M. G. Zhizhin

Binary and ternary compounds in the Mg-Sb-B and Mg-Bi-B systems as catalysts for the synthesis of cubic BN

We have studied the phase relations in the Mg-Pn and Mg-B-Pn (Pn = Sb, Bi) systems, synthesized the magnesium pnictides Mg3Sb2 and Mg3Bi2 and the new magnesium boropnictides Mg3Pn2(B2), and determined their structure and unit-cell parameters. The synthesized compounds have been investigated at high pressures (4.0–6.5 GPa) and temperatures (700–1400°C). All of them have been found to promote the hexagonal-to-cubic phase transformation of boron nitride.

Synthesis and crystal structure of new complex sodium lanthanide phosphate molybdates Na2MIII(MoO4)(PO4)(MIII = Tb, Dy, Ho, Er, Tm, Lu)

New complex sodium lanthanide phosphate molybdates Na2MIII(MoO4)(PO4)(MIII=Tb, Dy, Ho, Er, Tm, Lu) have been synthesized by the ceramic method (T = 600°C, τ = 48 h), and their unit cell parameters have been determined. The structures of Na2MIII(MoO4)(PO4)(MIII = Dy, Ho, Er, Lu) were refined by the Rietveld method. The compounds are isostructural: they are orthorhombic (space group Ibca, Z = 8) and have layered structures. In the structures of phosphate molybdates, chains of MIIIO8 polyhedra and MoO4 tetrahedra are linked by PO4 tetrahedra to form layers. The MoO42− anions are involved in dipole-dipole interaction. The sodium ions are arranged in the interlayer space. The compounds melt incongruently at 850–870°C.

New complex ytterbium molybdophosphates M 2 I Yb(PO4)(MoO4) (MI = K, Na): Synthesis and structure solution

Complex rare-earth molybdophosphates of sodium and potassium (Na2Yb(PO4)(MoO4) (I) and K2Yb(PO4)(MoO4) (II) are synthesized by solid-phase reactions at 600°C (for I) and 750°C (for II). The molybdophosphates are characterized using powder X-ray diffraction, laser second harmonic generation (SHG), IR spectroscopy, and differential thermal analysis. Their structures are refined using the Rietveld technique. The compounds are isostructural and crystallize in an orthorhombic system (space group Ibca, Z = 8). The unit cell parameters are a = 18.0086(1) Å, b = 12.0266(1) Å, c = 6.7742(1) Å for compound I and a = 19.6646(1) Å, b = 12.0570(1) Å, c = 6.8029(1) Å for compound II. The structures are built of YbO8 chains extended along axis c and linked into layers through PO4 tetrahedra. The Na+ cations (CN = 6) and the K+ cations (CN = 8) reside in the interlayer spaces.

Thermochemistry and thermal characteristics of Ba2MIIUO6 (MII = Mg, Ca, Sr, Ba)

A series of uranium compounds with the composition Ba2MIIUO6 (MII = Mg, Ca, Sr, Ba) were synthesized by a solid-phase procedure. The polymorphism for Ba2SrUO6 was studied by high-temperature X-ray diffraction, and the coefficients of thermal expansion were determined. The standard enthalpies of formation of crystalline Ba2MIIUO6 at 298.15 K were determined by the reaction calorimetry.

Synthesis and crystal structure of new double indium phosphates M 3 I In(PO4)2 (MI = K and Rb)

Double potassium indium and rubidium indium phosphates K3In(PO4)2 (I) and Rb3In(PO4)2 (II) are synthesized by solid-phase sintering at T = 900°C. The compounds prepared are characterized by X-ray powder diffraction (I and II), X-ray single-crystal diffraction (II), and laser-radiation second harmonic generation. Structure I is solved using the Patterson function and refined by the Rietveld method. Both compounds crystallize in the monoclinic crystal system. For crystals I, the unit cell parameters are as follows: a = 15.6411(1) Å, b = 11.1909(1) Å, c = 9.6981(1) Å, β = 90.119(1)°, space group C2/c, Rp = 4.02%, and Rwp = 5.25%. For crystals II, the unit cell parameters are as follows: a = 9.965(2) Å, b = 11.612(2) Å, c = 15.902(3) Å, β = 90.30(3)°, space group P21/n, R1 = 4.43%, and wR2 = 10.76%. Structures I and II exhibit a similar topology of the networks which are built up of { In[PO4]2} (I) and { In2[PO4]4} (II) structural units.

Microstructure and ionic conductivity of (La1/2Li1/3+x )TiO3 perovskite-like solid solutions

The lattice parameters of (La1/2Li1/3+x)TiO3 (x = 0, 1/10, 1/6, 1/5, 1/4) ceramics have been determined as functions of temperature, and their microstructure and transport properties have been studied. The results indicate that the oxides retain orthorhombic symmetry upon the structural changes at ≃925 K. According to atomic force microscopy results, the grains in the ceramics consist of nanocrystallites 60 to 120 nm in size. Analysis of the grain bulk and grain boundary contributions to the ionic conductivity of the (La1/2Li1/3+x)TiO3 solid solutions shows that their bulk conductivity σbulk decreases with increasing x because reducing the concentration of A-site vacancies impedes ionic transport.

Effect of irradiation on siloxane block copolymers at doses below 100 kGy

A study of radiation-induced changes in polydimethylphenylsilsesquioxane block copolymers demonstrated that the impurities of dimethylcyclosiloxanes (Dx) that are formed in the synthesis of block copolymers disappeared at doses of 10–50 kGy. An increase in the dynamic viscosity (by a factor of 2–3) of 20: 5 and 20: 10 block copolymers irradiated at 50 kGy suggests that the formation of ≡Si-CH-CH2-Si≡ bridges was not solely responsible for a structural rearrangement in the block copolymers. The rheological characteristics of the block copolymers changed under irradiation because of the transformations and interactions of Dx with the matrix.

Hydrothermal synthesis and crystal structure of a new ammonium gallium hydroxyphosphate (NH4)Ga(OH)PO4

A new ammonium gallium hydroxyphosphate (NH4)Ga(OH)PO4 was synthesized under mild hydrothermal conditions (200°C, τ = 168 h). The equimolar content of Ga and P was determined by chemical analysis and electron probe X-ray microanalysis. The presence of NH4 and OH groups was demonstrated by IR and Raman spectroscopy. An ab initio model of the crystal structure was refined by the Rietveld method (space group P21/m, Z = 2): a = 4.4832(1) Å, b = 6.0430(1) Å, c = 8.5674(1) Å, β = 98.019(1)°, Rp = 0.0552, Rwp = 0.0723. A zero SHG signal (T = 300 K) confirmed a centrosymmetric structure of the compound. The structure contains layers composed of GaO4(OH)2 octahedra and PO4 tetrahedra. The interlayer space accommodates ammonium cations. The layer is based on linear chains of edge-sharing GaO4(OH)2 octahedra with a zigzag trans-arranged-Ga-(OH)-Ga-(OH)-backbone. The construction of the layer in (NH4)Ga(OH)PO4 was found to be topologically related to that in (En)0.5Fe(OH)PO4. The effect of the gradual F− → OH− substitution in the quasi-morphotropic series (NH4)GaF1-δ(OH)δPO4 (δ = 0, 0.5, 1.0) on the degree of polarization of the mixed anionic radical was considered. (NH4)Ga(OH)PO4 is thermally unstable: removal of NH3 and H2O molecules in the range 170–450°C is accompanied by the formation of two polymorphs of GaPO4.

Synthesis and physicochemical study of CsUO2(VO3)3

The polymorphic transition and properties of CsUO2(VO3)3 prepared by solid-phase reaction were studied by high-temperature X-ray diffraction, IR spectroscopy, and thermal gravimetric analysis. The enthalpy of formation of α-CsUO2(VO3)3 was determined by adiabatic reaction calorimetry.