Conduction Mechanism of Single‐Crystal Alumina

Will, Fritz G.; deLorenzi, H. G.; Janora, Kevin H.

doi:10.1111/j.1151-2916.1992.tb08179.x

Cited by 58 publications

(26 citation statements)

References 37 publications

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“…Thus one can conclude that for ionic carrier concentrations above about 3 ϫ 10 −7 per Al atom the electrical conductivity is mainly ionic ͑H 3 O + ions͒, and for lower H + concentrations, such as in the samples of Ref. 57, the conductivity is mainly electronic. In Ref.…”

Section: H Electrical Conductivitymentioning

confidence: 94%

“…At lower temperatures the activation energy for conduction was much lower ͑about 40 kJ or 0.4 eV͒, suggesting extrinsic conduction with electron or hole carriers from ionization of impurities. 57 Therefore the large differences in electrical conductivities of different aluminas measured in different ways probably result from either of two different causes: extrinsic electronic conductivity caused by different impurity concentrations, or ionic conductivity resulting from different water ͑H 3 O + ͒ concentrations.…”

Section: H Electrical Conductivitymentioning

confidence: 99%

“…Magnesium ions dissolved in otherwise pure alumina acts as electron acceptors ͑see Ref. 57 and Sec. IV below͒, so the lack of a positive charge when Mg +2 is substituted for Al +3 is compensated by formation of a mobile electron hole.…”

Section: G Diffusion In Polycrystalline Alumina Especially Lucalox™mentioning

confidence: 99%

“…54,55 However, when electrical field is applied to alumina, the aluminum is immobile. 57 Thus neutral defects are possibly involved in diffusion in alumina.…”

Section: A Point Defects In Aluminamentioning

confidence: 99%

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Diffusion in alumina

Doremus

2006

Journal of Applied Physics

107

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Experimental results on diffusion in alumina are summarized and critically discussed. The most reliable results are those on volume diffusion in single crystals (sapphire), and are available for a wide variety of substances, including the structural elements oxygen and alumina, water, monovalent cations, and trivalent cations. Experimental results on volume diffusion in polycrystalline alumina have also been reported for hydrogen, water, some actinides, and rare earths. Diffusion coefficients have been deduced from deep penetration tails on diffusion profiles, and have been interpreted to result from fast diffusion along dislocations or grain boundaries. However, there are questions about these interpretations that are discussed. Mechanisms of diffusion in alumina are uncertain; a variety of charged defects has been suggested to control diffusion in alumina, but no interpretation is widely accepted because of discrepancies with experimental results. The possibility of an AlO defect is put forward to stimulate exploration and discussions; together with a diffusion-reaction mechanism, it can explain many puzzling features of diffusion in alumina. The electrical conductivity of alumina results from the transport of H+(H3O+) ions if the OH concentration in the alumina is greater than about 3×10−7 OH groups per Al atom. At lower OH concentrations electronic conductivity becomes dominant.

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Section: H Electrical Conductivitymentioning

confidence: 94%

Section: H Electrical Conductivitymentioning

confidence: 99%

Section: G Diffusion In Polycrystalline Alumina Especially Lucalox™mentioning

confidence: 99%

“…54,55 However, when electrical field is applied to alumina, the aluminum is immobile. 57 Thus neutral defects are possibly involved in diffusion in alumina.…”

Section: A Point Defects In Aluminamentioning

confidence: 99%

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Diffusion in alumina

Doremus

2006

Journal of Applied Physics

107

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“…7, since the doping of the oxide scale is reduced. The type and level of doping should also affect the activation energy for conduction [9,42]. That might explain why the activation energy increase with increasing oxidation temperature, however a thorough investigation into that matter is outside the scope of this paper.…”

Section: Total Conductivitymentioning

confidence: 96%

In-situ Impedence Spectroscopy Study of Electrical Conductivity and Ionic Transport in Thermally Grown Oxide Scales on a Commercial FeCrAl Alloy

Öijerholm

Pan

et al. 2007

Oxid Met

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In-situ impedance-spectroscopy measurements were performed at temperatures between 600 and 1,000°C to investigate ionic transport in oxide scales formed on Kanthal AF alloy. The samples were pre-oxidized at 800, 900 and 1,000°C in air. The impedance spectra of the oxide formed at 1,000°C exhibited essentially one semicircle, whereas samples oxidized at lower temperatures showed an additional semicircle at high frequencies suggesting a more heterogeneous oxide. The ionic-transference number, derived by measuring the voltage across the oxide scale, indicates that the oxide is a predominant electronic conductor. Ionic diffusivity in the oxide scales formed at different pre-oxidizing temperatures was calculated, using the ionic-transference number. The ionic diffusivities obtained in this way are in reasonable agreement with literature data acquired by other methods. The oxide-formation temperature has a significant influence on the conductivity and ionic-transport properties of the oxide scale.

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Electrical and Dielectric Properties of Thermally Grown Oxide (TGO) on Fecralloy Substrate Studied by Impedance Spectroscopy

Yang¹,

Shinmi²,

Xiao³

2009

Advanced Ceramic Coatings and Interfaces IV

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Thermally grown oxide (TGO) formed on Fecralloy substrate exposed to an oxidizing environment of 1100°C for 4 hours was characterized by impedance spectroscopy method. Electrical and dielectric properties of TGO were investigated. AC conductivities and dielectric constants were studied as a function of frequency and temperature. AC conductivity analysis indicates a change in conduction mechanism around 400°C. Dielectric constant shows remarkable dispersions at low frequencies and high temperatures, which is considered to be originated from the Maxwell-Wagner type polarization from the interface of grain and grain boundary. INTRODUCTIONThermal barrier coatings (TBCs) have been widely used in the hot section of aeroturbine engines to increase turbine efficiency and to extend the life of metallic components '" 3 TBCs have a multi-layered structure, typically consisting of a ceramic topcoat yttria stabilized zirconia (YSZ), a metallic bond coat, and a thermally grown oxide (TGO) layer formed at the topcoat/bond coat interface due to the oxidation of the bond coat at high temperature. The TGO, predominantly alumina, provides oxidation protection and has a major influence on the TBC durability 4 . Since TGO is a dominant factor leading to failure of TBCs 5 , a deep understanding of the properties of the TGO is a critical issue in TBCs.Impedance spectroscopy is a powerful method to characterize the electrical and dielectric properties of solid materials and their interfaces. Since 1999, impedance spectroscopy has been developed to examine degradation of TBCs as a non-destructive evaluation tool, which is critical for prediction of TBCs lifetime during service 6 " 16 . Much effort has been devoted to characterize the TGO layer in TBCs by impedance spectroscopy. For example, Song et al. studied the formation and growth of TGO layer in air plasma sprayed (APS) TBCs by impedance spectroscopy and found the formation, thickening, densification and composition change of the TGO layer during TGO growth can be qualitatively evaluated by the peak shifts on the Bode plot ", and the results were confirmed by finite element simulation by Deng et al. "; Wang et al. also studied the TGO growth in TBCs by impedance spectroscopy and found a linear relationship between the TGO thickness and the diameter of the semicircle on the electrical modulus spectra, which proved the thickness of TGO layer in TBCs can be estimated by measuring its impedance response 18 . The above studies may provide useful information in estimating the remaining lifetime of the TBC system. However, it is still necessary to characterize the TGO itself to obtain a better and clear understanding of the TGO layer inside the TBCs.Fecralloy is a high temperature oxidation-resistant alloy. Under high temperature, a continuous, adherent, slowly-growing alumina surface scale is formed on Fecralloy, which provides excellent oxidation resistance against a high temperature and a corrosive atmosphere 9 . A preliminary impedance spectroscopy study on thermally oxide alumina scal...

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Conduction Mechanism of Single‐Crystal Alumina

Cited by 58 publications

References 37 publications

Diffusion in alumina

Diffusion in alumina

In-situ Impedence Spectroscopy Study of Electrical Conductivity and Ionic Transport in Thermally Grown Oxide Scales on a Commercial FeCrAl Alloy

Electrical and Dielectric Properties of Thermally Grown Oxide (TGO) on Fecralloy Substrate Studied by Impedance Spectroscopy

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