a Materials Chemistry Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, India
b Materials Research Centre, Indian Institute of Science, Bangalore 560 012, India
Abstract:
Structural transformation and ionic transport properties are investigated on wet-chemically synthesized La1?xMnO3 (x=0.0–0.18) compositions. Powders annealed in oxygen/air at 1000–1080 K exhibit cubic symmetry and transform to rhombohedral on annealing at 1173–1573 K in air/oxygen. Annealing above 1773 K in air or in argon/helium at 1473 K stabilized distorted rhombohedral or orthorhombic symmetry. Structural transformations are confirmed from XRD and TEM studies. The total conductivity of sintered disks, measured by four-probe technique, ranges from 5 S cm?1 at 298 K to 105 S cm?1 at 1273 K. The ionic conductivity measured by blocking electrode technique ranges from 1.0×10?6 S cm?1 at 700 K to 2.0×10?3 S cm?1 at 1273 K. The ionic transference number of these compositions ranges from 3.0×10?5 to 5.0×10?5 at 1273 K. The activation energy deduced from experimental data for ionic conduction and ionic migration is 1.03–1.10 and 0.80–1.00 eV, respectively. The activation energy of formation, association and migration of vacancies ranges from 1.07 to 1.44 eV.