FeSi melting curve up to 70 GPa

The melting curve of iron monosilicide, FeSi, has been determined in a laser-heated diamond anvil cell from 6 up to 70 GPa by direct visual observation of the continuous laser-speckle motion in the liquid state. At 12 GPa and 1700 K, a discontinuous change in the slope of the melting curve indicates the first-order phase transition between the ɛ-FeSi (B20) and the CsCl-type FeSi structures (B2). During the phase transition the coordination number of both, Fe and Si atoms, increases from 7 to 8. Above this pressure, the melting curve rises steeply but shows significant flattening at higher pressures. A comparison with the melting curve of Fe shows that both curves cross at 32 ± 3 GPa, FeSi having higher melting temperatures (about 100 K) at high pressures.