Structural and electrical properties of nonstoichiometric semiconducting pyrochlores in Ca–Ce–Ti–Nb–O system

Deepa, M.; Rao, P. Prabhakar; Sumi, S.; Radhakrishnan, A. N.; Chandran, M.R.; Koshy, Peter

doi:10.1016/j.matchemphys.2011.01.053

Cited by 16 publications

(3 citation statements)

References 22 publications

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“…One doublet (884.8 and 903.7 eV) is characterized by the presence on Ce 3+ state and corresponds to the Ce (3d 9 4f 1 )O(2p 6 ) state [21]. The other doublet (881.4 eV and 899.4 eV) corresponds to Ce (3d 9 4f 2 )O(2p 5 ) state and is a shakedown feature involving electron transfer from a filled O2p orbital to a Ce 4f orbital during photoemission from Ce 3+ cations [23,27]. The XPS results indicate the existence of both Ce 3+ and Ce 4+ cations in the quenched CeNbO 4 sample.…”

Section: Methodsmentioning

confidence: 99%

Synthesis and characterization of mixed conductor CeNbO4

Zhang

Wan

Long

et al. 2014

Journal of Alloys and Compounds

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Section: Methodsmentioning

confidence: 99%

Synthesis and characterization of mixed conductor CeNbO4

Zhang

Wan

Long

et al. 2014

Journal of Alloys and Compounds

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“…Oxides with the pyrochlore structure have been the subject of a number of investigations in the last few decades and exhibit diverse properties such as semiconductivity, , ionic conductivity, , superconductivity, , high radiation tolerance, dielectric properties, and luminescence properties . Pyrochlore oxides have the general formula A 2 B 2 O 7 , where A is the larger cation and B is the smaller one.…”

Section: Introductionmentioning

confidence: 99%

Role of Bond Strength on the Lattice Thermal Expansion and Oxide Ion Conductivity in Quaternary Pyrochlore Solid Solutions

et al. 2012

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Quaternary pyrochlore-type solid solutions, CaGdZrNb(1-x)Ta(x)O(7) (x = 0, 0.2, 0.4, 0.6, 0.8, 1), were prepared by a high-temperature ceramic route. The pyrochlore phases of the compounds were confirmed by powder X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy. The crystallographic parameters of the pyrochlore compounds were accurately determined by Rietveld analysis of the powder XRD data. The isovalent substitution of Ta in place of Nb at the B site can reveal the effect of chemical bonding on lattice thermal expansion and oxide ion conductivity because both Nb and Ta have the same ionic radius (0.64 Å). Lattice thermal expansion coefficients of the samples were calculated from high-temperature XRD measurements, and it was found that the thermal expansion coefficient decreases with substitution of Ta. Oxide ion conductivity measured by a two-probe method also shows the same trend with substitution of Ta, and this can be attributed to the high bond strength of the Ta-O bond compared to that of the Nb-O bond. Microstructural characterization using scanning electron microscopy proves that the size of the grains has a small effect on the oxide ion conductivity. Our studies established the role of chemical bonding in deciding the conductivity of pyrochlore oxides and confirmed that the 48f-48f mechanism of oxide ion conduction is dominant in pyrochlore oxides.

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“…When the rare earth metals in the pyrochlores were replaced by cerium, the color of the compounds changed to gray or black, depending on cerium concentration, and the compounds exhibited semiconductor behavior [12][13][14]. Deepa et al [15] showed using X ray photoelec tron spectroscopy (XPS) that the cerium in CaCe x TiNbO 7 -δ (x = 0.5-1) pyrochlore solid solu tions prepared by reacting an oxide mixture in air was in the oxidation state 3+, atypical of it.…”

Section: Introductionmentioning

confidence: 99%