Anomalous structure transition in undercooled melt regulates polymorphic selection in barium titanate crystallization

The crystallization processes of titanates are central to the fabrication of optical and electrical crystals and glasses, but their rich polymorphism is not fully understood. Here, we show when and how polymorphic selection occurs during the crystallization of barium titanate (BaTiO3, BT) using in situ high energy synchrotron X-ray diffraction and ab initio molecular dynamic simulation. An anomalous structure transition is found in molten BT during cooling across the cubic-hexagonal transition temperature, which enables nucleation selection of BT by manipulating the undercooling: a cubic phase is preferred if nucleation is triggered at large undercooling, whereas a hexagonal phase is promoted at small undercooling. We further reveal that the nucleation selection between the cubic and the hexagonal phase is regulated by the intrinsic structure property of the melt, in particular, the degree of polymerization between Ti-O polyhedra. These findings provide an innovative perspective to link the polymorphic crystallization to the non-isomorphic structure transition of the melt beyond the conventional cognition of structural heredity. The crystallization processes of titanates are central to the fabrication of optical and electrical crystals and glasses, but their rich polymorphism is not fully understood. Here, authors identify when and how polymorphic selection takes place during the crystallization of an undercooled barium titanate melt using aerodynamic levitation, in situ time resolved high energy X-ray diffraction and ab initio molecular dynamics simulations.

Automated summary

The study investigates the polymorphism in the crystallization processes of titanates, specifically focusing on the nucleation selection between cubic and hexagonal phases during the crystallization of barium titanate. The researchers found that the intrinsic structure property of the melt, particularly the degree of polymerization between Ti-O polyhedra, plays a crucial role in regulating the polymorphic selection. This innovative perspective provides insights into the non-isomorphic structure transitions of the melt beyond the traditional cognition of structural heredity.