Directionally solidified Ni doped MgO-MgSZ eutectic composites for thermophotovoltaic devices

Ni-doped MgO-MgSZ eutectic composites were investigated as selective emitters for thermophotovoltaic devices. MgO-MgSZ:Ni eutectic rods were directionally solidified at 25 and 500 mm/h using the laser floating zone technique. Microstructure was strongly dependent on the growth rate, the size of the eutectic phases decreased as the growth rate increased. A hardness of ∼11 GPa and a fracture toughness of ∼1.6 MPa were obtained from indentation techniques, not showing dependence on the growth rate. Flexure strength increased from ∼400 MPa in samples grown at 25 mm/h up to ∼1 GPa for those solidified at 500 mm/h, which was attributed to the decrease of the phase size. Thermal emission of eutectic composites was studied up to 1400 °C. An intense broad emission band centred in 1.5 μm matching with the sensitive region of the GaSb photoconverter was found. The selective emission was ascribed to the de-excitation of the thermally excited Ni 2+ ions.