Structural degradation of tungsten sandwiched in hafnia layers determined by in-situ XRD up to 1520 °C

Abstract

The high-temperature stability of thermal emitters is one of the critical properties of thermophotovoltaic (TPV) systems to obtain high radiative power and conversion efficiencies. W and HfO2 are ideal due to their high melting points and low vapor pressures. At high temperatures and given vacuum conditions, W is prone to oxidation resulting in instantaneous sublimation of volatile W oxides. Herein, we present a detailed in-situ XRD analysis of the morphological changes of a 3-layer-system: HfO2/W/HfO2 layers, in a high-temperature environment, up to 1520 °C. These samples were annealed between 300 °C and 1520 °C for 6 h, 20 h, and 40 h at a vacuum pressure below 3 × 10–6 mbar using an in-situ high-temperature X-ray diffractometer, which allows investigation of crucial alterations in HfO2 and W layers. HfO2 exhibits polymorphic behavior, phase transformations and anisotropy of thermal expansion leads to formation of voids above 800 °C. These voids serve as transport channels for the residual O2 present in the annealing chamber to access W, react with it and form volatile tungsten oxides. An activation energy of 1.2 eV is calculated. This study clarifies the limits for the operation of W-HfO2 spectrally selective emitters for TPV in high-temperature applications.

Design and Spectral Performance of HfO2-Based Multilayer Spectrally Selective Emitters Embedded with VO2 Nanoparticles

“…Obviously, no other substance is generated during the heating, which means that the HfO 2 film can maintain thermal stability below 1300 K. The rising peaks at 28.3° and 30.4° can be attributed to the monoclinic phase of HfO 2 and the amorphous phase of HfO 2, respectively. This phenomenon is similar to the results in the study of Krishnamurthy et al Figure c shows the XRD patterns of the mixed powder after heating at 1300 K. There are only peaks of HfO 2 and VO 2 , which means that there is no reaction between HfO 2 and VO 2 during heating at 1300 K. According to the above analysis, the thermal stability of the VO 2 nanoparticles and HfO 2 film can meet the requirements of the design process.…”

Solvent-Treated Zirconium-Based Nanoporous UiO-66 Metal–Organic Frameworks for Enhanced CO2 Capture

“…To understand the thermal treatment impact on the UiO-66 sample, the in-situ XRD patterns of UiO-66 under air in the temperature range of 25–250 °C are shown in Figure B. The XRD patterns at all temperatures displayed the presence of only the UiO-66 structure phase but moving to higher angles due to relaxation approaching the equilibrium value at the adjusted temperatures . It confirmed that the UiO-66-200C-48h sample has the same crystal structure as the UiO-66 and methanol-treated UiO-66.…”

Comparative Study of High-Temperature Annealed and RTA Process β-Ga2O3 Thin Film by Sol–Gel Process

“…However, at the annealing temperature of 900 • C, the main peak intensity of (−201) was slightly decreased, while other minor peaks of (400) and (002) were increased. The degradation of the main peak of (−201) probably comes from the thermal migration and diffusion process due to the high annealing temperature [28,29]. We believe that more high thermal energy than 700 • C is required to increase the (400), (002) peaks.…”

“…due to the high annealing temperature [28,29]. We believe that more high thermal energy than 700 °C is required to increase the (400), (002) peaks.…”