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Yagi, Yuki; Hirano, Shingo; Ujihira, Yûsuke; Miyayama, Masaru

doi:10.1023/a:1006616030469

Cited by 18 publications

(12 citation statements)

References 4 publications

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“…In Ref. [3] the two components arise mainly from the annihilation of positrons inside nanograins, authors [4,5] related these components to the GB's. In our paper [6], the latter interpretation was further supported by the observed I 2 : I 1 ratios vs. the mean grain size.…”

Section: Resultsmentioning

confidence: 99%

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Positron Lifetimes in Zirconia-Based Nanomaterials

et al. 2008

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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 ZrO2 (monoclinic), yttria-stabilized ZrO 2 +3 mol.% Y 2 O 3 (tetragonal) and yttria-stabilized ZrO 2 +8 mol.% Y 2 O 3 (cubic), (ii) ceramic materials obtained by sintering of the above two yttriastabilized 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.

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Section: Resultsmentioning

confidence: 99%

“…Such a situation is a challenge for positron annihilation spectroscopy (PAS). Despite of several earlier PAS investigations [2][3][4][5], there is still a lack of unambiguous explanation of PAS data on YSZ materials.…”

Section: Introductionmentioning

confidence: 99%

Positron Lifetimes in Zirconia-Based Nanomaterials

et al. 2008

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“…Similar observations were made by Yagi et al in a lifetime PAS study on partially stabilized zirconia. 11 These authors concluded that in the range of 800-1200°C the change in the PAS parameters is related to the disappearance of the intra-agglomerate nanovoids.…”

Section: -4mentioning

confidence: 99%

“…On the other hand, it is well established that nanopores can be effective trapping centers for positrons. 11,28 In insulating materials positrons are probably trapped in the form of orthopositronium ͑o-ps͒. Pores of at least 0.3 nm in size are believed to be required in order to have an efficient trapping of o-ps.…”

Section: -4mentioning

confidence: 99%

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Characterization of densified fully stabilized nanometric zirconia by positron annihilation spectroscopy

Garay

Glade

Asoka‐Kumar

et al. 2006

Journal of Applied Physics

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Fully stabilized nanometric zirconia samples with varying degrees of porosity and grain sizes were analyzed using the coincidence Doppler broadening mode of the positron annihilation spectroscopy (PAS). A decrease in the low-momentum fraction was observed and coincided with a decrease in porosity. In addition to pores, it is proposed that defects in the negatively charged grain-boundary space region act as positron trapping centers; their effectiveness decreases with an increase in grain size. It is shown that PAS is sensitive to small grain-size differences within the nanometric regime in these oxide materials.

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Positron characterization of metastable phases in yttria stabilized zirconia

Damonte

Caracóche²,

Lamas

2007

Phys. Status Solidi (c)

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The thermal evolution of positron annihilation parameters in nanosized 10 mol % Y 2 O 3 doped ZrO 2 powders is presented. Three positron lifetimes have been determined up to 900 ºC annealing temperature. The two major ones have been interpreted, one as a mean between positron annihilation in the bulk and in vacancy-like open volume defects and the other, as due to annihilation in higher sized volume defects. The intensity ratio between the two defect structures depends on temperature and could be reflecting the thermal t"-to cubic metastable transformation known to occur in the studied system.1 Introduction Zirconia-based ceramic systems have been widely studied due to their excellent mechanical and electrical properties. Three equilibrium polymorphs are known for pure zirconia: monoclinic (up to 1200 ºC), tetragonal (up to 2400 ºC) and cubic (up to melting point) [1,2]. One of the main objectives in zirconia ceramics research is the stabilization of the tetragonal phase at RT, often achieved by the addition of a trivalent oxide as Y 2 O 3 is. As this situation provokes a certain amount of oxygen vacancies in the ZrO 2 host lattice for charge balance, the characterization and identification of the generated defects becomes most relevant since the electrical properties of yttria doped zirconias (YSZ) depend on the defect structure. Positron annihilation spectroscopy has proved to be an excellent tool for defect identification [3,4]. In particular, it was applied to the study of generated defects in ZrO 2 oxides upon doping with different trivalent oxides [5][6][7]. In the present work we present PALS results obtained on a 10 mol % Y 2 O 3 -stabilized ZrO 2 system (10YSZ) whose hyperfine interaction had been already determined [1]. The nanocrystalline powder synthesized by a nitrate-citrate gel-combustion process and stabilized in the metastable t"-form of the tetragonal phase, was characterized at the nanoscopic level using mainly the Perturbed Angular Correlations technique. Oxygen vacancy movement is revealed as a slow diffusion process involving a very small activation energy. As the powder was heated, a t"-to-cubic transformation occurred around 600 °C. Here, the evolution of the positron annihilation parameters with annealing temperature is analyzed in order to determine the existing different defect structures and correlate them with the phase evolution observed by PAC.

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Cited by 18 publications

References 4 publications

Positron Lifetimes in Zirconia-Based Nanomaterials

Positron Lifetimes in Zirconia-Based Nanomaterials

Characterization of densified fully stabilized nanometric zirconia by positron annihilation spectroscopy

Positron characterization of metastable phases in yttria stabilized zirconia

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