www.elsevier.com/locate/rgg Sound velocity measurement by inelastic X-ray scattering at high pressure and temperature by resistive heating diamond anvil cell E. Ohtani a,b, * , K. Mibe c , T. Sakamaki a , S. Kamada a , S. Takahashi a , H. Fukui d , S. Tsutsui e , A.Q.R. Baron f a Graduate School of Science, Tohoku University, Sendai 980-8578, Japan b V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, ul. Akademika Koptyuga 3, Novosibirsk, 630090, Russia c Earthquake Research Institute, University of Tokyo, Tokyo 113-0032, Japan d Graduate School of Material Science, University of Hyogo, Hyogo 678-1297, Japan e Research and Utilization Division, SPring-8, JASRI, Sayo, Hyogo, 679-5198, Japan f Materials Dynamics Laboratory, RIKEN SPring-8 Center, RIKEN, Sayo, Hyogo 679-5148, Japan Received 11 July 2014; accepted 25 July 2014 Abstract We determined the compressional velocity of hcp-Fe in a wide pressure and temperature range using high-resolution inelastic X-ray scattering (IXS) combined with in situ X-ray powder diffraction (XRD) on samples in resistively heated diamond anvil cells: our measurements extend up to 174 GPa at room temperature, to 88 GPa at 700 K, and to 62.5 GPa at 1000 K. Our data obtained at room temperature and high temperature are well described by a linear relation to density, extending the range of verification of Birch’s law beyond previous work and suggesting only a small temperature dependence up to 1000 K. When we compare the present results with the preliminary reference Earth model (PREM), we can conclude that there is either a strong temperature effect on Birch’s law at temperatures above 1000 K, or the composition of the core is rather different from that commonly expected, i.e., containing heavy elements. © 2015, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. Keywords: sound velocity; hcp-iron, high pressure and temperature; inner core; inelastic X-ray scattering; diamond anvil cell; resistive heating Introduction There is a longstanding controversy regarding the tempera- ture dependence of Birch’s law (Birch, 1952). Fiquet et al., (2001) measured the seismic velocity of hcp-Fe to 112 GPa at room temperature using inelastic X-ray scattering (IXS). Their Vp-density relation overlapped with that determined by the shock experiment along the Hugoniot (Brown and McQueen, 1986). Thus, they argued that there is no tempera- ture effect on Birch’s law. On the other hand, Mao et al. (2001) determined the seismic velocity of hcp-Fe up to 153 GPa using the Nuclear Inelastic Scattering, NIS (=Nuclear Resonant Inelastic X-ray Scattering, NRIXS), and reported higher V P than that determined by the shock compression experiments indicating there are a temperature dependency in Birch’s law. If temperature does modify Birch’s law, the light element contents of the inner core estimated by the previous authors (Antonangeli et al., 2010; Badro et al., 2007; Shibazaki et al., 2012) must be reconsidered. In order to clarify the V P -density relation of hcp-Fe, we measured the compressional velocity and density of hcp-Fe simultaneously up to 1000 K, in a wide pressure range using inelastic X-ray scattering (IXS). Here we present technical details on the sound velocity measurements using IXS spectroscopy combined with the external heating diamond anvil cell. Experimental method IXS measurements We determined the sound velocity and density at the same pressure and temperature conditions by the in situ IXS and XRD measurements. Inelastic X-ray scattering spectra were taken at the high-resolution inelastic X-ray scattering beam- line, BL35XU, of Spring-8 (Baron et al., 2000). The sample Russian Geology and Geophysics 56 (2015) 190–195 * Corresponding author. E-mail address: ohtani@m.tohoku.ac.jp (Eiji Ohtani) Available online at www.sciencedirect.com ScienceDirect ed. 1068-7971/$ - see front matter D 201 IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserv V.S. S bolev o http://dx.doi.org/10.1016/j.rgg.201 .0 .0 5, 5 1 12