CERAMICS INTERNATIONAL Available online at www.sciencedirect.com Ceramics International 41 (2015) 691–698 High-temperature colossal dielectric response in RFeO 3 (R ¼ La, Pr and Sm) ceramics Shuai Huang, Liran Shi, Zhaoming Tian, Songliu Yuan n , Liguang Wang, Gaoshang Gong, Chongyang Yin, Gebru Zerihun School of Physics, Huazhong University of Science and Technology, Wuhan 430074, PR China Received 4 June 2014; received in revised form 5 August 2014; accepted 28 August 2014 Available online 4 September 2014 Abstract Polycrystalline RFeO 3 (R ¼ La, Pr, and Sm) ceramics have been synthesized by a modified Pechini method. All the refined X-ray diffraction patterns reveal that the materials crystallized in orthorhombic structure with space group Pbnm. Clear grain and grain boundary are evident in PrFeO 3 and SmFeO 3 ceramics after sintering at 1200 1C for 4 h by scanning electron microscopy. Mixed valence of Fe 2 þ /Fe 3 þ has been determined using X-ray photoelectron spectroscopy. High-temperature dielectric behavior and impedance spectrum over the frequency range of 100 Hz to 10 MHz are investigated at different temperatures from 300 to 600 K. These materials exhibit relaxation-like dielectric behavior and colossal dielectric constant in a wide temperature and frequency range. Impedance spectrum analysis indicates the ceramics to be electrically heterogeneous consisting of semiconducting grains and insulating grain boundaries (corresponding to high and low frequency electrical response, respectively), which played important roles in the high-temperature dielectric properties of RFeO 3 ceramics. & 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: C. Dielectric properties; C. Impedance 1. Introduction Giant dielectric materials have received remarkable attention on account of the interesting physical mechanisms for their anomalous dielectric behaviors and the possible application for electronic devices, such as multilayer capacitors, memories, and resonators [1–3], and relatively high permittivity offers the opportunity to decrease the size of electronic devices. Among all of such materials, CaCu 3 Ti 4 O 12 with extraordinarily high dielectric constant of  10 5 at room temperature and weak temperature dependence over a wide temperature range (from 100 to 400 K), has been extensively studied [4]. For purpose of understanding the unusual dielectric response in this ceramic, various theoretical models are proposed, such as intrinsic local dipole fluctuation model [5], Cu deficiency model [6], internal domains model [7], nanoscale disorder model [8]. Among them, one of the leading explanations should be the internal barrier layer capacitor (IBLC) model [9,10], which is composed of semi- conducting grains and insulating grain boundaries. This model can be supported by impedance spectrum successfully since it is widely used to distinguish the contribution of different phases such as grains, grain boundaries, semiconductor to metal contacts and impurity inside polycrystalline samples. However, it has difficulty in explaining the appearance of giant dielectric behavior in single crystals because no grain boundary exists in single crystals. So the origin of the giant dielectric constant is still ambiguous. Further investigations of the giant dielectric behavior are still badly needed. Recently, dielectric properties of the rare earth-ion oxide system have been attracting scientific interest because of their colossal dielectric behavior similarly to the found one in CaCu 3 Ti 4 O 12 , and authors have carried out dielectric measure- ment in such ABO 3 perovskite system with different rare earth and alkaline earth elements in A site and different transition metal ions in B site [11–14]. Prasad et al. have systematically www.elsevier.com/locate/ceramint http://dx.doi.org/10.1016/j.ceramint.2014.08.124 0272-8842/& 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved. n Corresponding author. Tel.: þ86 2787556580; fax: þ 86 2787544764. E-mail address: yuansl@hust.edu.cn (S. Yuan).