The peculiarities of the solid-state interaction in the HfC-Ir system have been studied within the 1000-1600 °C temperature range using a set of modern analytical techniques. It was stated that the interaction of HfC with iridium becomes noticeable at temperatures as low as 1000-1100 °C and results in the formation of HfIr-based substitutional solid solution. The homogeneity range of the HfIr phase was evaluated and refined as HfIr-HfIr. The durability of the HfIr-based system under extreme environmental conditions was studied. It was shown that the HfIr-based material displays excellent ablation resistance under extreme environmental conditions. The benefits of the new designed material result from its relative oxygen impermeability and special microstructure similar to superalloys. The results obtained in this work allow us to consider HfIr as a very promising candidate for extreme applications.

Here we report the first synthesis of large-size (up to 2 cm), transparent, high-purity monoclinic HfO2 single crystals by reactive chemical vapor deposition (RCVD) using CF4 as a transport agent at 1000 °C. The single crystals were comprehensively characterized in terms of their phase and elemental composition, as well as morphology by the modern analytical techniques. Thermodynamic modeling of the Hf–C–Si–O–F heterogeneous system was undertaken to understand in detail the chemical equilibria that occur in this transport system. Based on modeling results, it was shown that HfO2 formation occurs through HfOF2 decomposition. Morphological peculiarities of RCVD-derived HfO2 single crystals were studied by optical and scanning electron microscopy. Vicinal hills and numerous growth steps were observed on the crystal surfaces. The HfO2 single crystals exhibit strong and broad emission under UV excitation. The fit of the broad optical emission into spectral components allowed us to identify the nature of emission and assign it to the intrinsic defects of crystals. The successful synthesis of plate-like high-purity monoclinic HfO2 single crystals may provide some insight into the design of optical or other devices.

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