The IRH-DAC: Resistive Heating of Non-Metallic Samples to 3000 K at 50 GPa in the Diamond Anvil Cell

Abstract:

We have developed a novel internal resistive heating (IRH) technique for the diamond anvil cell (DAC) capable of stably heating a non-metallic sample to 3000 K at 50 GPa, as confirmed by in situ synchrotron X-ray diffraction and simultaneous spectroradiometric temperature measurement. The primary technique for accessing conditions of deep planetary interiors is the laser-heated DAC. Laser heating can achieve temperatures of many thousands of K, but beam shape and variations in sample geometry and absorbance introduce significant thermal gradients with associated uncertainties. Spatial (radial) and temporal variations during an experiment can lead to uncertainties of the order 100 K or more. Resistive heating techniques provide greater temperature stability, more precise control, reduced thermal gradients and uncertainties an order of magnitude smaller. External resistive heaters surrounding the anvils are limited to ~1500 K beyond which the unpressurized back of the anvils begin to graphitize. Internal resistance heating in the DAC using metal heaters extends the accessible temperature range and has been successfully used to study the melting and electrical properties of fine metal wire, compressed between the anvils, that serves as both heating element and sample [1-3]. Designs that have been adapted for heating non-metallic samples are limited in the P-T conditions they can achieve (T < 2000 K) [4, 5]. Existing designs rely on a composite gasket to electrically isolate the heating filament. Our new design avoids this complexity, allows for thermal insulation between the heating filament and the anvil faces, and can reach 3000 K. The heater is stable for hours and can be precisely controlled during spectroscopic and scattering measurements. The IRH-DAC provides an important new tool for investigating materials at extreme conditions. It is well suited for collecting dense, accurate P-V-T data, precisely demarcating phase boundaries, and heating experiments over the long acquisition times required for techniques such as Brillouin spectroscopy and inelastic X-ray scattering.

References:

[1] Boehler et al. 1986 Physica B+C 139, 916-918 [2] Sinmyo et al. 2019 EPSL 510, 45-52 [3] Suehiro et al. 2019 High P. Res. 39, 579-587 [4] Zha et al. 2008 J. Appl. Phys. 103, 054908 [5] Ozawa et al. 2018 High P. Res. 38, 120-135