Experimental confirmation of Zener-polaron-type charge and orbital ordering in Pr1−xCaxMnO3

Pr{sub 1-x}Ca{sub x}MnO{sub 3} in the doping range between 0.3<x<0.5 represent an extremely interesting manganite system for the study of the interplay of different kinds of ordering (charge, orbital, lattice, and spin). While there is consensus that a charge- and orbital-ordered state develops below a transition temperature T{sub co}{approx_equal}230 K, recent controversial structural refinements resulting from neutron and x-ray diffraction studies challenged our understanding of the particular type of charge ordering (CO) and orbital ordering (OO), and consequently, the underlying mechanism of the colossal resistance effects. Here, we present a detailed high-resolution transmission electron microscopy and electron-diffraction study that, based on extinction rules, resolves the current controversy and confirms the existence of the Zener-polaron (ZP)-type CO and/or OO in Pr{sub 1-x}Ca{sub x}MnO{sub 3}. The ZP-type ordering is further verified by atomic-column-resolved electron energy-loss spectroscopy revealing strong charge ordering of the in-plane oxygen-Mn bonds, while valence disproportionation at the Mn sites is less than expected. Over wide doping and temperature ranges, we observed structural phase coexistence between the ZP-CO/OO P2{sub 1}nm and the disordered Pbnm structure.

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