Colossal Dielectric Permittivity in (Nb+Al) Codoped Rutile TiO2 Ceramics: Compositional Gradient and Local Structure

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• 作者：Wanbiao Hu ; Kenny Lau ; Yun Liu ; Ray L. Withers ; Hua Chen ; Lan Fu ; Bill Gong ; Wayne Hutchison
• 刊名：Chemistry of Materials
• 出版年：2015
• 出版时间：July 28, 2015
• 年：2015
• 卷：27
• 期：14
• 页码：4934-4942
• 全文大小：644K
• ISSN：1520-5002

文摘

(Nb+Al) codoped rutile TiO₂ ceramics with nominal composition Ti⁴⁺_0.995Nb⁵⁺_0.005yAl³⁺_0.005zO₂, z = (4鈥?y)/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 (>鈭?0⁴) with an acceptably low dielectric loss (鈭?0^鈥?) 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 G_r 卤 ¹/₃[011]* satellite reflections with the modulation wave-vector q = ¹/₃[011]_r* and sharp diffuse streaking running along the G_r 卤 蔚[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 鈭?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.