Defect fluorite type phase in anion deficient rare earth zirconates, RE3Zr0.5Nb0.5O6.75 (RE = Nd, Sm, Gd, Dy, Y): Synthesis and electrical properties

Abstract

Defect fluorite type phase in anion deficient rare earth zirconate compositions RE3Zr0.5Nb0.5O6.75 (RE ​= ​Nd, Sm, Gd, Dy, Y) were developed via the conventional solid state reaction route. The effects of anion deficiency on the crystalline structure and electrical properties of the compositions were analysed using powder X-ray diffraction, Raman spectroscopy, scanning electron microscopy and impedance spectroscopy techniques. Unusually, all the developed rare earth zirconates crystallise into a defect fluorite type structure with a space group Fm3m. The lattice parameter increases with the increase of the ionic radius of the lanthanide element present in the system following Vegard’s law. Raman spectra analysis further surmises the defect fluorite phase formation with some disorder from Nd to Y. The Cole Cole plot of the samples with temperature suggests non Debye type of relaxation process with an increase in conductivity through thermal activation of the charge carriers. The modulus spectrum analysis confirms the increased cooperative behaviour of the oxide ions from Nd to Y with a decrease in the lattice volume. This results in increased activation energy for long range conduction leading to a reduction in conductivity in the system. The composition, Nd3Zr0.5Nb0.5O6.75, exhibits maximum conductivity (4.29 ​× ​10-4 ​S/cm) at 1023 ​K, which shows less co-operative behaviour effects on the oxide ions due high lattice volume. Thus the present study demonstrates that creating oxygen vacancies in the system is not prime importance as cooperative behaviour among the ions increases and suppresses the conductivity more with contracted lattice volume.