Solving modulated structures by X-ray and electron crystallography

X-ray diffraction can be used for accurately determining not only classical , ordinary structures, but also modulated ones. For structures with weak mo dulations, the modulation induced satellite reflections are often hard to b e observed by X-ray diffraction, but they appear clearly in electron diffra ction. In these cases, X-ray diffraction will give only average structures whereas electron diffraction will yield information about the modulations. Sr1.4Ta0.6O2.9 is a complex modulated compound with weak modulation and sma ll modulated domains. Here we demonstrate the power of combining X-ray and electron crystallography for studying modulated structures on powders. The modulations of Sr1.4Ta0.6O2.9 were determined from electron diffraction (SA ED) and high resolution electron microscopy (HREM) images. With specially d eveloped image processing techniques, the weak modulations were enhanced, f acilitating the interpretation of HREM images in terms of atomic structure. (C) 2001 Elsevier Science Ltd. All rights reserved.