Abstract
A study of the PbF2-AlF3 system has resulted in a new material Pb5Al3F19 with a tetragonal structure at room temperature closely related to that of Pb5Cr3F19. A phase transition in Pb5Al3F19 has been detected by means of X-ray diffraction, calorimetric and dielectric measurements. The coexistence of the high and low-temperature Pb5Al3F19 phases over the range 270 to 300 K and the abrupt 0.7% increase in the a-axis and 1.5% decrease in the c-axis, on heating through the phase transition, are characteristic of a first-order phase change. The increase in symmetry from point group 4 below to point group 4/m above the phase transition is consistent with a ferroelectric to paraelectric transition, as found previously in Pb5Cr3F19.