Electronic structure and Raman spectroscopy study of dibarium magnesium orthoborate, Ba2Mg(BO3)2

Abstract

The samples of dibarium magnesium orthoborate Ba2Mg(BO3)2 were synthesized by solid-state reaction. The X-ray diffraction (XRD) patterns and Raman spectra of the samples were collected. Electronic structure and vibrational spectroscopy of Ba2Mg(BO3)2 were systematically investigated by first principle calculation. A direct band gap of 4.4eV was obtained from the calculated electronic structure results. The top valence band is constructed from O 2p states and the low conduction band mainly consists of Ba 5d states. Raman spectra for Ba2Mg(BO3)2 polycrystalline were obtained at ambient temperature. The factor group analysis results show the total lattice modes are 5Eu+4A2u+5Eg+4A1g+1A2g+1A1u, of which 5Eg+4A1g are Raman-active. Furthermore, we obtained the Raman active vibrational modes as well as their eigenfrequencies using first-principle calculation. With the assistance of the first-principle calculation and factor group analysis results, Raman bands of Ba2Mg(BO3)2 were assigned as Eg (42cm−1), A1g (85cm−1), Eg (156cm−1), Eg (237cm−1), A1g (286cm−1), Eg (564cm−1), A1g (761cm−1), A1g (909cm−1), Eg (1165cm−1). The strongest band at 928cm−1 in the experimental spectrum is assigned to totally symmetric stretching mode of the BO3 units.