Symmetry-induced modulation of proton conductivity in Y-doped Ba(Zr,Ce)O: insights from Raman spectroscopy

Y-doped Ba(Zr,Ce)O 3 (BZCY) proton conducting ceramics have attracted extensive attention because of their promising applications as electrolytes for intermediate-temperature proton ceramic electrochemical cells. The proton conductivity of BZCY is governed by their lattice volume and crystal symmetry; however, systematic studies of the competition between these two factors are lacking, hindering further improvement of their proton conductivity at low and intermediate temperatures. In this work, the crystal symmetry of BZCY epitaxial films deposited on NdGaO 3 (110) is compared to that of polycrystalline bulk BZCY based on Raman spectra. The Raman signal of BZCY epitaxial films is amplified using surface-enhanced Raman spectroscopy and subsequently extracted utilizing the nonnegative matrix factorization method. The relative Raman intensity ratio of the BO 6 octahedra motion to the Ba-BO 6 relative motion in the ABO 3 structure indicates that as the Ce content increases, the crystal symmetry of polycrystalline bulk BZCY decreases, whereas that of the epitaxial films on NdGaO 3 remains consistently lower compared to bulk BZCY. The relationship between the activation energy and relative Raman intensity of epitaxial films and bulk BZCY indicates quantitatively that higher activation energy is observed in the crystal structure with lower symmetry. This work suggests that crystal symmetry has a predominant effect on the activation energy of BZCY. The results provide a deeper insight for developing proton conducting electrolyte membranes with high proton conductivity and low activation energy. Quantitative comparison of crystal symmetry and lattice volume effects on the proton conductivity of Y-doped Ba(Zr,Ce)O 3 epitaxial films to polycrystalline bulk materials reveals that lower crystal symmetry correlates with higher activation energy.