  Near-equilibrium bottom-up crystallization of fully-ionized neutron star
crusts or white dwarf cores is considered. We argue that this process is
similar to liquid-phase epitaxial (i.e. preserving order of previous layers)
crystal growth or crystal pulling from melt in Earth laboratories whereby
lateral positions of newly crystallizing ions are anchored by already
solidified layers. Their vertical positions are set by charge neutrality.
Consequently, interplane spacing of a growing crystal either gradually
increases, tracing $n_\mathrm{e}$ decrease, as the crystallization front moves
away from the stellar center, or decreases, tracing decrease of $\langle Z
\rangle$, when the crystallization front crosses a boundary between layers of
different compositions. This results in a formation of stretched Coulomb
crystals, in contrast to the standard assumption of cubic crystal formation,
which is based on energetics arguments but does not take into account growth
kinetics. Overstretched crystals break, which limits the vertical sizes of
growing crystallites. We study breaking shear strain and effective shear
modulus of stretched matter and discuss possibility of macrocrystallite
formation. The latter has interesting astrophysical implications, for instance,
appearance of weak crustal layers, whose strength may increase by a few orders
of magnitude upon breaking and refreezing at a late-time event. We also analyze
interaction of adjacent Coulomb crystals, having different ion compositions,
and estimate the strength of such interfaces.
