Giant negative thermal expansion exceeding 1000 K in PrMnO3 via synergy of local structure distortion and orbital disordering

Giant negative thermal expansion (NTE), defined by volumetric expansion αV <ca. −50 × 10−6 K−1 (volume contraction (ΔV/V) < − 0.5% within ~100 K), is rarely observed at high temperatures. Here, we report a giant NTE persisting above 1000 K (ΔV/V = − 1.7 %, 900–1100 K) in stoichiometric PrMnO3 (PMON) with a peak coefficient αV = − 114 × 10−6 K−1 around 1000 K. Contrastingly, oxygen-rich PrMnO3+x (PMOA) exhibits only positive thermal expansion. The origin of NTE was uncovered via synchrotron X-ray total scattering, Cs-corrected STEM, and DFT calculations. Intriguingly, PMON uniquely hosts a local symmetry breaking featured by a 3D cross-arranged network of elongated Mn-O bonds, different from the 2D planar configurations in PMOA. By correlating atomic-scale symmetry breaking and thermally activated orbital reconfiguration to macroscopic thermal responses, we establish an unconventional paradigm for engineering giant NTE at elevated temperatures. This study discovers giant negative thermal expansion (volume contraction) in PrMnO3 above 1000 K, linked to a unique 3D network of elongated chemical bonds, offering a new design strategy for high-temperature volume contraction materials.