Effect of substituted IIIB transition metals on the energy gap of α‐Al<sub>2</sub>O<sub>3</sub> by first‐principle calculations

Benam, M. R.; Aliabad, H. A. Rahnamaye; Hosseini, S. M.

doi:10.1002/pssa.200566004

Cited by 8 publications

(7 citation statements)

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“…The calculated density of states (DOS) is in good agreement with recent experimental results. Benam et al [10] has made first principles study on the electronic structure of α-Al 2-x T x O 3 (T= Sc, Y, La, Ac; x=0.5). The results indicate that the size of the band gap in these alloys decreases considerably and these reductions are related to the ionic radius of the substitutional transition metal.…”

Section: Resultsmentioning

confidence: 99%

“…Recently, multi-component ordered solid solution has become one of the important fields for the investigation of these materials, for the performances of materials are determined by their structures. For instance, transition metal doped corundum type of α-Al 2-x T x O 3 (T = Sc, Y, La, Ac; x=0.5) crystals are high k-gate dielectric materials [9,10] ; corundum type solid solution α-FeAlO 3 were reported [11] . The investigations on multi-component coatings and composite coatings for oxidation resistance at high temperature [12][13][14] as well as on the property of other corundum type solid solution [15,16] are all hot points of materials research.…”

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confidence: 99%

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Ordered structures of rhombohedral system

Song

Jiang

2008

Chin. Sci. Bull.

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Lattice gas model is presented for rhombohedral lattice. Seven ordered structure types and four perfectly ordered structures are determined using concentration wave theory. The ordered structures of cation in corundum-type dimetal trioxides are predicted and reasonable explanations for typical experimental results are given.rhombohedral crystal, concentration wave, ordered structure, corundumRhombohedral system is one of the seven crystal systems. In recent years, many materials with rhombohedral structure have attracted many researcher's attention. For instance, sapphire (α-Al 2 O 3 ) is an infrared window material with excellent comprehensive performance [1] , and it is also a substrate material for the epitaxial preparation of ferroelectric materials [2,3] ; α-Al 2 O 3 is the main composition phase of scale on the surface of TiAl-based alloy, which contributes to the oxidation resistance at high temperature [4,5] ; ruby, based on α-Al 2 O 3 , is an important laser material; Ti-doped sapphire is widely used as important working crystal for tunable lasers and ultra-fast, high power light pumping. Zr-or Hf-doped BaTiO 3 is a new type of piezoelectric ceramic with stable rhombohedral phase above room temperature [6] . The r-BN is the precursor of new superhard materials c-BN [7] ; metastable rhombohedral α-Ga 2 O 3 has a smaller energy gap indicating very different photoelectric performance [8] . Recently, multi-component ordered solid solution has become one of the important fields for the investigation of these materials, for the performances of materials are determined by their structures. For instance, transition metal doped corundum type of α-Al 2-x T x O 3 (T = Sc, Y, La, Ac; x=0.5) crystals are high k-gate dielectric materials [9,10] ; corundum type solid solution α-FeAlO 3 were reported [11] . The investigations on multi-component coatings and composite coatings for oxidation resistance at high temperature [12][13][14] as well as on the property of other corundum type solid solution [15,16] are all hot points of materials research.Theoretically, while the main ordered structure types of cubic system [17][18][19] and hexagonal system [20,21] have been determined, the results about rhombohedral system have seldom been reported. Therefore, it is necessary to study the ordered structure types of rhombohedral system theoretically, which can give useful instruction to the research of related materials.

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Section: Resultsmentioning

confidence: 99%

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confidence: 99%

Ordered structures of rhombohedral system

Song

Jiang

2008

Chin. Sci. Bull.

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“…c [11]. [15], here the moving of ns states from the IIIA atoms contributes more. With the increase of the orbital quantum number, n, the ns states (in the conduction band) shift to lower energy relative to their own Fermi levels.…”

Section: Electronic Propertiesmentioning

confidence: 97%

First-principles study on the geometry and electronic structures of IIIA atoms doped α-Al₂O₃:V_O

Nie

et al. 2014

Can. J. Phys.

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We investigate the geometry and electronic structures of ␣-Al 2 O 3 :V O + Al X systems based on first-principles calculations where V O represents one oxygen vacancy and Al X stands for IIIA atoms (B, Ga, In, and Tl) substituting of one Al atom. It is found that all the aluminates maintain the hexagonal symmetry as the pure ␣-Al 2 O 3 structure and the lattice parameters a, b, and c are expanded with the increase of the IIIA atoms radius. The electronic property analysis indicates that the band gaps are considerably reduced and the reductions are also related to the radius of doping atoms. But unlike the situation of transition metal doped ␣-Al 2 O 3 the decreases of the band gap are not due to the spreading of d states, but are mainly owing to the ns states at the bottom of the conduction band. PACS No.: 71.20.Nr. Résumé : Nous étudions la géométrie et les structures électroniques de systèmes ␣-Al 2 O 3 :V O + Al X , à partir de calculs ab initio, où V O présente une lacune d'un atome d'oxygène et Al X signifie qu'un atome de Al est remplacé par un atome substitut de type IIIA (B, Ga, In et Ti). Nous trouvons que tous les aluminates conservent la symétrie hexagonale comme la structure de ␣-Al 2 O 3 pur et que les paramètres du réseau, a, b et c, augmentent avec le rayon de l'atome IIIA. L'analyse des propriétés électroniques indique que la bande interdite est considérablement réduite et que ces réductions sont aussi reliées au rayon de l'atome dopant.Contrairement au dopage de ␣-Al 2 O 3 par métal de transition, la diminution de la bande interdite n'est pas due à l'étalement des états d, mais est due surtout au maintien des états ns au fond de la bande de conduction. [Traduit par la Rédaction]

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“…2; it can be seen that the ceramic particle mainly contains quartz (JCPDS 33-1161) and mullite (JCPDS 15-776), whose sharp diffraction peaks imply a good crystallinity, which is an inert material and can be employed as a comparison. The α-Al 2 O 3 catalyst shows a high degree of crystallinity judged from the high and narrow diffraction peaks (JCPDS 42-1468), and its crystal structure is hexagonal closely packed that consists of closely packed planes of oxygen and aluminum (Benam et al 2006). This means that its chemical activity should be relatively low.…”

Section: Characterization Of Catalystsmentioning

confidence: 99%

Catalytic hydrolysis of urea from wastewater using different aluminas by a fixed bed reactor

Shen

et al. 2014

Environ Sci Pollut Res

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In order to find an effective method for treating urea wastewater, the experiments on the hydrolysis of urea in wastewater were conducted in a fixed bed reactor with different aluminas (α-Al2O3, γ-Al2O3, and η-Al2O3) as catalysts respectively in contrast with inert ceramic particle. The results indicate that the three alumina catalysts show obvious catalytic activity for urea hydrolysis at 125 °C. The order of activity is η-Al2O3 > γ-Al2O3 > α-Al2O3, and the activity difference increases with increasing temperature. According to the characterization results, surface acidity has little impact on the activity of catalyst. However, it was found that surface basicity of alumina catalyst plays an important role in catalytic hydrolysis of urea, and the activity of catalyst may be also influenced by the basic strength. With η-Al2O3 as catalyst, the urea concentration in wastewater is reduced to 4.96 mg/L at a temperature of 165 °C. Moreover, the η-Al2O3 shows a good stability for urea hydrolysis. The hydrolysis of urea over η-Al2O3 catalyst can evidently reduce the reaction temperature and is promising to replace industrial thermal hydrolysis process.

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Effect of substituted IIIB transition metals on the energy gap of α‐Al₂O₃ by first‐principle calculations

Cited by 8 publications

References 5 publications

Ordered structures of rhombohedral system

Ordered structures of rhombohedral system

First-principles study on the geometry and electronic structures of IIIA atoms doped α-Al₂O₃:V_O

Catalytic hydrolysis of urea from wastewater using different aluminas by a fixed bed reactor

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Effect of substituted IIIB transition metals on the energy gap of α‐Al2O3 by first‐principle calculations

Cited by 8 publications

References 5 publications

Ordered structures of rhombohedral system

Ordered structures of rhombohedral system

First-principles study on the geometry and electronic structures of IIIA atoms doped α-Al2O3:VO

Catalytic hydrolysis of urea from wastewater using different aluminas by a fixed bed reactor

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Effect of substituted IIIB transition metals on the energy gap of α‐Al₂O₃ by first‐principle calculations

First-principles study on the geometry and electronic structures of IIIA atoms doped α-Al₂O₃:V_O