Raman spectroscopy study of sillenites. II. Effect of doping on Raman spectra of Bi12TiO20

Atomistic origin of huge response functions at the morphotropic phase boundary of(1−x)Na0.5Bi0.5TiO3−xBa

“…The Raman scattering near 50 cm −1 of NBT-xBT is attributed to phonon modes localized in A-site cations [27] and again due to the mixed ionic-covalent character of Bi-O bonding versus the ionic type of Na-O and Ba-O interactions, it should be dominated by Bi vibrations. As expected, the wave number of this Raman scattering matches well that of Bi-localized modes in complex bismuth oxides [18,19] as well as of Pb-localized modes in perovskite-type relaxors and relaxor-ferroelectric solid solutions [15][16][17]. For all three compounds studied here, the Raman peak near 50 cm −1 persists at elevated temperatures (see Fig.…”

“…Bi 3+ is similar to Pb 2+ in mass and outermost electron shell and, therefore, Raman peaks generated by Bi-localized modes phonon modes (involving mainly Bi vibrations) in ABO 3 -type materials may appear near 50 cm −1 , like the phonon modes involving mainly Pb vibrations in Pb-based perovskite-type solid solutions [15][16][17] as well as like Bi-localized modes in complex bismuth oxides of other structure types [18,19]. Raman scattering near 50 cm −1 was indeed detected in pure NBT [20], but surprisingly, the majority of reported Raman spectroscopic studies of Bi-based perovskite-type ferroelectrics did not consider the important spectral range below 100 cm −1 [21][22][23][24][25][26].…”

Raman spectroscopy evidence of inhomogeneous disorder in the bismuth-oxygen framework of Bi25InO39and other sillenites

“…where one F mode is acoustic, all modes are Ramanactive (R) and only the F modes are IR-active (IR 18,20,22 give insight into the physical siginificance of the Raman modes. Table I shows the assignment of our spectra based on their calculations.…”

“…The ideal structure is held for the tetravalent cations M = Ge 4+ , Si 4+ , which is confirmed by neutron-scattering data on Bi 12 GeO 20 and Bi 12 SiO 20 that show a 100% occupancy of both tetrahedral and oxygen positions. 20,21 Bi 12 TiO 20 is another heavily studied compound and, stoichiometrically, it should have a 100% occupancy on the M and oxygen positions; however, its neutron-scattering data shows that the occupancy of the tetrahedral position is 0.9 while the O(3) position is 0.97, and the deficiency is explained by the higher ionic radii of Ti 4+ compared to Si 4+ and Ge 4+ . 20 For other valences the centers of the tetrahedra are shared with Bi 3+ to ensure charge balance.…”

“…20,21 Bi 12 TiO 20 is another heavily studied compound and, stoichiometrically, it should have a 100% occupancy on the M and oxygen positions; however, its neutron-scattering data shows that the occupancy of the tetrahedral position is 0.9 while the O(3) position is 0.97, and the deficiency is explained by the higher ionic radii of Ti 4+ compared to Si 4+ and Ge 4+ . 20 For other valences the centers of the tetrahedra are shared with Bi 3+ to ensure charge balance. For example, M 2+ cations occupy 1/3 of the M positions while Bi 3+ cations fill the rest.…”