Oxygen Content and Structures of La1−xCaxMnO3+d as a Function of Synthesis Conditions

Using thermogravimetric analysis measurements, oxygen content was measured for La1−xCaxMnO3+d (0≤x≤0.38) samples prepared at high oxygen pressure. The oxygen content was found to decrease uniformly with increasing x for samples annealed at 12 and 140 atm O2 at 800°C, slowly cooled in 1, 20, and 100% O2, as well as for samples in thermal equilibrium at high temperatures of ∼1000–1400°C. Annealing at a specific temperature and oxygen pressure leads to approximately constant hole doping over an extended range of Ca substitution x. The most favorable synthesis conditions for obtaining stoichiometric, d=0, samples were determined. The data suggest that several studies reported in the literature were done on significantly nonstoichiometric materials. Structural results show that, in addition to the orthorhombic Pbnm O′ (c/a