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

✍ Scribed by B Dabrowski; R Dybzinski; Z Bukowski; O Chmaissem; J.D Jorgensen

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 273 KB
• Volume: 146
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1999.8389

✦ Synopsis

Using thermogravimetric analysis measurements, oxygen content was measured for La 1؊x Ca x MnO 3؉d (04x40.38) 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 O 2 at 8003C, slowly cooled in 1, 20, and 100% O 2 , as well as for samples in thermal equilibrium at high temperatures of &1000 +14003C. Annealing at a speci5c 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 signi5cantly nonstoichiometric materials. Structural results show that, in addition to the orthorhombic Pbnm O (c/a<(2) and O* (a&b&c/(2) structures, the rhombohedral R3 c structure is stabilized at high oxygen contents for x40.14. A sequence of observed structures and a decrease of the unit cell volume with increasing d con5rm that the additional holes are doped uniformly by cation-vacancy defects for all studied x.