Tetrahedral Distortion Lab Report

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Tetrahedral distortion is defined as the change in both the distance of bond and angle of bond are present. The degree of distortion with respect to the beta phase can be related to the tetrahedral tilt angle and the intertetrahedral bridging angle. While for tetrahedral tilting, there is only change in the angle of the bond and no change in bond distance. When there is an increase in temperature, the Fe-O-P bridging angles increases and the tetrahedral tilt angles decreases. As the temperature increases from 294K to 1073K, Fe-O bond distance decreases and the bond tilt angle is also smaller. Whereas for PO4, the increase in temperature causes compression which cause the bond tilt angle to decrease. At high temperature which is the beta phase of FePO4, given that the increase in volume is only related to the changing of the angles between the tetrahedral (tilting angles), the structure should not be able to expand anymore and there would be no further change in volume. In beta phase of FePO4, the volume does not expand any further as the structure is fully expanded. In the beta phase of FePO4, the bond distance decreases as the temperature increases. The bond distance and angle also changes significantly with the temperature. For example, for Fe-O, the bond distance decrease from 1.75 to 1.73 from 1005K to 1073K. In the alpha phase of FePO4,…show more content…
With an increasing temperature, there would be an increase in volume and the tilt angle would decrease. By looking at the space group of alpha phase of FePO4 which is P3121, it shows that for low temperature form, there will be 3 one screw axis and for the space group of beta phase of FePO4 which is P6422, it shows that for high temperature form, there will be 6 four screw axis. This also explains the unit cell structure of alpha phase of FePO4 being trigonal and changing to hexagonal in the beta phase of
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