Ca2 PbGa8 O15 : Rational Design, Synthesis, and Structure Determination of a Purely Tetrahedra-Based Intergrowth Oxide.

Intergrowth oxides, like Aurivillius, Ruddlesden-Popper phase, comprise functional layers and exhibit interesting physical properties. The hitherto known intergrowth structures mainly were composed of closed-packing of oxygen ions, and it is very challenging to develop new types of intergrowth structures. We proposed the possible match between the tridymite and grossite, both of which are purely tetrahedra-based structures. We synthesized Ca2 PbGa8 O15 ((Ca0.5 Pb0.5 Ga2 O4 )2 (CaGa4 O7 )) and its structure was solved by ab-initio method. Pb2+ is vitally important to stabilize this first example of tetrahedra-based intergrowth oxide. The appropriate size difference between Pb2+ and Ca2+ causes the layered type cationic ordering, and reduced the thermodynamic potential, in addition, the high hybridization between Pb 6s6p and O 2p orbitals further consolidate the covalency of the tetrahedra-base framework.