Na+/Li+-ionic conductivity in Fe2Na2K[Li3Si12O30]

Mechanism for the Combined Li–Na Ionic Conductivity in Sugilite (Fe2Na2K[Li3Si12O30])-Type Compounds

“…Semi-empirical absorption correction was applied to obtain minimal and maximal transmission T min and T max , respectively. Rietveld refinements with HRNPD at 973 K were carried out using the program package JANA2006 [30] with an initial starting model delivered by the Rietveld analyses with HRNPD data at 923 K from our previous study [11]. The background was fitted with a Legendre polynomial.…”

“…In exploring prototype structures for Li-Na ionic conductors [10,11], the milarite family is regarded as a highly interesting candidate due to a highly flexible choice for its framework and non-framework constituents with general formula A 2 B 2 C[T(II) 3 T(I) 12 O 30 ] (A = Sn 4+ , Ti 4+ , Zr 4+ , Fe 3+ , Al 3+ ; Mg 2+ ; Zn 2+ ; B = Na + , H 2 O, vacancy; C = Na + , K + ; Minerals 2023, 13, 620 2 of 21 T(I) = Si 4+ , Al 3+ ; T(II) = Li + , Be 2+ , Mg 2+ , Zn 2+ ) [12][13][14][15][16]. These structure group members show the hexagonal space group symmetry P6/mcc with a ≈ 10 Å and c ≈ 14 Å.…”

“…Among Li-bearing milarite-type compounds [10,11,[17][18][19][20][21][22], sogdianite contains Zr 4+ as the main element at the octahedral A site but is mostly empty at the B site (6+3)-coordinated with framework oxygens, while sugilite is Fe 3+ -rich at the A site (Figure 1a), and Na fully occupies the B site (Figure 1b). A DC conductivity value of 1.7 × 10 −3 S•cm −1 of sugilite at T = 943 K, which was estimated from a frequency-independent part on Bode plots of impedance spectra (IS) ( [23] and this study), is two orders of magnitude higher than that of sogdianite [10].…”

“…Na cations co sate electrostatically the negative-charged framework unit [Fe2Li3Si12O30] 3− but als play a critical role for the charge transport in sugilite. To simplify the chemical content at the A site exclusively with Fe 3+ while hav maximal Na content at the B site, a sugilite analogue, Fe 3+ Na2K[Li3Si12O30], was synth under mild hydrothermal conditions [11]. In this previous study, we detected diffu sity distribution of neutron scattering lengths (nsl) of Li and Na from difference F (ΔF) maps evaluated with high-resolution neutron powder diffraction (HRNPD from 298 to 1123 K. This observation pointed to a high dynamic disorder of Li and Fe 3+ Na2K[Li3Si12O30] and their 2D hopping paths, which were strongly anisotropic p to the (a-b) plane.…”

“…In this previous study, we detected diffu sity distribution of neutron scattering lengths (nsl) of Li and Na from difference F (ΔF) maps evaluated with high-resolution neutron powder diffraction (HRNPD from 298 to 1123 K. This observation pointed to a high dynamic disorder of Li and Fe 3+ Na2K[Li3Si12O30] and their 2D hopping paths, which were strongly anisotropic p to the (a-b) plane. In the sugilite structure, there were several interstitials around 12 bered rings (MRs) of LiO4-FeO6 polyhedra (Figure 2a), other spacious interstiti To simplify the chemical content at the A site exclusively with Fe 3+ while having the maximal Na content at the B site, a sugilite analogue, Fe 3+ Na 2 K[Li 3 Si 12 O 30 ], was synthesized under mild hydrothermal conditions [11]. In this previous study, we detected diffuse density distribution of neutron scattering lengths (nsl) of Li and Na from difference Fourier (∆F) maps evaluated with high-resolution neutron powder diffraction (HRNPD) data from 298 to 1123 K. This observation pointed to a high dynamic disorder of Li and Na in Fe 3+ Na 2 K[Li 3 Si 12 O 30 ] and their 2D hopping paths, which were strongly anisotropic parallel to the (a-b) plane.…”