Fig. 2: Sequential structural phase transitions of T-Nb2O5 via Li-ion intercalation.
From: Li iontronics in single-crystalline T-Nb2O5 thin films with vertical ionic transport channels
a, In situ X-ray diffraction and resistance measurements during Li-ILG of a 50 nm T-Nb2O5/LSAT(110). b, In situ X-ray diffraction patterns for powder T-Nb2O5 until the deep discharge potential of 0.005 V versus Li in 34 hours. ‘Be’ indicates peaks from the Be window. Horizontal yellow dashed lines indicate the boundary of the transitions. Ewe represents the working electrode potential. c, Ex situ SXRD pattern (red) of Li1.6Nb2O5 and simulated patterns of the Pbam (black) and P2/m (blue) structural models. The (180) reflection is split by monoclinic tilting (left panel). SXRD pattern and Rietveld refinements of m-Li1.6Nb2O5. Red circles, black line and grey line represent the observed, calculated and difference patterns, respectively. The black spheres, red spheres, grey polyhedra and navy polyhedra in the unit cell represent Nb ions, O ions, octahedra (NbO6) and pentagonal bipyramids (NbO7), respectively (right panel). d, Rietveld refinement of an in situ SXRD pattern measured at 5 mV using the t-phase. The in situ cell produces peaks marked as *. Green circles, black line and grey line represent the observed, calculated and difference patterns, respectively. Blue vertical bars represent the Bragg position. The black spheres, red spheres and grey polyhedra in the unit cell denote Nb ions, O ions and octahedra (NbO6), respectively. Li positions are not considered in all refined structures due to the low scattering amplitude of Li ions. e, c lattice parameter as a function of x in LixNb2O5. Grey dots represent the average c parameter obtained from the SXRD data. Blue, red and green dots denote the c parameter of the o-, m- and t-phases, respectively, extracted from the in situ X-ray diffraction data. The purple line is the voltage curve obtained for a powder electrode in a coin cell during a galvanostatic measurement including open circuit voltage steps. Colour zones highlight four regions: (1) pristine o-phase from Li0Nb2O5 to Li0.8Nb2O5 (white), (2) a 25/75% mixture of the o- and m-phases from Li0.8Nb2O5 to Li1.8Nb2O5 (pink), (3) progressive formation of the t-phase from Li1.8Nb2O5 to Li3Nb2O5 (green), (4) no change of the X-ray diffraction pattern from Li3Nb2O5 to Li4Nb2O5 (grey). f, Comparison of the d(180) spacing for the powder and thin-film X-ray diffraction.
