Depth chemical profile in a CeIr3 sample

The polycrystalline sample of CeIr3 used in the present studies was synthesized by arc-melting cerium (4N) and iridium (3N5) in an arc furnace on a water-cooled copper hearth using a tungsten electrode under a high purity argon atmosphere. A piece of zirconium was used as an oxygen getter. First, a button of Ir was prepared by arc-melting the iridium powder pellet alone. The Ir ingot was then melted with Ce pieces with 3% excess to compensate expected loss of Ce. After the initial melt, the sample button was turned and re-melted several times (4-5) to improve homogeneity. Mass loss during the synthesis was lower than 1%, and the sample button formed was uniform, hard and silvery grey in color. The obtained sample was then wrapped in tantalum foil and annealed at 1370˚C for 12 hours under high vacuum (10-5 torr). Subsequently, the resulting material was ground well, pressed into a pellet using a hydraulic press and then heated under high vacuum to 1400˚C and held at this temperature for 36 hours.
To determine the valence state of cerium, X-ray photoelectron spectroscopy (XPS) was performed. The XPS measurement was performed using an Argus (Omicron NanoTechnology) X-ray photoelectron spectrometer. The photoelectrons were excited by a Mg-Ka X-ray source. The X-ray anode was operated at 15 keV and 300 W. The XPS measurement was performed at room temperature under ultra-high vacuum conditions, with pressures below 1.1 x10-8 mBar. It is known that the cerium at the surface tends to exist as Ce3+ rather than Ce4+.3 To avoid this surface impact, the CeIr3 sample was sputter-cleaned (three times) by Ar ions, (FDG 150 ion source mounted in the analytic chamber), before the XPS measurement.