Stability field and structural properties of intra-rare earth perovskites

A stability study of perovskitic LaREO(3) oxides (RE = Dy, Ho, Er, Tm, Yb, Lu) as a function of temperature was undertaken. A correlation between the Goldschmidt t value and the perovskitic stability field amplitude was found: the latter widens as t increases. Magnetic measurements, performed on all the perovskitic samples, showed that t is also related to the exchange interactions. LaREO(3) oxides were synthesized by thermal decomposition of the corresponding coprecipitated oxalates at temperatures ranging between 600 and 1800 degrees C. Simultaneous differential thermal and thermogravimetric analyses showed that all the La-RE mixed oxalates decompose similarly. All the oxides, except LaDyO(3), crystallize in the perovskitic form in a temperature range that depends on the ionic size difference between La and the smaller rare earth; above and below the perovskitic stability field, the B or C form, typical of rare earth sesquioxides, is present. Rietveld refinements, carried out on all the LaREO(3) samples synthesized at 1200 degrees C, showed the occurrence of an orthorhombic distorted perovskitic structure belonging to the Prima space group. (C) 2010 Published by Elsevier B.V.