Colossal Dielectric Permittivity in (Nb+Al) Codoped Rutile TiO 2 Ceramics: Compositional Gradient and Local Structure
2015; American Chemical Society; Volume: 27; Issue: 14 Linguagem: Inglês
10.1021/acs.chemmater.5b01351
ISSN1520-5002
AutoresWanbiao Hu, Kenny Lau, Yun Liu, Ray L. Withers, Hua Chen, Lan Fu, Bill Gong, W. D. Hutchison,
Tópico(s)Microwave Dielectric Ceramics Synthesis
Resumo(Nb+Al) codoped rutile TiO2 ceramics with nominal composition Ti4+0.995Nb5+0.005yAl3+0.005zO2, z = (4–5y)/3 and y = 0.4, 0.5, 0.6, 0.7, and Ti4+0.90Nb5+0.05Al3+0.05O2 have been synthesized. The resultant samples in ceramic pellet form exhibit a colossal dielectric permittivity (>∼104) with an acceptably low dielectric loss (∼10–1) after optimization of the processing conditions. It is found that a conventional surface barrier layer capacitor (SBLC) effect, while it contributes significantly to the observed colossal permittivity, is not the dominant effect. Rather, there exists a subtle chemical compositional gradient inward from the pellet surface, involving the concentration of Ti3+ cations gradually increasing from zero at the surface without the introduction of any charge compensating oxygen vacancies. Instead, well-defined Gr ± 1/3[011]* satellite reflections with the modulation wave-vector q = 1/3[011]r* and sharp diffuse streaking running along the Gr ± ε[011]* direction from electron diffraction suggest that the induced additional metal ions appear to be digested by a locally intergrown, intermediate, metal ion rich structure. This gradient in local chemical composition exists on a scale up to ∼ submillimeters, significantly affecting the overall dielectric properties. This work suggests that such a controllable surface compositional gradient is an alternative method to tailor the desired dielectric performance.
Referência(s)