Controllable Preparation Of Flexible Lithium Lanthanum Titanium Oxide Ceramic Nanofiber Films

Perovskite ceramics have been used in many fields because of their special structure and physical properties,especially in computer and electronic technology,medical diagnosi s,industrial intelligence and so on.Among perovskite ceramics,oxide perovskite ceramics are the cornerstone materials of electronic devices,but they are easy to fracture under bending.This mechanical brittleness limits their application in emerging flexible electronic devices.As one of the most important nanocrystalline materials,one-dimensional perovskite nanomaterials,such as lithium lanthanum zirconium oxide(LLZO),lithium lanthanum titanium oxide(LLTO)and other nanofibers,have the characteristics of high specific surface area,excellent heat resistance,biocompatibility and chemical durability,which make them widely used in biomedicine,electronics,energy,optics and other fields.The mechanical properties of oxide ceramics depend on the interaction of ions or covalent bonds and the internal microstructure.From the point of view of internal chemical bond,oxide perovskite ceramics have strong chemical bond and less dislocation slip system;From the perspective of microstructure,for polycrystalline ceramics,the calcination process is accompanied by multiphase chemical reactions,such as polymer,solvent evaporation and crystal growth.These competitive processes make it difficult to control grain coarsening and prone to free volume defects(cracks and pores).Uneven grain size will lead to volume defects in the material,and concentrated crack propagation is easy to occur at the grain boundary,so brittle fracture is easy to occur when the material is deformed.The effective way to create flexible ceramic crystals is to construct fiber structure with high aspect ratio and uniform and orderly microstructure.Nanofibers are usually prepared by chemical vapor deposition(CVD),high power density laser beam cutting and electrospinning.Electrospinning is a common technology for the preparation of polymers,oxides,carbon and organic-inorganic composite nanofibers.Inspired by the pinning effect,refining the grain size of ceramics to reduce internal defects,expand grain boundaries and smooth boundaries can effectively reduce crack propagation.Therefore,when the fiber is bent,the complex grain boundary system can effectively disperse the stress and prevent the brittle fracture of the fiber.Here,we propose an effective method of ball milling assisted sol-gel electrospinning,which can synthesize flexible perovskite Li_0.35La_0.55Ti O₃ nanofibers by controlling crystal nucleation and growth accurately.The strategy is to form a large number of uniform nuclei by ball milling sol before electrospinning,and reduce the porosity defects in LLTO nanofibers by refining grains.Ball milling sol improves the uniformity of LLTO nucleation and greatly reduces the size of colloidal particles.These polymer encapsulated colloidal particles containing nuclei are assembled into nanofibers after electrospinning.During calcination,the competitive growth of these homogeneous nuclei under polymer constraints refined the grains(about 30 nm)and reduced defects.A large number of disordered grain boundaries formed by uniform grain growth in nanofibers can absorb external energy and limit crack propagation.LLTO nanofiber films show excellent flexibility and fatigue resistance,and the young's modulus is 40 Gpa.The film can be folded into complex shapes and maintained well after 50 tensile buckling cycles at 40%strain.The proposed reinforcement strategy is of great significance for the development of flexible multi-element oxide ceramics.