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

Richard Laine

E Temeche, E Yi, V Keshishian, J. Kieffer, and R.M. Laine (2019)

Journal of the European Ceramic Society.

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 μm) can be produced by processing these NPs into green films by tape-casting, thermo-compression and then sintering to 1300 ℃/3 h/O2. Subsequent heat treatments in 20/80 H2/N2 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.

Nanopowder, Thin film, flame spray pyrolysis