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Positron-annihilation and photoluminescence studies of nanostructured ZrO2

Fidelus J. D., Karbowski A., Mariazzi S., Brusa R. S., Karwasz G.

Nukleonika

2010

Vol. 55, No. 1

85-89

In the present work, photoluminescence and Doppler broadening depth-resolved positron annihilation spectroscopy was performed on pure zirconia nanopowders. Zirconia nanopowders were grown by a hydrothermal microwave-driven process followed by annealing in oxygen atmosphere. Photoluminescence under 274 nm wavelength excitation from a 150 W high-pressure Xe exhibits similar spectra, in the region from 320 to 820 nm, although its intensity depends on the annealing. Positron annihilation Doppler-broadening spectra show low values of the normalized S-parameter, varying little with the depth, from 0.495 on the surface to 0.47-0.49 in bulk. Both high the annealing temperature and oxygen concentrations, lead to low bulk S-values. The ortho-positronium (o-Ps) fraction is about 10-11% for all samples on the surface, whereas it is reduced to 7-8% in the bulk for samples annealed at 700°C and 5-6% for samples annealed at 800°C. Both photoluminescence (PL) and positron studies show the presence of defects in all samples. The o-Ps signal suggests a high porosity of samples, particularly at a depth down to 10 nm.

Nanometric Y2O3-TiO2-ZrO2 solid solution powders and their utilization in the synthesis of composite powders with TiB2 and TiC inclusions

Moskała N., Morgiel J., Pyda W.

Materials Science Poland

2008

Vol. 26, No. 2

331--339

Carbothermal reduction of TiO2 dissolved in ZrO2 and B2O3 is a method of fabrication of fine composite powders in the ZrO2-TiB2-TiC system. The method requires nanopowders of the zirconia -titania solid solution with a high TiO2 concentration. A technique of fabrication of zirconia nanopowders doped with 18 mol % titania and 2-3 mol % yttria is described in the paper. The nanopowders were obtained in a co-precipitation process followed by hydrothermal crystallization at 240 °C. The phase composition (XRD) and EDS measurements proved formation of a solid solution as the only phase. DTA and TG analyses showed that there are no amorphous phases. A nanometric morphology was proved by the TEM observations and the specific surface area measurements (BET). Dynamic light scattering was used to measure the agglomerate size distribution. A usefulness of the zirconia-titania-yttria nanopowders to the in-situ syntheses of composite powders in the ZrO2-TiB2-TiC system was described. The composite powders were fabricated in the reaction of titanium oxide dissolved in the TiO2-Y2O3-ZrO2 solid solution with boron oxide and carbon. A mixture of zirconia solid solution nanopowder containing 2-3 mol % of Y2O3, 18 mol % of TiO2 and 79-80 mol % of ZrO2, boric acid and 20 wt. % alcohol solution of phenolformaldehyde resin was used for the synthesis. The phase compositions of the composite powders were characterized by X-ray diffractometry.