Dear all,
I have purchased a sample of flaky tungsten disulfide (WS2) and I'd like to depict more specifically (and more scientifically) which kind of WS2 it is. I found that you can call it 2H-WS2, but I am not completely sure if this is correct for this specific material (the supplier calls it "amorphous" which is clearly wrong). As far as I know, 2H describes the material's crystal structure, but I couldn't find any website explaining this denomination in detail. Moreover, I found a paper on 1T-WS2 and to be honest I have no clue how to discern the two. Can you help me?
Kind regards, Dietmar Haba
2H corresponds to 2 layers per H(exagonal) unit cell. 1T - one layer per (Trigonal) unit cell. Look for "polytype notations" and "polytype". In general you have to use diffraction methods (XRD, SAED, etc.). updated
2H corresponds to 2 layers per H(exagonal) unit cell. 1T - one layer per (Trigonal) unit cell. Look for "polytype notations" and "polytype". In general you have to use diffraction methods (XRD, SAED, etc.). updated
The prefix before the chemical formula is a notation for identifying polytypes in layered compounds. The number is the number of layers, the letter the crystal system (H for hexagonal, T for trigonal, other letters for other crystal systems). If there are more polytypes with the same number of layers and the same crystal system, additional number is added, e.g. 2M1 and2M2 in some micas.
How to identify the polytype? Most easily by diffraction. Each polytype has different lattice parameters and thus different diffraction pattern. Simple polytypes can be distinguished in powder diffraction patterns, in more complicated cases single-crystal x-ray diffraction or electron diffraction may be necessary. A mixture of several polytypes in the same sample is also not unusual.
I do not know the polytypism in WS2 well enough to suggest a detailed identification procedure in this case, but I would start by taking a powder diffraction pattern of the material and comparing it with the simulated patterns of the known WS2 polytypes.
Thanks a lot to both of you. This was very helpful. The article Polymorphism (materials science) on wikipedia covers this topic, although there is still not a lot information given there.
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