A NEW MONOCLINIC PEROVSKITE ALLOTYPE IN PR0.6SR0.4MNO3

We report the observation, in PT0.6Sr0.4MnO3, of a low-temperature pha se transition between Pnma and the monoclinic space group I2/a. The I2 /a allotype has never previously been observed in the (R(1-x)A(x))MnO3 manganese perovskite system. Furthermore, this space group symmetry i s not present in the recently published phase diagram obtained at 30% Mn+4, indicating that electronic doping has a direct effect on the pha se stability. The structural and magnetic parameters for the new phase , as obtained from Rietveld refinements of neutron powder diffraction data, are also reported. (C) 1996 Academic Press.