Structural transformation of HfO₂ nano-particles under compression

In recent years, nano-structured materials are extensively investigated for their wide applications in electronics, optics, magnetic data storage, catalysis, ceramics and many others as it show new physical and chemical properties with reduction of size. HfO₂ has a very high dielectric constant compared to SiO₂ and this is being considered as a gate insulator in FET as a replacement of SiO₂. So HfO₂ has become very important material for study in modern electronic world. In order to know the structure under compression, we have performed the high pressure X-ray diffraction of HfO₂ nano-particles using XPRESS beamline at Elettra synchrotron facility, Trieste. The pressure evolution of XRD is given. A new peak is observed at about 7.8 GPa pressure at an angle (2ϴ) 9.80 between the peaks for (-111) and (111) planes. Also a new peak is observed at about 11.3 GPa pressure at angle(2ϴ) 15.04°. We observe an increase in peak width as pressure increases indicating grain size decreases. We have estimated the grain size of HfO₂ nano-particle from the peak for (011) plane using the Scherrer formula and variation with pressure is shown. A change in slope of grain size variation is seen near 6.7 GPa and 11.3 GPa where a new peak appeared. However we observe discontinuity in grain size 3.3 GPa and 37 GPa. The intensity of peak from (011) plane decreases with increasing pressure and vanished above 11.3 GPa. The peak shifting with pressure is plotted and we observe a decrease in slope with increasing pressure indicating an increase in stiffness. The lines are for visual impression