Influence of Oxygen on PdCoO2: Structure, Thermogravimetry, Photoemission, Magnetic and μ‐Raman Spectroscopic Studies

Abstract

AbstractMolten salt synthesized PdCoO2 annealed in argon and air exhibits a reversible weight change of about 2.5 %. Le Bail refinements confirm rhombohedral structures without any appreciable change in the lattice parameters for the given weight change. X‐ray photoemission studies show that oxygen uptake/loss did not change the oxidation states of Pd from its nominal +1 state whereas Co4+ is detected in addition to the Co3+ and the fraction of Co4+ increases marginally with oxygen gain. The impact of weight change on the magnetization of PdCoO2 is very low with a minimum difference. As the low‐spin Co3+ ions are non‐magnetic, the observed magnetization with a ferromagnetic transition at ~25 K is attributed to the low‐spin Co4+ ions in the lattice. Raman active bands observed at 700 cm−1 (A1g) and 508 cm−1 (Eg) correspond to the Pd−O stretching and bending modes respectively with Co3+ environment. Additional peaks at 681 and 473 cm−1 with relatively less intensity arise from the weaker Pd−O bond with oxygen linked to Co4+.