Haines Research Paper

792 Words 4 Pages
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Compare and contrast the crystal structures and crystal chemistry of quartz, α-FePO4 and β-FePO4.
Haines’ research paper studies the change that occurs in the FePO4 structure as it is studied from temperatures 294K to 1073K. A transition is noticed at 980K, when it’s tetrahedral α-quartz structure experiences high pressure levels, changing the structure to β-phase, a more dense octahedral structure. Cell parameters of FePO4 in α-phase increases in cell parameters and volume as temperature increases. However, the significant increase is not dependent linearly between them. The thermal coefficient that the volume data abides to is α (K-1) = 2.924 x 10-5 + 2.920 x 10-10 (T-300)2. The Angular variations caused by the changes in the
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The symmetry of FePO4 at α-phase is Trigonal as compared to the hexagonal symmetry of FePO4 at β-phase. Cell parameter of FePO4 increases with much significance as the temperature increases, causing volume to increase also. Preferential expansion in a direction is also observed, causing a decrease in c/a ratio in accordance to the temperature increase. The Fe-O-P bond will also increase in size noticeably.
As FePO4 enters β-phase, the change in both bond distance and angle will not be very noticeable in accordance to the change in temperature. The bigger the bond distance, the higher the degree of dynamic disorder within β-phase. FePO4 uses tilt angle δ as its individual average tilt angles. PO4 Tetrahedra relies on O1 and O2 fractional atomic coordinates in the structure. As the structure gradually reaches the α-β transition temperature of 980K, the tetrahedral tilt angle δ can be noticed from the table below to decrease significantly. As the bridging angles of Fe-O-P increases, we can observe important discontinuities in the structure’s parameters as it undergoes this first order transition. No thermal expansion can be observed during this
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PO4 tetrahedrons, used to determine structural integrity and properties, can be found in FePO4. The tetrahedral tilt angle δ and intertetrahedral bridging angle θ of FePO4, can be said to be part of tetrahedral distortion. The change in its bond length and O-PO angle can be considered to bring about tetrahedral distortion during the increase temperature. We should consider the tetrahedral as an inflexible body as its tetrahedral tilt is a big factor to determine tetrahedral distortion. We can consider the tetrahedral tilt to cause tetrahedral distortion, expressed by tilt angle δ and its reliance on temperature changes. The cell parameters and volume of FePO4 in α-phase, show much increase, though not linearly with temperature. The main reason of thermal expansion is brought about by the angular variations created from altering both the bridging angles of symmetrically-independent intertetrahedral Fe-O-P and the related tilt angles. As such, it can be said that the reliance of temperature in thermal expansion is actually the angular variations of both intertetrahedral bridging angles and tetrahedral tilt angles, and their dependence on the temperature

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