Effect of heat treatment in HF atmosphere on the optical and electrical properties of BaF2 ceramics

Using optical spectroscopy and complex impedance measurements, we have studied the transmission spectra and electrical conductivity of different BaF2 samples: ceramic prepared by vacuum hot pressing (200 MPa, 870°C, 20 min), the same ceramic after heat treatment in a reactive HF atmosphere (1200°C, 120 min), and a single crystal grown from the melt in vacuum. Heat treatment of the as-prepared BaF2 ceramic in a fluorination atmosphere increases its optical transmission in the range 0.2–0.8 µm on average by a factor of 2 and markedly reduces the selective absorption in the range 6–11 µm. The heat-treated BaF2 ceramic is close in ionic conductivity to the BaF2 single crystal.