Synthesis and Properties of the Defect-Free La_1-xBa_xMnO_3
Abstract
Thermogravimetric analysis was used to determine the synthesis conditions for obtaining stoichiometric samples of Ba-substituted LaMnO_3. Single-phase and defect-free samples of La_1-xBa_xMnO3 have been prepared for x=0.10 - 0.24 in air by quenching from 1150-1450 C. The x<0.12 compositions required synthesis under reduced oxygen pressure. At room temperature, the structural transition from orthorhombic to rhombohedral structure occurs around x=0.13. The structure was studied using neutron powder diffraction and is discussed in the framework of the tolerance factor concept. The structural, magnetic and resistive measurements show that properties are similar to the Sr-substituted system for slightly smaller substitution level. Curie temperatures are higher than for the Sr-substituted samples for small x, x=0.10 - 0.14, due to a better match of the Mn-O and La(Ba)-O bond lengths, and slightly lower for larger x, x=0.20 - 0.24 due to an increased local distortions. By comparing the Ba- and Sr-substituted systems it is shown that structural properties are governed by the ionic sizes while physical properties are controlled by both the ionic sizes and the hole doping.(This work is supported by ARPA/ONR)
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 1998
- Bibcode:
- 1998APS..MAR.Q2107D