Diffusion of Al, O, Pt, Hf, and Y atoms on α-Al<sub>2</sub>O<sub>3</sub>(0001): implications for the role of alloying elements in thermal barrier coatings

Milas, Ivan; Hinnemann, Berit; Carter, Emily A.

doi:10.1039/c0jm02212h

Cited by 43 publications

(23 citation statements)

References 81 publications

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“…In spite of many studies about the defects 13-20 and defect diffusion [21][22][23][24][25][26] in Al 2 O 3 , V O diffusion in Al 2 O 3 has been remained as a discrepancy. The calculated V O diffusion energies by theoretical approaches are the order of 1-2.5 eV.…”

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confidence: 89%

Charge-dependent oxygen vacancy diffusion in Al2O3-based resistive-random-access-memories

Yang

Kamiya

Magyari-Köpe

et al. 2013

Applied Physics Letters

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We theoretically study an oxygen vacancy (V O ) diffusion in Al 2 O 3 -based resistive-randomaccess-memories (ReRAMs). We find that the activation energy of V O diffusion in Al 2 O 3 strongly depends on the charge state of V O . In ReRAM, the charge state of V O can be easily changed by applying voltage and the lowest activation energy is observed at q ¼ 2þ. The operation voltage on Al 2 O 3 -based ReRAM is close to the activation energy at q ¼ 2þ, indicating that V O diffuses with doubly positive state. Moreover, the activation energy at q ¼ 0 is close to that observed in bulk Al 2 O 3 , which explains the discrepancy between previous experimental and theoretical studies. V C 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4819772]The recent outstanding downscale of devices has led to the significant reduction of material size to nano-scale. Compared to conventional materials, these thin films contain only a few nanometer thicknesses with nano-interfaces, which may inevitably exhibit quite different physical properties. For the practical use, therefore, it is important to understand unconventional properties observed in nano-scale materials, which provides additional dimensions in thin filmbased applications.One of the representative examples of thin film application is resistive random-access-memory (ReRAM). ReRAM is known as promising candidate for the next generation of non-volatile memories and it is composed of one-or multilayer insulator with a few nanometer thickness sandwiched by two metal electrodes. 1-4 For a filamentary conductive path in the insulator, it has been believed that the origin is cohesion of oxygen vacancies (V O s), 5-7 which is controlled by the electron injection and removal by applying voltage. 8,9 Recently, the advanced ReRAM stack structure that contains a thin Al 2 O 3 layer has experimentally shown to improve properties in terms of high ON-OFF ratio and reliability. 10 In our previous studies, we have theoretically elucidated the atomic and electronic role of the Al 2 O 3 layer in advanced ReRAM stacks. 11,12 We revealed that small voltage is enough to make a V O filament in the Al 2 O 3 -based ReRAM because of its nano-scale thickness, even though Al 2 O 3 is a poor V O former. 12 However, further investigation of the V O diffusion should be discussed to fully understand the nature of the cohesion-isolation of V O in Al 2 O 3 .In spite of many studies about the defects 13-20 and defect diffusion 21-26 in Al 2 O 3 , V O diffusion in Al 2 O 3 has been remained as a discrepancy. The calculated V O diffusion energies by theoretical approaches are the order of 1-2.5 eV. According to the experiment, on the other hand, the V O migration energy is $5 eV, 25 which is significantly larger than not only previous theoretical calculations but also the operation voltage on Al 2 O 3 -based ReRAM, the order of 1-2 V. Although Aschauer et al. succeeded to reproduce the experimental result by performing a combination of empirical potential-based metadynamics and kinetic Monte Carlo methods, ...

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confidence: 89%

Charge-dependent oxygen vacancy diffusion in Al2O3-based resistive-random-access-memories

Yang

Kamiya

Magyari-Köpe

et al. 2013

Applied Physics Letters

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“…26–38 Fewer studies have explored atomic, molecular adhesion and adsorption on the same surfaces 39–53 with particular interest in H 2 O adsorption, 27,47,52,54,55 while doping effects were primary of interest of the bulk material due to the changes in the bandgap related properties. 56,57 or dehydroxylation effects.…”

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confidence: 99%

Electronic Properties and Reactivity of Simulated Fe³⁺and Cr³⁺Substituted α-Al₂O₃(0001) Surface

2012

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Metal oxide based minerals naturally contain transition metal impurities isomorphically substituted into the structure that can alter the structural and electronic properties as well as the reactivity of these metal oxides. Natural α-Al2O3 (corundum) can contain up to 9.17% (w/w) Fe2O3 and 1.81% (w/w) of Cr2O3. Here we report on changes in the structural and electronic properties of undoped and doped α-Al2O3 (0001) surfaces using periodic density functional theory (DFT) methods with spin unrestricted B3LYP functional and a local atomic basis set. Both structural and electronic properties are altered upon doping. Implications for doping effects on photochemical processes are discussed. As metal oxides are major components of the environment, including atmospheric mineral aerosol, DFT was also used to study the effect of transition metal impurities on gas/surface interactions of a model acidic atmospheric gas molecule, carbon monoxide (CO). The theoretical results indicated that the presence of Fe3+ and Cr3+ impurities substituted on the outer layer of natural corundum surfaces reduces the propensity toward CO adsorption relative to the undoped surface. However, CO-surface interactions resemble that of bulk α-Al2O3 when the impurity is substituted below the first surface layer. The presence and location of the mineral dopant was found to significantly alter the structural and electronic properties and gas/surface interactions studied here.

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“…As a baseline point of comparison for future GB diffusion studies, we chose the basal plane of alumina, i.e., the α-Al 2 O 3 ð0001Þ surface, on which to examine adsorption (30) and diffusion (32) of Al, O, Hf, Y, Pt, and S. The electropositive metals Al, Y, and Hf all adsorb on the same threefold hollow site, namely the site where the next Al ion would be if the bulk crystal continued. This is also the place one would intuitively place an adsorbate that donates electrons.…”

Section: Resultsmentioning

confidence: 99%

Atomic-scale insight and design principles for turbine engine thermal barrier coatings from theory

Marino

Hinnemann

Carter

2011

Proc. Natl. Acad. Sci. U.S.A.

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To maximize energy efficiency, gas turbine engines used in airplanes and for power generation operate at very high temperatures, even above the melting point of the metal alloys from which they are comprised. This feat is accomplished in part via the deposition of a multilayer, multicomponent thermal barrier coating (TBC), which lasts up to approximately 40,000 h before failing. Understanding failure mechanisms can aid in designing circumvention strategies. We review results of quantum mechanics calculations used to test hypotheses about impurities that harm TBCs and transition metal (TM) additives that render TBCs more robust. In particular, we discovered a number of roles that Pt and early TMs such as Hf and Y additives play in extending the lifetime of TBCs. Fundamental insight into the nature of the bonding created by such additives and its effect on high-temperature evolution of the TBCs led to design principles that can be used to create materials for even more efficient engines.A ircraft and power plants share a common source of usable energy: Both employ turbine engines that combust fuel to either propel airplanes or produce electricity. At a time in which efficient use of energy is paramount, improving the efficiency of turbine engines is one means to contribute to this global challenge. Turbine engines operate via the Brayton cycle, which offers lower carbon dioxide emissions and lower cost for power generation than other possible alternatives. Their efficiency can be increased by increasing the inlet temperature, which allows more expansion of gas that creates more pressure to drive the turbine. However, high-temperature operation, under oxidizing conditions, poses serious demands on the materials used to construct jet engine components. Materials must be found that are robust under such harsh operating conditions. Engineers over the past few decades have improved greatly the thermomechanical properties of the metal alloy comprising, e.g., the turbine blades, and have created a multilayer coating for the blades that protects against both heat and corrosion, referred to as a thermal barrier coating (TBC). These materials advances, along with internal component cooling, have been astonishingly successful, allowing the gas temperature to exceed the melting point of the metal alloy from which the engine components are constructed! Despite these advances, more robust TBCs are desired, either to extend TBC service lifetime under present-day operating conditions or to operate at even higher temperatures to achieve more efficient energy conversion. As a result, characterization and optimization of TBC properties have continued to be active areas of research. As is the case for most materials development, the usual path to improve TBCs relies on trial and error. Many materials compositions are fabricated, characterized, and tested. Unfortunately, characterization typically is performed postmortem, as virtually no instruments exist to characterize a TBC in situ during operation. The lack of in situ probes makes...

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Diffusion of Al, O, Pt, Hf, and Y atoms on α-Al₂O₃(0001): implications for the role of alloying elements in thermal barrier coatings

Cited by 43 publications

References 81 publications

Charge-dependent oxygen vacancy diffusion in Al2O3-based resistive-random-access-memories

Charge-dependent oxygen vacancy diffusion in Al2O3-based resistive-random-access-memories

Electronic Properties and Reactivity of Simulated Fe³⁺and Cr³⁺Substituted α-Al₂O₃(0001) Surface

Atomic-scale insight and design principles for turbine engine thermal barrier coatings from theory

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Diffusion of Al, O, Pt, Hf, and Y atoms on α-Al2O3(0001): implications for the role of alloying elements in thermal barrier coatings

Cited by 43 publications

References 81 publications

Charge-dependent oxygen vacancy diffusion in Al2O3-based resistive-random-access-memories

Charge-dependent oxygen vacancy diffusion in Al2O3-based resistive-random-access-memories

Electronic Properties and Reactivity of Simulated Fe3+and Cr3+Substituted α-Al2O3(0001) Surface

Atomic-scale insight and design principles for turbine engine thermal barrier coatings from theory

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Diffusion of Al, O, Pt, Hf, and Y atoms on α-Al₂O₃(0001): implications for the role of alloying elements in thermal barrier coatings

Electronic Properties and Reactivity of Simulated Fe³⁺and Cr³⁺Substituted α-Al₂O₃(0001) Surface