The effect of Zr/Nd ratio on Nd2Zr2O7 ionic conductivity

Pyrochlore based materials, due to their high ionic conductivity, have been characterized as potential solid electrolytes. In this paper Nd2-xZr2+xO7+x/2 pyrochlore materials (0 ≤ x ≤ 1) were prepared by mechanical... [ view full abstract ]

Pyrochlore based materials, due to their high ionic conductivity, have been characterized as potential solid electrolytes. In this paper Nd_2-xZr_2+xO_7+x/2 pyrochlore materials (0 ≤ x ≤ 1) were prepared by mechanical activation of the oxide mixtures, following by high temperature sintering (1500°C, 10 hrs) of uniaxial pressed pellets. Structure and microstructural characterization of prepared ceramic samples were done by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. The behavior of their TEC (thermal expansion coefficient) was also investigated. All Nd_2-xZr_2+xO_7+x/2 are single phase materials with a relative density higher than 90%.

Electrical characterization was performed by electrochemical impedance spectroscopy as a function of temperature and oxygen partial pressure. The electrical conductivity of Zr-rich (x > 0) compositions is more than one order of magnitude higher than the stoichiometric composition (x = 0), with a conductivity value close to 0.03 S/cm at 1000°C in air, and an activation energy of 1 eV. The oxygen partial pressure dependence shows a constant conductivity value within a large oxygen partial pressure range, typical of the ionic type conductivity. The increase of the ionic conductivity for Zr-rich compositions were interpreted by the interstitial oxygen ion formation, to compensate the Zr⁴⁺ in the Nd³⁺ positions. The ionic conductivity of this material was then attributed to interstitial oxygen ions migration.