Symmetry of LaAlO3 nanocrystals as a function of crystallite size

Properties of LaAlO3 nanocrystallites obtained by the precipitation method, doped with praseodymium and chromium ions were examined by spectroscopic means. Raman spectroscopy, high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and electronic spectroscopy proved that symmetry of LaAlO3 crystallites depends on their size. At room temperature the smallest obtained crystals (average size ∼5 nm) have cubic symmetry, while the largest ones (average size over 110 nm) exhibit rhombohedral symmetry. Possible explanations for this phenomenon are discussed.