Compare And Contrast The Crystal Structures And Crystal Chemistry Of

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Compare and contrast the crystal structures and crystal chemistry of quartz, α-FePO4 and β-FePO4
To compare quartz, α-FePO4 and β-FePO4, it is essential to look at their crystal structures and crystal chemistry. This can be done by observing their three-dimensional structures as well as their reactions to various degrees of temperature. This particular research takes a look at the structure of FePO4 between temperatures of 294K to 1073K. At lower temperatures, FePO4 takes on its α-phase structure, which is tetrahedral. α-FePO4 then gradually transitions as the temperature increases to β-FePO4 in terms of structure. This first-order transition occurs at 980K. However, this transition is not linear. For α-FePO4,
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At a high temperature (980K), FePO4 will undergo α-β phase transition. Tetrahedral distortion is caused by the tilt angle δ as well as the bridging angle θ, both of which vary according to temperature. During the α phase, cell parameters and volume increase non-linearly as temperature increases. Due to the two symmetrically-independent Fe-O-P bridging angles and the correlated tilt angles, the tilt angles become a significant factor to the cell volume and parameter. And because of that, the change in angles caused by a change in temperature will inevitably lead to a change in the cell parameter and volume. This results in the phenomenon of thermal expansion as exemplified by Table 2 above. Furthermore, the crystal structure of FePO4 tends more and more towards the β phase as temperature increases. As for the FeO4 and PO4 tetrahedra, the change in their structures can be seen through Table 5, where the O-Fe-O bond angles decrease. Furthermore, in Table 4 (taken from J. Haines, et al. (2003) A neutron diffraction study of Quartz-type FePO4: high-temperature behaviour and α-β transition Z. Kristallogr. 218, 193-200 (2003).) below, it can be seen that the bond distances of Fe-O decrease as temperature increases. Both of these factors result in the structure of FeO4 to change in size as temperature increases. By the same token, the O-P-O angles change as temperature increases, while the P-O bond distances change as temperature increases. This results in a change in size in the structure of PO4 as temperature increases. The equation δ^2 = 2/3 δ0^2 [1 + (1 – ¾ (T – Tc/T0 – Tc))^1/2] can be used here to describe quantitatively how the temperature affects the cell parameter and size, as we have earlier established how temperature affects the tilt angle which affects the cell parameter and

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