Modulation calorimetry in diamond anvil cells. II. Joule-heating design and prototypes

作者：Geballe Zachary M^*; Struzhkin Viktor V; Townley Andrew; Jeanloz Raymond

来源：Journal of Applied Physics, 2017, 121(14): 145903.

DOI：10.1063/1.4979850

Part I shows that quantitative measurements of heat capacity are theoretically possible inside diamond anvil cells via high-frequency Joule heating (100 kHz-10MHz), opening up the possibility of new methods to detect and characterize transformations at high-pressure such as the glass transitions, melting, magnetic orderings, and the onset of superconductivity. Here, we test the possibility outlined in Part I, using prototypes and detailed numerical models. First, a coupled electrical-thermal numerical model shows that specific heat of metals inside diamond cells can be measured directly using similar to 1MHz frequency, with < 10% accuracy. Second, we test physical models of high-pressure experiments, i.e., diamond-cell mock-ups. Metal foils of 2-6 mu m-thickness are clamped between glass insulation inside diamond anvil cells. Fitting data from 10 Hz to similar to 30 kHz, we infer the specific heat capacities of Fe, Pt, and Ni with +/- 20%-30% accuracy. The electrical test equipment generates -80 dBc spurious harmonics, which overwhelm the thermally induced harmonics at higher frequencies, disallowing the high precision expected from numerical models. An alternative Joule-heating calorimetry experiment, on the other hand, does allow absolute measurements with < 10% accuracy, despite the -80 dBc spurious harmonics: the measurement of thermal effusivity, root rho ck (rho, c, and k being density, specific heat, and thermal conductivity), of the insulation surrounding a thin-film heater. Using a similar to 50 nm-thick Pt heater surrounded by glass and 10 Hz-300 kHz frequency, we measure thermal effusivity with 66% accuracy inside the sample chamber of a diamond anvil cell. Published by AIP Publishing.

• 出版日期2017-4-14