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In this article we present a direct comparison between reflective (Schwarzschild mirrors) and refractive (achromatic doublets) optics commonly used in spectroradiometric temperature measurements in laser heated diamond anvil cells. Emission spectra are fitted with the Planck's law and are further analysed with the two-colour technique; theoretical simulations are used to compare the temperature measurement accuracy of the two optical systems. The first result obtained is that achromatic doublets with large numerical aperture () produce extensive accuracy errors in the full T range (1500-3000 K). When reduced apertures () are used a good agreement is found with measurements from reflective optics up to 2600 K while systematic differences (around 200 K) appear at higher temperatures. However, these temperature differences cannot explain the discrepancies between the iron melting curves obtained in the past years using laser heated diamond anvil cells. [ABSTRACT FROM AUTHOR]

In this article, the specification and application of the new double‐sided YAG laser‐heating system built on beamline I15 at Diamond Light Source are presented. This system, combined with diamond anvil cell and X‐ray diffraction techniques, allows in situ and ex situ characterization of material properties at extremes of pressure and temperature. In order to demonstrate the reliability and stability of this experimental setup over a wide range of pressure and temperature, a case study was performed and the phase diagram of lead was investigated up to 80 GPa and 3300 K. The obtained results agree with previously published experimental and theoretical data, underlining the quality and reliability of the installed setup. A double‐sided, off‐axis laser‐heating system for monochromatic X‐ray diffraction experiments using a diamond anvil cell has been installed at beamline I15 at Diamond Light Source. Measurements of the pressure–temperature phase diagram of Pb demonstrate the reliability of the setup and the high quality of the data. [ABSTRACT FROM AUTHOR]

Abstract: Precise knowledge of the melting temperatures of iron, nickel, and their alloys at pressures of the deep Earth would allow us to better constrain the parameters used for the Earth's heat budget and dynamics. However, melting curves of transition metals at pressures approaching 100 GPa and above are still controversial. To address this issue, we report new data on the melting temperature of nickel in a laser‐heated diamond anvil cell up to 100 GPa obtained by X‐ray absorption spectroscopy (XAS), a technique rarely used at such conditions. We couple this for the first time to ex situ analysis of the sample, providing a further validation of the melting criterion adopted here. Finally, a Simon‐Glatzel fit to the melting data obtained in this work, combined with those obtained in the most recent X‐ray diffraction experiments, gives T M ( K ) = 1727 × P M 17 ± 3 + 1 1 2 . 5 ± 0 . 1, defining the most up‐to‐date X‐ray‐determined melting curve for Ni. This result confirms that Ni could be ignored in the discussion on melting properties and thermal profile of the Earth's core, as it should affect the Fe melting point by only 10–20 K at 90 GPa. [ABSTRACT FROM AUTHOR]