The twofold superstructure of titanium(III) oxybromide at T = 17.5 K.

The low-temperature (T = 17.5 K) structure of titanium(III) oxybromide, TiOBr, is reported as a twofold superstructure of the crystal structure at room temperature. Weak superlattice reflections were measured with synchrotron radiation X-rays and were analyzed by structure refinements employing superspace techniques. Both the low-temperature and the room-temperature structures of TiOBr are isostructural with the corresponding structures of TiOCl. The results indicate that at low temperatures TiOBr is in a spin-Peierls state, similar to that of TiOCl, but with the modulations and relevant interactions smaller than in the latter compound.