Abstract
Controllable synthesis of boron nitride nanotubes (BNNTs) remains challenging due to the difficulty of stabilizing reactive boron species and regulating their conversion pathways during high-temperature reactions. In this study, lithium carbonate (Li(2)CO(3)) is employed as a controlled Li-O releasing precursor, which decomposes in situ to promote the formation of lithium borate-rich Li-B-O liquid phases. These lithium borates act as the true reactive species that activate boron and facilitate vapor-liquid-solid (VLS) growth of BNNTs. The effects of reaction temperature and Li(2)CO(3)/B molar ratio on the morphology, structure, and purity of BNNTs were systematically investigated. An optimal Li(2)CO(3)/B ratio of 0.06 produced uniform, high-purity BNNTs, whereas insufficient or excessive Li(2)CO(3) led to incomplete nitridation or the formation of Li-B-O byproducts. Structural analysesincluding FT-IR, XRD, Raman spectroscopy, and XPSreveal that the optimized conditions suppress defect formation and enhance B-N coordination, yielding BNNTs with well-defined tubular architecture. A refined VLS growth mechanism is proposed, in which the size, shape, and spatial distribution of Li-containing liquid droplets govern BNNT diameter, crystallinity, and nucleation density. This work establishes a mechanistic framework for Li(2)CO(3)-assisted BNNT synthesis, clarifying the precursor role of Li(2)CO(3) in generating active lithium borate species, and provides a controllable strategy for achieving BNNTs with uniform morphology and well-defined crystalline structures through liquid-phase-mediated growth.