Shift-Twin Option in Eight-Layer Hexagonal Perovskite Niobates BaMNbO.

Two new eight-layer hexagonal perovskites with the composition BaMNbO (M = Fe and Cu) are synthesized by solid-state reaction at 1350-1400 °C. Their crystal structures have been investigated using X-ray and electron diffractions as well as high-resolution transmission electron microscopy. Although both compounds have similar M size, BaFeNbO and BaCuNbO adopt shifted and twinned structures, respectively.

Substitution-Induced Structure Evolution and Zn/Ga Ordering in "114" Oxides MAZnGaO ( M = Ca, Sr; A = Sr, Ba).

The "114" oxides LnBa(Co/Fe)O represent a new family of materials that exhibits intriguing physical properties, including geometrically frustrated magnetism, oxygen storage, and magnetoelectric couplings. Various chemical substitutions have been conducted to modify their crystal and magnetic structures as well as physical properties. However, the principles beneath the substitution-induced structural evolution and charge/cationic ordering have not yet been understood.

8-Layer Shifted Hexagonal Perovskite BaMnNbO: Long-Range Ordering of High-Spin d Mn Layers and Electronic Structure.

A new 8-layer shifted hexagonal perovskite BaMnNbO has been synthesized in air, featuring unusual long-range B-cation ordering with single octahedral high-spin d Mn layers separated by ∼1.9 nm within the corner-sharing octahedral d Nb host, analogous to Ba(Zn/Co)NbO. The large size and charge differences between high-spin Mn and Nb, as well as the out-of-center distortion of NbO octahedra associated with the bonding covalence and second-order Jahn-Teller effect of Nb, drive long-range cationic ordering, thus stabilizing BaMnNbO.