Ordering of oxygen vacancies and magnetic properties in La0.5Ca0.5MnO3-δ (0≤δ≤0.5)

The study by electron diffraction and high resolution electron microscopy of several samples of the system La0.5Ca0.5MnO3-delta, apart from strikingly confirming the correctness of the orthorhombic perovskite-related unit cell of a approximate to a(c)root 2, b approximate to a(c)root 2, c approximate to 2a(c) for 0 less than or equal to delta less than or equal to 0.25, points to the existence of three dimensional multitwinning which gives rise to an apparently double cubic cell. For delta=0.5, the ordering of the anionic vacancies leads to a new material isostructural to Sr2FeO5 and unit cell a = 5.361(3), b = 16.463(9), c = 5.340(3) Angstrom, space group Ibm2. The magnetic characterization of the three compositions has been carried out and related to the structure. (C) 1999 Academic Press.