Fig. 2. Room-temperature and in situ EEL spectra of m-Pr₂Co₃Ge₅ and o-Pr₂Co₃Ge₅.

Core-loss EELS of the Pr M_4,5 (A) and Co L_2,3 edges (B) for room-temperature m-Pr₂Co₃Ge₅ (blue) and o-Pr₂Co₃Ge₅ (black). Dashed lines indicate the peak maxima, highlighting differences in the distribution of density of states between the two structures. Pr valency was determined by fitting reference M_4,5 spectra for Pr³⁺ and Pr⁴⁺ (see Methods) to the acquired data, as shown in the inset of (A). The M₄ edge feature at 945 eV (marked with an arrow) is a signature of Pr³⁺. This feature increases in prominence when the sample undergoes transformation. Temperature-dependent EEL spectra across the structural phase transformation are shown in (C and D). The Pr M_4,5 edges correspond to 4f orbital occupancy and the Co L_2,3 edges to 3d occupancy. The shading in (C) shows the linear fit contributions of the initial and final structures’ M_4,5 edges to the spectra of the intermediate structures, indicating a gradual transition in Pr valency with structural transformation. The total integrated area of the spectra taken at room temperature and 333 K are shaded beneath their respective curves. Data were normalized on the basis of the M₅ or L₃ edge maxima.