High temperature charge ordering in Bi1-xSrxMnO 3 (0.45 ≤ x ≤ 0.8)

We have investigated the charge ordering transition from the temperature dependence of inverse susceptibility, resistivity, and thermoelectric power (TEP) for Bi_1-xSr_xMnO₃ (BSMO) from 300 K to 700 K. At high temperatures, susceptibility and resistivity follow a Curie-Weiss law and variable range hopping behavior, respectively. TEP (S(T)) value is negative and weakly temperature-dependent in the high temperature regime. The slope of S(T) changes dramatically near the charge ordering temperature (TCO), indicating an increase of energy gap due to the charge ordering. In the vicinity of TCO, thermal hysteresis is observed in TEP data as well as in the resistivity data, which is consistent with the nature of the martensitic transition of the charge ordering phenomena. As Sr concentration increases, TCO shifts to lower temperature from TCO∼490 K for x=0.45 to TCO∼435 K for x=0.8, and the thermal hysteretic behavior becomes less pronounced. The electrical transport properties have been discussed in terms of carrier localization accompanied by the local lattice distortions due to Bi³⁺ lone pairs. © 2005 Elsevier B.V. All rights reserved.