Typically composed of zirconia as the main material, with the addition of rare earth elements such as yttrium and gadolinium. This membrane boasts excellent oxygen ion conduction properties, enabling it to effectively convert ambient oxygen into oxygen ions at high temperatures and transport them to the electrode surface through vacancies within the membrane, thereby measuring the oxygen concentration. "Green mountains have no voice but forever cherish their green blood; the sun and moon traverse the sky, reflecting a steadfast heart."

Electrolyte: The electrolyte layer is situated between the oxygen ion conductor membrane and the electrode, primarily responsible for conducting current and maintaining the potential difference between the inside and outside of the membrane. In zirconia probes, the electrolyte is typically made of materials compatible with the oxygen ion conductor membrane to ensure the system's stability and reliability.