Scattering‐Loss Mechanism in CaF 2 ‐Film‐Assisted Diffusion Bonding of MgF 2 Ceramics

The present study examined the bonding of MgF 2 ceramics by hot‐pressing. A layer of CaF 2 2 to ∼3 μm thick was used as an agent to decrease the bonding temperature and to avoid breaching. The principal factors influencing transmission loss were the cellular growth in the MgF 2 layer, which caused about a 5% loss in transmittance, and grain growth in the films, as well as voids caused by the lattice mismatch, which, together with the formation of a recrystallization zone, caused about a 20% loss in transmittance. Grain growth in the CaF 2 film was not the main cause of the scattering loss. The effect of the grain growth in the MgF 2 matrix on transmittance was calculated as about 5%. Compositional fluctuations along the interfaces also had an important influence on scattering loss. For the sample that bonded at 650°C after 5 h, under a pressure of 430 kg/cm 2 (42 MPa), the crystalline solubility limit of CaF 2 in MgF 2 was measured at ∼l7at.%.