Synthesis and crystal structure of a new hexagonal perovskite 7H-Ba₇Li_1.75Mn_3.5O_15.75with Mn⁴⁺/Mn⁵⁺charge distribution

Abstract

.75 Mn 3.5 O 15.75 is a new hexagonal perovskite whose crystal structure has elements typical for the layered hexagonal perovskites and quasi-one-dimensional oxides, hence representing a new polytype. It has been synthesized via a solid-state microwave route. The crystal structure was solved using a combination of X-ray and neutron diffraction data, which show that Ba 7 Li 1.75 Mn 3.5 O 15.75 crystallizes in a hexagonal unit cell with parameters a = 5.66274(2) Å and c = 16.7467(1) Å (V = 465.063(4) Å 3 ), with one formula unit, and can be described as columns of face-shared octahedra occupied by Mn 4+ and Li + cations and vacancies along the c axis separated in the ab plane by barium atoms. Every sixth layer, the coordination of Mn 5+ and Li + changes to tetrahedral. Additional local ordering of manganese and lithium atoms among cationic sites leading to the formation of a rhombohedral supercell has been observed by scanning transmission electron microscopy.

Property control from polyhedral connectivity in ABO3 oxides

“…For example, BaIrO 3 and BaRuO 3 exhibit structures with 67% facesharing, 25,26 while BaMnO 3 exhibits a wide variety of polytypes depending on synthesis conditions. 27 These compounds are of recent interest because they exhibit metal-insulator 28 and ferromagnetic Mott insulator to paramagnetic charge-ordered insulator 25 transitions.…”