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 3ω-method are investigated using the SmecticA-Nematic (SmA/N) transition in the liquid crystal octyloxycyanobiphenyl (8OCB). 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 ΔTh and the heater power P: ΔTh=55.2P. An estimation of the maximum temperature gradient in the 8OCB sample shows that the correction of the sample temperature due to the gradient is small compared to ΔTh (<−0.01 K for ω=3.98. 2π rads−1 and −0.14 K for ω=0.01. 2π 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.