Optimizing giant dielectric performance in CCTO ceramics through Cr and Zn co-doping

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The CaCu3Ti4O12 and CaCu2.95Zn0.05Ti4-xCrxO12 (x = 0, 0.05, and 0.10) ceramics were synthesized via solid-state reaction and sintered at 1110 °C for 3 h. XRD analysis confirmed that all samples maintained a single phase, free from impurities. SEM images revealed minor differences in grain size when comparing the undoped ceramic to those with co-doping. Notably, the co-doped CaCu2.95Zn0.05Ti3.95Cr0.05O12 ceramic exhibited significantly enhanced dielectric properties, including a high dielectric permittivity of 4.17 × 104 and a low loss tangent of 0.027. This ceramic also demonstrated stable dielectric permittivity with less than a 22 % variation from −60 to 90 °C, meeting the X5S and Y5S ceramic capacitor standards. In our first-principles calculations, we selected the CaCu2.95Zn0.05Ti3.95Cr0.05O12 structure because of its superior dielectric characteristics compared to the others. Our total energy calculations revealed that the Cr and Zn dopants are likely to be far apart from each other, indicating the absence of defects caused by the Zn and Cr dopants in the grains of our samples. The electrical property results indicate that the substitution of Zn2+ and Cr3+ ions into the CCTO lattice may help reduce oxygen loss during the sintering process at high temperatures. As a result, the need for charge compensation of Cu and Ti ions is diminished, leading to an increase in the grain and grain boundary resistances in the CaCu2.95Zn0.05Ti3.95Cr0.05O12 ceramic. Based on these results, the electrical conductivity of the material decreases, which contributes to a lower loss tangent value and improved temperature stability of the dielectric permittivity. The experimental and computational results indicated that the high dielectric permittivity is primarily due to the formation of an internal barrier layer capacitor, while improvements in dielectric properties may be associated with changes in intrinsic defects, which enhance the grain boundary response.