Analyses of Superstructure of Layered Perovskite Manganites in Charge/Orbital Ordering State by Low-Temperature TEM

The variation of the superstructure related to the charge/orbital ordering in layered manganites RE0.5 (Ca1-ySry) 1.5MnO4 (RE = Pr or Eu) has been systematically investigated by lowtemperature transmission electron microscopy (TEM), It is found that the superstructure is collapsed as increasing (1) the average ionic radius (rA) of A-site cations or enhancing (2) the quenched disorder by the substituting Sr for Ca. The results indicate that the electronic phase of the single layered manganites is controlled not only by the average ionic radius of A-site, but also by the quenched disorder ascribed as the variance in A-site ionic radii (σ2 = Σixiri2-rA2) .