Preparation and Ferroelectric Characterization of Calcium Doped Barium Titanate Ceramics

Topics: Crystal structure, Crystal system, Piezoelectricity Pages: 8 (2224 words) Published: February 18, 2011
Preparation and Ferroelectric Characterization of Calcium doped Barium Titanate ceramics


Barium Titanate (BT) is widely used in electro-optical and electroceramic industry because of its ferroelectric, thermoelectric and piezoelectric properties when it assumes the tetragonal structure. In addition to its Lead free composition, its perovskite structure allows variation of ionic size and small displacement of atoms that lead to the distortion of the structure which has a profound effect on physical properties. The research aims to synthesize calcium doped barium titanate ceramics according to chemical formula Ba1-xCaxTiO3 using solid state reaction method. The product will be characterized in terms of their crystalline structure (Powder X-Ray Diffraction), microstructural behavior (Scanning electron microscopy), Dielectric property (Permittivity analyzer) and crystal lattice vibration (Fourier-Transform Infrared Spectroscopy). In the X-Ray diffraction spectra, it is expected to observe the presence of a doublet peak from the reflection of (002) and (200) planes in tetragonal BT and an increase in its diffraction angle due to shorter distance between crystal planes. SEM image of doped BT will show smaller grain size due to substitution of Ca ions to Ba ions. Permittivity plot will show a shift to lower temperature and an increase in dielectric constant value. Lastly, the IR spectra will show a shift of absorption peak to a value slightly grater than 539 cm- attributed to Ti-O bond interaction enhancement.

1. Significance of the Study
Barium Titanate has become the basic ceramic capacitor dielectric material in use today. As earlier with rutile, the main mode of its use has been in combination with other materials [1]. It was the first developed piezoelectric ceramic and is widely used even now. The crystallographic dimensions of the barium titanate lattice change with temperature due to distortion of the TiO6 octahedra as the temperature is lowered from the high temperature cubic form which corresponds to paraelectricity. Because the distorted octahedral are coupled together, there is a very large spontaneous polarization, giving rise to a large dielectric constant [2]. In the paraelectric BaTiO3 there is a random dipole orientation, and in the ferroelectric form (tetragonal structure) there is an aligned dipole orientations. Under an applied electric field, dipole orientations can be reserved, that is the structure is polarisable [3]. Primary application requisites are a high capacitance over the temperature range of use of the component. Practical temperature ranges of use have been specified as from -55°C to 125°C or segments within that range. Since pure crystalline barium titanate has a peak permittivity at about 130°C, corrective modification is required for practical application [1]. One way to improve the tetragonality of barium titanate in the room temperature range is the substitution in the perovskite lattice using Pb2+, Sr2+, Ca2+ and Cd2+ for part of the Ba ions maintaining the ferroelectric characteristics [1]. Thus understanding the doping mechanism is important prior to their application in the electroceramic industry. The basic research done in this study will reveal the use and significance of doped BaTiO3 as a good capacitor, sensor and electronic materials. Results of this study will also be of great help to easily predict the possible behavior of the ceramic once incorporated to the necessary materials. 2. Objectives of the Study

The main objective of this study is to prepare the calcium doped barium titanate ceramics using the solid state reaction mechanism. Specifically, the product will be characterized in terms of the following properties: 1. Crystalline structure with the use of Powder X-ray Diffraction 2. Microstructural Behavior using Scanning Electron Microscopy 3. Dielectric...
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