Charge- and orbital ordering in LaSr2Mn2O7 examined by HRTEM and low-temperature electron diffraction

New layered manganite LaSr2Mn2O7 is prepared, and examined by HRTEM and by low-temperature electron diffraction to examine the possibility of charge and orbital-ordered states occuring below 200K. The crystal structure of this layered manganites is almost perfect and no planar or intergrowth defects has been detected by HRTEM. At low temperature of 200K-110K, hkO electron diffraction patterns clearly exhibit the appearances of characteristic super-reflection spots along the a*+b* direction. The superstructure is interpreted in terms of the Mn3+/Mn4+ charge-ordering, associated with d(z)(2) orbital-ordering to induce Jahn-Teller distortion around the Mn3+ ions.