The two-fold 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 two-fold superstructure of the crystal structure at room temperature. Weak superlattice reflections could be measured with synchrotron radiation x-rays, and they were analysed by structure refinements employing superspace techniques. Both the low temperature and room temperature tructures of TiOBr are isostructural to the corresponding structures of TiOCl. The results indicate that at low temperatures TiOBr is in a spin-Peierls state similar to TiOCl, but with the modulations and relevant interactions smaller than in the latter compound.