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<p>Co-doped TiO₂ ceramics are widely used as model systems to study colossal permittivity, yet the interplay between defect-related relaxations and interfacial barrier layers remains debated. Here we investigate (Mg₁/₃Nb₂/₃)<i>ₓ</i>Ti<sub>(1−<i>x</i>)</sub>O₂ (<i>x</i> = 0.02, 0.04, 0.06 and 0.08) ceramics prepared by a solid-state route under a fixed sintering schedule. X-ray diffraction and Raman spectroscopy confirm single-phase rutile with systematic lattice expansion on co-doping, while plan-view SEM and EDS reveal dense microstructures with micrometre diameter grains and a continuous grain boundary network. Dielectric spectroscopy over a wide temperature and frequency window shows two distinct relaxations, a low-temperature process consistent with defect-cluster-assisted hopping, and a high-temperature, low-frequency enhancement of <i>ε′</i> characteristic of interfacial polarization. Impedance and electric-modulus analysis are fitted with a two-RC model and used to separate grain and grain-boundary contributions, yielding <i>R</i><sub>g</sub>, <i>R</i><sub>gb</sub>, <i>C</i><sub>g</sub> and <i>C</i><sub>gb</sub> together with activation energies that agree with those obtained from ac conductivity and dc resistivity. Within the present series, <i>x</i> = 0.04 exhibits the most reasonable combination of <i>ε′</i> and tan<i>δ</i>, with <i>ε′</i> ≈ 2.5 × 10⁴ and tan<i>δ</i> ≈ 0.5 at 320&#xa0;K and 1&#xa0;kHz, values that lie in the colossal permittivity range but with loss typical for internal barrier-layer capacitor behaviour. The combined structural, microstructural and electrical evidence demonstrates a crossover from defect cluster dominated relaxation at low temperature to an IBLC-type response at elevated temperature and identifies an optimal composition under controlled processing conditions.</p> Graphical abstract <p></p>

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Cross over from colossal permittivity to space charge polarization regime in (Mg₁/₃Nb₂/₃)ₓTi(₁₋ₓ)O₂

  • 期刊论文

  • 发表日期：

    2026年3月17日

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  • Layiq Zia,
  • Muhammad Akram,
  • Awais Ali,
  • Wei Jiang,
  • Ghulam Hassnain Jaffari

摘要

Co-doped TiO₂ ceramics are widely used as model systems to study colossal permittivity, yet the interplay between defect-related relaxations and interfacial barrier layers remains debated. Here we investigate (Mg₁/₃Nb₂/₃)ₓTi(1−x)O₂ (x = 0.02, 0.04, 0.06 and 0.08) ceramics prepared by a solid-state route under a fixed sintering schedule. X-ray diffraction and Raman spectroscopy confirm single-phase rutile with systematic lattice expansion on co-doping, while plan-view SEM and EDS reveal dense microstructures with micrometre diameter grains and a continuous grain boundary network. Dielectric spectroscopy over a wide temperature and frequency window shows two distinct relaxations, a low-temperature process consistent with defect-cluster-assisted hopping, and a high-temperature, low-frequency enhancement of ε′ characteristic of interfacial polarization. Impedance and electric-modulus analysis are fitted with a two-RC model and used to separate grain and grain-boundary contributions, yielding Rg, Rgb, Cg and Cgb together with activation energies that agree with those obtained from ac conductivity and dc resistivity. Within the present series, x = 0.04 exhibits the most reasonable combination of ε′ and tanδ, with ε′ ≈ 2.5 × 10⁴ and tanδ ≈ 0.5 at 320 K and 1 kHz, values that lie in the colossal permittivity range but with loss typical for internal barrier-layer capacitor behaviour. The combined structural, microstructural and electrical evidence demonstrates a crossover from defect cluster dominated relaxation at low temperature to an IBLC-type response at elevated temperature and identifies an optimal composition under controlled processing conditions.

Graphical abstract