Investigation of Photoelectrocatalytic and Magnetic Properties of Sr₂YbRu_1–<i>x</i>Ta_<i>x</i>O₆ (<i>x</i> = 0, 0.25, 0.5, 0.75, and 1)

We report the effect of substitution of Ru by Ta in Sr₂YbRuO₆ on its magnetic and photoelectrocatalytic properties. The powder X-ray diffraction data, was satisfactorily refined in the monoclinic space group, <i>P</i>2₁/<i>n</i>. The DC magnetization studies indicated that Sr₂YbRuO₆ shows antiferromagnetic interaction through Yb–O–Ru orbital ordering, with the highest Weiss temperature, among Sr₂YbRu_1–<i>x</i>Ta_<i>x</i>O₆ (<i>x</i> = 0, 0.25, 0.5, and 0.75) which have values of −148, −125, −118, and −102 K, respectively. The difference in observed and theoretical magnetic moments was found to increase as <i>x</i> increases. It was also observed that with the increase of Ta concentration in Sr₂YbRu_1–<i>x</i>Ta_<i>x</i>O₆, the band gap increased almost linearly, from 1.78(1) eV (<i>x</i> = 0) to 2.08(1) (<i>x</i> = 0.75), and thereafter a sharp increase 2.65(1) eV (<i>x</i> = 1) was observed, with the lowering of energy level of valence band, along with disruption in orbital ordering as <i>x</i> increases. The photoelectrocatalytic oxygen evolution reaction (OER) studies carried out on the series yield a maximum photocurrent density of 17 μA/cm² and photoresponse current of 5.5 μA/cm² at 0.8 V at an onset potential at 0.29 V vs Ag/AgCl for Sr₂YbRuO₆. The XPS analysis showed Ta and Ru to be in +5/+4 oxidation states, with the highest concentration of Ru⁴⁺ ion observed for Sr₂YbRuO₆. The presence of oxygen vacancies was confirmed by XPS as well as EPR studies.