Theoretical and Experimental Study of the Crystal Structures, Lattice Vibrations, and Band Structures of Monazite-Type PbCrO4, PbSeO4, SrCrO4, and SrSeO4

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• 作者：Daniel Errandonea ; Alfonso Mu帽oz ; Placida Rodr铆guez-Hern谩ndez ; John E. Proctor ; Fernando Sapi帽a ; Marco Bettinelli
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：August 3, 2015
• 年：2015
• 卷：54
• 期：15
• 页码：7524-7535
• 全文大小：656K
• ISSN：1520-510X

文摘

The crystal structures, lattice vibrations, and electronic band structures of PbCrO₄, PbSeO₄, SrCrO₄, and SrSeO₄ were studied by ab initio calculations, Raman spectroscopy, X-ray diffraction, and optical-absorption measurements. Calculations properly describe the crystal structures of the four compounds, which are isomorphic to the monazite structure and were confirmed by X-ray diffraction. Information is also obtained on the Raman- and IR-active phonons, with all of the vibrational modes assigned. In addition, the band structures and electronic densities of states of the four compounds were determined. All are indirect-gap semiconductors. In particular, chromates are found to have band gaps smaller than 2.5 eV and selenates higher than 4.3 eV. In the chromates (selenates), the upper part of the valence band is dominated by O 2p states and the lower part of the conduction band is composed primarily of electronic states associated with the Cr 3d and O 2p (Se 4s and O 2p) states. Calculations also show that the band gap of PbCrO₄ (PbSeO₄) is smaller than the band gap of SrCrO₄ (SrSeO₄). This phenomenon is caused by Pb states, which, to some extent, also contribute to the top of the valence band and the bottom of the conduction band. The agreement between experiments and calculations is quite good; however, the band gaps are underestimated by calculations, with the exception of the bang gap of SrCrO₄, for which theory and calculations agree. Calculations also provide predictions of the bulk modulus of the studied compounds.