Investigation of the Sluggish Diffusion and Dielectric Properties of Single-Phase High-Entropy (Sr0.2Ca0.2Ba0.2Bi0.2Na0.2)MoO4 Ceramics

A (Sr_0.2Ca_0.2Ba_0.2Bi_0.2Na_0.2)MoO₄ high-entropy ceramic has been engineered to enable a tunable phase transition from dual-phase to single-phase at varying sintering temperatures while optimizing the temperature coefficient of resonant frequency. The results demonstrate that with increasing sintering temperature, a phase transition takes place from a biphasic to a monophasic structure with all phases adopting a tetragonal crystal structure. The linear decrease in relative permittivity is closely related to the variation in the space charge region at the grain boundaries. Dielectric loss is positively correlated with variations in porosity, and Raman spectroscopy further elucidates that lattice vibrations serve as the intrinsic factors governing the observed dielectric property variations. Furthermore, the increase in τ_f is strongly correlated to lattice distortion and the presence of microstrain. Theoretical calculations substantiate the presence of sluggish diffusion in high-entropy ceramics, which impedes grain growth, disrupts atomic diffusion pathways, and restricts the migration rates of electrons or ions, ultimately leading to a reduction in dielectric loss. Notably, the disparity in atomic diffusion coefficients and interatomic interactions is likely to be a key factor underlying the formation of distinct phases. Ultimately, the (Sr_0.2Ca_0.2Ba_0.2Bi_0.2Na_0.2)MoO₄ ceramic, sintered at 1050 °C, displays remarkable dielectric properties: ε_r = 10.29, Q × f = 42,002 GHz, τ_f = -37.74 ppm/°C.