Variation of charge/orbital ordering in layered manganite Pr1-xCa1+xMnO4 investigated by transmission electron microscopy

Structural features of the charge/orbital ordering (CO/OO) in single-layered manganites Pr1-xCa1+xMnO4 (0.3 <= x <= 0.65) have been investigated systematically by transmission electron microscopy. Analyses of electron-diffraction patterns as well as dark-field images have revealed that the CO/OO shows a striking asymmetric behavior as the hole doping x deviates from x=0.5. The modulation wave number linearly decreases with increasing x in the over-hole-doped (x > 0.5) crystals, while much less dependent on x in the under-hole-doped (x < 0.5) crystals. A temperature-induced incommensurate-commensurate crossover is observed in 0.35 < x < 0.5 and x=0.65. The correlation length of CO/OO in x=0.3 was proven to become shorter than that in 0.35 <= x <= 0.65.