Phase Transition Induced by High Pressure in a New LaBaCuGaO5 Compound

The structure of a new LaBaCuGaO5 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.