Symmetry: Alpha Beta

Writing Exercise – FePO4 Polymorphs (1,214 words written)

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It is commonly known that the FePO4 is arranged in a quartz-like structure and differs significantly from other alpha-quartz due to the presence of its transition metal cation. A structural transformation takes place for the FePO4 over a time of flight neutron powder diffraction range ranging from a temperature of 294 K up to 1073 K. The low-temperature alpha phase structural components move towards the figures exhibited by the high-temperate beta-quartz-type FePO4 gradually. Particularly, significant gaps in the cell parameters and atomic coordinates takes place when the first order transition is executed at 980K, increasing the bridging angles of Fe-O-P while resulting in a large fall in the tetrahedral tilt angles. To put it simply, the transformation into a tetrahedral alpha-quartz structure happens when the temperature is relatively low, whereas a high temperature brings about the formation of a denser octahedral beta-phase structure. The angular variations resulting from the developments in the 2 bridging angles of Fe-O-P and tilt angles are the dominant contributing factor giving rise to the strongly non-linear thermal expansion of the cell parameters happening in the alpha phase. This brings about a thermal expansion coefficient of (K-1) = 2.924 x 10-5 + 2.920 x 10-10 (T-300)2. The beta phase differs largely as compared to the alpha phase. The lack of such operations in the beta phase explains why the beta phase has no signs of thermal expansion. The greater angular variations and the inexistence of scaling with the initial structural distortion that takes place in the alpha phase are two of the factors that in reality accounts for the difference in alpha phase behavior as compared to those of other alpha-quartz homeotypes present. These two factors also demonstrate clearly how there is a possibility of alpha-quartz-type FePO4 having dynamic instability. How the δ and θ tilt...