Phase transitions induced on hexagonal manganites by the incorporation of aliovalent cations on A or B lattice sites

The phase transition to perovskite-type structure, that occurs in some hexagonal manganites when foreign cations are incorporated into solid solution, has been studied. Several solid solution series belonging to the Y(Mn, Ni)O-3, (Er, Ca)MnO3, (Y, Ca)MnO3, systems have been prepared by solid state reaction between the corresponding oxides. The crystalline structure of the different solid solutions has been established. The behaviour of the (Gd, Ca)MnO3 system has been taken as a reference. The obtained results are discussed as a function of the tolerance factor and the Mn3+/Mn4+ ratio. The transition to perovskite structure is governed by this Mn3+/Mn4+ ratio rather than the increase of the tolerance factor.