Anomaly in the viscosity of liquid KCl at high pressures

We measured viscosity of KCl and NaCl liquids up to 7.3 GPa and observed a clear discontinuity in the pressure dependence of viscosity for liquid KCl at around 2 GPa. The viscosity of liquid KCl increased rapidly at 1.5-2.2 GPa, above which it remained virtually constant. Structural data of KCl liquid also showed a pronounced change signified by the ratio r(2)/r(1), where r(1) and r(2) are the nearest- and the second-neighbor distances, respectively. In contrast, both viscosity and the r(2)/r(1) ratio changed linearly with pressure for liquid NaCl. Our observation suggests that viscosities of KCl and NaCl liquids strongly correlate with the structural changes in terms of the r(2)/r(1) ratio. The viscosity anomaly in liquid KCl is found to be at pressures close to that of the B1-B2 transition in solid KCl. DOI: 10.1103/PhysRevB.87.024302