Electrical conductivity and crystallization of amorphous bismuth ruthenate thin films deposited by spray pyrolysis

Abstract

Amorphous oxide thin films with tailored functionality will be crucial for the next generation of micro-electro-mechanical-systems (MEMS). Due to potentially favorable electronic and catalytic properties, amorphous bismuth ruthenate thin films might be applied in this regard. We report on the deposition of amorphous bismuth ruthenate thin films by spray pyrolysis, their crystallization behavior and electrical conductivity. At room temperature the 200 nm thin amorphous films exhibit a high electrical conductivity of 7.7 × 10⁴ S m⁻¹, which was found to be slightly thermally activated (E_a = 4.1 × 10⁻³ eV). It follows that a long-range order of the RuO₆ octahedra is no precondition for the electrical conductivity of Bi₃Ru₃O₁₁. Upon heating to the temperature range between 490 °C and 580 °C the initially amorphous films crystallize rapidly. Simultaneously, a transition from a dense and continuous film to isolated Bi₃Ru₃O₁₁ particles on the substrate takes place. Solid-state agglomeration is proposed as the mechanism responsible for disintegration. The area specific resistance of Bi₃Ru₃O₁₁ particles contacted by Pt paste on gadolinia doped ceria electrolyte pellets was found to be 7 Ω cm² at 607 °C in air. Amorphous bismuth ruthenate thin films are proposed for application in electrochemical devices operating at low temperatures, where a high electrical conductivity is required.