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What does an 2H in front of a chemical symbol mean? (i.e. 2HMoX_2) 
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#1
Apr2514, 03:45 PM

P: 1,164

Title says it all. I'm reading a lot about the transition metal dichalcogenides and I often see something like
2HMoS_2 What does that 2H mean? My best guess is that it has something to do with a hexagonal lattice or stacking or something. Anybody know? 


#2
Apr2614, 10:26 PM

P: 182

Yeah, it has to do with stacking. There are several notations, of which I'm most used the ABC one myself. However, I think this is Ramsdell notation, in which H=hexagonal and the number two would signify the number of layers. Hence 2H should correspond to AB stacking, which agrees with the figure here.



#3
Apr2714, 10:48 PM

P: 142

Indeed, 2H is the hexagonal stacking motif, with two layers per unit cell. Note that this isn't quite ABAB stacking, since one layer is not a simple translation of the other, but rather requires a rotation. 2H should be contrasted with the 3R (rhombohedral) structure, with three layers per unit cell, all simple translations. See here for example.



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