Structural transitions in the manganite Pr0.5Sr0.5MnO3

The structural transitions in the Pr0.5Sr0.5MnO3 CMR perovskite have been studied, coupling neutron powder diffraction (NPD) and electron microscopy (EM) techniques. Both techniques show the existence of a Fmmm type structure at low temperature (T < 135 K) that corresponds to the antiferromagnetic insulating (AFMI) state. No evidence of charge ordering is observed. At 135 K a transition to a ferromagnetic I4/mcm structure is observed by NPD. Further increasing the temperature (T greater than or equal to 265 K), Pr0.5Sr0.5MnO3 becomes paramagnetic but keeps its I4/mcm structure. By EM, the transition occurring around 135 K is also observed, but it corresponds to a change from the Fmmm to an Imam structure, with a simultaneous disappearance of the twinning domains present in the Fmmm structure. This effect is reversible. The EM study also evidences that at high temperature (T similar to 430 K) another transition from the Imam to an I4/mcm structure occurs. The divergence between the NPD and EM observations is attributed to the fact that the structure of Pr0.5Sr0.5MnO3 may be sensitive to the magnetic field that exists in the electron microscope (1 or 2 T). (C) 1998 Elsevier Science B.V. All rights reserved.