Ba, Ti & O Atoms Has Been Considerably Changed. The Three

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Ba, Ti & O atoms has been considerably changed. The three dimensional view of enlarged portion of Ba-O and Ti-O bonds for three different Sr doping levels is given in figure 2.32. The increasing incorporation of Sr in the crystal structure of BaTiO3 increases the volume of the electron density distribution around Ba atom. The reduction in the bond lengths of Ba-O and Ti-O has also been clearly visualized from this figure.
To analyze the nature of bonding qualitatively, 2D electron density contour maps have been constructed for the Sr doped samples for three different crystallographic planes, with contour interval of 0.04 e/Å3. Figure 2.33(a) shows the 3D unit cell of BST with (100) plane shaded and (b), (c) & (d) represent 2D electron
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The density of the contour lines along the Ti-O bonding region increases with the increasing doping levels of Sr. The overlapping of contour lines along Ti-O bond exhibits the covalent nature of bonding which is due to the result of hybridization between the O-2p and Ti-3d orbitals. When the smaller Sr ion is substituted at the lattice site of larger Ba, the volume of the unit cell become smaller and Ti ions can be in good touch with all the O ions which increases the covalent nature of Ti-O bond.
The quantitative analysis of chemical bonding between the constituent atoms has been carried out by drawing the 1D electron density line profiles for Ba-O and Ti-O bond. Figure 2.36 shows the 1D electron density line profiles for Ba-O bond for three different Sr concentrations. Figure 2.37 shows the 1D electron density line profiles for Ti-O bond for three different Sr concentrations.
The bond lengths and mid bond electron density values for Ba-O and Ti-O bonds of Ba1-xSrxTiO3 (x=0.2, 0.4 & 0.6) are given in table 2.15. The value of mid bond electron density along Ba-O bond decreases with respect to Sr incorporation. The values of electron density show the increase in ionic nature of the prepared samples due to Sr doping. Along the Ti-O bond, the mid bond density values show increasing trend with the addition of Sr content which confirms the decrement in ionic nature

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