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Defects in Zirconia Nanomaterials Doped with Rare-Earth Oxides

100%

Prochazka I., Cizek J., Melikhova O., Konstantinova T., Danilenko I.

Acta Physica Polonica A

2014

vol. 125

issue 3

760-763

Positron lifetime and coincidence Doppler broadening measurements on ZrO_2+3 mol.% RE_2O_3 (RE = Eu, Gd, Lu) nanopowders and ceramics obtained by sintering these nanopowders are reported. The initial nanopowders were prepared by a co-precipitation technique and exhibited a mean particle size of ≈ 15 nm. The nanopowders were calcined and pressure-compacted. All compacted nanopowders exhibited the prevailing tetragonal phase with at most 15% of the monoclinic admixture. Positrons in compacted nanopowders were found to annihilate almost exclusively at grain boundaries: (i) vacancy-like misfit defects along grain boundaries and (ii) larger defects situated at intersections of grain boundaries (triple points). In nanopowders, a small portion of positrons formed positronium in pores between crystallites. Sintering of nanopowders at 1500C caused a substantial grain growth and formation of ceramics. Sintering-induced grain growth led to a disappearance of the triple points and pores. The ceramics containing Eu and Gd dopants consist of mixture of the monoclinic and the tetragonal phase, while the ceramics with Lu dopant exhibits almost exclusively the tetragonal phase.

Positron Lifetimes in Zirconia-Based Nanomaterials

86%

Procházka I., Čížek J., Kuriplach J., Melikhova O., Konstantinova T., Danilenko I.

Acta Physica Polonica A

2008

vol. 113

issue 5

1495-1499

Positron lifetime spectroscopy is employed in a comparative study of several zirconia-based materials: (i) the pressure-compacted nanopowders of the three zirconia polymorphs - pure ZrO_2 (monoclinic), yttria-stabilized ZrO_2+3 mol.% Y_2O_3 (tetragonal) and yttria-stabilized ZrO_2+8 mol.% Y_2O_3 (cubic), (ii) ceramic materials obtained by sintering of the above two yttria-stabilized zirconia nanopowders and (iii) the tetragonal and cubic yttria-stabilized zirconia monocrystals. Positron lifetime data observed on the nanopowders suggest that the two shortest components, exhibiting lifetimes of ≈180 and ≈370 ps, arise from the annihilation of positrons trapped in defects associated with grain boundaries, presumably the vacancy-like defects and tripple points, respectively. Positron lifetime spectra observed on the ceramic materials resemble those found for the corresponding monocrystals, giving thus an additional support to the above interpretation of the nanopowders results.

Positronium Probing of Pores in Zirconia Nanopowders

73%

Prochazka I., Cizek J., Lukac F., Melikhova O., Hruska P., Anwand W., Liedke M., Konstantinova T., Danilenko I.

Acta Physica Polonica A

2017

vol. 132

issue 5

1564-1567

In the present paper, conventional positron lifetime measurements on selected zirconia-based nanopowders are reported. The nanopowders were doped with various metal cations (Y³⁺, Eu³⁺, Gd³⁺, Lu³⁺ and Mg²⁺). Lifetime experiments were conducted in air and supplemented with mass density measurements. In a range of lifetimes, from a few ns to ≈70 ns, up to two individual lifetime components could be identified. Such observations confirmed positronium (Ps) formation with subsequent ortho-Ps pick-off annihilation as well as the occurrence of pores of different size. Pore sizes were estimated using a shape-free model of the correlation between pore size and ortho-Ps lifetime. The origins of pores are discussed on the basis of the ortho-Ps data in combination with the results of mass density measurements.

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3 Acta Physica Polonica A

1 2017

1 2014

1 2008

3 Danilenko I.

3 Konstantinova T.

3 Melikhova O.

2 Cizek J.

2 Prochazka I.

1 Anwand W.

1 Hruska P.

1 Kuriplach J.

1 Liedke M.

1 Lukac F.

1 Procházka I.

1 Čížek J.

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Defects in Zirconia Nanomaterials Doped with Rare-Earth Oxides

Positron Lifetimes in Zirconia-Based Nanomaterials

Positronium Probing of Pores in Zirconia Nanopowders