Written Exercise
Paragraph 1
1. Lattice symmetry of quartz, α-FePO4 and β-FePO4:
Quartz has a trigonal lattice structure with space group P3121 (group no. 152).
At any temperature below 980K, Iron phosphate exists as α-FePO4, which has a trigonal lattice structure with space group P3121 (group no. 152) where iron, phosphate and oxygen occupy Wyckoff position 3a, 3b and 6c respectively. As the temperature rises up to and above 980K, α-FePO4 exhibits α-β transition and becomes β-FePO4 that shows a distinct lattice and space symmetry from α-FePO4. β-FePO4 has hexagonal lattice structure with space group P6422 (group no. 181), in which iron, phosphate and oxygen occupy Wyckoff position 3d, 3c and 12k respectively.
2. Crystal chemistry and …show more content…
With a rise in temperature, the atoms with in crystal vibrate more vigorously, resulting in an expansion of thermal ellipsoids. As such, the atomic volume increases and the internal crystal structure changes through tetrahedral tilting. An ordered structure with high level of symmetry is formed.
As temperature increases from 294K to 969K, α-FePO4 undergoes thermal expansion in which the cell parameters and volumes increases in a non-linear manner. This is due to a change in the intertetrahedral Fe-O-P angles and the tilt angles. As temperature exceeds 980K, α-FePO4 is transited to β-FePO4 with a change in lattice structure from trigonal to hexagonal. There is still increase in cell parameters and expansion in cell volume as temperature continues to increase, yet the increment is much smaller compared to α-FePO4. The bond angles and bond distances decrease in β-FePO4.
Paragraph 2
1. Unit cell relationship between α-FePO4 and β-FePO4: α-FePO4 has a trigonal unit cell with lattice structure a = b = c; α = β = γ ≠ 90° and β-FePO4 has hexagonal unit cell with a lattice structure a = b ≠ c; α = β = 90°, γ = 120°. The dimensions are broadly the same even though there is a temperature
Paragraph 1
1. Lattice symmetry of quartz, α-FePO4 and β-FePO4:
Quartz has a trigonal lattice structure with space group P3121 (group no. 152).
At any temperature below 980K, Iron phosphate exists as α-FePO4, which has a trigonal lattice structure with space group P3121 (group no. 152) where iron, phosphate and oxygen occupy Wyckoff position 3a, 3b and 6c respectively. As the temperature rises up to and above 980K, α-FePO4 exhibits α-β transition and becomes β-FePO4 that shows a distinct lattice and space symmetry from α-FePO4. β-FePO4 has hexagonal lattice structure with space group P6422 (group no. 181), in which iron, phosphate and oxygen occupy Wyckoff position 3d, 3c and 12k respectively.
2. Crystal chemistry and …show more content…
With a rise in temperature, the atoms with in crystal vibrate more vigorously, resulting in an expansion of thermal ellipsoids. As such, the atomic volume increases and the internal crystal structure changes through tetrahedral tilting. An ordered structure with high level of symmetry is formed.
As temperature increases from 294K to 969K, α-FePO4 undergoes thermal expansion in which the cell parameters and volumes increases in a non-linear manner. This is due to a change in the intertetrahedral Fe-O-P angles and the tilt angles. As temperature exceeds 980K, α-FePO4 is transited to β-FePO4 with a change in lattice structure from trigonal to hexagonal. There is still increase in cell parameters and expansion in cell volume as temperature continues to increase, yet the increment is much smaller compared to α-FePO4. The bond angles and bond distances decrease in β-FePO4.
Paragraph 2
1. Unit cell relationship between α-FePO4 and β-FePO4: α-FePO4 has a trigonal unit cell with lattice structure a = b = c; α = β = γ ≠ 90° and β-FePO4 has hexagonal unit cell with a lattice structure a = b ≠ c; α = β = 90°, γ = 120°. The dimensions are broadly the same even though there is a temperature