Deciphering structural changes in Gd³⁺ and Ce⁴⁺ co-doped lanthanum zirconates using X-ray diffraction and Raman spectroscopy

This study explores the structural evolution of Gd³⁺ and Ce⁴⁺ co-doped lanthanum zirconates synthesized via the co-precipitation method, focusing on two distinct stoichiometric compositions: (La_0.9Gd_0.1)₂(Zr_0.9Ce_0.1)₂O₇ and (La_0.1Gd_0.9)₂(Zr_0.9Ce_0.1)₂O₇. The phase transformations were investigated at temperatures ranging between 700 °C and 1300 °C by X-ray diffraction and Raman spectroscopy. The sample (La₀.₉Gd₀.₁)₂(Zr₀.₉Ce₀.₁)₂O₇ was observed to be evolving from a disordered to an ordered pyrochlore structure which was evidenced by emergence of superlattice reflections. On the other hand, the Gd³⁺ rich composition, (La_0.1Gd_0.9)₂(Zr_0.9Ce_0.1)₂O₇ shows stabilization in the defect fluorite phase and no superlattice reflections observed through XRD. However, Raman spectra revealed the appearance of weakly ordered pyrochlore microdomains, indicating a co-existing defect fluorite and pyrochlore phase in this sample. This observation is further confirmed through diffraction analysis in TEM. The structural evolution was understood in terms of the average radius ratio of the cations in the samples due to the incorporation of Gd³⁺ and Ce⁴⁺ ions. Williamson-Hall analysis was performed to quantify microstructural parameters, including crystallite size and lattice strain. The results confirmed the retention of nanostructure in both samples with crystallite sizes remaining below 100 nm. SEM analysis corroborated the structural stability observations.