X-RAY-DIFFRACTION STUDY OF INPLANE AND INTERLAYER CORRELATIONS IN LAYERED COMPOUNDS AGXTIS2

X-ray measurements have been performed on the development on in-plane and interplanar correlations of intercalated Ag atoms in stage-2 and -1 Ag(x)TiS2 single crystals. The abrupt change of the c-axis parameter for stage-2 Ag0.15TiS2 at around 250 K, due to the structural transformation of the stacking sequence, was observed, although the a-axis parameter changes continuously. Rodlike diffuse scattering parallel to c* at 1/3 1/3.O, 2/3 2/3.O, and their equivalent positions is observed for stage-2 Ag0.15TiS2 above 250 K and shows the two-dimensional (2D) feature of the disordered state. Such a diffuse rod is modulated below 250 K, with maxima appearing at every half-integer. This reveals an enhancement of the three-dimensional nature and a stacking sequence alpha-beta-alpha-beta.... By analyzing rodlike diffuse scattering at 350, 300, 280, and 250 K for stage-2 Ag0.15TiS2, the 2D short-range-order parameters were determined. By comparing the 2D short-range-order parameters with the 2D Ornstein-Zernike correlation function, it was obtained that the correlation length varies from 4.1 +/- 0.6 angstrom at 350 K to 37.1 +/- 1.6 angstrom at 250 K. These results can be interpreted with the use of the Daumas-Herold island model. On the other hand, for stage-1 Ag(x)TiS2, the modulation of the diffuse rod parallel to the c* axis at 1/3 1/3.O, 2/3 2/3.O, and their equivalent positions was observed at room temperature, which shows the 3D nature.