Thermal diffusivity measurement in a diamond anvil cell using a light pulse thermoreflectance technique

Abstract

Apparatus to measure the thermal diffusivity of a plate between diamond anvils at high pressure was developed. The Mg(OH)2 plates coated with Pt films on both sides were used for testing the apparatus. One side of the Pt film played the role of an absorber of a laser pulse, and the other side was used for the detection of the temperature change. The sample was loaded into a hole drilled in a rhenium foil gasket together with the insulation layers of NaCl as a pressure medium. Subsequently, the sample was compressed with 150 µm culet beveled diamond anvils. The pressure in this study reached 57 GPa. Then, a front face of the sample was heated by laser pulses with a duration of 2 ns and a wavelength of 1064 nm. To probe the temperature change at the back face of the sample, a continuous wave laser beam with a wavelength of 782 nm was irradiated. Using the reflected intensity of the continuous wave laser beam, a transient temperature curve was measured when the heat transferred across Pt/Mg(OH)2/Pt layers. The thermal diffusivity of Mg(OH)2 was calculated by analyzing the transient temperature curves. The thermal diffusivity of Mg(OH)2 is 5.9 × 10−6 m2 s−1 at 57 GPa, which is larger than that at ambient pressure by a factor of ≈6.