SOLUTION TO THE 1T2 DISCOMMENSURATE STATE OF 1T-TAS2 - AN EXAMPLE OF ROTATED HEXAGONAL DISCOMMENSURATION

The discommensurate structure of 1T2-TaS2 has been resolved by combining electron diffraction results with very recent scanning tunnelling microscopy data. The solution is provided by the hitherto unconsidered 192/3-by-22/3 rotated honeycomb array of discommensurations (DCs). Being non-integral but rational, these numbers relate to a yet larger supercell for the 1T2 state, giving an associated ultra-fine micro-mesh in reciprocal space upon which to base the diffraction pattern. The resulting enlarged and 30 degrees rotated cell is well suited to an ABC three-sandwich stacking sequence for the honeycomb arrays, without any further cell enlargement. Within each individual sandwich the DC honeycombs themselves are just over 70 AA across, very much as for the hitherto considered 18-by-5 rotated, discommensurate superstate. The actual DC-phase-jog is precisely as for 18-by-5, but only one in three of the DC domains find themselves centred by a CDW thirteen-atom star. The final 1T 2 structure succeeds in not stacking its CDW charge hills (and their concomitant distortions) directly above each other. The favoured ABC domain stack, however, impairs DC array visibility. Some discussion is finally given regarding further possible states on the approach to full square root 13a 0 commensuration.