Perovskite Lanthanum‐Doped Barium Stannate: A Refractory Near‐Zero‐Index Material for High‐Temperature Energy Harvesting Systems

Abstract The recent interests in bridging intriguing optical phenomena and thermal energy management has led to the demonstration of controlling thermal radiation with epsilon‐near‐zero (ENZ) and the related near‐zero‐index (NZI) optical media. In particular, the manipulation of thermal emission using phononic ENZ and NZI materials has shown promise in mid‐infrared radiative cooling systems operating under low‐temperature environments (below 100 °C). However, the absence of NZI materials capable of withstanding high temperatures has limited the spectral extension of these advanced technologies to the near‐infrared (NIR) regime. Herein, a perovskite conducting oxide, lanthanum‐doped barium stannate (La:BaSnO 3 [LBSO]), as a refractory NZI material well suited for engineering NIR thermal emission is proposed. This work focuses on the experimental demonstration of superior high‐temperature stability (of at least 1000 °C) of LBSO films in air and its durability under intense UV‐pulsed laser irradiation below peak power of 9 MW cm −2 . Based on the low optical‐loss in LBSO, a selective narrow‐band thermal emission utilizing a metal‐insulator‐metal (MIM) Fabry–Pérot nanocavity consisting of LBSO films as metallic component is demonstrated. This study shows that LBSO is an ideal candidate as a refractory NZI component for thermal energy conversion operating at high temperatures in air and under strong light irradiations.