Neutron diffraction studies of pristine HfO₂ and Ta-doped HfO₂

Hafnia is a material of technological interest as it is being considered as a replacement of SiO₂ in microelectronics. But, following reports on HfO₂ systems exhibiting ferroelectric properties, interest in orthorhombic phase of HfO₂ renewed. Under application of external pressure, it undergoes phase transformation to an orthorhombic-I phase at ~ 3.7 GPa, that subsequently transforms to orthorhombic-II at ~ 8.2 GPa. The space group of the orthorhombic-I phase was determined to be Pbcm from Rietveld refinement and peak decomposition of high-pressure X-ray diffraction data. Based on simulations studies, it was realized in the study that in situ neutron diffraction data at high pressure has the potential to detect space group of the high-pressure orthorhombic-II phase of HfO₂. Thus performing an in situ high pressure neutron diffraction experiment is a requirement understanding the high pressure phase of HfO₂. As oxygen position can be determined with better precision with neutron diffraction studies, further studies are planned with higher Ta-doping concentrations for understanding different phase formation in doped HfO₂ samples