Dielectric property enhancement and environmental stability in (AlxCr0.05−x)Nb0.05Ti0.9O2 ceramics: influence of Al3+/Cr3+ ratio and Al3+ site preference

Abstract

The development of TiO₂-based ceramics with enhanced dielectric properties and environmental stability is crucial for next–generation capacitor applications. In this study, (Al_xCr_0.05–x)Nb_0.05Ti_0.9O₂ ceramics (x = 0, 0.005, 0.01, and 0.025) were synthesized to investigate the role of Al³⁺/Cr³⁺ ratio and Al³⁺ site preference on dielectric behavior. All sintered ceramics exhibited a single–phase rutile TiO₂ structure with dense microstructures and uniform elemental distribution. Raman and structural analyses indicated the presence of oxygen vacancies in Cr_0.05Nb_0.05Ti_0.9O₂, which were significantly reduced upon Al³⁺ incorporation, suggesting a predominant interstitial occupation of Al³⁺. Partial substitution of Cr³⁺ with Al³⁺ improved densification and grain growth, likely due to interstitial diffusion. Although Cr_0.05Nb_0.05Ti_0.9O₂ showed a high dielectric permittivity (ε′ ≈ 60,500 at 1 kHz), it suffered from a high loss tangent (tanδ ≈ 0.3) and poor frequency and temperature stability. With increasing Al³⁺ content, ε′ remained above 10⁴ while tanδ decreased below 0.1, and both frequency and temperature stability were greatly improved. The dielectric variation under 30–95 % RH was less than 4.2 %, and long–term aging over 5 years resulted in <1.2 % deviation, demonstrating excellent environmental stability. Impedance spectroscopy confirmed electrically heterogeneous microstructures composed of semiconducting grains and insulating grain boundaries, suggesting that the giant dielectric response arises from an interfacial polarization mechanism. These results highlight the promising potential of (Al_xCr_0.05–x)Nb_0.05Ti_0.9O₂ ceramics for robust dielectric capacitor applications.