Characterization of the Structural, Optical, and Dielectric Properties of Oxynitride Perovskites AMO2N (A = Ba, Sr, Ca; M = Ta, Nb)
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- 作者：Young-Il Kim ; Patrick M. Woodward ; Karim Z. Baba-Kishi ; and Cheuk W. Tai
- 刊名：Chemistry of Materials
- 出版年：2004
- 出版时间：April 6, 2004
- 年：2004
- 卷：16
- 期：7
- 页码：1267 - 1276
- 全文大小：185K
- 年卷期：v.16,no.7(April 6, 2004)
- ISSN：1520-5002
文摘
The syntheses, crystal structures, electrical properties, and optical absorbance spectra ofsix perovskite oxynitrides, AMO2N (A = Ba, Sr, Ca; M = Ta, Nb) have been investigated.The average crystal structure of BaTaO2N is a cubic perovskite, with a Ta-O/N distance of2.056 Å. SrTaO2N and CaTaO2N are distorted by octahedral tilting, showing noticeablysmaller Ta-O/N distances of approximately 2.02 Å. Electron diffraction studies of BaTaO2Nare consistent with the simple cubic perovskite crystal structure determined using X-raypowder diffraction methods. Each of the niobium oxynitrides is isostructural with its tantalumanalogue, though the Nb-O/N distances are observed to be slightly longer. The optical bandgaps are estimated from diffuse reflectance spectra as follows: BaTaO2N, 1.8 eV; SrTaO2N,2.1 eV; CaTaO2N, 2.4 eV; BaNbO2N, 1.8 eV; SrNbO2N, 1.9 eV; CaNbO2N, 2.1 eV. Impedancespectroscopy was carried out on sintered pellets of the ATaO2N and BaNbO2N to investigatethe dielectric and electrical transport properties. The BaNbO2N sample shows metallic-typeconductivity apparently from a slight reduction that occurs during sintering. In contrast,the tantalum compounds are semiconductors/insulators with conductivities of ~10-5 S/cm(A = Ba, Sr) and ~10-8 S/cm (A = Ca). Interpretation of the impedance data for BaTaO2Nand SrTaO2N reveals that these two compounds have unexpectedly high bulk dielectricconstants, 
4900 and 2900, respectively, at room temperature. The dielectric constantsof both compounds are frequency dependent and show a relatively weak linear dependenceupon temperature with no sign of a phase transition over the temperature range 300-180K.
4900 and 2900, respectively, at room temperature. The dielectric constantsof both compounds are frequency dependent and show a relatively weak linear dependenceupon temperature with no sign of a phase transition over the temperature range 300-180K.