Strontium and cerium tungstate materials SrWO4 and Ce2(WO4)3: Methane oxidation and mixed conduction

Arab, Madjid; Moriyama, André Luís Lopes; Santos, Tiago Renovato dos; Souza, Carlson Pereira de; Gavarri, J.R.; Leroux, C.

doi:10.1016/j.cattod.2012.09.036

Cited by 30 publications

(31 citation statements)

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“…For this reason this material is often utilized in electrochemical applications and electrochromic devices [20][21][22]. Also, both crystalline and amorphous WO 3 can host vacancies and interstitial atoms, thus allowing cation accommodation and diffusion, with a tendency to form compounds such as tungsten bronzes [23,24]. Recent progress demonstrated the high-quality growth of WO 3 thin films on perovskite materials [25][26][27].…”

mentioning

confidence: 99%

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO₃ Overlayers

Mattoni

Baek²,

Manca

et al. 2017

ACS Appl. Mater. Interfaces

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Interfaces between complex oxides constitute a unique playground for 2D electron systems (2DES), where superconductivity and magnetism can arise from combinations of bulk insulators. The 2DES at the LaAlO 3 /SrTiO 3 interface is one of the most studied in this regard, and its origin is determined by both the presence of a polar field in LaAlO 3 and the insurgence of point defects, such as oxygen vacancies and intermixed cations. These defects usually reside in the conduction channel and are responsible for a decreased electronic mobility. In this work, we use an amorphous WO 3 overlayer to control the defect formation and obtain an increased electron mobility in WO 3 /LaAlO 3 /SrTiO 3 heterostructures. The studied system shows a sharp insulator-to-metal transition as a function of both LaAlO 3 and WO 3 layer thickness. Low-temperature magnetotransport reveals a strong magnetoresistance reaching 900% at 10 T and 1.5 K, the presence of multiple conduction channels with carrier mobility up to 80 000 cm 2 V −1 s −1 and an unusually high effective mass of 5.6 me. The amorphous character of the WO 3 overlayer makes this a versatile approach for defect control at oxide interfaces, which could be applied to other heterestrostures disregarding the constraints imposed by crystal symmetry.The formation of a two-dimensional electron system (2DES) at the interface between band insulators SrTiO 3 (STO) and LaAlO 3 (LAO) is among the most intriguing effects studied in oxide electronics [1]. Gate tunable superconductivity [2,3], strong spin-orbit coupling [4,5] and magnetism [6,7] are some of the many phenomena observed. The origin of this 2DES is a long standing question in the solid state community and recent results indicate that a consistent picture should take into account both the built-in polar field and the presence of point defects [8][9][10]. Among these, oxygen vacancies and cation off-stoichiometry in STO are capable of inducing a 2DES [11,12]. However, defects residing in the conductive channel are usually responsible for a decreased electronic mobility [13]. In order to promote high electron mobility, it is crucial to confine donor sites away from the conducting plane, without preventing the 2DES formation in the STO top layers. Previous attempts to control the defect concentration profile and thus enhance the mobility involved the use of crystalline insulating overlayers [14,15] [18,19]. A promising material to control defect formation is tungsten oxide WO 3 . The several possible oxidations states of tungsten make WO 3 particularly active in undergoing redox reactions. For this reason this material is often utilized in electrochemical applications and electrochromic devices [20][21][22]. Also, both crystalline and amorphous WO 3 can host vacancies and interstitial atoms, thus allowing cation accommodation and diffusion, with a tendency to form compounds such as tungsten bronzes [23,24]. Recent progress demonstrated the high-quality growth of WO 3 thin films on perovskite materials [25][26][27].In this work we co...

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mentioning

confidence: 99%

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO₃ Overlayers

Mattoni

Baek²,

Manca

et al. 2017

ACS Appl. Mater. Interfaces

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“…As a reference, unsupported Ce 2 (WO 4 ) 3 was prepared using a complex method combining ethylenediamine tetraacetic acid and citrate ions, as described in previous reports4041.…”

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confidence: 99%

Low-temperature catalytic oxidative coupling of methane in an electric field over a Ce–W–O catalyst system

Sugiura

Ogo

Iwasaki

et al. 2016

Sci Rep

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We examined oxidative coupling of methane (OCM) over various Ce–W–O catalysts at 423 K in an electric field. Ce2(WO4)3/CeO2 catalyst showed high OCM activity. In a periodic operation test over Ce2(WO4)3/CeO2 catalyst, C2 selectivity exceeded 60% during three redox cycles. However, Ce2(WO4)3/CeO2 catalyst without the electric field showed low activity, even at 1073 K: CH4 Conv., 6.0%; C2 Sel., 2.1%. A synergetic effect between the Ce2(WO4)3 structure and electric field created the reactive oxygen species for selective oxidation of methane. Results of XAFS, in-situ Raman and periodic operation tests demonstrated that OCM occurred as the lattice oxygen in Ce2(WO4)3 (short W–O bonds in distorted WO4 unit) was consumed. The consumed oxygen was reproduced by a redox mechanism in the electric field.

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“…Cerium tungstate was synthesized using the complexing method combining ethylenediaminetetracetic acid (EDTA) and citrate ions, as described previously (Arab et al, 2013). Cerium(III) nitrate was dissolved in deionized water.…”

Section: Sample Preparationmentioning

confidence: 99%

“…In previous work, Ce 2 (WO 4 ) 3 was successfully synthesized for the first time by the EDTA-citrate method (Arab et al, 2013), with grain sizes around 100 nm. In an attempt to synthesize a new cerium tungstate phase with a molar ratio of 1/4, a two-phased powder was obtained, namely a mixture of Ce 2 (WO 4 ) 3 and a cerium tungstate phase presenting similarities with RE 10 W 22 O 81 .…”

Section: Introductionmentioning

confidence: 99%

Monoclinic superstructure in orthorhombic Ce₁₀W₂₂O₈₁from transmission electron microscopy

Patout

Jacob

Arab

et al. 2014

Acta Crystallogr Sect B

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Synopsis -A monoclinic superstructure occurring in a Ce 10 W 22 O 81 compound was identified by transmission electron microscopy. The partial oxidation of Ce 3+ along with interstitial oxygen ions could explain this superstructure.Abstract -A complex rare earth tungstate structure, present in a two-phased powder, was solved by electron diffraction, precession and high resolution electron microscopy. The orthorhombic space group Pbnm and the atomic positions deduced from X-rays diffraction experiments were confirmed for Ce 10 W 22 O 81 . A C2/c monoclinic superstructure, with cell parameters a = 7.8 Å, b = 36.1 Å, c = 22.2 Å and β = 100.2°, was evidenced and attributed to a partial oxidation of Ce 3+ leading to interstitial oxygen ions.

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Strontium and cerium tungstate materials SrWO4 and Ce2(WO4)3: Methane oxidation and mixed conduction

Cited by 30 publications

References 25 publications

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO₃ Overlayers

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO₃ Overlayers

Low-temperature catalytic oxidative coupling of methane in an electric field over a Ce–W–O catalyst system

Monoclinic superstructure in orthorhombic Ce₁₀W₂₂O₈₁from transmission electron microscopy

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Strontium and cerium tungstate materials SrWO4 and Ce2(WO4)3: Methane oxidation and mixed conduction

Cited by 30 publications

References 25 publications

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO3 Overlayers

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO3 Overlayers

Low-temperature catalytic oxidative coupling of methane in an electric field over a Ce–W–O catalyst system

Monoclinic superstructure in orthorhombic Ce10W22O81from transmission electron microscopy

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Insulator-to-Metal Transition at Oxide Interfaces Induced by WO₃ Overlayers

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO₃ Overlayers

Monoclinic superstructure in orthorhombic Ce₁₀W₂₂O₈₁from transmission electron microscopy