Journal of Physics and Chemistry of Solids 69 (2008) 1877–1882 Dielectric properties of valence compensated Ca 1x Bi x Ti 1x Cr x O 3 perovskite prepared using the sol–gel process Ching-Chang Chung a , Yin-Lai Chai b,Ã , Yee-Shin Chang c a Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan b Department of Resources Engineering, Dahan Institute of Technology, Hualien 971, Taiwan c Department of Electronic Engineering, National Formosa University, Huwei, Yunlin 632, Taiwan Received 3 April 2007; received in revised form 30 November 2007; accepted 30 November 2007 Abstract Ca 1x Bi x Nb 1x Cr x O 3 (x ¼ 0.01–0.5) ceramic powders were synthesized using the sol–gel process. The single-phase solids can be presented at x ¼ 0.01 and 0.03. The coexistence of orthorhombic perovskite and the secondary phase of BiCrO 3 was verified, as presented for x ¼ 0.05–0.5. Grains with a micro-cube topography were obtained for x ¼ 0.3–0.5. The average grain size is about 0.4 and 1.1 mm for x ¼ 0.3 and 0.5, respectively. The highest dielectric constant peak was measured at around 55 1C for x ¼ 0.5 and at 75 1C for x ¼ 0.3. The high dielectric constant was caused by the formation of barrier layers at the interface of the bi-phase mixed ceramics. Space charge polarization contributed to the observed behavior. r 2007 Elsevier Ltd. All rights reserved. Keywords: A. Ceramics; B. Sol-gel growth; C. X-ray diffraction; D. Crystal structure 1. Introduction CaTiO 3 with a distorted orthorhombic lattice of the perovskite structure was first studied in 1943 by X-ray diffraction [1]. It is paraelectric at room temperature, having dielectric permittivity above 180 1C and a dissipa- tion factor (D) 10 3 at 1 kHz [2]. Generally, its dielectric properties have been improved by suitable substitutions in the perovskite oxides [3–5]. There are three types of substitutions in the perovskite oxides (ABO 3 ): namely at the A site, at the B site, and at both sites. Recently, extensive studies of the formation of perovskite-type oxides of the systems Ca 1x A x Ti 1x B x O 3 (A=Y, Sr, Ba, Pb; B=Co, Al, Fe, Cr) with rare earth elements have been conducted. This class of materials has been increasingly used in a variety of electronic devices [6–9]. The replace- ment of Ca 2+ by high-valence ions creates additional positive charges, which compensate for the negative charges created from the replacement of Ti 4+ by low- valence ions, leading to charge neutrality. From studies of acceptor (Cr ions substituted into Ti sites) and donor doping (Bi ions substituted into Ca sites), it was found that doping can shift the Curie temperature. BiCrO 3 is a multi- ferroic material [10]. Multi-ferroic magnetoelectrics are materials which are both ferroelectric and ferromagnetic in the same phase [11]. A spontaneous polarization can be achieved by an applied electric field in BiCrO 3 . The material is unstable in the cubic perovskite phase; it can be stable against the displacement of an isolated atom, but collective atom displacements are required to stabilize the distorted structure. Cr 3+ ions will move to off-center positions, leading to strong polarization in the structure. There are several methods for preparing Ca 1x A x Ti 1x B x O 3 powders. In recent years, the sol–gel method has been regarded as the best method for the synthesis of nano- powders, as subsequent thermal treatment may be performed at relatively low temperatures and highly homogeneous ceramic powders can be obtained. In this paper, the ceramics of the Ca 1x Bi x Ti 1x Cr x O 3 system were produced using the sol–gel process. The phase relationships and dielectric proper- ties were also evaluated. ARTICLE IN PRESS www.elsevier.com/locate/jpcs 0022-3697/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2007.11.028 Ã Corresponding author. Tel.: +886 3 8210866; fax: +886 3 8267051. E-mail address: laser@ms01.dahan.edu.tw (Y.-L. Chai).