Cosubstitution effect on the magnetic, transport, and thermoelectric properties of the electron-doped perovskite manganite CaMnO3

We have investigated magnetic, transport, and thermoelecric properties of polycrystalline Ca1-xSrxMn1-yMoyO3, and have tried to optimize the n-type thermoelectric response below room temperature. The Sr substitution enlarges a Mn-O-Mn bond angle and increases a crystal symmetry, which enhances one electron transfer of the electrons doped by the Mo substitution. This effect promotes the competition between correlations of a G-type antiferromagnetic (AF) order and a C-type AF order accompanying a 3d(3z2-r2) orbital order, leading to the more complicated magnetic phase diagram of Ca0.75Sr0.25Mn1-yMoyO3 than that of CaMn1-yMoyO3. A subtle balance between the effects of the enhanced one electron transfer and the introduced disorder into the A(Ca)-site upon the transport properties enhances a dimensionless thermoelectric figure-of-merit ZT up to 0.03 at room temperature. However, a correlation of the 3d(3z2-r2) orbital order is also promoted by the Sr substitution, which bounds a further enhancement of ZT. (C) 2010 American Institute of Physics. [doi:10.1063/1.3505756]