Ab initio calculation of vibrational frequencies of GexPxS1−2x glass

The vibrational frequencies of GeS₄, GeP₄, Ge₂S₆, GeP₃, Ge₃P, Ge₂P₂, P₂S₂, P₃S, P₄S₃, α-P₄S₄, β-P₄S₄, α-P₄S₅, β-P₄S₅, P₄S₇, P₄S₉ and P₄S₁₀ are theoretically computed from the first principles. The Raman frequencies of Ge_xP_xS_1−2x glass are obtained for x varying from 0.05 to 0.019. The computed fundamental frequencies of clusters are compared with those experimentally found. In this way, we are able to identify the vibrating clusters in the real glass. The clusters identified in the real glass are found to be Ge₂P₂, P₄S₃, α-P₄S₄, β-P₄S₄, β-P₄S₅, P₄S₇, P₄S₉, β-P₄S₅, Ge₂S₆, Ge₃P.     

Effects of Sn addition on the glass forming ability and crystallization behavior in Ni-Zr-Ti-Si alloys

The effect of Sn substitution for Si on the glass forming ability (GFA) and crystallization behavior has been studied in Ni₅₉Zr₂₀Ti₁₆Si_5 − xSn_x (x=0, 3, 5) alloys. A bulk amorphous Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy with diameter up to 3 mm can be fabricated by injection casting. Partial substitution of Si by Sn in Ni₅₉Zr₂₀Ti₆Si_5 − xSn_x alloys improves the glass forming ability. The improved GFA of the Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy is can be explained based on the lowering of liquidus temperature. The crystallization sequence becomes completely different with addition of Sn. The amorphous Ni₅₉Zr₂₀Ti₁₆Si₅ alloy crystallizes via precipitation of only a cubic NiTi phase in the first crystallization step, whereas the amorphous Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy crystallizes via simultaneous precipitation of orthorhombic Ni₁₀(Zr,Ti)₇ and cubic NiTi phases. Addition of Sn in the Ni₅₉Zr₂₀Ti₁₆Si₅ alloy suppresses the formation of the primary cubic NiTi phase. The bulk amorphous Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy exhibits high compressive fracture strength of about 2.7 GPa with a plastic strain of about 2%.     

Distorted icosahedral Ni5Nb3Zr5 clusters in the as-quenched and hydrogenated amorphous (Ni0.6Nb0.4)0.65Zr0.35 alloys

Local structures of the hydrogenated (Ni_0.6Nb_0.4)_1-xZr_x (x = 0.3-0.4) amorphous alloys attract much attention for the sake of their epoch-making electronic transport behaviors. We investigated the local structures by XAFS for the as-quenched (Ni_0.6Nb_0.4)_0.65Zr_0.35 and hydrogenated [(Ni_0.6Nb_0.4)_0.65Zr_0.35]_0.922H_0.078 amorphous alloys, in which ballistic conductivity has been observed. XAFS results of the Ni K-edge are analyzed based on the structure model deduced by the first principle calculation. The analysis suggests that highly distorted icosahedral Ni₅Nb₃Zr₅ cluster, which has a centered-Ni and a surrounding Nb triangle, is a main structural unit of (Ni_0.6Nb_0.4)_0.65Zr_0.35 and the [(Ni_0.6Nb_0.4)_0.65Zr_0.35]_0.922H_0.078 amorphous alloys. This distorted icosahedral Ni₅Nb₃Zr₅ cluster can be associated with the occurrence of the singular electronic transport behaviors of the hydrogenated (Ni_0.6Nb_0.4)_0.65Zr_0.35 alloy.     

Production of complex rubidium and cesium hydrogen sulfate‒phosphates

The solubility in the CsH₂PO₄?CsHSO₄?H₂O system at different temperatures (25, 50, and 75°C) is studied and the phase equilibria in the Rb₃H(SO₄)₂?RbH₂PO₄?H₂O system under isothermal conditions (at 25°C) are analyzed. The temperature and concentration conditions for forming Rb₂(HSO₄)(H₂PO₄), Rb₄(HSO₄)₃(H₂PO₄), Cs₄(HSO₄)₃(H₂PO₄), Cs₃(HSO₄)₂(H₂PO₄), Cs₂(HSO₄)(H₂PO₄), and Cs₆H(HSO₄)₃(H₂PO₄)₄ compounds (the latter has been obtained for the first time) are determined. The conditions for growing large single crystals of complex acid rubidium and cesium salts are found.     

The significance of X-ray investigations for the classification of multicomponent systems with mixed crystals in a solid phase

The X-ray investigations of solid phases in the multicomponent systems KCl KBr H₂O, K₂SO₄ (NH₄)₂SO₄ H₂O and KNO₃ NH₄NO₃ H₂O were conducted and the crystal lattice parameters of mixed crystals forming in these systems were determined. It was confirmed that in the KCl KBr H₂O system the continuous solid solutions were formed and in the K₂SO₄ (NH₄)₂SO₄ H₂O system the solid solutions with a miscibility gap were formed. In the KNO₃ NH₄NO₃ H₂O system the presence of two series of mixed crystals, namely the mixed crystals between ammonium nitrate and the double salt KNO₃ · 2 NH₄NO₃ and between potassium nitrate and the same double salt was confirmed. In this system a wide region of discontinuity (for x_NH4NO₃ = 0.083 – 0.67) also occurred. According to Roozeboom's classification, the KCl KBr H₂O system belongs to the 3^rd type, the K₂SO₄ (NH₄)₂SO₄ H₂O to the 5^th type (the discontinuous mixed crystals, the systems of peritonic type) and the KNO₃ NH₄NO₃ H₂O system is not comprised in this classification.     

Ab initio calculation of vibrational frequencies of Ge0.25S0.75−yIy glass

The vibrational frequencies of Ge₄, S₄, I₄, SI₃, Ge₂I₂, S₂I₂, Ge₂S₂, Ge₂SI, GeS₃, GeI₂S, Ge₃S and GeI₃ are computed using first principles. These frequencies are compared with those found experimentally in the Raman spectra of Ge_0.25S_0.75−xI_x glass. In this way, it is found that Ge₄, GeI₂S and GeI₃ tetrahedra occur in the glass. These tetrahedra are of different sizes so they stack to form the floppy phase of the glass.     

Calculation of thermodynamic parameters of melts from experimentally determined liquidus‐curves

Thermodynamic parameters of melts (ΔH_S, A₀, A₁) in the system Anorthite‐Diopside and Bi₂O₃‐Bi₄B₂O₉ have been calculated by a rigorous application of solution thermodynamics. The data are internally consistent and yield values of ΔH_S for Anorthite = 133 kJ/mole, Diopside = 81 kJ/mole, Bi₂O₃ = 19 kJ/mole and Bi₄B₂O₉ = 39 kJ/mole. The activity of Anorthite and Diopside in an anorhtitic melt deviates negative from ideality, whereas a diopsidic melt behaves almost ideal. In a “Bi₂O₃” melt the activity of the Bi₂O₃ component is strongly positive, that of Bi₄B₂O₉ is strongly negative. The opposite is observed for the “Bi₄B₂O₉” melt. All calculated liquidi except the Bi₄B₂O₉ liquidus closely match the experimental ones. In contrast to the experimental liquidus the calculated Bi₄B₂O₉ liquidus has an inflection point. The crest of the metastable spinode (solvus) for a “Bi₂O₃” melt is close to the liquidus indicating melt separation at undercooling. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Recrystallization of natural chrysoberyl in multicomponent melts

Chrysoberyl and alexandrite crystals have been grown from solutions in melts based on the Li₂CO₃-MoO₃, Bi₂O₃-MoO₃, PbO-V₂O₅, Na₂B₄O₇, and K₂MoO₄-MoO₃ systems using natural alexandrite and chrysoberyl debris as the initial BeAl₂O₄ compound. An analysis of the morphology and homogeneity of the crystals grown has revealed the Bi₂O₃-MoO₃ solvent to be the most appropriate. The optimal color characteristics (??quality?? of alexandrite effect) manifest themselves when adding about 5 mol % Cr₂O₃. The largest crystals (up to 10 mm in size) were obtained from a solution in melt based on PbO-V₂O₅ at a ratio of the crystal-forming component to the solvent of 9: 91 wt %; These characteristics, along with a relatively low operating temperature (970°C), give grounds to consider this type of solvent promising.     

Phase Formation and Structure of (RE,M)2Ca0.5Sr0.5Cu2O6+δ (RE=La,Pr, M=Ca,Sr)

The samples of (RE,M)₂Ca_0.5Sr_0.5Cu₂O_6+d are prepared by solid state reaction method. The single phase boundary of RE and M in (RE,M)₂Ca_0.5Sr_0.5Cu₂O_6+d is 1.0 ∼2.0 and 0 ∼1.0 respectively. In (Pr,M)₂Ca_0.5Sr_0.5Cu₂O_6+d, the phase boundary of Sr is 0 ∼1.0. The structure of (RE,M)₂Ca_0.5Sr_0.5Cu₂O_6+d belongs to the structure type of 212 cuprate superconductors with space group I4/mmm.     

Effect of grinding on the low temperature photoluminescence of certain inorganic crystals

The broadening as well as shift in the photoluminescence spectra of K₂[Pt(CN)₄] · 3 H₂O, Ba[Pt(CN)₄] · 4 H₂O, CdS:Te and Ru(C₁₅H₁₁N₃)₂I₂ · H₂O crystals take place with their grinding. The original vibronic peaks at 632 and 628 nm of CdS:Te and Ru(C₁₅H₁₁N₃)₂I₂ · H₂O crystals, respectively, disappear with the grinding. A new vibronic peak at 650 nm appears with grinding of Ru(C₁₅H₁₁N₃)₂I₂ · H₂O crystals. It is concluded that the change in the photoluminescence spectra is attributed to the creation of dislocations during the process of grinding.     

Crystal structure, vibrational spectra, and thermal decomposition and nitrogen adsorption behaviour of a new tetramanganese(II) dipyrophosphate decahydrate, Mn4(P2O7)2·10H2O

A new manganese(II) pyrophosphate, Mn₄(P₂O₇)₂·10H₂O, has been synthesized and characterized by single-crystal X-ray diffraction [orthorhombic space group Pnma, with unit cell parameters of a=9.3288(3) ?, b=25.9532(9) ?, c=8.4783(3) ?; Z=4]. All the pyrophosphate anions show non-linear P–O–P bonds with an average angle of 128.60°. The framework of this new pyrophosphate is made up of packed layers of MnO₆ octahedra connected by double-tetrahedra P₂O₇ groups and a layer of Mn(H₂O)₆ units. The [P₂O₇]⁴⁻ anions adopt a bent, near-staggered conformation. The absence of coincidences for the majority of the IR and Raman bands is in accord with the centrosymmetric structure of the material. The vibrational spectra have been interpreted in part on the basis of factor group effects. The structural changes occurring during heating have been investigated by TG-ATD. When Mn₄(P₂O₇)₂ ^.10H₂O is gradually heated, it decomposes into an intermediate hydrated salt at 96°C and then to anhydrous Mn₂P₂O₇ at 325°C. This thermal behaviour is different from that of Zn₄(P₂O₇)₂·10H₂O. The crystal structure of the new managenese(II) pyrophosphate is compared with the known structures of Zn₄(P₂O₇)₂·10H₂O, Mn₂P₂O₇·2H₂O and anhydrous Mn₂P₂O₇. The adsorption and desorption isotherms of Mn₄(P₂O₇)₂·10H₂O, Zn₄(P₂O₇)₂·10H₂O and MnKHP₂O₇·2H₂O have been investigated by BET measurements and the results show that the capacity for N₂ sorption of the Mn(II) salt is two times lower than is that of the Zn(II) isotype and two or three times higher than is that of MnKHP₂O₇·2H₂O.     

Formation of new oxide glasses by laser spin melting and free fall cooling

Glass spherules have been made by laser spin melting and free fall cooling techniques from ceramic rods. Thus, the materials were not in contact with a container at any time. Glasses of 100 to 800 μm diameter were formed from at least 80 wt% of the oxides Al₂O₃, Ga₂O₃, In₂O₃, La₂O₃, ZrO₂, HfO₂, Nb₂O₅ and Ta₂O₅ with 20 or less weight percent of CaO + SiO₂. The best glass formers were in the Nb₂O₅- and Ta₂O₅-based systems. The indices of refraction of most of the glasses and Abbe numbers of many were measured.     

Elastic properties of the dithionates Na2S2O6 · 2 H2O,K2S2O6, Rb2S2O6, CaS2O6 · 4H2O and SrS2O6 · 4 H2O

Single crystals of the title compounds having optical quality and dimensions of several cm were grown from aqueous solutions. The elastic and thermoelastic constants were determined from ultrasonic resonance frequencies of thick plates. The true point symmetry of K₂S₂O₆ and Rb₂S₂O₆, which is screened by a hexagonal hypermorphy, could be clearly revealed to be trigonal (32) by the existence of the elastic constant c₁₄. In the case of CaS₂O₆ · 4H₂O and SrS₂O₆ · 4H₂O the constant c₁₄ of the specimens appeared too small to confirm the trigonal symmetry group required from electrooptic and non-linear optic effects unambiguously. The isotypy of K₂S₂O₂ and Rb₂S₂O₆ as well as that of CaS₂O₆ · 4H₂O and SrS₂O₆ · 4H₂O is confirmed by their elastic behaviour. The mean elastic stiffness of dithionates is closely related to that of the corresponding sulphates. In the vicinity of the second-order phase transition of K₂S₂O₆ near 235 K weak anomalies of the temperature derivatives of the longitudinal elastic stiffnesses are observed.     

Crystal structure of octapotassium octasulfatodiceriate pentahydrate

Single crystals without Co and Ni have been crystallized by the substitution method in the K₂Ni(SO₄)₂-Ce(SO₄)₂-H₂SO₄-H₂O system using K₂Co(SO₄)₂ · 6H₂O, K₂ (Co,Ni)(SO₄)₂ · 6H₂O, or K₂Ni(SO₄)₂ · 6H₂O as protocrystals. The structure of the single crystals obtained has been established by X-ray diffraction analysis. The crystal structure contains dimer complex anions [Ce₂(μ-SO₄)₂(SO₄)₆]⁸⁻, K⁺ cations, and crystallization water molecules.     

Growth and scintillation properties of the Na2W2O7 crystal

The growth and scintillation properties of the Na₂W₂O₇ crystal are reported. The solid reaction between Na₂CO₃ and WO₃ is used to synthesise the Na₂W₂O₇ material. The Na₂W₂O₇ single crystal has been grown by the Bridgman method. And the Na₂W₂O₇ single crystal with sizes 14×7×6 mm³ has been achieved. The transmission spectra, the Ultraviolet fluorescence spectra and the X-ray excited luminescence spectra of the Na₂W₂O₇ crystal are measured. The measurement results show that the Na₂W₂O₇ crystal is a promising intrinsic scintillator.     

Single Crystal Growth and Pyroelectric,Dielectric, Piezoelectric,Elastic, and Thermoelastic Properties of Orthorhombic Li2SiO3, Li2GeO3, and Na2GeO3

Single crystals of optical quality of isotypic Li₂SiO₃, Li₂GeO₃, and Na₂GeO₃, space group Ccm2₁, with diameters of ca 16 mm and lengths of ca 20 mm (Li₂SiO₃) and ca 60 mm (Li₂GeO₃ and Na₂GeO₃) have been grown from the melt using the Czochralski technique. On Li₂SiO₃, Li₂GeO₃, and Na₂GeO₃ pyroelectric coefficients and complete dielectric, piezoelectric, elastic, and thermoelastic tensor properties have been determined; the latter from the temperature dependence of resonance frequencies. All crystals investigated exhibited only a small amount of 180° twins. They all possess large pyroelectric coefficients about-five times that of tourmaline. The longitudinal piezoelectric constant d₃₃₃ is about five times larger than d₁₁₁ of alpha quartz. Qualitative measurements on Na₂SiO₃ revealed similar values of pyroelectric and piezoelectric effects. The technical application of these crystals encounters some difficulties: Li₂SiO₃ is excellently cleavable parallel (010). This face contains the polar direction [001]. Na₂GeO₃ suffers from chemical decomposition in humid atmosphere and is well cleavable too. Both happens to a much less extent in Li₂GeO₃. Na₂SiO₃ proved to be hardly suitable for any application of its polar properties due to its bad chemical stability against humid air and its excellent cleavage.     

Optical activity along the optical axis of crystals with ordered langasite structure

Optical activity along the optical axis of four piezoelectric crystals Sr₃TaGa₃Si₂O₁₄ (STGS), Sr₃NbGa₃Si₂O₁₄ (SNGS), Ca₃TaGa₃Si₂O₁₄ (CTGS) and Ca₃NbGa₃Si₂O₁₄ (CNGS) with ordered langasite structure were studied via a convenient method. All the crystals investigated show unusually large values of the specific rotation. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of composition on spinel crystals equilibrium in low-silica high-level waste glasses

The liquidus temperature (T_L) and the equilibrium mass fraction of spinel were measured in the regions of low-silica (less than 42 mass% SiO₂) high-level waste borosilicate glasses within the spinel primary phase field as functions of glass composition. The components that varied, one at a time, were Al₂O₃, B₂O₃, Cr₂O₃, Fe₂O₃, Li₂O, MnO, Na₂O, NiO, SiO₂, and ZrO₂. In the low-silica region, Cr₂O₃ increased the T_L substantially less, and Li₂O and Na₂O decreased the T_L significantly less than in the region with 42-56 mass% SiO₂. The temperature at which the equilibrium mass fraction of spinel was 1 mass% was 25-64 °C below the T_L.     

Growth of K(DxH1 − x )2PO4 single crystals from solutions in the K2O-P2O5-(D, H)2O system

Based on the analysis of the K₂O-P₂O₅-D₂O solubility phase diagram, the optimum conditions of KD₂PO₄ crystallization—the compositions of mother solutions and the temperature range of crystallization—in the KH₂PO₄-D₂O system have been determined. The technique of K(D_xH_{1 ? x} )₂PO₄ growth is developed. The DKDP single crystals with deuterium concentration up to 88 wt % are grown on DKDP seeds from KH₂PO₄ solutions in D₂O by the method of temperature decrease.     

Crystal structures of K-and Cs-exchanged forms of zorite

The crystal structures of K-and Cs-exchanged forms of zorite were studied by X-ray diffraction and IR spectroscopy: K_4.75Na_1.82[Ti(Ti_0.79Nb_0.20)₄Si₁₂O₃₄(O,OH)_5.2] × 10.62 H₂O (sp. gr. Cmmm, R= 0.0481 for 516 independent reflections) and Cs_4.34Na_1.90[Ti(Ti_0.80Nb_0.18)₄Si₁₂O₃₄(O,OH)₅] × 5.37 H₂O (sp. gr. Cmmm, R = 0.0285 for 621 independent reflections). Both structures retain the mixed polyhedral framework of zorite: Na₆Ti(Ti,Nb)₄(Si₆O₁₇)₂(O,OH)₅ × nH₂O, where n ～ 11. It is shown that the positions of the atoms located in the cavities of the frameworks of these compounds differ from those in the structures of zorite and its synthetic analogs.