Iron phosphate (FePO4) has a trigonal lattice structure with space group P3121. It resembles that of quartz very closely. Iron phosphate exists as α-FePO4 below 980oK. This exhibits trigonal lattice structure, with the space group of P3121. Wyckoff positions of the atoms are as follows: iron on 3a; phosphate on 3b; oxygen on 6c. Each of the iron and phosphate atom is connected to 4 oxygen atoms. This forms a connected FeO4 and PO4 tetrahedra. At temperature levels above 980oK, α-FePO4 will transition from α to β and result in β-FePO4. This new β-FePO4 has a hexagonal lattice structure which is essentially the space group P6422. Wyckoff positions of the atoms are as follows: iron on 3d; phosphate on 3c; oxygen on 12k.
Consider…show more content… But in contrary, the inter-tetrahedral bridging angle will increase as temperature increases. This similar trend can also be observed in β-FePO4. However, the trend of thermal expansion is not clear for β-FePO4. As temperature is increasing from 1005K to 1073K, the unit cell volume will not increase that much, only increasing 0.18 Å3. This can be explained by the fact that the tilt angles are already at the minimum value 0o in β-FePO4. The volume of the cage is therefore at its maximum and further increase in temperature will never lead to a significant expansion in…show more content… The tetrahedra atoms in PO4 tilts more than those in FeO4. Quoting from the article, “the tilt angle of the smaller tetrahedron is greater than that of the larger one”, the fact before is therefore consistent. The phosphate(V) ions have5 smaller ionic radii compared to the iron(III) ions. This causes the tetrahedron of FeO4 to be greater than that of PO4, and will result in larger tilt angles. Analyzing from the temperature range levels, when the temperature level ranges from 294oK to 969oK, the bond distance between Iron and Oxygen decreases from 1.858 Å to 1.818 Å. The bond length continues to decrease beyond the transition phase of α-β at 980oK. The bond distance between iron and oxygen atoms (Fe-O) continues to decrease to 1.75 Å after transition, and continues to decrease even further to 1.73 Å as the temperature levels rise beyond 1073oK. This consistent decrease in bond length only occurs in FeO4 tetrahedron. In the PO4 tetrahedron, the bond length varies between different temperature levels