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Abstract
The spontaneous birefringence, Δns, of the rhombohedral ferroelectric phase of PFT has been measured between 20K and the hitherto unknown first order transition at 210K (heating)/205K (cooling). Above that transition a weakly birefringent phase is evinced, which undergoes a second order transition to cubic at ∼ 248K. Pronounced photoconductivity occurs below room temperature. A strong reversible temperature shift (-5. 7 cm-1K-1) of the absorption edge obscures the material upon heating.