Based on the synthesis conditions and the broad feature in the XRD of BiAlTeO 6 , it was hypothesized that the sample contains amorphous sodium tellurate(s). Na MAS NMR supports this hypothesis, showing a broad asymmetric resonance centered around -35 ppm (Supplementary Figure ), which is similar to reported Na NMR of (Na 2 O) x (TeO 2 ) 1-x glasses. 84 expected. Owing to the layered nature and chiral structure of BiMTeO 6 , the next-nearestneighbor (NNN, Figure ) coordination of bismuth (i.e., BiAl 6 Te 6 or BiGa 6 Te 6 ) should be considered for the origin of the observed (ultra-)wideline CT (Figure , Supplementary Figure ). The NNN distances are in a narrow range from 3.844-3.846 Å but the geometry is that of a hexagonal prism. Thus, the BiAl 6 Te 6 or BiGa 6 Te 6 units deviate strongly from spherical symmetry; however, there is D 3h symmetry with the three-fold axis along the c direction (Figure ). Accordingly, the largest component of the electric field tensor (V 33 ) at the bismuth nucleus is oriented along c.