Due to slight variation in color in LLZO-b (blue vs blue greenish) two different sample batches were investigated: (i) small chips of the central part of the crystal (see Figure ). Some fragments of LLZO-b(s) show also cubic symmetry and behave like the LLZO-b(c) having similar high electron density at 12a, almost the same electron density at 12b and 48e sites with respect to the Li sites. The 24c (La 3+ ) and 16a (Zr 4+ ) sites appear to be fully occupied. Most other fragments of LLZO-b(s) experience a symmetry reduction from cubic 𝐼4 & 3𝑑 to tetragonal 𝐼4 ! /𝑎𝑐𝑑. This is proven by powder X-ray diffraction and evidently can be seen in direct comparison with reference pattern of cubic and tetragonal LLZO (see Figure ). Interestingly, among the single-crystals investigated, a decrease of tetragonal distortion with increasing Co content, expressed by the difference Dtetr between a and c lattice parameters, has been observed (see Figure ). While in pure endmembered Li7La3Zr2O12 Dtetr amounts 0.471 Å 31 , values between 0.07 and 0.311 Å are observed herein. All tetragonal crystals show intense twinning, nevertheless, some general information can be deduced. The structure, obtained from direct methods and residual electron density map analyses closely resembles the one found by Awaka, et al. , including the three clearly detectable Li positions. When refining the site occupation factors with Li only, it is evident, that systematically only the 4-fold coordinated Li1 (8e) site shows overpopulation, while for the other Li sites Li2 at 16f and Li3 at 32g almost full occupation or Li deficiency is observed.