Multi‐Heterovalent Defect Complexes for Enhanced Capacitive Energy Storage in High‐Entropy Ceramic Capacitors

The proliferation of smart electronic devices such as drones has driven an urgent demand for ceramic capacitors with both high energy storage performance (ESP) and reliable thermal monitoring capability. Conventional strategies often suffer from a trade‐off between maximum polarization and efficiency, limiting practical applications. Here, we propose a multi‐heterovalent defect‐engineering strategy within a high‐entropy framework to overcome this challenge. Based on Bi 0.5 Na 0.5 TiO 3 and by introducing heterovalent multi‐ions to induce point defects with high polarizability, we construct a local polarization configuration featuring continuously distributed multiphase polar nanoclusters, which significantly reduces the domain switching barrier while maintaining high polarization. At room temperature and 1 Hz, the optimized composition achieves a high recoverable energy density of 15.53 J cm −3 and an efficiency of 90.06% at 890 kV cm −1 , together with excellent temperature and cycling stability. Furthermore, Yb 3+ /Er 3+ co‐doping enables upconversion luminescence with sensitive fluorescence intensity ratio response, reaching a maximum relative sensitivity of ∼5.3 × 10 −3 K −1 , thus endowing the capacitors with in situ temperature sensing capability. This work establishes a paradigm for designing smart high‐entropy ceramic capacitors that synergistically combine superior ESP with self‐diagnostic functionality.