= Single crystal
{wiki}
A <single crystal> is a crystalline specimen whose ordered structure has one continuous crystallographic orientation, rather than being divided into differently oriented <crystal grains>. It can still contain <dislocations>, impurities and other defects; the term does not mean an absolutely perfect lattice.
A <diffraction> pattern from one well-oriented specimen resolves its crystallographic directions, while rotating it changes which reflections are observed. Mechanical or thermal measurements along different directions can reveal intrinsic <anisotropy> that would be averaged over many orientations in a <polycrystalline material>. The absence of internal <grain boundaries> also changes transport and deformation mechanisms that depend on those boundaries. A specimen's outline is not the criterion: cutting a piece from a <single crystal> changes its external shape without necessarily changing its internal crystallographic identity.
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