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Ultra–low loss tangent and giant dielectric permittivity with excellent temperature stability of TiO2 co-doped with isovalent-Zr4+/pentavalent-Ta5+ ions
Journal of Materiomics 2022, 8 (6): 1269-1277
Published: 27 April 2022
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The excellent giant dielectric properties (ExGDPs) are represented in the isovalent–Zr4+/pentavalent–Ta5+ ions co–doped TiO2 with different co–doping percentages (x%ZrTTO). The dopants were dispersed homogeneously in a highly compact–grained ZrTTO microstructure. The mean grain size and cell parameters with bond lengths slightly enlarged as x% increased. The (1%–5%) ZrTTO oxides exhibited ultra–low tanδ values of 0.004–0.016 with the giant dielectric permittivity (ε′~2.7–3.7 × 104); while the ε′ of the 5%ZrTTO was slightly dependent on the temperature ranging from −60 to 200 ℃, following the temperature dependence requirement for application in the X7/8/9R capacitors. Impedance spectroscopy showed a very large resistance of the grain boundaries. The dielectric properties of the 1%ZrTTO were strongly dependent on the applied DC electric field, indicating the dominant internal barrier layer capacitor (IBLC) effect. However, the dielectric properties of the 5%ZrTTO were nearly independent on the applied DC electric field up to 30 V/mm, which was primarily resulted from electron localization in defect dipoles. Therefore, the ExGDPs of the x%ZrTTO were attributed to the combined effects of the IBLC and localized–electron defect–dipoles related to oxygen vacancies (Ti4+·eVO••−e·Ti4+ and 3(Ti4+e)VOTaTi) and Ti4+eTaTi.

Open Access Research Article Issue
Enhanced giant dielectric properties and improved nonlinear electrical response in acceptor-donor (Al3+, Ta5+)-substituted CaCu3Ti4O12 ceramics
Journal of Advanced Ceramics 2021, 10 (6): 1243-1255
Published: 26 July 2021
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The giant dielectric behavior of CaCu3Ti4O12 (CCTO) has been widely investigated owing to its potential applications in electronics; however, the loss tangent (tanδ) of this material is too large for many applications. A partial substitution of CCTO ceramics with either Al3+ or Ta5+ ions generally results in poorer nonlinear properties and an associated increase in tanδ (to ~0.29-1.15). However, first-principles calculations showed that self-charge compensation occurs between these two dopant ions when co-doped into Ti4+ sites, which can improve the electrical properties of the grain boundary (GB). Surprisingly, in this study, a greatly enhanced breakdown electric field (~200-6588 V/cm) and nonlinear coefficient (~4.8-15.2) with a significantly reduced tanδ (~0.010-0.036) were obtained by simultaneous partial substitution of CCTO with acceptor-donor (Al3+, Ta5+) dopants to produce (Al3+, Ta5+)-CCTO ceramics. The reduced tanδ and improved nonlinear properties were attributed to the synergistic effects of the co-dopants in the doped CCTO structure. The significant reduction in the mean grain size of the (Al3+, Ta5+)-CCTO ceramics compared to pure CCTO was mainly because of the Ta5+ ions. Accordingly, the increased GB density due to the reduced grain size and the larger Schottky barrier height (Φb) at the GBs of the co-doped CCTO ceramics were the main reasons for the greatly increased GB resistance, improved nonlinear properties, and reduced tanδ values compared to pure and single-doped CCTO. In addition, high dielectric constant values (ε′ ≈ (0.52-2.7) × 104) were obtained. A fine-grained microstructure with highly insulating GBs was obtained by Ta5+ doping, while co-doping with Ta5+ and Al3+ resulted in a high Φb. The obtained results are expected to provide useful guidelines for developing new giant dielectric ceramics with excellent dielectric properties.

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