Infrared low-index evaporation materials are essential in the broadband antireflection coatings to reduce Fresnel reflections on the surfaces of infrared optical components. Although the layers of praseodymium fluoride (PrF3) show an excellent transparency and the lower refractive index n and extinction coefficient k in the spectral range of thermal infrared, the tensile stress presented in the layers prohibits PrF3 from being used as infrared low-index coating materials. A practical solution to reduce stress is to directly evaporate the admixture of PrF3 with alkaline fluorides, such as barium fluoride (BaF2). However, due to the significant difference of vapor pressures between PrF3 and BaF2, it is commonly difficult to congruently deposit PrF3-BaF2 thin films utilizing evaporating directly from a single source. Moreover, more details are unknown about the phase compositions of PrF3-BaF2 thin films. In our investigation, BaF2-PrF3 thin films were deposited using electron beam evaporation from the sintered ingots of PrF3 admixed with BaF2. The compositions of thin films were characterized using energy dispersive X-ray spectroscopy (EDX), the crystallographic structures were explored by X-ray-diffraction (XRD). It was revealed that the concentration of BaF2 in thin films can be correlated to that in the admixtures. Moreover, in addition to PrF3 and BaF2, the phase compositions in thin films include also secondary phases, such as PrOF, PrF4, Pr2F2, BaPrF6, and that of elemental Ba.