Liquid-feed flame spray pyrolysis derived nanopowders (NPs) as a route to electrically conducting calcium aluminate (12CaO.7Al2O3) films

Traditionally, C12A7 materials have been processed via solid-state reaction followed by pulsed laser deposition (PLD) or floating zone (Fz) crystallization methods at high temperature, high cost approaches to single-phase films. These techniques require a significant number of process steps to generate C12A7:e(-) materials that have been shown to exhibit exceptional electrical conductivities as high as 1 S/cm. We demonstrate here an effective alternative method using flame made C12A7 nanopowders (NPs) produced via liquid-feed flame spray pyrolysis (LF-FSP). Nearly fully dense, single phase, and transparent C12A7 films ( < 50 mu m) can be produced by processing these NPs into green films by tape-casting, thermo-compression and then sintering to 1300 degrees C/3 h/O-2. Subsequent heat treatments in 20/80 H-2/N-2 replaces cage trapped O2- ions forming C12A7:H- followed by UV irradiation to generate C12A7:e(-) with electrical conductivities of 35 mS cm(-1). C12A7:e- appears to belong to a new class of transparent conducting oxides (TCOs) that may offer commercial potential on further optimization due to low materials and processing costs, environmental stability, and natural abundance when processed efficiently.