Mechanisms of Thermal Expansion and Shrinkage of La[sub 0.8]Sr[sub 0.2]MnO[sub 3+δ] Perovskites with Different Densities during Thermal Cycling in Air

The mechanisms of thermal expansion and shrinkage for sintered samples, with different relative densities, have been investigated in air during thermal cycle measurements between 50 and . The perovskite samples showed a large thermal expansion coefficient (TEC) at approximately due to a change from monoclinic and hexagonal phases to a single hexagonal one. The TEC of the porous samples with initial relative densities decreased at temperatures and continued to shrink during thermal cycling up to approximately . The dense samples with relative densities showed no shrinkage during thermal cycling, and their TEC increased monotonically with increasing temperature. It was found that the shrinkage rates of the samples showed a linear dependency on their initial relative density and had a tendency to decrease with increasing the heating/cooling rate.