Giant Negative Thermal Expansion in the Iron Perovskite SrCu₃Fe₄O₁₂

BaFeO3: A Ferromagnetic Iron Oxide

“…As discussed in our recent report on an Fe 4+ oxide SrCu 2+ 3 Fe 4+ 4 O 12 ,7 the specificity of Fe 4+ oxides can be assigned to the fact that the approximate effective charge transfer energy Δ eff drastically drops from 8 eV for FeO and 5.5 eV for LFO to −3 eV for SFO. Thus, Fe 3+ (O 6 ) 11− or Fe 3+ L (L: ligand hole) is the realistic picture rather than Fe 4+ (O 6 ) 12− 8.…”

Switching Between Giant Positive and Negative Thermal Expansions of a YFe(CN)6‐based Prussian Blue Analogue Induced by Guest Species

“…[1][2][3][4][5] Theo ccurrence of negative thermal expansion (NTE) materials offers ap romising possibility.I n 1968, Hummel et al first observed the NTE phenomenon in the framework material ZrW 2 O 8 . [33][34][35] However,i no pen-framework materials,chemical substitution might not be adirect method to adjust thermal expansion, because the NTE of such materials is associated with the lattice dynamics rather than the electronic structures.For example,the linear coefficient of thermal expansion (CTE, a l )for Zr 1Àx M x W 2 O 8Ày (M = Sc, In, Y) materials only varies over an arrow range (À7.3 to À8.7 10 À6 K À1 ). Subsequently,m any more NTE framework materials were found, such as oxides containing MÀOÀMo xygen atom bridges with the general chemical formulae AMO 5 , [7] A 2 M 3 O 12 , [8,9] AO 3 , [10] AM 2 O 7 , [11] and AM 2 O 8 ; [1,12] ReO 3 -type fluorides, [13][14][15][16] cyanides,a nd the Prussian blue analogues formed by double atom M-CN-M bridges in Zn(CN) 2 , [17] Ag 3 Co(CN) 6 , [18] LnCo(CN) 6 , [19] and FeCo(CN) 6 ; [20] and metal-organic frameworks (MOFs) [21][22][23][24] with carboxylate linkages.…”

Covalency Competition in the Quadruple Perovskite CdCu3Fe4O12

“…On the other hand, it was recently reported that the quadruple perovskites with unusual valence Fe ions (typically Fe 4+ ), ACu 3 Fe 4 O 12 (A = Ca 2+ , Sr 2+ , trivalent rare-earth metals R 3+ , Bi 3+ , and Ce 4+ ), demonstrate a wide range of intriguing properties strongly depending on the valences and/or sizes of A-site ions: charge disproportionation (2Fe 4+ → Fe 3+ + Fe 5+ ), charge ordering/disordering of the Fe 3+ and Fe 5+ ions, bidirectional intersite charge transfers (Cu 2+ + Fe 4+ ⇄ Cu 3+ + Fe 3+ ), negative thermal expansion, and high catalytic activity for oxygen evolution reaction. [33][34][35][36][37][38][39][40][41][42]…”