Constructing a Relaxation Calorimeter

Hank A. Anderson

Abstract


Relaxation calorimetry is a technique used todetermine the specific heat of various materials. Many strongly correlatedelectron materials exhibit interesting phenomenon such as superconductivity,magnetism, metal to insulator transition, and structural transformations. Withthe specific heat data we can determine the temperature at which many of thesephase transitions occur. The specific heat can also provide insight into theinternal energy of a material, which includes properties such as entropy,electronic behavior, and lattice stiffness. By developing a betterunderstanding of these properties; the strongly correlated electron materials,can then be applied to new technology such as energy transfer and storage. Theobjective of our research is to develop calorimeters used to study the specificheat of rare earth compounds. Our calorimeter is connected to a cryocooler,which is isolated from the environment by a heat shield and vacuum shroud. Whenin operation this creates a cold reservoir referred to as the bath. The bathcan be regulated between 11 K and 300 K. Inside the calorimeter the sample ismounted onto a substrate suspended by cotton threads, which thermally isolatesthe calorimeter from the bath. However, electrical wires attached to thecalorimeter’s heater and thermometer cause a finite thermal link to the bath.In addition, depending on the thermal contact between the sample andcalorimeter substrate, relaxation calorimetry will show either a 1-τ or 2-τeffect. If the internal thermal conductance between the sample and calorimeteris large relative to the external thermal conductance from the calorimeter tothe bath, a 1-τ effect can be seen. This is characterized by a smoothexponential decay of the time dependent temperature curve. When the internalthermal conductance is small or comparable to the external thermal conductance,a more complicated decay curve is observed, known as the 2-τ effect. In ourexperiment we use a Labview program that analyzes data by using 1-τ and 2-τmodels to determine the heat capacity of the sample. By continuing to improveupon the design of our relaxation calorimeters we can obtain more accuratelymeasured data.

Keywords


Relaxation, Calorimetry, τ

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