A Neutron Diffraction Study of Quartz-Type FePO4: High-Temperature Behavior and α-β Phase Transition
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MODEL ANSWER
Haines et al., A neutron diffraction study of quartz-type FePO4: high-temperature behavior and α-β phase transition Z. Kristallogr. 218, 193-200 (2003).
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Paragraph 1
This research paper discussed about the structural evolution of FePO4 from temperature range of 294K to 1073K. The cell parameters and atomic coordinates in the α phase tend to wars the value obtained in the high-temperature β-phase and exhibit first order transition at 980K.
The cell parameters of the α-phase FePO4 increased in a non-linear fashion with respect to temperature. The volume data is govern by a thermal expansion coefficient α (K-1)= 2.924 x
10-5 + 2.920 x 10-10 ( T-300)2. Main factors contributing to the thermal expansion are; the angular variations caused by the changes in the 2 symmetrically-independent intertetrahedral
Fe-O-P bridging angles as well as the tilt angles. Volumetric dependence on temperature is governed by the behaviour of the average δ and θ angles as a function of temperature. The
Fe-O distance in the tetrahedral phase was found to have an inverse relationship with temperature, which is similar to the behaviour observed in Si-O distance in α-quartz. This phenomenon can be explained by the non-physical behaviour due to the increasing disorder coupled by the increasing temperature from low-energy, high-amplitude vibrations. For the αβ transition δ2 = 2/3 δ02 [1 + (1 – ¾ (T – Tc/T0 – Tc))^1/2], the temperature dependence of tilt angle δ. Where δ0 is the decrease in tilt angle at the transition temperature (980K) and Tc is the temperature for the second-order transition. The overall average tilt angle δ is taken as the individual average tilt angles. The behaviour of FePO4 does not follow the behaviour of other α-quartz homeotypes. The δ angle begins to decrease in a more rapid fashion than quartz.
Figure 2: Crystal structure α-phase FePO4
Figure 1: Crystal structure of quartz
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Group A:
GROUP A
MODEL ANSWER
Haines et al., A neutron diffraction study of quartz-type FePO4: high-temperature behavior and α-β phase transition Z. Kristallogr. 218, 193-200 (2003).
DO NOT PLAGIARISE THIS MODEL ANSWER
Paragraph 1
This research paper discussed about the structural evolution of FePO4 from temperature range of 294K to 1073K. The cell parameters and atomic coordinates in the α phase tend to wars the value obtained in the high-temperature β-phase and exhibit first order transition at 980K.
The cell parameters of the α-phase FePO4 increased in a non-linear fashion with respect to temperature. The volume data is govern by a thermal expansion coefficient α (K-1)= 2.924 x
10-5 + 2.920 x 10-10 ( T-300)2. Main factors contributing to the thermal expansion are; the angular variations caused by the changes in the 2 symmetrically-independent intertetrahedral
Fe-O-P bridging angles as well as the tilt angles. Volumetric dependence on temperature is governed by the behaviour of the average δ and θ angles as a function of temperature. The
Fe-O distance in the tetrahedral phase was found to have an inverse relationship with temperature, which is similar to the behaviour observed in Si-O distance in α-quartz. This phenomenon can be explained by the non-physical behaviour due to the increasing disorder coupled by the increasing temperature from low-energy, high-amplitude vibrations. For the αβ transition δ2 = 2/3 δ02 [1 + (1 – ¾ (T – Tc/T0 – Tc))^1/2], the temperature dependence of tilt angle δ. Where δ0 is the decrease in tilt angle at the transition temperature (980K) and Tc is the temperature for the second-order transition. The overall average tilt angle δ is taken as the individual average tilt angles. The behaviour of FePO4 does not follow the behaviour of other α-quartz homeotypes. The δ angle begins to decrease in a more rapid fashion than quartz.
Figure 2: Crystal structure α-phase FePO4
Figure 1: Crystal structure of quartz
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