Lattice Constant, Resistivity, Specific Heat, and Thermal Expansion Studies in the Mixed Valent-Kondo System CERIUM-INDIUM(3-X)TIN(X)
This thesis focuses on a study of the CeIn(,3 -x)Sn(,x) system, of which, the terminal compound CeIn(,3) was known to be trivalent and exhibit Kondo behavior, while CeSn(,3) was thought to be weakly mixed valent. The object of the study was primarily to determine how the thermodynamic and transport properties evolve as we go from the mixed valent behavior of CeSn(,3) into the trivalent behavior of CeIn(,3), by alloying. From room temperature x-ray measurements, the lattice constants of the CeIn(,3-x)Sn(,x) system follow a linear behavior for x < 1.8 indicative of a stable trivalent character of Ce. The lattice constants depart from the linear behavior at x = 1.8, suggesting a mixed valent region for 1.8 < x < 3.0. The resistivity measurements yield a behavior of the maximum in the magnetic resistivity of CeIn(,3-x)Sn(,x) that increases in the mixed valent region (i.e. 1.8 < x < 3.0) as the mixed valent-trivalent boundary is approached, that is, as x decreases; the maximum magnetic resistivity peaks at the transition region (i.e. x (TURNEQ) 1.8) and drops precipitously in the trivalent side. The coefficient of the electronic specific heat as measured by us and other workers, as well as the very low temperature values of the magnetic susceptibility, also increase as x decreases in the mixed valent region, peak at x (TURNEQ) 1.8, and decrease in the trivalent region (i.e. 0 < x < 1.8). The behavior of the three quantities, resistivity, electronic coefficient of specific heat and zero temperature susceptibility can be fitted to what a Fermi liquid theory of mixed valence predicts, but only if the valence of CeSn(,3) is taken to be 3.6 at T = 0 K and not 3.1 as previously thought. From thermal expansion measurements we obtain a behavior of the valence of CeSn(,3) that is well fitted by the same Fermi liquid theory of mixed valence. The temperature dependence of the magnetic resistivity of samples in the mixed valent region near the mixed valent -trivalent boundary is compared to a theory of the resistivity due to spin fluctuations. The theory is found to fit well the measured resistivity and yield parameters that agree with specific heat and susceptibility measurements. The resistivity of some samples in the trivalent side is compared to a theory of the Kondo effect with crystal fields. This fits yield parameters that agree with susceptibility results.
- Pub Date:
- Physics: Condensed Matter