Evidence of the Bi3+ lone-pair effect on the charge-ordering state:: resistivity and thermoelectric power of Bi0.5-yLaySr0.5MnO3 (0.0 ≤ y ≤ 0.4)

Polycrystalline samples of Bi0.5-gamma La gamma Sr0.5MnO3 (0.0 <= gamma <= 0.4) (BLSMO) have been synthesized to investigate the Bi3+ lone-pair effect on the long-range charge-ordering (CO) state. Since the ionic size of La3+ is similar to that of Bi3+ and the Mn valence state does not change with La doping, we obtained the Bi lone-pair effect on the CO state without disturbance by other effects. The resistivity rho(T) and thermoelectric power S(T) of BLSMO have been measured. A hysteretic behaviour was observed in both rho(T) and S(T) for gamma = 0.1 and 0.2. From the onset of the hysteretic behaviour, we defined a charge-ordering temperature (T-CO) and compared it to that of Bi1-xSrxMnO3 (BSMO). Finally, we found that the Bi3+ lone pairs play an important role in the anomalously high T-CO in BSMO.