New eight‐layer twinned hexagonal perovskite microwave dielectric ceramic Ba8NiNb6O24. Issue 3 (2nd November 2016)

• Record Type: Journal Article
• Authors: Tao, Fengqiong; Wang, Xiaoming; Gong, Mielu; Lu, Fengqi; Allix, Mathieu; Kuang, Xiaojun; Fang, Liang
• Is Part Of: Journal of the American Ceramic Society. Volume 100:Issue 3(2017)
• Page Start: 1212
• Page End: 1220
• Publication Date: 2016-11-02
• Subjects: cation ordering -- eight‐layer hexagonal perovskite -- microwave dielectric property -- twin‐shift option; Ceramics -- Periodicals; 620.1405
• DOI: 10.1111/jace.14601
• Languages: English
• ISSNs: 0002-7820

Abstract

Abstract: A new eight‐layer hexagonal perovskite Ba8 NiNb6 O24 was synthesized via the high‐temperature solid‐state reaction and its structure was characterized using selected area electron diffraction, high‐resolution transmission electron microscopy, and synchrotron X‐ray diffraction. Unlike the eight‐layer ordered shifted Ba8 CoNb6 O24 and Ba8 ZnNb6 O24, Ba8 NiNb6 O24 adopts a twinned structure with stacking sequence ( ccch )2 for the BaO3 layers and displays more disordered cation and vacancies over the face‐sharing octahedral (FSO) sites than the twinned tantalates Ba8 M Ta6 O24 ( M =Zn, Ni, Co). The stabilization of twinned structure and cation/vacancy ordering in Ba8 NiNb6 O24 composition is correlated with the smaller size difference between Ni 2+ and Nb 5+ in comparison with those between (Zn/Co) 2+ and Nb 5+ in the shifted Ba8 CoNb6 O24 and Ba8 ZnNb6 O24 . The Ba8 NiNb6 O24 pellet exhibits high dielectric permittivity ε r ~ 40, modest Qf ~ 41 319 GHz, and large temperature coefficient of resonant frequency τ f ~ 60 ppm/°C. The lower Qf value compared with the high‐ Q Ba8 M Ta6 O24 is ascribed to the reduced short‐range B‐cationic ordering inside the FSO dimers in Ba8 NiNb6 O24 . These results contribute to understanding the interplay among chemical composition, structure, and dielectric properties of the eight‐layer twinned and shifted hexagonal perovskites.