Boron nitride nanotubes synthesis from ammonia borane by an inductively coupled plasma

•Ammonia borane (AB) decomposes efficiently in thermal plasma and generates abundant BNNTs.•The elemental hydrogen in AB facilitates efficient BNNTs precursors formation.•AB significantly restricts large boron (B) particles formation and generates more small B seeds.•AB-derived BNNTs (AB-BNNTs) contain substantially less residual B contamination.•AB-BNNTs contain no hBN contamination, and reduced BN shells and tBN impurities.