively steady environment during the synthesis process and led to the formations of Fe₃O₄ tetrahedron subunit and monodisperse Fe₃O₄ microspheres. As the reaction time increased from 3 to 24 h, the Fe₃O₄ microspheres tended towards dispersion and becoming large in size from 10–20 to 50–55 μm, and the subunits formed Fe₃O₄ microspheres that varied from spheroid to tetrahedron and from a small nanoparticle (20–30 nm) to a large one (90–110 nm). A reasonable explanation for the formations of the Fe₃O₄ microsphere and the tetrahedron subunit was proposed through Ostwald ripening and the attachment growth mechanism, respectively.     

EPR study of RLi2O.V2O5, RNa2O.V2O5, RCaO.V2O5, and RBaO.V2O5 modified vanadate glass systems

Experimental EPR spectra in several modified vanadate glass systems reveal hyperfine structure (hfs) lines whose widths vary with the molar ratio of modifier to vanadium pentoxide, R. In the RNa₂O.V₂O₅ system, for example, hfs lines show no resolution at low R values (near 0.1); by contrast, these lines exhibit dramatic narrowing as R approaches 0.5. In the model proposed here, this narrowing is due to an increase in hopping time for small polarons associated with V⁴⁺ ions in these systems. Increases in polaron hopping times are accompanied by increases in electron spin-spin relaxation times T₂'s, and, an associated narrowing of EPR linewidths. Experiments confirm that spectral widths are limited by electron T₂'s due to the fact that EPR linewidths do not vary with temperature down to 4.2 K. Resolved spectra in RNa₂O.V₂O₅ at R = 0.5 reveal a hyperfine coupling parameter of 0.0177 ± 0.0008 T, corresponding to an upper-limit polaron hopping frequency of 487 ± 20 MHz. By similar analyses, the systems of RCaO.V₂O₅, RBaO.V₂O₅, and RLi₂O.V₂O₅ exhibit comparable polaron hopping frequencies limits of 480 ± 20 MHz, 469 ± 20 MHz, and 468 ± 20 MHz, respectively, when R is near 1.0. In addition to the relaxation effects discussed here, results of modeling of resolved spectra to obtain hyperfine coupling constants A_|| and A_┴, and g_┴ values g_|| and g_┴ are presented and discussed.     

Synthesis, spectroscopic characterisation and X-ray structure of [trans-Co(en)2(NO2)2]2(Cr2O7)

Dark red crystals of bis[trans-dinitrobis(ethylenediamine)cobalt(III)] dichromate, [trans-Co(en)₂(NO₂)₂]₂(Cr₂O₇) have been obtained by slowly allowing to mix the solutions of potassium dichromate and trans-dinitrobis(ethylenediamine)cobalt(III) nitrate in 1:2 molar ratio in aqueous medium. Elemental analyses and spectroscopic techniques (IR, UV/visible, ¹H and ¹³C NMR) were used for characterizing the complex salt. The complex salt crystallizes in the orthorhombic space group Fdd2 with unit cell dimensions a = 24.778(2) ?, b = 30.457(2) ?, c = 6.5364(5) ?, Z = 8, V = 4932.8(7) ?³, R₁ = 0.0617 and wR₂ = 0.1518. X-ray structure determination revealed an ionic structure consisting of cationic cobaltammine [trans-Co(en)₂(NO₂)₂]NO₃ and dichromate anion. It is the first crystal structure of this cation with a dianion.     

New Ln[B6O9(OH)3] borates (Ln = Sm-Lu): Structure, properties, and structural relation to cationic Li4[B7O12]Cl conductors (Li-Boracites)

Crystals of new rare earth borates of the composition Ln[B₆O₉ (OH)₃] (Ln = Sm-Lu), sp. gr. R3c are synthesized under hydrothermal conditions. Their crystal structures are determined on single crystals with Ln = Ho, Gd without preliminary determination of their chemical formulas. The polar anionic framework of the crystals consists of BO₃ triangles and BO₄ tetrahedra and has wide channels along the threefold axis of the structure, which are similar to the channels along the a, b, and c axes in cubic Li₄[B₇O₁₂]Cl boracite with Li conductivity. Rare earth atoms are arranged in the structure over the cubic F pseudolattice, whereas the analogous positions in Li boracites are filled with Cl anions. The squared optical nonlinearity of the new crystals is comparable with the nonlinearity of quartz, whereas the electrical conductivity in borates at 300°C exceeds 10⁻⁶ S/cm. __________ Translated from Kristallografiya, Vol. 49, No. 4, 2004, pp. 681–691. Original Russian Text Copyright ? 2004 by Belokoneva, Ivanova, Stefanovich, Dimitrova, Kurazhkovskaya.     

Bi1.65Zn1.0Nb1.5O7.225陶瓷和薄膜的结构和介电性能对比

以立方焦绿石Bi1.5Zn1.0Nb1.5O7(BZN)为配方基础,通过掺入过量10％的Bi2O3,形成Bi1.65Zn1.0Nb1.5O7.225非化学计量比分子式.采用固相反应法合成具有焦绿石立方结构的Bi1.65Zn1.0Nb1.5O7.225陶瓷,并采用脉冲激光沉积法在Pt/SiO2/Si(100)基片上制备其薄膜.对比研究了非化学计量比Bi1.5Zn1.0Nb1.5O7.225陶瓷和薄膜的结晶性能,微观形貌以及介电性能的差异.结果表明烧结的Bi1.65Zn1.0Nb1.5O7.225陶瓷和沉积的BZN薄膜都保持立方焦绿石单相结构,但是薄膜展现出较强的(222)晶面择优取向.陶瓷和薄膜的晶格常数,微观形貌都体现出差异.对比二者的介电特性后发现,Bi1.65Zn1.0Nb1.5O7.225薄膜的介电常数明显高于陶瓷的介电常数,这归因于薄膜和块体材料之间的差异,例如厚度,致密度,择优取向等.     

Synthesis, structure and supramolecular assembly in the crystalline state of a bifunctionalized arylimido derivative of hexamolybdate [n-Bu4N]2[Mo6O17(o,p-(MeO)2C6H3N)2]

A novel bifunctionalized arylimido derivative of hexamolybdate [n-Bu₄N]₂[Mo₆O₁₇(o,p-(MeO)₂C₆H₃N)₂] (1) was synthesized by self-assembled metathesis of α-type octamolybdate ion and 2,4-dimethoxyaniline and structurally characterized by crystal X-ray diffraction. Crystallographic data for1: monoclinic system, space group:C2/c,a = 17.319(4),b = 18.087(4),c = 21.357(5) ?, β = 106.486(4),V = 6415(2) ?³, andZ = 4,D_c = 1.693 g/cm³,R₁ = 0.0439. The complex has a short Mo–N bond length of 1.735(5) ? and an imido (Mo–N–C) bond angle of 177.8(4)^∘. The complex has also been characterized by¹H NMR, IR, and UV–vis spectroscopy.     

Synthesis and characterization of MxNb4P2O17

A new series of niobium phosphates with the composition of M_xNb₄P₂₁₇17 (M=Li and Na, X=4; M=Zn, Ca, Mg, Sr and Ba, X=2) have been successfully synthesized. The powder X-ray diffraction (XRD) data of these isostructural compounds, was studied The powder Second Harmonic Generation (SHG) effects of these compounds were about twice of that of KH₂PO₄ (KDP).