Barium Titanate Lab Report

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Crystal structure of barium titanate Barium titanate (BaTiO3) is a potential candidate of a large family of compounds with general formula ABO3 termed as perovskite [Hench et al. 1990]. The perovskite structure is a primitive cube, with larger A-cations situated at eight corners, smaller B-cations at the body centre position of the cube and the anions commonly Oxygen are in the face centres. Generally A is a monovalent, divalent (or) trivalent metal and B is a pentavalent, tetravalent (or) trivalent atom [Vijotovic et al. 2008]. The unit cell of the ideal cubic perovskite BaTiO3 is shown in the figure 1.1(a). The coordination number of barium(atomic number: 56, valency: 2+) is 12, and for titanium (atomic number: 22, valency: 4+) is 6. The…show more content…
The transition temperature (Curie point) Tc of BaTiO3 is 120 ºC. Above this Curie point, the ideal cubic structure is stable up to the temperature1460 ºC. Above 1460 ºC, hexagonal structure with space group P63/mmc (space group number: 194) is stable [Cho, 1998]. When the transition temperature is below the Curie point, a phase transition between cubic and tetragonal structure with space group P4mm, (space group number 99) takes place. At 5 ºC, the phase transition to the orthorhombic structure with space group Amm2 (space group number 38) goes on and at -90 ºC to the low temperature phase has a rhombohedral structure with space group R3m (space group number: 160) [Koelzynski et al. 2005]. Figure 1.2(a-d) shows the various crystallographic changes of BaTiO3. Stability and formation of the ABO3 perovskite based compounds have been related to the tolerance factor (t) given by Goldschmidt [Goldschmidt, 1926], which is represented as, t=(r_A+r_0)/(√2 (r_B+r_0 )…show more content…
It is white to grey in color when in powder form. It possesses high chemical and mechanical stability. It is soluble in sulfuric, hydrochloric and hydrofluoric acids, but insoluble in alkalis and water. The density of BaTiO3 is 6.02g/cm3 and the melting point is 1625 ºC. The transition temperature (Curie point, Tc) is 120 ºC. BaTiO3 is a perfect insulator in its pure form with the band gap of 3.2eV, and when doped, the insulating property changes. It also exhibits semiconducting property depends upon the type of dopants. However, when doped with particular amounts of isovalent (or) aliovalent metal ions, the significant properties of BaTiO3 can be greatly modified. It exhibits high dielectric constant, low dielectric loss and prominent electrical tunability. Doped BaTiO3 ceramic materials show positive temperature coefficient of resistivity (PTCR) property and piezoelectric property. At a certain temperature called Curie temperature (Tc), the resistivity of the material dramatically shoots up to several orders of magnitude (Li et al. 2005). It was also reported that single crystal of barium titanate exhibits a negative temperature coefficient of resistance (NTCR) property. It also exhibits optical property and pryoelectric

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