An improved technique for accurate heat capacity measurements on powdered samples using a commercial relaxation calorimeter

We have modified our earlier technique for accurate PPMS heat capacity measurements on powdered samples by means of applying Wakefield grease or small copper strips in the sample preparation instead of using Apiezon N high-vacuum grease. For the Wakefield grease measurements, we put a small amount of Wakefield thermal compound in a copper cup instead of potting with Apiezon N, and the accuracy of measurements on powdered benzoic acid was determined to be ±1% and ±4% in the temperature ranges of 10 K < T < 280 K and 280 K < T < 300 K, respectively. The Wakefield grease was found to improve the accuracy somewhat but overall there was no noticeable improvement in the “grease region” above T = 220 K. To overcome the known shortcomings of using Apiezon N grease above 220 K, we have replaced the Apiezon N grease with small copper strips in the sample preparation to aid thermal conductivity, which results in a less time-intensive two-step technique for the PPMS heat capacity measurement but with an accuracy, based on measurements of benzoic acid, that is ±1% from T = (10 to 300) K and, more importantly, the elimination of the “grease problem”. As an additional test of the new technique, the heat capacity of powdered bulk rutile has been measured twice within the temperature range from (2 to 300) K using the PPMS, and its standard entropy at T = 298.15 K was calculated to be (50.39 ± 0.50) and (50.31 ± 0.50) J · K−1 · mol−1, which deviates 0.08% and −0.08% from the measurement results of our low-temperature adiabatic and semi-adiabatic calorimeters, respectively. We recommend that this technique become the standard for accurate heat capacity measurements on insulating powdered samples using a PPMS system and the corresponding thermodynamic calculations.

► We have previously published a method for accurate PPMS eat capacity measurements.
► The older method had a significant grease problem above 250 K.
► Here we publish new results using copper strips instead of grease to pot the sample.
► The new method now requires on two measurements instead of four.