title: Theoretical and Experimental Study of the Crystal Structures, Lattice Vibrations, and Band Structures of Monazite-Type PbCrO4, PbSeO4, SrCrO4, and SrSeO4.
abstract: 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.
authors.affiliation: †Departamento de Física Aplicada, ICMUV, MALTA Consolider Team, Edificio de Investigación, Universidad de Valencia, C. Dr. Moliner 50, 46100 Burjassot, Spain.
authors.forename: Daniel
authors.initials: D
authors.lastname: Errandonea
authors.affiliation: ‡Departamento Física, Malta Consolider Team, and Instituto de Materiales y Nanotecnología, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain.
authors.forename: Alfonso
authors.initials: A
authors.lastname: Muñoz
authors.affiliation: ‡Departamento Física, Malta Consolider Team, and Instituto de Materiales y Nanotecnología, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain.
authors.forename: Placida
authors.initials: P
authors.lastname: Rodríguez-Hernández
authors.affiliation: §Joule Physics Laboratory, University of Salford, Manchester M5 4WT, U.K.
authors.forename: John E
authors.initials: JE
authors.lastname: Proctor
authors.affiliation: ⊥Institut de Ciencia dels Materials (ICMUV), Universitat de Valencia, C/Catedrático José Beltrán 2, 46890 Paterna, Spain.
authors.forename: Fernando
authors.initials: F
authors.lastname: Sapiña
authors.affiliation: ∥Luminescent Materials Laboratory, Department of Biotechnology, University of Verona and INSTM, UdR Verona, Strada Le Gracie 15, 37134 Verona, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Bettinelli
mesh_terms: D002840:Chromates / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004583:Electrons; D007854:Lead / Q000737:chemistry*; D008674:Metals, Rare Earth / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory; D064586:Selenic Acid / Q000737:chemistry*; D013324:Strontium / Q000737:chemistry*; D014732:Vibration
chemical_list: D002840:Chromates; D008674:Metals, Rare Earth; C015370:monazite; D007854:Lead; C048629:strontium chromate; C031895:lead chromate; D064586:Selenic Acid; D013324:Strontium