Is Ba 3 In 2 O 6 a high- T c superconductor?

It has been suggested that Ba 3 In 2 O 6 might be a high- T c superconductor. Experimental investigation of the properties of Ba 3 In 2 O 6 was long inhibited by its instability in air. Recently epitaxial Ba 3 In 2 O 6 with a protective capping layer was demonstrated, which finally allows its electronic characterization. The optical bandgap of Ba 3 In 2 O 6 is determined to be 2.99 eV in-the (001) plane and 2.83 eV along the c -axis direction by spectroscopic ellipsometry. First-principles calculations were carried out, yielding a result in good agreement with the experimental value. Various dopants were explored to induce (super-)conductivity in this otherwise insulating material. Neither A - nor B -site doping proved successful. The underlying reason is predominately the formation of oxygen interstitials as revealed by scanning transmission electron microscopy and first-principles calculations. Additional efforts to induce superconductivity were investigated, including surface alkali doping, optical pumping, and hydrogen reduction. To probe liquid-ion gating, Ba 3 In 2 O 6 was successfully grown epitaxially on an epitaxial SrRuO 3 bottom electrode. So far none of these efforts induced superconductivity in Ba 3 In 2 O 6, leaving the answer to the initial question of whether Ba 3 In 2 O 6 is a high- T c superconductor to be 'no' thus far.