Dielectric Relaxation Studies of the Fast Lithium-Ion Conductor La_2/3-xLi_3xTiO₃ (x=0.06, 0.11)

Abstract:

The diffusion processes of lithium ions in La_2/3-xLi_3xTiO₃ (x=0.06, 0.11) compounds were investigated by dielectric relaxation method. Prominent relaxation dielectric loss peaks, peaks P1 and P2 in La_0.56Li_0.33TiO₃ and peaks P3 and P4 in La_0.61Li_0.18 TiO₃, were observed. From the shift of peak position with frequency, the activation energy of 0.36~0.42 eV and the pre-exponential factor of relaxation time in the order of 10^-14 ~ 10^-13 s were obtained if one assumes Debye relaxation processes. The activation energies of lithium ion diffusion in La_2/3-xLi_3xTiO₃ compounds and the characteristic vibration frequency for the ionic hopping motion are higher than those measured by ⁷Li nuclear magnetic resonance (NMR) spectroscopy and that of the typical phonon frequency (about 10¹³Hz). These values of relaxation parameters strongly suggest the existence of interaction between the relaxation species (here lithium ions or vacancies). Basing on the coupling model, the decoupled relaxation parameters of the dielectric relaxation peaks is: P₁ (0.14 eV, 2×10^-13 s), P₂ (0.25 eV, 1.8×10^-13 s), P₃ (0.17 eV, 4×10^-13 s) and P₄ (0.3 eV, 2.7×10^-13 s). These decoupled parameters are very close to the NMR measurement results and the reciprocal of the typical phonon frequency. Judging from the relaxation parameter of the peaks and combining with the crystallographic characterization, it is suggested that the P₁ (P₃) and P₂ (P₄) peaks are associated with the lithium ion diffusion in the ab planes and between the adjacent ab planes, respectively.

• Periodical: Advanced Materials Research (Volumes 457-458)
• Pages: 1019-1024
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.457-458.1019
• Online since: January 2012
• Authors: Wei Guo Wang, Qian Feng Fang, Gang Ling Hao
• Keywords: Dielectric Relaxation, Lithium Ion Conductor, Lithium Ion Diffusion

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