Thermodynamic modeling of pressure-dependent phase diagram in alkali metals Li, Na and K

The high-pressure behavior of the alkali metals has attracted much attention in both experimental and theoretical aspects. This study is focused on the thermodynamic optimization of the temperature and pressure dependence of the molar volumes, the compressibility and phase diagrams of Li, Na and K according to the CALPHAD method. The pressure-temperature phase diagrams of lithium, sodium and potassium up to 50–100 GPa were calculated using the obtained thermodynamic parameters. The available experimental data, such as extremely low melting temperatures at high pressure, pressure-induced structural transitions between simple bcc and fcc crystals and the molar volume changes with the increasing pressure, were well reproduced in our calculations. The good agreements between our calculations and the experiments assessed in the literature indicated that our thermodynamic parameters are reasonable. Our thermodynamic calculations would assist to understand the phase transitions and structural properties of alkali metals at high pressure.