Isothermal compressibility and thermal expansion of nitrogen doped hafnia Hf7O11N2

The isothermal compressibility of nitrogen doped hafnia (β′ hafnium oxonitride, Hf7O11N2) has been measured at room temperature up to 28 GPa in a hydrostatic pressure medium, using a diamond anvil cell and X-ray powder diffraction. From a least squares fit to the third-order Birch-Murnaghan Equation of State the values for the bulk modulus and its first pressure derivative were determined to B0=269.4GPa and B0′=14.9. The exceptionally high value for B0′ arises as consequence of vacancy ordering and subsequently the almost one-dimensional compression of Hf7O11N2 up to pressures of about 12 GPa. The thermal expansion was investigated using temperature dependent X-ray powder diffraction. The coefficient of thermal expansion was calculated according to αv=1/V∗δV/δT=a0+a1∗T. The parameters were determined to a0=10.389±2.296∗10−6K−1 and a1=7.34±1.89∗10−9K−2.