Quartz-Type Fepo4 Lab Report

Paragraph 1
The research paper written by Haines et al. concerns the investigation of structural and chemical properties of quartz-type FePO4, where observations are made regarding the quartz-type FePO4 at elevated temperatures and during the occurrence of the α- β transition stage. The temperature range that was selected for the investigation was from 294K to 1073K and the investigation was carried out by neutron powder diffraction. The properties of the quartz-type FePO4 was compared to other α-quartz homeotypes such as SiO2 and AlPO4, and it was discovered that the quartz-type FePO4 behaves in a markedly different manner from SiO2 and AlPO4 in the α- phase. The space group of FePO4 is P3121 in the α- phase, P6422 in the β phase, and for
The lattice symmetry of quartz-type FePO4 is trigonal in the α- phase, and in the β phase the lattice symmetry is hexagonal. As for SiO2, the lattice symmetry is trigonal. The lattice symmetry of FePO4 in the α- phase and SiO2 is similar as 2 silicon atoms can replace 1 iron and 1 phosphorus atom in the crystal structure. Looking at this stoichiometric equation, Fe3+ + P5+  2Si4+, we can see that there are 2 atoms on both side of the equation and total charge on both sides is equal, therefore both SiO2 and FePO4 in the α- phase have a similar lattice symmetry. At low temperatures quartz-type FePO4 ¬exists in the α phase, while at elevated temperatures quartz-type FePO4 exists in the β phase. During the α phase, a noticeable rise in the cell parameters and volume in quartz-type FePO4 was observed, when there was a corresponding increase in the temperature. However, this increase in cell parameters and volume did not increase in a linear fashion with respect to temperature. The thermal expansion coefficient was acquired and is shown as such: α (K-1) = 2.924 x 10-5 + 2.920 x 10-10¬ (T – 300)2. In comparison with α-quartz homeotypes SiO2 and AlPO4, the thermal expansion in quartz-type FePO4 was found to be lesser than that in
The quartz-type FePO4 is observed to exhibit behaviour that is very different from the other α-quartz homeotypes SiO2 and AlPO4, and a major factor for the differences is the fact that the A cation is a transition metal. The Fe cation is proportionately bigger compared to the closed shell cations of groups 13 to 15 due to the partially occupied d orbitals that are present in the cation. Consequently, the proportionately bulkier size of the Fe-centered tetrahedron results in a lower mass in relation to its size. This presence of a transition metal cation is likely the cause of the transition from the α phase to the β phase for quartz-type FePO4 as other similar α-quartz isotypes do not demonstrate this transition phase