Glass-like thermal conductivity of (010)-textured lanthanum-doped strontium niobate synthesized with wet chemical deposition

We have measured the cross-plane thermal conductivity (κ) of (010)-textured, undoped, and lanthanum-doped strontium niobate (Sr_2-xLa_xNb₂O_7-δ) thin films via time-domain thermoreflectance. The thin films were deposited on (001)-oriented SrTiO₃ substrates via the highly-scalable technique of chemical solution deposition. We find that both film thickness and lanthanum doping have little effect on κ, suggesting that there is a more dominant phonon scattering mechanism present in the system; namely the weak interlayer-bonding along the b-axis in the Sr₂Nb₂O₇ parent structure. Furthermore, we compare our experimental results with two variations of the minimum-limit model for κ and discuss the nature of transport in material systems with weakly-bonded layers. The low cross-plane κ of these scalably-fabricated films is comparable to that of similarly layered niobate structures grown epitaxially.