We have investigated the charge ordering phenomenon from the temperature dependence of inverse susceptibility, resistivity, and thermoelectric power (TEP) for Bi<sub>1-x</sub>Sr<sub>x</sub>MnO<sub>3</sub> (BSMO) from 300 K to 700 K. At high temperatures, susceptibility follows Curie-Weiss law. The resistivity data indicate insulating behavior of BSMO. TEP (<i>S</i>(T)) value is negative and weakly temperature-dependent in the high temperature regime. The slope of TEP changes dramatically near the charge ordering temperature (<i>Τ<sub>CO</sub></i>), indicating an increase of energy gap due to the charge ordering. In the vicinity of <i>Τ<sub>CO</sub></i>, 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. From this hysteretic behavior, we estimated <i>Τ<sub>CO</sub></i>. As Sr concentration increases, <i>Τ<sub>CO</sub></i> shifts to lower temperature from <i>Τ<sub>CO</sub></i> ~ 490 K for <i>x</i> = 0.45 to <i>Τ<sub>CO</sub></i> ~ 435 K for <i>x</i> = 0.8, and the thermal hysteretic behavior becomes less pronounced. The electrical transport properties have been discussed in terms of carrier localization due to charge ordering transition accompanied by the local lattice distortions.
The lattice effects on the magnetic and transport properties in La<sub>0.67-x</sub>Gd<sub>x</sub>Sr<sub>0.33</sub>CoO<sub>3</sub> series are studied. The introduction of smaller Gd<sup>3+</sup> ions leads to an enhanced mismatch between the La-O layer and the CoO<sub>2</sub> layer and a decrease of the tolerance factor <i>t</i>. The spin-state of trivalent Co ion transits to low-spin state with the decrease of Co-O bond length. The doping of Gd<sup>3+</sup> drives the system from the cluster-glass state to the spin-glass state and progressively decreases the Curie temperature. At high Gd<sup>3+</sup> doping content, an interesting negative
magnetoresistance occurs at low temperature.