Birefringence study of the α-β transformation of berlinite, AlPO4
- 20 March 1984
- journal article
- Published by IOP Publishing in Journal of Physics C: Solid State Physics
- Vol. 17 (8), 1375-1383
- https://doi.org/10.1088/0022-3719/17/8/012
Abstract
The variation of birefringence in AlPO4 is investigated between 300 and 90K. In the alpha phase it can be fitted very well with a classical law for first-order phase transitions. In qualitative agreement with previous cp measurements the possibility of intermediate states between the alpha and beta phases is derived from local birefringence measurements. Taking into account the existence of an incommensurate phase, the results are interpreted as a manifestation of a Devil's staircase regime, with pinning due to impurities. A slight anomaly occurring 2.5K above the alpha phase on heating is proposed to be due to the alpha beta -incommensurate phase transition. Finally, the observed proportionality between the birefringence derivative d Delta n/dT and cp is briefly discussed.Keywords
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