Quasiequilibrium determination of high-Tc superconductor transition temperatures

A fast and inexpensive method for making accurate determinations of transition temperatures above 77 K in superconducting oxides is presented. The technique is based upon cooling in liquid nitrogen, then warming the sample in the vapors above the liquid level inside a standard glass or stainless steel vacuum bottle. Proper sample support and placement of the thermocouple, key elements in this technique, are discussed. Once pads have been placed on the sample, Tc can be determined, to an accuracy of ±1 K, within 15 min. Due to its speed, accuracy, and low cost, this technique is well suited for application in an advanced undergraduate laboratory experiment