Transition metals electronic heat capacity

The electronic heat capacity naturally has a pronounced effect on the energetics of insulator-metal transitions and the entropy of a first-order transition between an insulating phase with y = 0 and a metallic phase with y= ymet at Ttrs is in the first approximation Ains met5m = 7met7trs. 

In the field of not only traditional metallurgy but also recently developed nano-technology, it is very interesting and important what change is introduced when it is surrounded by other atoms. Such a change in electronic states has been investigated as chemical shift detected by X-ray (XPS) and UV (UPS) photoemission spectroscopy [1] as well as X-ray emission and absorption spectroscopy [2,3]. Also, such a chemical shift has been simulated by theoretical calculation [4]. However, many problems have been unsolved. In the case of XPS and UPS, since the most outer layers of substances are analyzed, the spectra are easily affected by absorbed gaseous molecules. Also, with the X-ray emission and absorption spectroscopy it is difficult to analyze the complicated X-ray transition states for substances composed of heavy metal elements. Therefore, a complementary method has been demanded for the spectroscopy such as XPS, UPS and X-ray emission and absorption spectroscopy. The coefficient y of the electronic contribution to heat capacity, Cp, near absolute zero Kelvin reflects the density of states (DOS) in the vicinity of Fermi level (EF) [5]. Therefore, the measurement of y is expected to be one of the useful methods to clarify the electronic states of substances composed of heavy metal elements. 

A salt such as NaN03 has a vibrational heat capacity of 6R contributed by vibrations of Na and NO/" in the solid and an additional contribution from the vibrations within the nitrate ion, which are partly but not fully excited. Some metals, notably the transition metals, exhibit values of C greater than 3R at high temperatures this extra contribution comes from the heat capacity of the electron gas in the metal. 

The SmS semiconductor to metal transition was later verified by the direct observation of a discontinuous change in the optical reflectivity at 6 kbar (Kirk et al., 1972). This is consistent with a first order magnetic phase transition which was directly verified by magnetic susceptibility measurements under pressure by Maple and Wohlleben (1971). In the collapsed phase the susceptibility of SmS showed no magnetic order down to 0.35 iC and was almost identical to the susceptibility of SmBa (see fig. 20.10 of volume 2). Bader et al. (1973) measured the heat capacity (fig. 11.16) and electrical resistivity (fig. 11.17) of SmS under pressure. They found a large electronic contribution to the heat capacity ( y = 145 mJ/mole-K ) and a resistivity reminiscent of SmB. Mossbauer isomer shift measurements of SmS under pressure by Coey et al. (1976) reveal the transition from a Sm isomer shift at zero pressure to an intermediate value at pressures above 6 kbar (fig. 11.18). The isomer shift of SmS above 6 kbar was found to be about the same as the isomer shifts for chemically collapsed Smo.77Yo.23S and SmBo at zero pressure. 

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