Tetrahedral Cr4+ and Cr5+ in Bi12TiO20 single crystals

Cr-doped Bi12TiO20 (BTO) single crystals have been grown by the Czochralski technique. The optical absorption at 4.2 K of as-grown crystals is compared to that observed after vacuum annealing of the samples. This treatment modifies the visible and near infrared optical absorption. The absorption spectrum of Cr-doped BTO crystals before vacuum annealing is interpreted as the superposition of the crystal-field transition bands of (CrO4)4- and (CrO4)3- and charge transfer bands of (CrO4)3-. Annealing in vacuum leads to Cr5+ → Cr4+ conversion. Chromium reduction to lower oxidation states has not been observed. The optical absorption shows a vibrational character. The energy shifts of Cr4+ bands are as expected from the coupling with the T2(v3) fundamental mode of (CrO4)4- clusters. On the other hand, it is proposed that the series of sharp lines observed in the 9500 to 11500 cm-1 range arises from the interaction with a vibration of about 300 cm-1, which seems to be the T2(v4) fundamental mode of (CrO4)3- and with the lattice modes.Peer Reviewe

High electrorheological effect in Bi1.8Fe1.2SbO7 suspensions

We report on the first experimental evidence of the electrorheological effect in suspensions of superfin