UBC Theses and Dissertations
Heat capacity measurement of YBa₂Cu₃O7 -- 197 Bahrami, Mahin
A modified AC method is developed for measuring the specific heat of very small high quality single crystal samples of Y₁B₂C₃O6+x (Yttrium Barium Copper Oxide). The system developed combines the original AC calorimetry method introduced by Sullivan et al. and the thermal relaxation method by Bachmann et al. The modification involves the use of a sapphire as substrate to support the crystal, heater and the temperature sensor. A complete thermal analysis of the experimental setup is presented in addition to a detailed experimental procedure for measuring the heat capacity of a small sample. Some experimentation with diamond substrate is performed as well and compared with sapphire. Another feature added to our AC calorimetry setup is a Dewar pressure regulation system. This was to minimize the variations in the liquid bath temperature due to changes in ambient pressure. Our system also allows for multiple sweeps, as bath temperature is monitored, from which the best sweeps corresponding to the most stable temperature interval is chosen for further analysis. Considering the different mathematical models developed so far for explaining the behavior of the specific heat fluctuation of YBCO, our results seem to support the 3D XY model near the transition temperature of 93.IK. From the heat capacity data our crystal sample showed a transition width, ΔTc, of 0.45K, and a superconducting transition jump ACp, of 6.1mJ/gK.
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