Dielectric relaxation in A 2 FeNbO 6 (A=Ba, Sr, and Ca) perovskite ceramics Shanming Ke & Huiqing Fan & Haitao Huang Received: 29 March 2007 / Accepted: 15 October 2007 / Published online: 30 October 2007 # Springer Science + Business Media, LLC 2007 Abstract A 2 FeNbO 6 (A=Ba, Sr, and Ca, abbreviated as AFN) ceramics were synthesized by a wolframite method with monoclinic FeNbO 4 precursor. X-ray diffraction studies revealed that Sr 2 FeNbO 6 and Ca 2 FeNbO 6 had a orthorhombic structure, while Ba 2 FeNbO 6 had a cubic symmetry. Dielectric properties of the AFN ceramics were characterized in a broad frequency range (1 Hz–10 MHz) at a temperature ranged from -120 to 300 °C. Two dielectric relaxations were observed to follow the Arrhenius law at both low and high temperatures for all samples. Polaron relaxation was proposed to explain the low temperature dielectric relaxations in AFN. The high temperature dielectric relaxations in AFN were a competitive phenom- enon between the dielectric relaxation and the electrical conduction of the relaxing species. Keywords AFN . Dielectric relaxation . Polaronic relaxation 1 Introduction Fe-containing double perovskites of the general form A 2 FeNbO 6 (A=Ba, Sr, and Ca; abbreviated as AFN) have been actively investigated in order to understand the nature of magnetism and transport in these compounds [1, 2]. Recently, these perovskites were reported by Raevski et al. [3] to show high permittivity behavior similar to what was previously observed in CaCu 3 Ti 4 O 12 (CCTO) [4]. In these oxides, dielectric permittivity shows weak temperature dependence over a very wide temperature range and a steplike decrease by almost three orders of magnitude without any detectable long-range crystal structural changes. Besides the steplike dielectric relaxation, a higher temperature relaxor-like dielectric relaxation has also been reported in Ba 2 FeNbO 6 ceramics by Chen et al. [5], which was attributed to an oxygen defect induced dielectric abnormity. Although it is generally accepted that the giant ɛ′ in CCTO must have a non-intrinsic origin [4], the physical mechanism of the dielectric response in AFN is still not well understood. In the present work, A 2 FeNbO 6 (A=Ba, Sr, and Ca) ceramics are synthesized by a wolframite method with monoclinic FeNbO 4 precursor. The dielectric characteristics of AFN ceramics are evaluated in broad temperature and frequency ranges. Both the low- and high temperature dielectric relaxations were observed in all the three synthesized materials Ba 2 FeNbO 6 (BFN), Sr 2 FeNbO 6 (SFN) and Ca 2 FeNbO 6 (CFN). The differences among the above materials were compared and discussed. 2 Experiments FeNbO 4 (FN) precursor with a monoclinic phase was firstly synthesized by solid state reaction of reagent grade iron oxide, Fe 2 O 3 , and niobium oxide, Nb 2 O 5 . The starting powders were mixed and ball milled in ethyl alcohol for 12 h. As reported by Raymond et al. [6], the calcination J Electroceram (2009) 22:252–256 DOI 10.1007/s10832-007-9353-6 S. Ke : H. Fan (*) State Key Laboratory of Solidification Processing, School of Materials Science, Northwestern Polytechnical University, Xian 710072, China e-mail: hqfan3@163.com S. Ke : H. Huang Department of Applied Physics and Materials Research Center, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China H. Huang e-mail: aphhuang@polyu.edu.hk