Figure 2.7. Heat capacity per ion versus T (bottom axis) and r (top axis) for iron plasma at p = 108 g cm~3 (left) and carbon plasma at p = 105 g cm~3 (right). The dotted line is for classical ions; the dot-dash line additionally includes the first quantum correction; the short-dash line is the harmonic-lattice approximation in the solid phase; the solid line is the same plus anharmonic and electron polarization corrections in the solid phase and the sum of classical, quantum, and electron polarization contributions in the liquid. The long-dashed line is the ideal electron gas contribution, and the short-dash-long-dash line on the right panel is the approximation of strongly degenerate electrons. The vertical line is the melting point, and the grey band shows the range r = 150-200. The insets present the competition between the electron and ion contributions at low T (left inset on each panel) and the behavior near the melting point (right inset on each panel).
In reality, the picture discussed above is further complicated owing to the band structure in the electron energy spectrum in a crystal (§ 2.1.2). Thus the problem deserves further study.
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