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Tetrahedral Cr 4+ and Cr 5+ in Bi 12 TiO 20 Single Crystals
Author(s) -
Egorysheva A. V.,
Volkov V. V.,
Coya C.,
Zaldo C.
Publication year - 1998
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/(sici)1521-3951(199805)207:1<283::aid-pssb283>3.0.co;2-m
Subject(s) - annealing (glass) , absorption spectroscopy , materials science , doping , infrared , infrared spectroscopy , single crystal , crystal (programming language) , molecular physics , atomic physics , condensed matter physics , optics , chemistry , crystallography , optoelectronics , physics , metallurgy , programming language , organic chemistry , computer science
Cr‐doped Bi 12 TiO 20 (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 (CrO 4 ) 4— and (CrO 4 ) 3— and charge transfer bands of (CrO 4 ) 3— . Annealing in vacuum leads to Cr 5+ → Cr 4+ conversion. Chromium reduction to lower oxidation states has not been observed. The optical absorption shows a vibrational character. The energy shifts of Cr 4+ bands are as expected from the coupling with the T 2 (ν 3 ) fundamental mode of (CrO 4 ) 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 T 2 (ν 4 ) fundamental mode of (CrO 4 ) 3— and with the lattice modes.