Avoiding water reservoir effects in ALD of functional complex alkali oxides by using O₃ as the oxygen source

Toxic Pb-containing piezo-, pyro- and ferroelectrics continue to dominate the market even though they were banned from use in consumer products more than a decade ago. There is a strong need for sustainable alternatives, but the lack of facile synthesis routes for thin films exhibiting suitable functional properties have limited the transition from Pb workhorse materials like Pb(Zr,Ti)O₃ and Pb(Mg,Nb)O₃ - PbTiO₃. Atomic layer deposition has proven capable of the deposition of possible successors, such as LiNbO₃, (K,Na)NbO₃ and K(Ta,Nb)O₃, albeit with limited control due to water reservoir effects resulting from the hygroscopicity of intermediate products. In this article, we show that replacing H₂O with O₃ in the deposition of complex alkali oxides provides an alternative and much more controlled process. We exemplify this by deposition of crystalline K(Ta,Nb)O₃ with high compositional control and over a larger composition range than previously reported. This opens new doors to a simplified synthesis of polar functional lead-free alternatives.