Paragraph 1
The research paper talks about how the temperature of formation and crystallinity of iron phosphate, FePO4, is critical in determining its electrochemical behaviour. FePO4 is known to crystalline in several different structures. At 600 degrees, FePO4 irreversibly changes into an electrochemically inactive quartz-like structure, which shows that the olivine form is metastable. FePO4 at a high temperature is limited to measurements of call parameters. In the case of α-phase FePO4, cell parameters tend to increase exponentially as temperature increase. The volume of the metal has the tendency to increase exponentially as well. It is governed by thermal expansion coefficient α (K-1)= 2.924 x 10-5 + 2.920 x 10-10 (T-300)2. There are two factors that affect the thermal expansions:
1. Angular variations due to the changes of Fe-O-P bridging angles.
…show more content…
When the temperature falls below temperature of 980K, the structure is trigonal and posses the lattice boundaries a=b=c, α= β= γ ≠ 90°. The structure will transform from a α-model to the β-model and become a hexagonal unit cell. This then portrays the difference between the symmetries of the two different structures. According to Table 2, it shows the changes in cell parameters as well as volume in relation to the temperature of the metal. It therefore shows us that when temperature rises, the crystal forms will change as they are affected by changes in temperature. This will then result in an expansion in the volume of the crystal when the temperature rises. As mentioned, at the transition point of 980K, the structure will transform from a α-model to the β-model and become a hexagonal unit cell. The various diagrams below portray this, which reflects the changes that the crystal form undergoes at 980K-transition