Study of the structure, magnetic properties and free energy of the three phase composites La0.7−y−zSr0.3−xMn1−δ/3O3−δ/(La2O3)y/2/(La(OH)3)z

Abstract The structural and magnetic properties and the free energy of manganites with the nominal composition La 0.7 Sr 0.3− x MnO 3− δ (0 ≤  x  ≤ 0.10) have been investigated. X-ray diffraction patterns indicate that the materials possess three phases with the R 3 ¯ c perovskite being the dominant phase, La 2 O 3 being the second phase and La(OH) 3 being the third phase. Due to the samples were prepared using a solid-state reaction method with the highest heat treatment temperature being 1173 K, we assume that there were no vacancies in the perovskite phase. These materials can be represented as La 0.7− y − z Sr 0.3− x Mn 1− δ /3 O 3− δ /(La 2 O 3 ) y /2 /(La(OH) 3 ) z , with δ  = 3( x + y  +  z ). Magnetization measurements showed that the dependence of the Curie temperature T C on the Mn 4+ ion content, is similar to that of the typical perovskite manganite La 1− x Sr x MnO 3 . The paramagnetic–ferromagnetic transition region of the samples is wider than 315 K. We have also calculated the free energy of the perovskite phase, and explained successfully the dependences on the doping level x of the unit cell volume in the perovskite phase.