In recent years there have been increasing activities in studying infrared transparent polycrystalline ceramics,such as Al2O3,MgAl2O4,AlON and Y2O3.But increased mechanical strength,thermal shock resistance and lower emissivity are required for future infrared transparent windows working in severer mechanical and thermal environment than those used today.Both Y2O3 and MgO are infrared transparent,have a longer wavelength cutoff and lower emissivity than other intermediate infrared materials.