Fabrication and investigation of Ca/Tb co-doped HfO2 infrared coatings

In this study, Ca/Tb co-doped HfO2 coatings were prepared by atmosphere plasma spraying. The chemical composition, morphology and infrared property of the coatings were characterized. The coatings possessed a layer-stacked morphology. When the Ca/Tb doping atomic ratio was 1:1, the phase of the coatings gradually changed from monoclinic to cubic with increasing the doping mass. The CTH2 coating had the highest emissivity which was 0.820 in 0.75–6.5 µm and 0.902 in 6.5–15 µm respectively. The enhancement in short band was mainly due to the introduction of Ca2+ and Tb3+ ions that generated oxygen vacancies in the lattice forming impurity levels within the forbidden band, moreover, the transfer of Tb3+ to Tb4+ increased the concentration of free electrons, which promoted the absorption of free carriers. The increase in long band attributed to the lattice distortion that reduced the lattice symmetry and strengthened the absorption of lattice polar vibration.