Transport, magnetic, and structural properties of La1-xMxMnO3 (M=Ba, Sr, Ca) for 0≤x≤0.20 -: art. no. 014422

At high temperatures both the resistivity (rho) and thermopower of La1-xMxMnO3 (M=Ba, Sr, Ca) single crystals can be described well by a small-polaron hopping model. The polaron binding energy decreases while the orbital ordering transition (T-JT) to a state with a static Jahn-Teller distortion increases as the ionic size of M reduces from Ba to Ca. With doping (x), T-JT decreases and Curie temperature T-C increases. Orthorhombic to rhombohedral transition (T-OR) decreases almost linearly with x up to 0.125 and 0.20 for Ba- and Sr-doped samples, respectively. For Ca-doped system, T-OR decreases at a much slower rate with x. Unlike Sr-doped sample, both Ca- and Ba-doped systems do not show large drop in rho at T-C followed by an abrupt increase below T-C for x=1/8 doping. Both distortion and disorder due to the difference in size between La and M affect transport, magnetic, and structural properties of manganites. A phase diagram has been constructed from this study.