| abstract |
A material and method of formation is disclosed where the material has a Formula (I): MyAxWOz (I) where M represents one or more monoatomic species; A represents one or more polyatomic cationic species, each having an ionic radius of no more than 2Å, W is tungsten, O is oxygen, y is non-zero and is up to and including 0.32, x is non-zero and up to and including 0.32, and z is from 2.5 to 4.0, provided that x+y≤0.33. A may be NH4+, H3O+, VO2+, H2F+ or H3S+. M may be an alkali metal, tin (Sn) or lead (Pb). |