Hydrogen solubility in amorphous Mg<Subscript>0.6</Subscript>SiO<Subscript>2.6</Subscript> at high pressure

The solubility of hydrogen in amorphous Mg_0.6SiO_2.6 at a temperature of 250°C and pressures up to 75 kbar is studied using a quenching technique. The molar ratio H₂/formula unit is found to nonlinearly increase with pressure from x = 0.12 at P = 10 kbar to x = 0.303 at P = 75 kbar. An investigation of the quenched samples by Raman spectroscopy demonstrated that hydrogen dissolves in amorphous Mg_0.6SiO_2.6 in the form of H₂ molecules. X-ray diffraction and Raman studies showed that the hydrogenation of the samples is likely to be accompanied by a phase transition in the amorphous lattice of Mg_0.6SiO_2.6 at P ≈ 52.5 kbar to a denser amorphous modification.     

An ultra-low hydrolysis sol-gel route for titanosilicate xerogels and their characterization

In this work TiO₂-SiO₂ xerogels were prepared through an ultra low hydrolysis method using titanium and silicon alkoxide. The samples were heat treated to 500°C. The xerogels were characterized using TGA/DTA, FTIR, XRD and TEM. The samples showed the formation of Si–O–Ti bridges by its characteristic vibration within 925–960 cm⁻¹ range. Si–O–Si bond angles were calculated using the central force network model. The TiO₂ in all the samples crystallized on heat treatment to 500°C. The crystallite size calculated using the Scherer formula from the XRD was verified from the Transmission Electron Micrograph. Samples heat treated to 350°C remained amorphous and hence could be used as hosts for biomaterials and organic optical materials.     

On hydrolysis of Ba–Bi–O and K–Ba–Bi–O oxide systems

Fundamentally different behavior of Ba–Bi–O (Ba : Bi = 11 : 4, 1 : 1, 2: 3, and 1 : 5 mol/mol) and K_nBa_mBi_m+nO_y (m = n = 1, 2,...; exhibiting superconducting properties with T_c = 28–32 K) oxides and BaO₂ in hydrolysis reactions has been revealed by means of potentiometry and chemical analysis. Products of the oxides treatment with water do not contain H₂O₂, evidencing the absence of peroxide ions in their structure. The perovskite-type barium-bismuth(III) oxides are completely hydrolyzed into Ba(OH)₂ and Bi₂O₃ at room temperature.     

BaO-BiO1.5 phase diagram in the region 80–100 mol % BiO1.5 at p o 2 = 21 kPa

The phase equilibria in the region from 80 to 100 mol % BiO_1.5 are studied in the BaO-BiO_1.5 system in air and under an argon atmosphere using visual polythermal analysis (VPA), X-ray powder diffraction, differential thermal analysis (DTA), electron diffraction (ED), and elemental analysis in a transmission electron microscope (EA/TEM). A series of discrete layered rhombohedral phases (RPs) with the composition Ba₂Bi_8+n O_y, where n = 0, 1, 2, 4, 8, or 10, is discovered. The melting character is determined for these RPs: the 1: 4 phase melts congruently; the 2: 9, 1: 5, 1: 6, and 1: 8 phases melt incongruently. The crystallization fields are 10–30°C. At p _{o 2} = 21 kPa, the 1: 4 phase in the subsolidus region decomposes into a 4: 13 perovskite-like phase and the 2: 9 phase. The other rhombohedral phases decompose into stages to yield Bi₂O₃ and a neighboring RP that is richer in barium. The Ba₂Bi_8+n O_y oxides are stable in argon and experience a first-order phase transformation at about 560°C.     

On the theory of the linear electro-optical effect in cubical crystals

The linear electro-optical effect in cubical crystals of acentric classes is considered by an approximate covariant method. Simple analytic expressions for the induced optic axes and for the eigenvalues and eigenvectors of the inverse dielectric tensor are obtained for all directions of the electric field in these crystals. The method used enables one to determine the above quantities with a high degree of accuracy. The cases where the electric field rotates in planes orthogonal to the crystallographic directions and in the planes of symmetry of the crystal are considered in detail.     

On the phenomenological theory of the linear electrooptical effect in uniaxial crystals

The linear electrooptical effect in uniaxial crystals is considered with the aid of direct tensor methods. Covariant expressions for finding biradials and ray refractive indices are developed. A general expression is derived relating the nonlinear optical polarizability parameters and the electrooptical properties of a crystal. The results are applied to cuts of uniaxial ammonium dihydrogen phosphate (ADP), potassium dihydrogen phosphate (PDP), and quartz crystals often used for light modulation. The induced phase differences between the light waves propagating in such crystals are found for the field orientations considered.