Phase Transition of Dehydrated Calcined AlPO4-5 Investigated by in-situ Synchrotron XRD

 

Hwo-Shuenn Sheu,a Jey-Jau Lee,a Khin Win Phyu,a and Kuei-Jung Chaob

aNational Synchrotron Radiation Research Center, Hsinchu 300, Taiwan; bDepartment of Chemistry, National Tsinghua University, Hsinchu 300, Taiwan (hsheu@srrc.gov.tw)

 

 


Fig. 1. Variable temperature synchrotron XRD of dehydrated AlPO4-5. The modulation peaks are marked (*). Baseline of each pattern was shifted for clarify.

 
AlPO4-5 (IUPAC structure type AFI) was reported to consist of 4, 6, 12-membered rings and forms a hexagonal arrangement of parallel and one-dimensional channels. A commensurate modulated structure along c axis was observed in the dehydrated, calcined AlPO4-5. The commensurate modulated structure is reversible during hydration and dehydration at room temperature. The modulation structure of dehydrated AlPO4-5 was determined to give the wave vector q being one-dimensional and a value of 3/8c*. In-situ synchrotron XRD studied found that modulation peaks disappear at the temperature above 70¡C. This phase transition is reversible during heating and cooling between room temperature and 90¡C (Fig. 1). No further phase transition was found up to 400¡C. The crystal structure at 90¡C was refined by Rietveld method with space group P 6cc. This crystal structure is similar to that of hydration form at room temperature.