There is nothing 2-dimensional about the Apatite structure, and the preprints I have seen do not show any kind of “quasi two-dimensional” structure. If anything, it’s more like an array of tubes and chains, more 1D than 2D. Do you have a source making this claim?
First, you’re not talking about synthesis anymore. And if you try to grow a single crystal, how easy it is to get polycrystals from powder is not really relevant. Ease to synthesise and ease to assemble are very different things and both are controlled by different phenomena.
Also, again, not really. Graphene is quasi 2-dimensional and very easy to bunch up and form graphite, for example. Boron nitride, not that much.
> For 3D material you could probably just grind your impure sample down into a powder, isolate the grains that levitate, and press them back together.
You can do something like that (hot or cold pressing), but it still requires the right material to be synthesised in the first place. It works more or less well depending on chemistry and physical properties, not dimensionality.
Separating “grains that work” and “grains that don’t” is not something we really do when we create materials. It sounds more like QA in semiconductors than something we’d do in a lab.
> That wouldn't preserve structures in 2D though, let alone 1D.
Why not? If you grind a 2-D structure joint you just get flat grains. How well they assemble depends on their properties.
The whole discussion is not very productive: however truthy it sounds, dimensionality does not control how easy it is to synthesise a material. Apatites are very easy to make. Things like chalcogenide glasses are easy to make despite having a 1-dimensional structure at the atomic scale. There are many other examples. And, also again: it does not matter because apatites are fully 3-d structures, with linear elements if you squint and ignore how these elements are placed in the overall structure.