Crystal structure and thermal expansion behavior of oxygen stoichiometric lanthanum strontium manganite at high temperature

In this study, the crystal structures and the thermal expansibilities of La_{1 - x}Sr_xMnO_{3 + δ} (LSM) with oxygen stoichiometric composition, δ = 0, were studied by an atmosphere and temperature controlled X-Ray diffractometer (XRD). Pre-heat-treatment conditions for the samples and oxygen partial pressures for XRD measurements at high temperature were carefully selected to keep oxygen stoichiometric composition. The crystal structures of La_{1 - x}Sr_xMnO₃ at room temperature were rhombohedral, tetragonal, and cubic symmetry for 0.2 ≤ x ≤ 0.45, 0.5 ≤ x ≤ 0.6, x = 0.7, respectively. The second order phase transition from rhombohedral to cubic symmetry was confirmed for x = 0.4 compound at 923-973 K. Meanwhile, the second order phase transition from tetragonal to cubic symmetry was confirmed for x = 0.5 compound at 623-673 K, x = 0.6 compound at 423-473 K, respectively. Furthermore, the pure thermal expansibilities of LSM without chemical expansion were discussed based on XRD analysis.