Structural-magnetic phase diagram of Mo-substituted CaMnO3: consequences for thermoelectric power properties

The substitution of molybdenum for manganese has been studied in the CaMn1-xMoxO3 series for 0less than or equal toxless than or equal to0.15. We establish a structural and magnetic diagram combining electron microscopy, neutron diffraction and magnetic susceptibility measurements. Four regions have been evidenced versus composition (x) and temperature. The transport properties and thermoelectric power have been analyzed on the basis of this diagram. The structural transition temperature, linked either to a monoclinic deformation characteristic for antiferromagnetism (AFM) with a C-type orbital polarization (0.07less than or equal toxless than or equal to0.12) or associated with ordered stripes (x>0.12), significantly increases with x. The fact that these orders develop at high temperatures (exceeding 300 K) is determined by two favourable parameters: the A-site cationic mismatch is zero and the magnetic order, linked with the orbital one, is not confronted with the magnetic sub-lattice of rare-earth ion. The great analogy of these materials with the Mn4+-rich manganites Sm1-xCaxMnO3 is discussed, referring to the injection of electrons in the (CaMnO3)-O-IV matrix.