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 α_V <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 α_V = - 114 × 10^-6K^-1 around 1000 K. Contrastingly, oxygen-rich PrMnO_3+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.