Phase transition induced by high pressure in a new LaBaCuGaO5 compound

The structure of a new LaBaCuCaO5 material has been elucidated by means of X-ray diffraction (XRD), selected-area electron diffraction (SAED), and high-resolution transmission electron microscopy (HRTEM), This oxide shows the brownmillerite-type structure, built-up of alternating octahedral and tetrahedral layers sharing corners with space group Ima2 and lattice parameters a = 1.6707 nm, b = 0.5511 nm, and c = 0.5485 nm, The presence of some structural disorder at the equatorial oxygen is discussed. When this material is treated under high pressure a phase transition takes place. Although X-ray diffraction data suggest an average cubic perovskite structure, electron diffraction and microscopy show the presence of perpendicular microdomains constituted by the intergrowth of some perovskite-related superstructures. Paramagnetic behavior is observed in all cases, (C) 2000 Academic Press.