“…Rietveld Refinement results indicated that by incrementing the copper amount, the perovskite unit cell dimensions increased, as already observed in the literature with other perovskite oxides (Cowin et al, 2017): the unit cell length was slightly larger (3.8727 ± 0.0001 and 3.8747 ± 0.0003 Å for SCFCC10 and SCFCC20, respectively) and, accordingly, the cell volume expanded (from 58.08 ± 0.01 to 58.17 ± 0.01 Å 3 ). In fact, Cu 2+ , the most common oxidation state of copper, has an ionic radius of 0.73 Å under octahedral coordination (Nagrare and Bhoga, 2010;Renaudin et al, 2017), which is larger than Fe 3+ high spin (0.645 Å), Fe 4+ (0.585 Å), Co 3+ low spin (0.545 Å), and Co 4+ high spin (0.53 Å) in the same oxygen coordination. Thus, in a Sr 0.85 Ce 0.15 FeO 3 (whose volume is 58.5 Å 3 ), the substitution of iron with cobalt decreased the cell dimension (bringing the volume to 57.8 Å 3 ) (Tummino et al, 2017;Tummino et al, 2020), while copper addition enhanced it again.…”