Setup to study the electronic structure of iron-bearing compounds in situ at conditions of the Earth&#8217;s lower mantle&#160;
Authors: Albers Christian , Sakrowski Robin , Spiekermann Georg , Libon Lélia , Wilke Max , Thiering Nicola , Gretarsson Hlynur , Sundermann Martin , Kaa Johannes , Tolan Metin , Sternemann Christian 
Published: March 2022

&lt;p&gt;The determination of the electronic structure of iron-bearing compounds at high pressure and high temperature (HPHT) conditions is of crucial importance for the understanding of the Earth&amp;#8217;s interior and planetary matter. Information on their electronic structure can be obtained by X-ray emission spectroscopy (XES) measurements, where the iron&amp;#8217;s K&amp;#946;&lt;sub&gt;1,3&lt;/sub&gt; emission provides information about the spin state and the valence-to-core region focusses on the coordination chemistry around the iron and its electronic state. Furthermore, resonant XES (RXES) at the iron&amp;#8217;s K-edge reveals even more detailed information about the electronic structure [1].&lt;/p&gt;&lt;p&gt;We present a setup to investigate the electronic structure of iron-bearing compounds &lt;em&gt;in situ&lt;/em&gt; at HPHT conditions using XES and RXES. The HPHT conditions are accomplished by diamond anvil cells (DACs) in combination with a portable double-sided Yb:YAG-laser heating setup [2]. The spectroscopy setup contains a wavelength dispersive von Hamos spectrometer in combination with a Pilatus 100K area detector [3]. This setup provides a full K&amp;#946;&lt;sub&gt;1,3&lt;/sub&gt; emission spectrum including valence-to-core emission in a single shot fashion. In combination with a dedicated sample preparation and use of highly intense synchrotron radiation of beamline P01 at PETRA III, the duration of the measurements is shortened to an extend that &lt;em&gt;in situ&lt;/em&gt; XES, including valence-to-core, as well as &lt;em&gt;in situ&lt;/em&gt; spin state imaging becomes feasible. The use of miniature diamonds [4] enables RXES measurements at the Fe-K edge. By using different analyzer crystals for the von Hamos spectrometer, simultaneous K&amp;#945; and K&amp;#946; detection are feasible, which provides L-edge and M-edge like information.&lt;/p&gt;&lt;p&gt;The presented sample is siderite (FeCO&lt;sub&gt;3&lt;/sub&gt;), which is in focus of recent research as it is a candidate for the carbon storage in the deep Earth. Siderite exhibits a complex chemistry at pressures above 50 GPa and temperatures above 1400 K resulting in the formation of carbonates featuring tetrahedrally coordinated CO&lt;sub&gt;4&lt;/sub&gt;-groups instead of the typical triangular-planar CO&lt;sub&gt;3&lt;/sub&gt;-coordination. These carbonates are well understood on a structural level but information on their electronic structure is scarce [5-7]. We present information on the sample&amp;#8217;s spin state at &lt;em&gt;in situ&lt;/em&gt; conditions of about 75 GPa and 2000 K XES K&amp;#946;&lt;sub&gt;1,3&lt;/sub&gt; imaging &amp;#160;as well as RXES measurements for low and high pressure siderite at ambient temperature conditions for K&amp;#945; and K&amp;#946; emission.&lt;/p&gt;&lt;p&gt;[1] M. L. Baker et al., &lt;em&gt;Coordination Chemistry Reviews &lt;/em&gt;345, 182 (2017)&lt;/p&gt;&lt;p&gt;[2] G. Spiekermann et al.&lt;em&gt;,&amp;#160; Journal of Synchroton Radiation,&lt;/em&gt; 27, 414 (2020)&lt;/p&gt;&lt;p&gt;[3] C. Weis et al., &lt;em&gt;Journal of Analytical Atomic Spectroscopy&lt;/em&gt; 34, 384 (2019)&lt;/p&gt;&lt;p&gt;[4] S. Petitgirard et al., &lt;em&gt;J. Synchrotron Rad&lt;/em&gt;. , 24, 276 (2017)&lt;/p&gt;&lt;p&gt;[5] J. Liu et al., &lt;em&gt;Scientific Reports, &lt;/em&gt;5, 7640 (2015)&lt;/p&gt;&lt;p&gt;[6] M. Merlini et al., &lt;em&gt;American Mineralogist&lt;/em&gt;, 100, 2001, (2015)&lt;/p&gt;&lt;p&gt;[7] V. Cerantola et al., &lt;em&gt;Nature Communications&lt;/em&gt; 8, 15960 (2017)&lt;/p&gt;