cg5b00187_si_005.cif (8.24 kB)
Non-Topotactic Phase Transformations in Single Crystals of β‑Glycine
dataset
posted on 2015-06-03, 00:00 authored by Qi Jiang, Alexander G. Shtukenberg, Michael D. Ward, Chunhua HuThe
metastable β polymorph of glycine exhibits a single-crystal-to-single-crystal
transformation (SCSCT) to either the α or γ phase with
retention of the crystal habit of the parent β phase. X-ray
diffraction and optical microscopy reveal that of 51 single crystals
of the β parent phase, 24 form single domain crystals of α
or γ with a single orientation matrix, confirming an SCSCT.
The remaining 27 β parent crystals transform to crystals with
a few domains of either α and/or γ, each domain arising
from a single nucleation event. In three cases the β →
α and β → γ transformations occurred within
the same glycine single crystal. In all cases, regardless of the number
of domains, the transformation occurred with retention of the original
habit of the parent phase. Both β → α and β
→ γ transformations proceed in a non-topotactic manner,
as evident from the random orientations of the daughter phases in
the crystallographic reference frame of the parent β phase.
The transformation rates, as measured by advancement of the growth
front with polarized optical microscopy, vary from crystal to crystal
as well as for different regions within the same crystal. Moreover,
the transformation rate increases substantially with relative humidity,
and at a relative humidity of 90% α-glycine was observed as
the only product.