Abstract: Compressive deformation behavior of a polycrystalline magnesium fluoride (MgF2) ceramic was investigated at temperatures ranging from 760 to 830°C in an argon atmosphere at strain rates between 2×10−6 and 4×10−5 s−1. Steady-state flow stresses increased with increasing strain rates and ranged between 2 and 38MPa. Stress exponents of ≈1.4±0.2 were determined at temperatures >760°C, indicative of a viscous diffusion-controlled deformation mechanism. Activation energy, determined from flow stress as a function of temperature, at a constant strain rate, was ≈476±60kJ/mol. Self-joining by plastic deformation of MgF2 was demonstrated at 830°C at a strain rate of 5×10−6 s−1. The joined samples were characterized by optical transmission measurements and their transmittivity was ≈80% of the unjoined sample in the 2.5–8μm wavelength range. [Copyright &y& Elsevier]