Investigations of the temperature gradients affecting the temperature scale of a 3ω-heat capacity spectrometer

The temperature gradients affecting the temperature scale of a dynamic heat capacity spectrometer based on the 3 omega-method are investigated using the SmecticA-Nematic (SmA/N) transition in the liquid crystal octyloxycyanobiphenyl (80CB). The heater (sample) temperature was obtained from a thermocouple by superimposing the temperature increase of the heater, where the increase was calculated from the heater power. The calibration using the SmA/N transition yields a linear relation between the temperature rise of the heater Delta T-h and the heater power P: Delta T-h=55.2P. An estimation of the maximum temperature gradient in the 80CB sample shows that the correction of the sample temperature due to the gradient is small compared to Delta T-h (<-0.01 K for omega=3.98. 2 pi rads(-1) and -0.14 K for omega=0.01. 2 pi rads(-1)). For high heating powers there is a significant temperature gradient in the heater, which causes a broadening of the SmA/N peakwidth from 0.5 K for P=7.7 mW to 2 K for P=29.4 mW. (C) 2000 Elsevier Science B.V. All rights reserved.