Effects of distance between tungsten wire and glass substrate on particle size and photochromic characteristic of tungsten oxide prepared by electric current heating method

Tungsten oxide films consisting of particles were prepared on the substrates placed at various distances from the tungsten wires heated by electric current. The shapes of the particles were sphere in an area on the substrate just above the wire while octahedral shape was found in other area. For the spherical particles, with increasing the distance, the mean particle diameter increased, reached its maximum value and gradually decreased. The particles in each area showed the photochromism especially in near-infrared region. The spherical particles with the smallest size exhibited a significant photochromic effect which could be controlled by changing the distance between the wire and the substrate.