Nanocrystalline ZrO 2 thin films as electrode materials using in high temperature–pressure chemical sensors

Abstract

The nature of the ZrO 2 thin films in the Zr/ZrO 2 electrode plays a vital role to build Zr/ZrO 2 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 NaCO 3 melt to form a thin film of ZrO 2 on the surface of Zr, then an oxidation–reduction electrode was performed. The electro-chemical properties of the Zr/ZrO 2 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 ZrO 2 thin films revealed that Zr/ZrO 2 interface is divided in to 5 zones from the outmost zone to the center: 1) prismatic and oxygen-rich ZrO 2, 2) ZrO 2; 3) oxygen-rich Zr; 4) oxygen-bearing Zr; 5) Zr metal. Especially, the outmost oxygen-rich ZrO 2 zone of the thin films is composed of nanometer-sized monoclinic crystals with high oxygen content, when Zr/ZrO 2 electrode is conducted to make a good high temperature chemical sensor.