Discovery of a critical line in ferroelectric BaTiO3-BaZrO3-BaSnO3 Ternary system and designing of multi-layer multi-critical-composition ceramics with high permittivity over a broad temperature range utilizing the line

Critical ferroelectric transitions are significant because they lead to remarkable material properties such as exceptionally high dielectric permittivity and enhanced piezoelectricity, a phenomenon that arises from the diminishing energy barrier between paraelectric and ferroelectric phases. However, ferroelectric materials with such critical transitions are exceedingly rare in nature. In this work we explore the phase diagram of the pseudoternary system (1-x) BaTiO3-x (1-y) BaZrO3-xy BaSnO₃, where we identify a continuous line of compositions that demonstrate critical ferroelectric transitions. These compositions all exhibit high dielectric permittivity (ε>40,000), coupled with a substantial electrocaloric effect (an adiabatic temperature change ΔT_ad >0.49 K at 20 kV/cm) at their corresponding Curie temperatures. To leverage the potential of these critical compositions, we fabricated multilayer ceramics consisting of various compositions along this critical line with sequential Curie temperatures, resulting in large dielectric permittivity values across a broad temperature range (a maximum of 23,800 over a temperature span of ∼50 K). This study not only unveils a general approach to discovering a range of ferroelectric materials with critical transitions but also presents exciting opportunities for the development of innovative electroactive devices.