Nanophotonic materials offer spectral and directional control over thermal emission, but in high-temperature oxidizing environments, their stability remains low. This limits their applications in technologies such as solid-state energy conversion and thermal barrier coatings. Here we show an epitaxial heterostructure of perovskite BaZr_0.5Hf_0.5O₃ (BZHO) and rocksalt MgO that is stable up to 1,100 °C in air. The heterostructure exhibits coherent atomic registry and clearly separated refractive-index-mismatched layers after prolonged exposure to this extreme environment. The immiscibility of the two materials is corroborated by the high formation energy of substitutional defects from density functional theory calculations. The epitaxy of immiscible refractory oxides is, therefore, an effective method to avoid prevalent thermal instabilities in nanophotonic materials, such as grain-growth degradation, interlayer mixing and oxidation. As a functional example, a BZHO/MgO photonic crystal is implemented as a filter to suppress long-wavelength thermal emission from the leading bulk selective emitter and effectively raise its cutoff energy by 20%, which can produce a corresponding gain in the efficiency of mobile thermophotovoltaic systems. Beyond BZHO/MgO, computational screening shows that hundreds of potential cubic oxide pairs fit the design principles of immiscible refractory photonics. Extending the concept to other material systems could enable further breakthroughs in a wide range of photonic and energy conversion applications.

纳米光子材料对热发射提供光谱和方向控制，但在高温氧化环境中，它们的稳定性仍然很低。这限制了它们在固态能量转换和热障涂层等技术中的应用。在这里，我们展示了钙钛矿 BaZr _0.5 Hf _0.5 O _{3的外延异质结构}(BZHO) 和岩盐 MgO，在空气中的温度高达 1,100 °C。在长时间暴露于这种极端环境后，异质结构表现出一致的原子记录和明显分离的折射率失配层。来自密度泛函理论计算的取代缺陷的高形成能证实了这两种材料的不混溶性。因此，不混溶的难熔氧化物的外延是避免纳米光子材料中普遍存在的热不稳定性（例如晶粒生长退化、层间混合和氧化）的有效方法。作为一个功能示例，将 BZHO/MgO 光子晶体用作滤波器，以抑制来自主要体选择性发射器的长波长热发射，并有效地将其截止能量提高 20%，这可以在移动热光伏系统的效率中产生相应的增益。除了 BZHO/MgO，计算筛选表明数百个潜在的立方氧化物对符合不混溶难熔光子学的设计原则。将这一概念扩展到其他材料系统，可以在广泛的光子和能量转换应用中取得进一步的突破。