FY04 LDRD Final Report Small Sample Heat Capacity Under High Pressure LDRD Project Tracking Code: 04-FS-020

McCall, S K ; Jackson, D D

Lawrence Livermore National Laboratory

关键词: Specific Heat;    Thermal Conductivity;    75 Condensed Matter Physics, Superconductivity And Superfluidity;    Phonons;    Magnons;   

DOI  :  10.2172/15014668
RP-ID  :  UCRL-TR-209726
RP-ID  :  W-7405-ENG-48
RP-ID  :  15014668

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来源: UNT Digital Library

【 摘 要 】

Specific heat provides a probe of bulk thermodynamic properties, including low energy excitations (phonons, magnons, etc), the electron density of states, and direct observation of phase transitions. The ability to measure specific heat as a function of pressure permits study of these properties as a function of lattice parameters. This in turn should allow construction of an equation of state for a given system. Previous measurements of specific heat under pressure done by adiabatic methods were limited to materials with extremely large heat capacities because it was difficult to decouple the sample heat capacity from the surrounding pressure cell. Starting in the late Seventies, Eichler and Gey[1] demonstrated an AC technique to measure heat capacity of relatively small samples ({approx}100's mg) in a piston pressure cylinder at pressures up to 2 GPa. More recently, this technique has been expanded to include work on significantly smaller samples (< 1mg) in large diamond anvil cells (DAC)[2]. However, these techniques require a relatively weak coupling of the sample to the surrounding thermal bath, which limits the base temperature, particularly for radioactive samples possessing significant self-heating such as plutonium. A different technique, sometimes referred to as the 3{omega}-technique, utilizes a two dimensional heat flow model to extract heat capacity, C, and {kappa}, the thermal conductivity, from an oscillating heat input. One advantage of this method is that it does not require that the sample be thermally isolated from the heat bath, so lower base temperatures should be accessible to interesting self-heating samples. From an experimental perspective, the design requirements of the 3{omega} and AC techniques are quite similar. We focused on development of these techniques for a copper-beryllium (CuBe) pressure clamp for use on small samples at temperatures down to 1.7K and at pressures up to 1.6 GPa. The successful development of this capability will enable a new class of important physical property measurements on a variety of advanced and special materials, including plutonium.