Defects in Zirconia Nanomaterials Doped with Rare-Earth Oxides

Abstract

Positron lifetime and coincidence Doppler broadening measurements on ZrO2+3 mol.% RE2O3 (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 mist 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 1500• C 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.

Characterisation of Porosity in Zirconia-Based Nanopowders

“…The initial nanopowders were prepared by the co-precipitation method [7] from water solutions of chemical grade salts and then calcined in air at temperature T c . The phase compositions of nanopowders were examined by means of X-ray diffraction (XRD) and the average nanoparticle size, d, was estimated using transmission electron microscopy or XRD spectra [1,4,5]. The calcined nanopowders were then pressure-compacted under different uniaxial pressures P into disk-shaped pellets of ≈ 10 mm diameter and ≈ 2 mm thickness.…”

“…Our previous research on zirconia-based nanomaterials using positron annihilation techniques allowed to draw the following main conclusions [1][2][3][4][5][6]: (1) In pressure-compacted nanopowders, positrons are trapped in Zr vacancy-like misfit defects, situated along grain boundaries (GB's), or in intersections of three GB's (triple points) equivalent in size to few-vacancy clusters. (2) A small fraction of positrons (≈10 %) was found to form Ps in many of studied nanopowders.…”

“…Investigations [1][2][3][4][5][6] were focused primarily on annihilation of positrons and only a poor and inaccurate knowledge about the ortho-Ps probing of larger pores, which gives rise to PLT components above 5 ns, could be revealed by these studies. In order to obtain more detailed data on the long ortho-Ps lifetimes, we attempted new PLT spectra measurements with a time domain expanded to ≈ 1 µs width.…”

Free volume defects and transport properties of mechanically stable polyhedral oligomeric silsesquioxane embedded poly(vinyl alcohol)‐poly(ethylene oxide) blend membranes

“…The gamma rays resulting from the subsequent annihilation of these atoms normally populate the peak region of the spectrum as the electron momentum gets significantly reduced due to its confinement with the positron . The prominent peak at p L = 9.09 × 10 −3 m 0 c is the signature of positron annihilation with the 2p electrons of carbon and oxygen atoms . It shows that positrons are getting trapped in the vacancies caused by the absence of the atoms of these elements at some sites.…”

Thermally activated charge transport in modified tetragonal zirconia thin films prepared by sol–gel method

“…Doped zirconia (ZrO 2 ) has potential applications because it has good thermal, mechanical, electrical, and optical properties. 1,2) For these applications, it is necessary to understand the associated growth mode of ZrO 2 nanocrystals and to modify the microstructure by incorporation of dopants, which will have a great influence on the properties. 3,4) Zirconium oxide is a widely studied material because of its enormous applications in electrochemical devices such as oxygen pumps 5) and semiconductor electrolyte for fuel cells.…”