Crystal structure and ferroelectric properties of Ca(Cu3−xMx)Ti4O12 (M = Fe and Ni) ceramics
Highlights
► M-substituted Ca(Cu3−xMx)Ti4O12 (CCMTO) ceramics, where M = Fe and Ni, were synthesized. ► The influence of M substitution for Cu on crystal structure and ferroelectric properties of CCMTO ceramics were investigated. ► Analysis of CCMTO ceramics revealed the single phase of CCMTO ceramics belongs to I23 non-centrosymmetric space group of I23. ► As a result, the Pr and Ec values of CCFTO ceramics at x = 0.05 were 1.8 μC/cm2 and 40 kV/cm, respectively.
Introduction
In recent years, materials, which have high dielectric constant, have been attracted much attention due to the application in miniaturization of electronic devices such as static and dynamic random access memories, high dielectric capacitors, and thin film devices. It has been reported that the CaCu3Ti4O12 (CCTO) ceramic has a very high dielectric constant above 10,000 for bulk at room temperature which is shown to be stable over a wide temperature range from 100 to 600 K [1], [2], [3], [4], [5], [6]. Therefore, many researchers have been paid for the attention to the dielectric behavior of the CCTO ceramic to understand the intrinsic behavior. The crystal structure of CCTO ceramic has been reported to be body-centered cubic structure with a space group of [7], composing of a CaO12 polyhedron, a TiO6 octahedron, and a CuO4 plane. In a CCTO ceramic, the Ti4+ cations are located at the center of the TiO6 octahedra and the octahedra are mutually linked by sharing the oxygen ions of the CuO4 plane. Moreover, many attempts have been carried out to characterize the dielectric properties of these materials because these properties of the CCTO ceramic are known to extremely depend on the processing conditions and dopant cations [8], [9], [10], [11], [12]. For example, the effect of Mg substitution for Cu on the temperature dependence of the dielectric constant of Ca(Cu1−xMgx)3Ti4O12 ceramics has been reported by Ni et al. [12]. They found that the dielectric constants of Ca(Cu1−xMgx)3Ti4O12 ceramics are enhanced by the Mg doping in the single phase region. As for the ferroelectric properties of the CCTO ceramic and their solid solutions, Shri et al. [13] reported that the remnant polarization (Pr) and the coercive field (Ec) of the CCTO ceramic are approximately 0.1 μC/cm2 and 132 V/cm, respectively, and suggested that the ferroelectric behaviors were arisen from the presence of Ti4+ and Ti3+ cations, though the CCTO ceramic preserve a centro-symmetric crystal structure. However, the influence of the M (M = Fe and Ni) substitutions for Cu on the ferroelectric properties and crystal structure of Ca(Cu3−xMx)Ti4O12 (CCMTO) ceramics have not been evaluated to date. Thus, in this study, M-substituted CCMTO ceramics were synthesized and the relationships between the ferroelectric properties and crystal structure of the CCMTO ceramics were investigated.
Section snippets
Experimental methods
The CCMTO ceramics were prepared by the conventional solid-state reaction method. The stoichiometric amounts of CaCO3 (99.99%), CuO (99.9%), NiO (99.9%), FeO (99.9%), and TiO2 (99.9%) powders were weighed and mixed using an alumina mortar and pestle with acetone. After drying, the composite powders were calcined at 800 °C for 12 h in air. The calcined powders were then reground and 5 wt % polyvinyl alcohol was added as a binder. The samples were uniaxially pressed into disks (approximately 10 mm in
Results and discussion
XRPD profiles of the CCMTO ceramics sintered at 1000 °C for 24 h are shown in Fig. 1. A single pseudo-perovskite phase with the CCTO-type structure was obtained by the Fe substitution for Cu in the composition range of 0–0.05, and the TiO2 compound was detected at x = 0.075 as a secondary phase. In the case of Ni substitution for Cu, the XRPD profiles of the CaCu3−xNixTi4O12 (CCNTO) ceramics were recognized to be a single phase in the composition range of 0–0.2. In order to clarify the influence of
Conclusions
The CCMTO ceramics were synthesized by the conventional solid state reaction method; the effects of the M substitutions for Cu on the crystal structure and ferroelectric properties of the ceramics were characterized in this study. The Rietveld analysis was performed in both the space groups of and I23; the crystal structure of the CCMTO ceramics was determined to be a non-centrosymmetric space group of I23. From the refined lattice parameter, the solubility limit of the Fe substitution for
References (22)
- et al.
Materials Research Bulletin
(2008) - et al.
Journal of Solid State Chemistry
(2000) - et al.
Solid State Communications
(2009) - et al.
Physica B
(2008) - et al.
Journal of Rare Earths
(2010) - et al.
Microwave and Optical Technology Letters
(2003) - et al.
Advanced Materials
(2007) - et al.
Chemistry of Materials
(2004) - et al.
Materials Research
(2008) - et al.
Chemistry of Materials
(2010)