Successive phase transitions–induced multiple boundaries and unprecedented electrocaloric effect in Pb(Yb_1/2Nb_1/2)O₃–Pb(Mg_1/3Nb_2/3)O₃ system

Temperature stability of electrocaloric effect (ECE) is a thorny problem in ferroelectrics (FE). A general method is to design ferroelectric-to-relaxor phase transition at a sacrifice of electrocaloric (EC) strength. The Pb(Yb_1/2Nb_1/2)O₃ antiferroelectrics (AFE) + Pb(Mg_1/3Nb_2/3)O₃ relaxors strategy designed in this work is effective to tackle this dilemma [(1 − x)PYN–xPMN, x = 0.08–0.36]. PMN addition induces a successive phase transition and dual phase boundaries of ferrielectric (FIE)-nonergodic relaxor (NER) and NER-ergodic relaxor (ER), where ferroelectric polarization/strain and ECE reach a local maximum. Thermally stable ΔT is unexpectedly achieved in FIE (x = 0.14) and NER (x = 0.24), except for a generality for ER state (x = 0.30). A dome-like variation trend is observed in x = 0.14 and 0.24 with a wide temperature span of ∼60 and ∼55 K (±15%ΔT_max). Notably, x = 0.24 NER possesses a large directly measured ΔT_max ∼0.64 K simultaneously. Dielectric/ferroelectric properties clarify that two-stage transition of AFE rigid-order de-texture and dissociation of de-textured AFE domains into polar nano-entities accounts for thermal stability of ΔT as the alternation of ordered antipolar domains to disorder relaxors serves as a buffer to compensate for the thermal-shock enhanced random field. This work not only accounts for the underlying mechanism for thermal stability of ΔT at FIE and NER side for the first time in physics but also provides an exotic approach to seek for high-performance EC materials in practical applications.