Diffusion of the 65Zn radiotracer in ZnO polycrystalline ceramics

Nogueira, Maria Auxiliadora das Neves; Ferraz, Wilmar Barbosa; Sabioni, Antônio Claret Soares

doi:10.1590/s1516-14392003000200010

Cited by 39 publications

(26 citation statements)

References 8 publications

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“…The above relation has been derived for (2l/ D pi ) = 0.83, where l is the neck radius and D pi the initial primary-particle diameter, and assumes that the grain-boundary width remains constant during the coalescence process. The literature values of bD GB , [58] g, [59,60] and u are listed in Table 2. To the best of our knowledge, there is only one report on the grain-boundary diffusion coefficients for ZnO.…”

Section: Particle Growth Investigationmentioning

confidence: 99%

“…To the best of our knowledge, there is only one report on the grain-boundary diffusion coefficients for ZnO. [58] Based on that report, it was possible to calculate t GB values after extrapolating the grain-boundary diffusion coefficient in the studied temperature range. The grainboundary diffusion coefficient of zinc was used for calculation because of the much higher diffusivity value of zinc compared to that of oxygen.…”

Section: Particle Growth Investigationmentioning

confidence: 99%

“…The grainboundary diffusion coefficient of zinc was used for calculation because of the much higher diffusivity value of zinc compared to that of oxygen. [58,61] Figure 7 a shows the dependence of the primary-particle diameter (D pi = 2r i ) on t GB as a function of temperature. The experimental residence times in the sintering furnace at 25 8C (4.6 s) and 1000 8C (1.1 s) are also shown in Figure 7 a and it should be noted that the residence time decreases with an increase in sintering temperature.…”

Section: Particle Growth Investigationmentioning

confidence: 99%

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Chemical Vapor Synthesis of Size‐Selected Zinc Oxide Nanoparticles

Polarz

Roy

Merz

et al. 2005

Small

153

108

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ZnO can be regarded as one of the most important metal oxide semiconductors for future applications. Similar to silicon in microelectronics, it is not only important to obtain nanoscale building blocks of ZnO, but also extraordinary purity has to be ensured. A new gas-phase approach to obtain size-selected, nanocrystalline ZnO particles is presented. The tetrameric alkyl-alkoxy zinc compound [CH 3 ZnOCH(CH 3 ) 2 ] 4 is chemically transformed into ZnO, and the mechanism of gas-phase transformation is studied in detail. Furthermore, the morphological genesis of particles via gas-phase sintering is investigated, and for the first time a detailed model of the gas-phase sintering processes of ZnO is presented. Various analytical techniques (powder XRD, TEM/energy-dispersive X-ray spectroscopy, magic-angle spinning NMR spectroscopy, FTIR spectroscopy, etc.) are used to investigate the structure and purity of the samples. In particular, the defect structure of the ZnO was studied by photoluminescence spectroscopy.

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Section: Particle Growth Investigationmentioning

confidence: 99%

Section: Particle Growth Investigationmentioning

confidence: 99%

Section: Particle Growth Investigationmentioning

confidence: 99%

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Chemical Vapor Synthesis of Size‐Selected Zinc Oxide Nanoparticles

Polarz

Roy

Merz

et al. 2005

Small

153

108

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“…At high Zn pressures Hagemark [9] and Tomlins et al [15] found the component vapour pressure p Zn 1/3 relationship, corresponding to a (p O 2 ) -1/6 dependence of the concentration of electrons. Very high Zn diffusivity was revealed and explained by fast-moving Zn interstitials; however, experimental data appear of the controversial role of grain boundaries in the self-diffusion of ZnO components [16,17]. Static vapour photometry is the method that enables us to increase the sensitivity of tensimetric measurements and thereby develop the study of nonstoichiometry.…”

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confidence: 99%

Excess Zn in ZnO

Lott

Shinkarenko

Kirsanova

et al. 2004

phys. stat. sol. (c)

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Excess Zn in ZnO was experimentally investigated. The ZnO samples tested were prepared by heat treatment of ZnO powder or polycrystalline ceramics at a temperature of 900 °C and at fixed Zn pressures from 0.2 to 0.6 of saturated Zn vapour pressure at a given temperature. To determine the excess Zn, atomic absorption photometry of Zn vapour was used under conditions of solid-vapour equilibrium. The optical absorbance, proportional to the concentration of Zn atoms in the vapour phase, was registered photoelectrically on the Zn resonance line. During the atomic absorption photometry measurements all excess Zn was extracted from the solid state into the vapour phase. The analysis of the temperature dependence of Zn pressure indicated that the value of Zn excess lies in the concentration interval of 10 18 -10 19 cmand depends on the sample history and the conditions of preliminary heat treatment. The experimental results were used for preliminary estimation of high-temperature defect equilibrium in ZnO. Chemical analysis is not a reliable technique for evaluating the excess Zn in ZnO. Chemical analysis can only serve as a qualitative technique for comparing different samples. In our investigations of atomic absorption photometry of polycrystalline II-VI materials it became evident that the metal component adsorbed on crystallite surfaces must be taken into account [5]. In Ref.[6] different HTDE models from different authors are compared. ZnO exhibits n-type high-level electrical conductivity, which is due to intrinsic donor [7] or to hydrogen as a shallow donor [8]. The dominating high-temperature defects are interstitial Zn [9][10][11] or oxygen vacancies [2,12]. Atomic absorption photometry studies of the nonstoichiometry of II-VI compounds have shown that the analytically determined concentration of the metal component excess appears to be bigger than the concentration of electrically active defects [13,

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“…In Zn rich condition interstitial Zn (Zn i ) or O vacancy (V O ) have relatively lower formation energies than other defects [21]. In polycrystalline ceramics in the same experimental conditions, the grainboundary diffusion coefficients of Zn are approximately 4 orders of magnitude greater than the volume diffusion coefficients of Zn in ZnO [22]. The main stable faces of ZnO consist of distinctly different sites with mainly acid or mainly basic or mixed character.…”

mentioning

confidence: 99%

Atomic absorption photometry of excess Zn in ZnO

Lott

Shinkarenko

Kirsanova

et al. 2005

phys. stat. sol. (c)

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PACS 61.50. Nw, 61.72.Ji, 64.70.Hz Zn excess in ZnO is built up automatically at high temperatures. Excess Zn in hydrothermally grown ZnO single crystals were investigated by the atomic absorption photometry (AAP) method. To determine the excess zinc in ZnO samples, the AAP of zinc vapour was used in the conditions of solid-vapour equilibrium. Zn AAP allowes to eliminate excess Zn connected differentially in ZnO samples. To fix Zn non-stoichiometry, all the ZnO samples tested were previously heat treated at temperature interval from 850 to 900 0 C and at fixed Zn vapour pressures from 0.1 to 0.9 of saturated zinc vapour pressure at given treatment temperature. The analysis of temperature dependence of zinc vapour pressure indicated that the impurity metals take active role in the determination of non-stoichiometric zinc. The impurities Mn, Fe, Co, Ni and Cu form oxides which will reduce during annealing in Zn vapor up to metals form. During AAP measurement in optical cuvette, these metals react with ZnO and give additional Zn vapor pressure.1 Overview ZnO is used in a wide range of scientific and technological applications, such as optoelectronic devices, varistors, devices for surface acoustic waves and planar optical waveguides, transparent electrodes and transparent windows for a solar cell, gas sensors, flat panel diplays, catalysts, ferroelectric memories and spintronic devices, antibacterial agent and ZnO can satisfy the commercial desire for blue and ultraviolet light emitting devices -it is suitable to grow the high quality ZnO homoepilayer on the ZnO substrate [1][2][3]. For that reason, it is important to produce high quality ZnO bulk crystals for substrates of ZnO-related devices. The hydrothermal method has an advantage to grow large bulk crystals due to the growth under low supersaturation [4][5][6]. Some doubts were raised about the quality of such crystals because they have often exhibited large X-ray rocking curve widths and low photoluminescence yield with large linewidths [7]. But if the surface damage due to mechanical polishing was overcome, hydrothermal ZnO crystals provided a competitive substrate for homoepitaxial growth [7,8]. As the hydrothermal crystals invitably involve alkali metals from solution and small amounts of metallic impurities then one of the problems in hydrothermally grown ZnO crystals is the contamination of the crystal with metallic impurities. The concentration of impurities exceeds often the concentration of intrinsic defects. The colourless crystals were found with a total impurity content of less than 1 ppm [4,9] but it is found that the green colouration of the hyrothermally grown crystals may be due to the presence of iron in concentration up to 60 ppm [9]. The solubilities of metal oxides in ZnO are high. For example the solubility of Fe in ZnO is 7 mole% at 800 0 C [10]. Fe in ZnO appears as a result of the corrosion of the inner wall of the autoclave [11]. The thermal treatment of ZnO crystal results in the formation of associates between metal impurities [12,...

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Diffusion of the 65Zn radiotracer in ZnO polycrystalline ceramics

Cited by 39 publications

References 8 publications

Chemical Vapor Synthesis of Size‐Selected Zinc Oxide Nanoparticles

Chemical Vapor Synthesis of Size‐Selected Zinc Oxide Nanoparticles

Excess Zn in ZnO

Atomic absorption photometry of excess Zn in ZnO

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