Polaron Dynamics and Dielectric tuning via Ni-Driven B-site Engineeringin Dy2CoMnO6 Double Perovskites

Double perovskites of the type R2(Co/Ni)MnO6 are known for their high dielectric constants at low frequencies, but their performance typically declines at higher frequencies, limiting their suitability for advanced electronic applications. This study explores the effect of substituting nickel for cobalt in Dy2CoMnO6 to improve stability at higher frequencies. Compositions with 10% and 15% nickel were prepared and examined for structural, chemical, and electrical behav- ior.The sample with 10% nickel substitution exhibited a markedly enhanced dielectric constant (∼ 10^5 at 1 kHz) and retained values above 10^3 at 1 MHz, with reduced loss. The dielectric relaxation did not follow a single, ideal response but instead showed a broad range of relaxation times. Electrical behavior revealed contributions from both the internal structure of grains and the interfaces between them, with the dominant mechanism shifting from grain boundaries at lower frequencies to grain interiors at higher ones. A change in charge transport mechanism was also observed with increasing nickel content, suggesting a transition from electron-based to hole-based hopping driven by the reduction in oxygen vacancy concentration. These findings highlight the effectiveness of B-site substitution in tuning dielectric relaxation behavior and enhancing performance in double perovskite materials for high-frequency applications.