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For α-Quartz, its lattice symmetry is trigonal, and for β-Quartz, its lattice symmetry is hexagonal. For α-FePO4, its space group is P3121 and thus its lattice symmetry can be inferred to be also trigonal, just like α-Quartz. Similarly, β-FePO4 space group is P6422 and its lattice symmetry can be inferred to be hexagonal, just like β-Quartz. Although the chemical structures of quartz and FePO4 are different, with quartz having a formula of SiO2, they can actually be in the same structure and have the same space symmetry. Fe atom is trivalent, and P atom is pentavalent. This means that their total charge will be +8, and as such can be bonded to up to 4 oxygen atoms. For Si to be bonded to 4 oxygen, there needs to be 2 Si atoms too. And since Si is tetravalent, it means that 2Si also has a total charge of +8, similar to that of Fe and P combined. Thus, both structures each have 2 atoms …show more content…
For the volume to increase, the ‘cages’ of molecules has to be ‘inflated’, thereby making it bigger and occupy more space. To make the ‘cage’ bigger, the bond angle has to change and as such, FeO4 and PO4 tetrahedral will change as well. This changing of bond angle causes a tetrahedral distortion. Tetrahedral tilting also contributes to the tetrahedral distortion, where the tilt angle will decrease with temperature, causing the tetrahedral to become distorted from its original form. When increasing the temperature in α phase, the tetrahedral tilting will decrease until it reaches 0 in the β phase. However, once in the β phase, the tilt angle has reached 0. Thus the ‘cage’ has been fully expanded, and there can be no more extra increase in volume. This is supported by data in the paper, where volume does not increase anymore in β phase as temperature increases. The α-β transition can be modelled using the parameter, tilt angle, δ. Average tilt angle is temperature dependent where this Landau-type model is
For α-Quartz, its lattice symmetry is trigonal, and for β-Quartz, its lattice symmetry is hexagonal. For α-FePO4, its space group is P3121 and thus its lattice symmetry can be inferred to be also trigonal, just like α-Quartz. Similarly, β-FePO4 space group is P6422 and its lattice symmetry can be inferred to be hexagonal, just like β-Quartz. Although the chemical structures of quartz and FePO4 are different, with quartz having a formula of SiO2, they can actually be in the same structure and have the same space symmetry. Fe atom is trivalent, and P atom is pentavalent. This means that their total charge will be +8, and as such can be bonded to up to 4 oxygen atoms. For Si to be bonded to 4 oxygen, there needs to be 2 Si atoms too. And since Si is tetravalent, it means that 2Si also has a total charge of +8, similar to that of Fe and P combined. Thus, both structures each have 2 atoms …show more content…
For the volume to increase, the ‘cages’ of molecules has to be ‘inflated’, thereby making it bigger and occupy more space. To make the ‘cage’ bigger, the bond angle has to change and as such, FeO4 and PO4 tetrahedral will change as well. This changing of bond angle causes a tetrahedral distortion. Tetrahedral tilting also contributes to the tetrahedral distortion, where the tilt angle will decrease with temperature, causing the tetrahedral to become distorted from its original form. When increasing the temperature in α phase, the tetrahedral tilting will decrease until it reaches 0 in the β phase. However, once in the β phase, the tilt angle has reached 0. Thus the ‘cage’ has been fully expanded, and there can be no more extra increase in volume. This is supported by data in the paper, where volume does not increase anymore in β phase as temperature increases. The α-β transition can be modelled using the parameter, tilt angle, δ. Average tilt angle is temperature dependent where this Landau-type model is