THERMAL-EXPANSION AND INDEX-OF-REFRACTION VARIATION IN LEAD FLUORIDE BETWEEN 300 AND 850K

Diffuse transitions have been observed in alkaline-earth and lead fluorides at temperatures below their melting points. High ionic conductivity saturates above the transition temperature. One also observes lattice melting, a peak in the heat capacity, and an onset of disorder associated with lattice defects. We have observed an anomalous variation in the thermal variation of optical path length and the coefficient of linear expansion. This anomalous behavior occurs at about 705 K and appears to be associated with the formation of defects. © 1990 The American Physical Society.