Equation of state of pure iron and Fe0.9Ni0.1 alloy up to 3 Mbar

Pure iron and Fe0.9Ni0.1 alloy were compressed to a pressure of 279 GPa and 272 GPa, respectively. The compression data sets were fitted using the third order Birch–Murnaghan equation of state based on six different pressure scales. Our result shows the nickel increase the density and the c/a ratio, decrease the bulk modulus. The high temperature data obtained the thermal equation of state parameters. At high temperature, although the nickel effect on density slightly decrease due to the a little larger thermal expansion, the bulk modulus difference increase to 7.3–7.8% at 329 GPa and 5000 K. Nickel effects on elasticity might be important at multimegabar pressure and especially high temperature such as the inner core condition. The core density deficit was estimated to be 3.4(1)–5.1(1)% for pure iron and 4.7(1)–6.5(2)% for Fe0.9Ni0.1 alloy if the temperature at the inner core boundary is 5000 K.