Shrinkage Behavior of La1−xMnO3+δ Perovskites (0 ≤ x ≤ 0.1) by Phase Change during Thermal Cycling in Air

The shrinkage mechanism of nondoped lanthanum manganite perovskites, La1−xMnO3+δ (0 ≤ x ≤ 0.1), during a thermal cycling in air has been investigated. For the La1−xMnO3+δ samples annealed at 600°C, they shrank during a thermal cycle measurement in the temperature range from 600 to 1100°C, and a decrease of their linear thermal expansion coefficients at temperatures > around 940°C was observed. It was found during the thermal cycle measurement in the temperature range from 50 to 800°C that the LaMnO3+δ sample quenched from 1000°C exhibited a large shrinkage at around 700°C by phase change from the orthorhombic into the hexagonal perovskite. For the La0.95MnO3+δ and La0.9MnO3+δ perovskite samples without the phase change, no shrinkage behavior was observed.