On the interface crystallography of heat induced self-welded TiO2 nanofibers grown by oriented attachment.

The heat induced self-welding of nanomaterials is an important method for the artificial design and synthesis of heterogeneous composite materials. The connection and growth of solid-state crystalline nanomaterials under heat treatment normally follow the oriented attachment growth mechanism. However, there is a lack of systematic research on the interface crystallography under such formation conditions, especially for crystals with relatively large structure differences. In this work, hydrothermally grown TiO2 (B) (TB) nanofibers are chosen as examples to investigate the welded interface structure and crystallography between the same and different TiO2 polymorphs. Through the manipulation of calcination temperature, TB–TB and TB–anatase (TA) self-welded nanofiber pairs can be firstly obtained. The transmission electron microscopy (TEM) results suggest that two TB nanofibers with the same {100} single crystal form (SCF) can be connected with the same orientation or by being rotated along the fiber growth direction for certain angles. In addition, the TB nanofibers with different SCFs can also be welded through the extension and growth of (010)TB. For TB–TA self-welded pairs, the welding direction is confirmed along the long axis direction of the fiber, which is different from that of TB–TB self-welded pairs. Moreover, it is proved that the TB nanofibers with both SCFs can be welded with TA, leading to the formation of two different interfaces with typical orientation relationships. Furthermore, fewer dislocations can be found in the welded pairs with the {100} SCF of TB, which is due to the similar distribution of the voids between TiO6 octahedra for TB and TA with the orientation relationships of [010]TB//[010]TA, [100]TB//[100]TA and [106]TB//[001]TA. For the self-welded cases between TA nanofibers, the mutual rotation along different axes followed by the attachment growth was considered to be the mechanism of different interface formations. The results of this work can provide useful experimental support for the controlled synthesis of heat induced self-welded metal-oxide nanofibers. [ABSTRACT FROM AUTHOR]