Nanocrystalline ZrO2 thin films as electrode materials using in high temperature–pressure chemical sensors

The nature of the ZrO2 thin films in the Zr/ZrO2 electrode plays a vital role to build Zr/ZrO2 high temperature–pressure chemical sensors, when the electrode is utilized to be in situ measuring electro-chemical properties of hydrothermal fluids. Zr metal was oxidized with a NaCO3 melt to form a thin film of ZrO2 on the surface of Zr, then an oxidation–reduction electrode was performed. The electro-chemical properties of the Zr/ZrO2 electrode were tested from room temperature to high temperatures and high pressures. By using SEM, EPMA and HRTEM, analyses of topography, chemical composition and structure of the ZrO2 thin films revealed that Zr/ZrO2 interface is divided in to 5 zones from the outmost zone to the center: 1) prismatic and oxygen-rich ZrO2, 2) ZrO2; 3) oxygen-rich Zr; 4) oxygen-bearing Zr; 5) Zr metal. Especially, the outmost oxygen-rich ZrO2 zone of the thin films is composed of nanometer-sized monoclinic crystals with high oxygen content, when Zr/ZrO2 electrode is conducted to make a good high temperature chemical sensor.