Phase separation induced by oxygen deficiency in La0.67Ca0.33MnO3 thin films

Epitaxial La0.67Ca0.33MnO3 thin films deposited on (001)- LaAlO3 under different oxygen partial pressures (PO2) from 50 mTorr to 500 mTorr are investigated. An oxygen-deficiency-activated phase separation is observed by X-ray diffraction (XRD), microstructure and temperature coefficient of resistance (TCR) studies. The transport properties are strongly related to the strain state of films. All films show phase separation behavior except for the film deposited at 50 mTorr at which most of the strain was relieved by serious crystal defects. The films deposited at 300 and 350 mTorr show insulating behavior in the whole temperature range, which is attributed to charge-ordered (CO) state and can be suppressed by applied field.