Studies of a Glass-Ceramic Capacitance Thermometer between 0.025 and 2.4 K

Abstract

Capacitance measurements from 0.025 to 2.4 K are reported for capacitance thermometers (made from an SrTiO₃ glass‐ceramic crystallized at 1100 and 1203°C), two of which were the ones reported in the previous article. It was found that the 1200‐type thermometer has a useful thermometric range down to 0.06 K and a linear C‐T region down to 0.5 K. The 1100‐type thermometer has a useful range down to 0.110 K and a linear region down to 1.1 K. The measured data do not appear to be influenced by self‐heating or adiabatic correction effects. Both thermometers display an unexpected increase in capacitance with decreasing temperature below their monotonically decreasing ranges. The 1100‐type thermometer displays the more pronounced increase, with C∝T⁻¹ from 0.100 to 0.025 K. It is argued that this T⁻¹ behavior is due to the onset of an ultralow temperature phase transition in the glass crystallized SrTiO₃, and the possibility of using this effect to achieve adiabatic depolarization cooling is discussed.