New rare earth hafnium oxynitride perovskites with photocatalytic activity in water oxidation and reduction.

RHfON perovskites with R = La, Nd and Sm show a GdFeO-type structure and are semiconductors with band gaps of 3.35, 3.40 and 2.85 eV and relative dielectric constants of 30, 16 and 28 respectively. These compounds have adequate reduction and oxidation potentials to conduct the overall water splitting reaction, and the analogous perovskite LaZrON with a band gap of 2.8 eV shows photocatalytic activity under visible light irradiation for O evolution.