Pressure dependence of the structure of liquid Sn up to<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>19.4</mml:mn><mml:mspace width="0.3em"/><mml:mi>GPa</mml:mi></mml:mrow></mml:math>

The structure of liquid Sn was investigated up to $19.4\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ by synchrotron x-ray diffraction. Upon compression up to about $3--6\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, the structural features, which reflect the anisotropic local structure, become less prominent, i.e., the hump on the high-$Q$ side of the first peak in the structure factor $S(Q)$ becomes smaller, the position of the second peak relative to that of the first peak in $S(Q)$, ${Q}_{2}∕{Q}_{1}$, decreases, and the coordination number increases. These features indicate that the liquid structure changes toward a simple liquid metal upon compression. However, at higher pressures, the structural parameters are nearly unchanged. The parameters in this pressure range are still deviated from their respective values for simple liquid metals. These findings suggest that, contrary to previous expectations, the liquid does not monotonically approach a simple liquid metal but takes a relatively stable intermediate form with an anisotropic local structure before approaching a simple liquid metal. The high-pressure behavior of liquid Sn is compared to those of liquid Si and liquid Ge and the systematics in liquid group 14 elements are discussed.