EFFECT OF OXYGEN-CONTENT ON THE ANOMALIES AT SUCCESSIVE PHASE-TRANSITIONS OF LA2CUO4-CRYSTAL BELOW 320 K(DELTA SINGLE)

A detailed study of electronic and thermal transport properties and li near thermal expansion of La2CuO4+delta single crystals with both high oxygen pressure oxidation and electrochemical oxidation were carried out. A series of anomalies of resistivity, thermoelectric power, and l inear thermal expansion have been observed at three successive phase t ransitions below room temperature in samples with 0<delta less than or equal to 0.035. These anomalies are gradually depressed with delta>0. 035, achieved by the electrochemical oxidation, and nearly disappear a fter electrochemical oxidation for 40 days.