Charge Disproportionation in SrBiFeO Containing Unusually High Valence Fe.

A Sr analogue of CaBiFeO, SrBiFeO, containing unusually high valence Fe ions was synthesized by using a high-pressure technique. It relieves the electronic instability due to the unusually high valence of Fe by a single charge disproportionation (CD) transition (Fe → 0.75Fe + 0.

Successive Charge Transitions of Unusually High-Valence Fe : Charge Disproportionation and Intermetallic Charge Transfer.

A perovskite-structure oxide containing unusually high-valence Fe was obtained by high-pressure synthesis. Instability of the Fe in Ca Bi FeO is relieved first by charge disproportionation at 250 K and then by intermetallic charge transfer between A-site Bi and B-site Fe at 200 K. These previously unobserved successive charge transitions are due to competing intermetallic and disproportionation charge instabilities.

Two Charge Ordering Patterns in the Topochemically Synthesized Layer-Structured Perovskite LaCaFeO with Unusually High Valence Fe.

A-site-ordered layer-structured perovskite LaCaFeO with unusually high valence Fe was obtained by low-temperature topochemical oxidation of the A-site layer-ordered LaCaFeO. The unusually high valence Fe in LaCaFeO shows charge disproportionation of Fe and Fe first along the layer-stacking ⟨010⟩ direction below 230 K. Fe is located between the La and Ca layers, while Fe is between the Ca layers.

From Tetrahedral to Octahedral Iron Coordination: Layer Compression in Topochemically Prepared FeLaTiO.

Synthesis, characterization, and thermal modification of the new layered perovskite FeLaTiO have been studied. FeLaTiO was prepared by ion exchange of the triple-layered Ruddlesden-Popper phase LiLaTiO with FeCl at 350 °C under static vacuum. Rietveld refinement on synchrotron X-ray diffraction data indicates that the new phase is isostructural with CoLaTiO, where Fe cations occupy slightly compressed/flattened interlayer tetrahedral sites.

Determination of Elemental Ratio in an Atomic Column by Electron Energy Loss Spectroscopy.

Atomic-resolution quantification of the elemental ratio of Fe to Mn at the octahedral and tetrahedral sites in brownmillerite Ca2Fe1.07Mn0.93O5 was determined using electron energy-loss spectroscopy combined with aberration-corrected scanning transmission electron microscopy.

Geometrical Spin Frustration of Unusually High Valence Fe(5+) in the Double Perovskite La2LiFeO6.

A double perovskite-structure oxide La2LiFeO6 with unusually high-valence Fe(5+) was synthesized using a high-pressure technique. The Li(+) and Fe(5+) ions at the B site in the rhombohedral R3̅ perovskite structure are ordered in a rock salt manner, and the resultant tetrahedral network of Fe(5+) gives geometrical spin frustration, which is consistent with a large frustration index f (|θ|/TN) ≈ 10. Mg(2+) substitution for Li(+) produces Fe(4+) from some Fe(5+) and changes the magnetic properties.

Ferromagnetism Induced by Substitution of the Iron(IV) Ion by an Unusual High-Valence Nickel(IV) Ion in Antiferromagnetic SrFeO3.

Novel cubic perovskites SrFe(1-x)Ni(x)O3 (0≤x≤0.5) with unusual high-valence iron(IV) and nickel(IV) ions were obtained by high-pressure and high-temperature synthesis. Substantial magnetic moments of Ni(IV), which is intrinsically nonmagnetic with a nominal d(6) electron configuration, were induced by the large magnetic moments of Fe(IV) through orbital hybridization with oxygen.

Two-dimensional charge disproportionation of the unusual high valence state Fe(4+) in a layered double perovskite.

The crystal and magnetic structures of charge-disproportionated Ca2FeMnO6 were analyzed by neutron powder diffraction. Ca2FeMnO6 is a layered double perovskite oxide with a two-dimensional arrangement of Mn(4+) and unusual high valence Fe(4+) at room temperature. When cooled, the compound shows charge disproportionation followed by magnetic transition.