Electron diffraction study of La2Li0.5Cu0.5O4

La2Li0.5Cu0.5O4 has been investigated by electron diffraction and high reso lution electron microscopy at room temperature. Ordering between Li and Cu cations is nearly perfect within the (a, c) plane but there is disorder bet ween Cu and Li cations along the b axis. The detection nf weak reflections which violate the C centering of the Cmmm space group (initially proposed [ 1] for this compound), indicates that the crystal symmetry allows lattice d istortions. The evolution of the structure as a function of the temperature may lead to the determination of whether the low energy singlet-triplet ex citation, found in NMR/NQR studies, is coupled with lattice distortions. (C ) 1998 Elsevier Science Ltd. All rights reserved.