A microcontact impedance study on NASICON-type LiAlTi(PO) (0 ≤ ≤ 0.5) single crystals

We successfully demonstrated the applicability of microcontact impedance spectroscopy (MC IS) on Li + conducting solid electrolytes and measured the Li + bulk conductivity ( σ b ) of LiTi 2 (PO 4 ) 3 (LTP) and Li 1+ x Al x Ti 2− x (PO 4 ) 3 (LATP) single crystals independent of microstructural effects ( e.g. , grain boundaries, pores, and density). The crystals had a size of about 100 μm in each direction and crystallized with NASICON-type structure ( R 3&cmb.macr; c ). Finite element calculations were performed to validate the impedance data analysis. A strong increase in σ b in the order of three magnitudes (3.16 × 10 −6 to 1.73 × 10 −3 S cm −1 ) was found after incorporating 0.1 mol Al 3+ per formula unit into LTP. Moreover, since the crystal structural changes are almost linear in the LATP system up to x = 0.5, the increase of σ b is most probably related to additional Li + sites at the M 3 (36 f ) position. The additional Li + leads to a displacement of Li + occupying the M 1 (6 b ) sites towards the nearest-neighboring M 3 position, and therefore opens the fast-conducting pathway within the NASICON structure. A significant change in σ b was also observed as the Al 3+ content further increased ( x = 0.1 to 0.5). The highest σ b value of 5.63 × 10 −3 S cm −1 was obtained for samples with x = 0.4. We successfully demonstrated the applicability of microcontact impedance spectroscopy (MC IS) on Li + conducting solid electrolytes and measured the Li + bulk conductivity ( σ b ) of LiTi 2 (PO 4 ) 3 (LTP) and Li 1+ x Al x Ti 2− x (PO 4 ) 3 (LATP) single crystals independent of microstructural effects ( e.g. , grain boundaries, pores, and density).