Growth behavior of nanograins in NiO fibers

► Individual NiO nanofiebrs synthesized by electrospinning consist of nanograins. The nanograins coalesce and grow at the expense of smaller ones under higher calcination temperatures and prolonged calcination times. ► The growth kinetics of nanograins in NiO fibers makes a transition during growth at a critical size of ∼30 nm in diameter. ► At the later stage of growth at the critical size of nanogrians, bamboo-like grains start to evolve.