P. Jakubus

Texture of zirconia obtained by forced hydrolysis of ZrOCl2 solutions

The structure and surface properties of ZrO2 strongly depend on its preparation. In the present work the impact of prolonged aging at basic conditions (pH = 9, T = 100°C, t = 48 h), on the phase composition and textural properties, obtained by calcination of the precipitate, was investigated using several techniques conjointly (DTA/TG, DSC, XRD, porosimetry). The thermal effects accompanying the ZrO2·xH2O gel formation, the coalescence of the particles and crystallization were evaluated and discussed in terms of the structural differences between the aged and non-aged samples.

Crystal structure determination of AlVMoO7 from X-ray powder diffraction data

Abstract The structure of AlVMoO 7 was solved by direct methods from high resolution X-ray powder diffraction data and refined by the Rietveld method. The lattice constants are a=5.3763(3)A, b=8.1644(3)A and c=12.7312A. Space group Pmcn followed from the systematic extinctions and was confirmed by the successful structure solution. Aluminum is octahedrally coordinated by oxygen, whereas vanadium possesses a distorted pyramidal coordination and molybdenum is tetrahedrally coordinated by oxygen atoms. A three dimensional framework structure results from corner and edge connection of the coordination polyhedra. VO 5 pyramids are edge linked to infinite (VO 2 + ) ∞ chains. Therefore, AlVMoO 7 can be classified as a polyvanadate.

Metastabilization of tetragonal zirconia by doping with low amounts of silica

Nanocrystalline tetragonal zirconia was obtained from ZrOCl2 via the modified forced hydrolysis method combined with aging of the hydrous amorphous precipitate in the mother liquor at 100 °C for 48 h (pH = 9.3). The role of the precipitation and aging temperatures in the metastabilization of the tetragonal ZrO2 polymorph is discussed in terms of the structural and textural data of the resultant oxide. The influence of low concentrations of silica (0.01 – 0.35 wt. % Si), spontaneously leached from the glass vessel or intentionally introduced to the parent solution, was shown to be a vital factor, controlling the phase composition of the final prepared zirconia. Using the concepts of zirconium aquatic chemistry, this effect was explained by incorporation of silicates into hydrous zirconia protostructures.

The structure and selected properties of Co2.5VMoO8

The structure of Co2.5VMoO8 was refined by the Rietveld method. The lattice constants are: a = 0.50453 nm; b = 1.03448 nm; c = 1.73925 nm, space group Pnma. The crystal structure of the compound is isotypic with Mg2.5VMoO8. The structure is a framework of MoO4 and VO4 tetrahedra with linking octahedral and trigonal prismatic CoO6 groups. Co2.5VMoO8 melts incongruently at 1080 ± 5°C depositing solid CoMoO4.

The structure of CrVMoO7

Abstract The structure of CrVMoO 7 has been refined from high-resolution X-ray powder diffraction data. The unit cell is triclinic (space group P1¯) with a=5.531(1)A, b=6.585(1)A, c=7.864(1)A, α =96.143(6)°, β =89.847(6)° and γ =101.942(6)°. A two-step refinement yields R p =8.7% in the first step (pattern matching) and in the second step (structure refinement)as well. The crystal structure of the compound is isotypic to FeVMoO 7 . The distortion of the coordination polyhedra has been discussed within the framework of the bond valence concept and effective coordination numbers.