Differential thermal analysis of individual specimens by thermal EMF measurement

The thermal electromotive force (EMF) generated across a specimen owing to a small nonuniformity in the sample’s temperature is used to follow phase transitions in the specimen. As the temperature is scanned, a first‐order phase transition yields a sharp S‐shaped peak in the EMF versus time, t, and temperature, T(t), curves. A transition to a superconducting state exhibits a sharp drop in EMF as was observed during measurements on YBa₂Cu₃O₇. The dependence of the EMF on time and temperature is calculated for a first‐order phase transition. Predictions are confirmed by experiment. This method is therefore useful for detecting phase transition temperatures. A practical feature of this measurement is the ability to precisely calibrate, in situ, the temperature measuring element, e.g., thermometer or thermocouple, when the transition temperature is already known.