Iridium-Based Selective Emitters for Thermophotovoltaic Applications.

Area of Science:

• Materials Science
• Nanotechnology
• Solid State Physics

Background:

• Refractory-metal-based metamaterials are vital for thermophotovoltaics but prone to oxidation failure.
• Tungsten (W), Molybdenum (Mo), Tantalum (Ta), Niobium (Nb), and Rhenium (Re) commonly used refractory metals degrade via oxidation.
• Gold (Au) has suitable optical properties but lacks thermal stability for high-temperature applications.

Purpose of the Study:

• To investigate the thermal endurance and oxidation resistance of Iridium (Ir) as a potential alternative to refractory metals in metamaterials.
• To evaluate the stability of a HfO2/Ir/HfO2 multilayer system for high-temperature applications.
• To compare the long-term stability of Ir/HfO2 and W/HfO2 metamaterials under annealing conditions.

Main Methods:

• Annealing experiments of HfO2/Ir/HfO2 systems up to 1240°C in vacuum and inert atmospheres.
• In situ X-ray diffraction (XRD) analysis of Ir/HfO2 and W/HfO2 multilayered selective emitters.
• Long-term annealing tests (100 hours) at 1000°C under vacuum (2 × 10^-6 mbar).

Main Results:

• The Ir layer in the HfO2/Ir/HfO2 system showed no oxidation in vacuum and inert gas atmospheres up to 1240°C.
• Ir layer agglomeration was observed above 1100°C due to HfO2 layer degradation.
• In situ XRD confirmed the oxidation stability of Ir/HfO2 multilayers, while W/HfO2 multilayers degraded significantly over 100 hours at 1000°C.
• W-based metamaterials demonstrated poor long-term stability even at 1000°C.

Conclusions:

• Iridium (Ir) exhibits excellent oxidation resistance, making it a promising material for refractory plasmonic metamaterials.
• The HfO2/Ir/HfO2 system demonstrates potential for high-temperature applications, although HfO2 stability needs further optimization.
• Ir-based metamaterials are suitable for selective emitters in thermophotovoltaic systems, offering strong suppression of long-wavelength radiation.