Anomalous Thermal Expansion in (Pr,Ca)MnO3 Due to Orbital Ordering

The monoclinic lattice parameters of the perovskite manganites Pr1−x,CaxMnO3 were systematically measured by XRD at the Ca doping levels x = 0.4, 0.5 and 0.1 at temperatures from 83 K to 403 K. The orbital ordering transition observed around 250 K at x = 0.4 and x = 0.5, located by SQUID magnetometry, was associated with a transient cell volume expansion of order 0.1%, during which the CO-related monoclinic distortion set in. The anomalous cell expansion, arguably driven by electrostructural disorder, was of sufficient magnitude to locally dominate the thermal expansion.