Structural control of ionic conductivity in LiAlSi₂O₆ and LiAlSi₄O₁₀ glasses and single crystals

Abstract

In order to better understand the mechanisms of lithium dynamics and to elucidate the influence of defects in lithium mobility, we have studied the Li-ion propagation through natural single crystals of α-spodumene, LiAlSi2O6 and petalite, LiAlSi4O10 using impedance spectroscopy. Electrical conductivity in petalite and α-spodumene is 4–5 orders of magnitude lower than in glasses of the same composition, and three orders of magnitude lower than in synthetic β-spodumene. Conductivity in α-spodumene is anisotropic with conductivity along the c-axis being 0.3–0.4 log units higher than perpendicular to the c-axis. Contrary to α-spodumene, isotropic conductivity was observed for petalite single crystals. Despite the large difference in conductivity values, the activation energies for ionic conduction of α-spodumene along the c-axis (74 to 86 kJ/mol) are only slightly higher than for LiAlSi2O6 and LiAlSi4O10 glasses (∼67 kJ/mol). On the other hand, much higher activation energies of 112–134 kJ/mol were determined for petalite. Based on our investigation, a vacancy-controlled transport mechanism is indicated for the densely packed α-spodumene structure, while in the open framework structure of petalite formation and movement of Li interstitials is proposed to be dominant mechanism for charge transfer.

Scintillation and Dosimeter Properties of LiAlSi2O6 and LiAlSi4O10 Crystals

“…Although this evaluation is not a quantitative analysis, the emission intensity of LiAlSi 4 O 10 was very low compared with that of LiAlSi 2 O 6 . In neutron detectors, the energy deposited is typically 4.8 MeV in 6 Li-containing materials based on the 6 Li(n,α) 3 H reaction, and a higher emission intensity can be expected. Figure 7 shows scintillation decay time profiles of LiAlSi 2 O 6 and LiAlSi 4 O 10 .…”

“…As scintillation detectors, they can be used as thermal neutron detectors since they contain Li in their chemical composition. Owing to the limited 3 He gas supply, (3,4) (6) Sometimes, the former was studied for optically stimulated luminescence (OSL (7) ) or thermally stimulated luminescence (TSL (8) ) dosimeter applications. (9)(10)(11) On the other hand, there have been no reports on the luminescence properties of LiAlSi 4 O 10 .…”

Lithium conductivity in glasses of the Li2O–Al2O3–SiO2system

“…However, the temperature corresponding to the centre of the conductivity plateau was always determined with a precision better than AE1 K. The accuracy of conductivity measurements was verified to be better than AE0.10 log units by comparison of conductivity data of LiAlSi 2 O 6 glasses with literature data. 15 …”

“…Compared to crystals of the same composition (LiAlSi 2 O 6 : a-and b-spodumene; LiAlSi 4 O 10 : petalite) the mobility of lithium in the glasses is decreased by several orders of magnitude. 15 Denser packing in the crystalline phases reduces, on one hand, the number of possible sites, which can host lithium ions and may affect, on the other hand, the energy barrier for transition from one site to the other. A vacancycontrolled transport mechanism was proposed for the densely packed a-spodumene structure, while in the open framework the structure of petalite formation and movement of Li interstitials were assumed to be the dominant mechanism for charge transfer.…”

“…A vacancycontrolled transport mechanism was proposed for the densely packed a-spodumene structure, while in the open framework the structure of petalite formation and movement of Li interstitials were assumed to be the dominant mechanism for charge transfer. 15 However, for alkali silicate glasses there is strong evidence for an unmixing of structural units on the nanometre scale (see Discussion in Bauer et al). 3 A separation of Li-rich regions within a Si-rich matrix was observed using different experimental methods 1,5,[54][55][56][57]59,60 as well as in theoretical modelling.…”