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.