Papers by Keyword: Hafnia

Abstract: The conditions of formation of the ZrO₂ and HfO₂ high-temperature (tetragonal and cubic) phases in the ablated nanoparticles were investigated. X-ray diffraction and transmission electron microscopy data demonstrate that laser intensities above 10⁹ W/m² ensure the formation of the ZrO₂ high-temperature phases, while intensities above 5·10⁹ W/m² do the formation of the HfO₂ high-temperature phases. Quantitative content of the high-temperature phases in layers of the ablated nanoparticles increases with raising the intensity. The obtained nanoparticles exhibit good thermal stability.

Abstract: The ferroelectricity of hafnia-based thin films with a dominant phase of orthorhombic Pca2₁ has been reported. However, the relationship of structural transformations between the orthorhombic Pca2₁ and other hafnia structures remains unclear. In this work, all the structures have been optimized. Then, the fluorite-related structures have been used to analyze the structural relationship. Calculations of the lattice energies and the relative atomic displacements between the structures suggest that the Pca2₁ phase may originate from the P4₂/nmc or Pbca phases.

Abstract: HfO2-added Si3N4 ceramics are known to exhibit excellent high-temperature strength and excellent damage characteristics because HfO2 assists the crystallization of the grain boundary phase. However, the sintering shrinkage behavior and mechanical properties of HfO2-added Si3N4 have not been well clarified so far, although it has been reported that TiO2, in which Ti is from the same group as Hf in the periodic table, enhances the densification of the Si3N4-Y2O3-Al2O3-AlN system and wear resistance due to TiN formed from TiO2 and AlN in the grain boundary. In the present study, we focus on HfO2 as the sintering aid to investigate the sintering shrinkage behavior and mechanical properties of HfO2-added Si3N4. The powder mixtures are prepared by the addition of HfO2 to the Si3N4-Y2O3-Al2O3 or Si3N4-Y2O3-Al2O3-AlN system. The sintering shrinkage curves of HfO2-added Si3N4 ceramics show rapid shrinkage at 1600°C as compared with those of the Si3N4 ceramics without HfO2.The shrinkage can be explained by the formation of SiO2-Y2O3-HfO2 derived liquid phases. Furthermore, the mechanical properties of HfO2-added Si3N4 were as excellent as those of the Si3N4 ceramics without HfO2.