Doctor of Philosophy
Richard A. Secco
The electrical resistivity of high purity Cu, Zn and Co has been measured at pressures (P) up to 5GPa and at temperatures (T) in the liquid phase. The electrical resistivity of solid state Nb was also measured up to 5GPa and ~1900K. All measurements were made in a large volume cubic anvil press. Using two thermocouples placed at opposite ends of the sample wire, serving as temperature probes as well as resistance leads, a four-wire technique resistivity measurement was employed along with a polarity switch. Post-experiment compositional analyses were carried out on an electron microprobe.
The expected resistivity decrease with P and increase with T were found in all metals in the solid state and comparisons with 1atm data are in very good agreement. The melting temperature data were obtained from the large resistivity jumps at the solid-liquid transition and these agree with other experimental studies.
The main results of this work are that resistivity of Cu decreases along its P,T-dependent melting boundary, while the resistivity of Zn and Co remain constant along their P,T-dependent melting boundaries. These findings are interpreted in terms of the competing effects of P and T on the electronic structure of filled and unfilled d-band liquid transition metals.
For Nb, an electronic transition was observed in the T-dependence of electrical resistivity at high P, T. The transition is discussed in terms of the effects of P and T on the electronic band structure of Nb causing a change in resistivity from behavior characterizing the ‘minus group’ to the ‘plus group’.
The electronic thermal conductivity is calculated from resistivity data using the Wiedemann-Franz law and is shown to increase with P in both the solid and liquid states for Cu, Zn and Co but upon T increase, it decreases in the solid and increases in the liquid state. For Nb, above the transition T, the T-dependence of electronic thermal conductivity of Nb remains constant at 2GPa and exhibits an increasingly negative slope at higher P. The electronic thermal conductivity of Nb increased with increasing pressure at any given isotherm.
The implications for heat flow and thermal evolution in Earth’s and other terrestrial planetary cores are based on the similarity of electronic structure of Co and Fe. The invariance of resistivity along the melting boundary of Co suggests thermal conductivity at the inner core boundary of an Fe dominated core may be similar to the value of Fe at its 1 atm melting temperature.
Ezenwa, Innocent Chinweikpe, "Experimental Studies of Electrical Resistivity Behavior of Cu, Zn and Co Along Their Melting Boundaries: Implications for Heat Flux at Earth’s Inner Core Boundary" (2017). Electronic Thesis and Dissertation Repository. 4428.