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J. Korean Ceram. Soc. > Volume 57(4); 2020 > Article
Journal of the Korean Ceramic Society 2020;57(4): 432-439.
doi: https://doi.org/10.1007/s43207-020-00041-0
Syntheses and characterizations of complex perovskite oxynitrides (Ca, Sr, Ba)TaO2N
Jae Won Seol1, Young‑Il Kim1 , Thuy Linh Pham2, Jong‑Sook Lee2
1Department of Chemistry, Yeungnam University, Gyeongsan 38541, Republic of Korea
2School of Materials Science and Engineering, Chonnam National University, Gwangju 61186, Republic of Korea
Correspondence  Young‑Il Kim ,Email: yikim@ynu.ac.kr
Jong‑Sook Lee ,Email: jongsook@jnu.ac.kr
Received: January 31, 2020; Revised: March 3, 2020   Accepted: March 17, 2020.  Published online: April 30, 2020.
ABSTRACT
The syntheses, crystal structures, thermal decomposition, and optical absorbance spectra of the tantalum-based complex perovskite oxynitrides Ca1/2Sr1/2TaO2N, Sr1/ 2Ba1/2TaO2N, and Ca1/3Sr1/3Ba1/3TaO2N were investigated. Synchrotron X-ray Rietveld refinement showed that Ca1/2Sr1/2TaO2N, Sr1/2Ba1/2TaO2N, and Ca1/3Sr1/3Ba1/3TaO2N were tetragonal, cubic, and orthorhombic, respectively. Additionally, the lattice volume and Ta − O/N bond lengths varied in accordance with the mean ionic radius of the A-site cations. As determined using thermogravimetry and differential scanning calorimetry, the above complex perovskite oxynitrides underwent a two-step thermal decomposition consisting of O2- uptake at 800–900 K with ΔH = − 2620 to − 2400 kJ/mol and the N2 release at 1300–1450 K with ΔH = − 45 to −66 kJ/mol. The optical band gaps were estimated from diffuse reflectance spectra as follows: Ca1/2Sr1/2TaO2N (light orange), 2.35 eV; Ca1/3Sr1/3Ba1/3TaO2N (light brown), 2.0 eV; Sr1/2Ba1/2TaO2N (red brown), 1.95 eV.
Key words: Complex perovskite · Oxynitride · Thermal analysis · Color coordinate
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