Session: IMECE Undergraduate Research and Design Exposition

Paper Number: 115192

115192 - Residual Resistivity Ratio of Niobium and Copper 

As the space industry grows, power electronics must be able to maintain reliability at cryogenic temperatures. The goal of this study is to investigate the ability of candidate substrate and backplane materials to operate at cryogenic temperatures (~4K).  Superconductivity can be achieved in numerous ways, but chemical doping is the most common. Theoretically, a material loses all its electrical resistance at 0 K, although some materials lose all their resistance at higher temperatures. The temperature at which a pure substance loses all electrical resistance is called the critical temperature (Tc).

 

It's helpful to know the conductive properties of a material at Tc when examining a sample. We can determine residual resistivity ratio (RRR) by taking the ratio of the electrical resistance of a material at room temperature (300K) over that at Tc (normally 0K). A material's RRR can indicate its purity and suitability for use as a superconductive material.  

Conductivity can be determined by determining a material's resistance. In order to determine the resistance of a material, we use the four-point probe method in combination with a current source and a voltmeter. Using the colinear setup of the four-point probe method, the two outer probes can run a current for which the two inner probes can measure the voltage along the substance.

In this experiment, copper and niobium are tested for their RRR. Copper is useful because it is a reliable conductor whose data is easily measurable. It is known to consistently reach its RRR at 4K. Niobium has the potential to become a superconductor because its STT is at 4K. The experiment measures the voltage of a current in a material compared to its original charge and determines its resistance using a four-point probe method.  

 

Through the use of software, we obtain RRR and STT semi-automatically. It is possible to calculate and plot desired measurements automatically using Matlab and Lakeshore's MeasureLink software. The sample holder in the cryostat will be wired to a Lakeshore machine and testing computer. Two wires connect the outer probes to the current source. The two inner probes are connected to a voltmeter and to the testing computer with two wires each. Data acquisition and postprocessing provide graphs of the data based on measured voltage, physical dimensions of our sample, current, and a correction factor.  

It is expected that the resistivity of copper will gradually diminish to 0.020ohm before leveling off at that resistance, no matter how cold the sample gets without reaching 0K. Meanwhile, niobium’s resistance will decrease with temperature until it reaches below 9K. At this point, niobium should read a resistance of 0.00ohm or a value very close to it.

Presenting Author: Quentin Taylor Howard University

Presenting Author Biography: Quentin Taylor is a Chemical Engineering major at Howard University. He is a member of the 6th cohort of the Karsh STEM Scholars Program at Howard University, a program dedicated to guiding students to ascertain their PhDs in the STEM fields. Quentin is interested in fields related to material sciences, process engineering, and environmental sustainability.

Authors:

Sonya Smith Howard University
Quentin Taylor Howard University
Damon Gresham-Chisolm Howard University