• Question: What is the NLC effect?

    Asked by jakehaighting to Andrew on 23 Nov 2011.
    • Photo: Andrew Cairns

      Andrew Cairns answered on 23 Nov 2011:

      NLC stands for ‘Negative Linear Compressibility’ – and is not necessarily the best name for the effect – it is just what we are stuck with!

      So when we put most materials under hydrostatic pressure (that is, pressure equally in all directions) the material will shrink in all directions. This is normal behaviour that we expect.

      Now, it is absolutely necessary that the volume of a material has to decrease when we compress it – this is one of the laws of thermodynamics. However this does not mean that we could decrease the volume by decreasing the size of a material in two directions a lot and increasing the size in another. This is negative linear compressibility; that the compressibility is negative. This can only ever happen in one or two directions.

      We understand this effect by comparing materials to wine racks or garden trellis – if we try and compress them in all directions they will decrease in the direction that is softest and increase dimension in the other.

      I hope this makes some sense!

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