Transmission electron microscopy study of Y1-x square xCr2S4, x similar to1/3 phase

A preliminary transmission electron microscopy study of the YCr3S6 phase ha s been performed. The compound crystallises with an orthorhombic average st ructure, space group Pmnb, a = 3.385 (2) Angstrom, b = 10.847 (3) Angstrom, c = 12.701 (3) Angstrom. The average crystal structure can be related to t he CaFe2O4-type. In addition, the electron diffraction patterns show a thre e-fold superstructure along the a axis due to an ordered occupancy of the t rigonal prismatic environment position by the yttrium atoms. In some cases it has been found that the modulation is slightly incommensurate. The prese nce of disorder giving rise to layers of diffuse intensity perpendicular to a* is related to the electron beam interaction as well as changes in the p hase of the structure modulation. (C) 2001 Elsevier Science B.V. All rights reserved.