Microstructure and Kinetics of Intermediate Crystallization State of Amorphous Nb₂O₅

Nb₂O₅ has a variety of crystalline states. However, the intermediate process of forming a long-range ordered structure is still unclear. Nb₂O₅ precursor was prepared by a sol–gel method. The intermediate-state samples in the crystallization of amorphous Nb₂O₅ were obtained at 460 ℃ –520 ℃ . The crystal structure, morphology, pore structure and crystallization kinetics of the intermediate-state samples were investigated. The results show that the atomic ordering process of the sample is from 1.0 nm short-range order with an amorphous state, to 1.0 nm short-range order with a small amount of crystal and amorphous mixed state, to 1.5 nm medium-range order with a pseudo hexagonal and amorphous mixed state, and then to more than 2.0 nm long-range order with a pseudo hexagonal, orthorhombic and a small amount of amorphous mixed state. The crystallinity of the samples at >495 ℃ increases rapidly from 20% to 86%. The samples are formed due to the crisscross accumulation of massive flaky particles and a small amount of rod-shaped particles. From a short-range order to a long-range order, the growth process of flake particles is the main process, while the rod-shaped particles have little change. The particles are mesoporous, and the size of the main pore becomes 10 nm as the calcination temperature increases. The Avrami index (n) of the samples is 1–2, and the main nucleation mode is the surface nucleation. During the transformation from short program to medium program, there exists a crystallization incubation period. This study provides a working basis for the investigation of Nb₂O₅ crystallization intermediate state.