Designing High Dielectric Permittivity Material in Barium Titanate

Developing high dielectric permittivity material is vital to satisfy the ongoing demands for the miniaturization of electronic and energy storage devices. Recent investigations uncover the role of a thermodynamical tricritical phenomenon on enhancing the dielectric response. However, such a tricritical point always locates in an extremely narrow composition region, which makes it time-consuming for exhaustive experimental searching of the optimal dielectric permittivity in a given material system. In the present paper, we employ an accelerated discovery strategy to seek the largest dielectric permittivity in Ba(Ti_1-x%Hf_x%)O₃ ceramic material by using an iterative method between computational machine learning and the experimental synthesis and property measurement. The optimal composition is found to be x = 11 with the highest permittivity of ε_r = 4.5 × 10⁴ after 4 loops of iteration involving 6 compositions, which shows higher efficiency compared with conventional experimental searching. Further thermal analysis study suggests that such a permittivity-maximum location on the phase diagram is indeed a tricritical point. Moreover, the microstructure investigation by TEM observation indicates that the tricritical point shows a mottled morphology consisting of numerous nanodomains with multiple phases coexisting, and a phenomenological thermodynamic model based on the experimental result implies that the tricriticality is responsible for the enhanced dielectric permittivity.