Ba7Li1.75Mn3.5O15.75 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 Ba7Li1.75Mn3.5O15.75 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.

A small review of notions about fracture mechanisms and fracture toughness of ceramics is presented. Using widely the scanning electron microscopy and related techniques, the combined influence of fracture mechanisms and a number of microstructural parameters on fracture toughness are considered. The essential role of the internal interfaces, such as boundaries of grains, powders, their chemical state on the fracture toughness as well as the role of modern analytical methods in understanding of influence of the structure of materials on their properties are shown.