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Fe–Ni–S–Si alloy is considered to be one of the plausible candidates of Mercury core material. Elastic properties of Fe–Ni–S–Si liquid are important to reveal the density profile of the Mercury core. In this study, we measured the P-wave velocity (V_P) of Fe–Ni–S–Si (Fe₇₃Ni₁₀S₁₀Si₇, Fe₇₂Ni₁₀S₅Si₁₃, and Fe₆₇Ni₁₀S₁₀Si₁₃) liquids up to 17 GPa and 2000 K to study the effects of pressure, temperature, and multiple light elements (S and Si) on the V_P and elastic properties.

The V_P of Fe–Ni–S–Si liquids are less sensitive to temperature. The effect of pressure on the V_P are close to that of liquid Fe and smaller than those of Fe–Ni–S and Fe–Ni–Si liquids. Obtained elastic properties are K_S0 = 99.1(9.4) GPa, K_S’ = 3.8(0.1) and ρ₀ =6.48 g/cm³ for S-rich Fe₇₃Ni₁₀S₁₀Si₇ liquid and K_S0 = 112.1(1.5) GPa, K_S’ = 4.0(0.1) and ρ₀=6.64 g/cm³ for Si-rich Fe₇₂Ni₁₀S₅Si₁₃ liquid. The V_P of Fe–Ni–S–Si liquids locate …