Soft anharmonic coupled vibrations of Li and SiO4 enable Li-ion diffusion in amorphous Li2Si2O5. Issue 4 (4th January 2023)

• Record Type: Journal Article
• Authors: Kumar, Sajan; Gupta, Mayanak K.; Goel, Prabhatasree; Mittal, Ranjan; Mukhopadhyay, Sanghamitra; Le, Manh Duc; Shukla, Rakesh; Achary, Srungarpu N.; Tyagi, Avesh K.; Chaplot, Samrath L.
• Is Part Of: Journal of materials chemistry. Volume 11:Issue 4(2023)
• Page Start: 1712
• Page End: 1722
• Publication Date: 2023-01-04
• Subjects: Materials -- Research -- Periodicals; Chemistry, Analytic -- Periodicals; Environmental sciences -- Research -- Periodicals; 543.0284
• DOI: 10.1039/d2ta08170a
• Languages: English
• ISSNs: 2050-7488

Abstract

Abstract : Coupled vibrations of Li and SiO4 enable Li-ion diffusion in amorphous Li2 Si2 O5 . Abstract : We present investigations on atomic dynamics and Li + diffusion in crystalline and amorphous Li2 Si2 O5 using quasielastic neutron scattering (QENS) and inelastic neutron scattering (INS) studies supplemented by ab initio molecular dynamics simulations (AIMD). The QENS measurements in the amorphous phase of Li2 Si2 O5 show a narrow temperature window (700 < T < 775 K), exhibiting significant quasielastic broadening corresponding to fast Li + diffusion. Our INS measurements clearly show the presence of large phonon density of states (PDOS) at low energy (low- E ) in the superionic amorphous phase, which disappear in the non-superionic crystalline phase, corroborating the role of low- E modes in Li + diffusion. The frustrated energy landscape and host flexibility (due to random orientation and vibrational motion of SiO4 polyhedral units) play an essential role in diffusing Li + . We used AIMD simulations to identify that these low- E modes involve a large amplitude of Li vibrations coupled with SiO4 vibrations in the amorphous phase. At elevated temperatures, these vibrational dynamics accelerate Li + diffusion. Above 775 K, these SiO4 vibrational dynamics drive the system into the crystalline phase by locking SiO4 and Li + into deeper minima of the free energy landscape and making them disappear in the crystalline phase. Both experiments and simulations provide valuable information about the atomic level stochastic and vibrational dynamics in Li2 Si2 O5 and their role in Li + diffusion and vitrification.