Phy-O-Quartz Lab

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SYMMETRY WRITING EXERCISE

PARAGRAPH I

FePO4 is a type of -quartz, and when the temperature is relatively low, FePO4 still has the tetrahedral structure as seen in Figure 1. The Fe-O-P bridging angles are more similar between the FePO4 and -quartz. Change in the cell parameters become more significant between temperatures of 294K and 1073K, and it slowly acquires an octahedral structure as the temperature increases. When temperature reaches 980K, the compound transitions and the tilt angles decrease rapidly at an exponential rate. The thermal expansion coefficient α (K-1) = 2.924 x 10-5 + 2.920 x 10-10 (T-300)2 is below that of α-quartz’s. This is because the tilt angles vary and this is in turn caused by alterations between the Fe-O-P bridging
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α-FePO4’s unit cell structure is trigonal, and that of the -FePO4’s is hexagonal. The following lattice parameters: a = b = c and α = β = γ ≠ 90° are relevant to the trigonal unit cell structure of α-FePO4. α-FePO4 and β-FePO4 have pretty much identical symmetry when examined closely. The lattice parameters of hexagonal unit cells are: a = b ≠ c and α = β = 90°, γ = 120°. β-FePO4 contains Fe in the 3D sites, and Fe has an A cation which is a transition metal. The higher temperature leads to the atoms shaking violently and excitedly and drawing closer to one another. This results in the reduction of tilt angles as temperature …show more content…
The tetrahedral tilt angle δ, together with the inter-tetrahedral bridging angle θ, interact to set up tetrahedral deformation. At elevated temperatures, the bond length change and the O-PO angle could also affect tetrahedral deformation. One thing to note, we have to imagine that the tetrahedrons are in a fixed configuration because the tetrahedral deformation is caused by tetrahedral tilt with its tilt angle δ, and is easily influenced by temperature. As mentioned in the previous paragraphs for the α phase, the cell parameters and volume increase significantly and non-linearly in relation to temperature. Angular deviations exhibited by alterations in the two symmetrically-independent inter-tetrahedral Fe-O-P bridging angles, and the associated tilt angles are the main factors that cause thermal expansion, which means that the temperature dependence of thermal expansion is actually that of the angular deviations of θ and δ. This is depicted via the Landau-type

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