Neutron and X-ray diffraction studies of a powder sample of the high-temperature superconductor Hg0.8Tl0.2Ba2Ca2Cu3O8+delta have been performed in the temperature ranges 300-4.5 and 300-80K, respectively, to investigate a structural anomaly at similar to 138 K. We have found that this anomaly is connected to a distortion of the CuO2-layers. The X-ray intensity and wavelength influence have been investigated and a conclusion about a possible photo-domain effect is made. (C) 2000 Elsevier Science B.V. All rights reserved.</p
