X-ray study of the incommensurate phase of TlInS2

The successive structural phase transitions in the layer compound TllnS(2) have been studied using single-crystal x-ray diffraction. The intermediate phase between 194 K and 214 K is found to be incommensurate; the satellite maps show that the modulation mode which characterizes the intermediate pha se has q(i) = (delta, 0, 0.25) (delta approximate to 0.044). It is shown th at the previously reported satellite reflections at q = (delta, delta, 0.25 ) are ascribable to twins. A structure model is presented for the incommens urate phase. In the low-temperature phase below 197 K, the satellite reflec tions are shifted to a commensurate position, q(c) = (0, 0, 0.25).