Growing evidence suggests that crystal formation can follow nonclassical pathways that involve multistep reactions, ion clusters and amorphous precursors. These non-classical pathways lower the overall energy barrier to nucleation of the crystals, but it is not clear which pathways are most common. Both nonclassical and classical pathways can produce crystals with structural defects and lattice strain, as well as impurities in the solution, but how these preserved defects and strain affect crystal growth and their overall reactivity has been unclear.
To answer this question, researchers from two U.S. Department of Energy national laboratories - Oak Ridge and Argonne – compared the formation of two different types of crystal grown from supersaturated solutions with and without strontium ions in the solution, which was introduced as an impurity. The team used a technique called Bragg coherent diffractive imaging (BCDI) performed using beamline 34-ID-C at the Advanced Photon Source, a DOE Office of Science user facility at Argonne, for dynamic imaging of crystal growth. They also imaged the post-reaction crystals using high-resolution transmission electron microscopy (HRTEM) and performed molecular scale simulations to gain further insight into the defect structures. Their findings shed light on crystal nucleation and growth mechanisms from complex solutions and could help advance the fields of geochemistry, biomineralization, and materials synthesis.
The researchers worked with barite and calcite, both commonly observed as mineral scales in geothermal energy operation, oil and gas production, and water treatment pipelines. Previous research has found contrasting evidence for formation of barite, but is often interpreted using a classical crystallization pathway, whereas calcite more frequently appears to nucleate via nonclassical crystallization processes. These nonclassical pathways, particularly those involving the attachment and fusion of either amorphous or crystalline particles, might have the possibility of inducing high internal strain and structural defects in the final crystal due to particle misorientation during aggregation. Previous studies have also shown that strontium incorporation can significantly influence the nucleation pathways in sulfate and carbonate minerals, potentially affecting strain and defect formation.
To investigate these possibilities, the researchers grew barite crystals on calcite substrates, and calcite crystals on barite substrates. In both cases, they kept the concentration of the supersaturated growth solution constant, but applied new solution over the crystals, adding strontium as an impurity to promote defect formation.
For the barite crystals, BCDI showed only minor increases in strain as crystal growth proceeded, with affected regions mainly where the crystal was attached to the substrate. Even after the addition of the Sr-rich solution, the barite crystals’ volume fraction of high strain was still less than 30%. In contrast, BCDI demonstrated increasing strain as the calcite crystals grew, with a dramatic increase after the addition of the higher concentration Sr-rich growth solution that boosted the volume fraction of high strain regions up to 80%. A closer look showed that this increased strain appeared to result from dislocation defects within the crystals’ interiors. The researchers also observed changes in calcite lattice dimensions consistent with Sr incorporation.
HRTEM confirmed the high defect density in the calcite crystals suggested by BCDI. To gain more insight into the atomic structures of these defects, the researchers used computer modeling to determine the effects of deforming barite and calcite crystals with a shear force along their cleavage planes. Results showed that the lattice shearing caused lattice defects in the calcite similar to those seen in HRTEM but didn’t generate analogous defects observed in barite.
Together, these findings indicate that calcite grew from nonclassical mechanisms in this experiment, which might have occurred through the attachment of prenucleation clusters or dissolution-reprecipitation of amorphous precursors. This mechanism could lead to defects to be sealed into the crystal’s interior as growth proceeds. Contrasting with barite’s classical growth patterns, these differences in growth mechanisms could explain the variability in the measured crystal growth and dissolution rates between the two materials. They also highlight how subtle variations in solution composition can modulate ion incorporation pathways and lead to structural changes. The authors suggest that this study provides a potential framework for reconciling diverse growth and dissolution rates observed in crystalline materials by considering the effect of strain and defect density. – Christy Brownlee
See: K. Yuan1, J. Weber1, N. Rampal1, Z. Fang1, J. You1, M.G. Boebinger1, R. Zhang1, W. Cha2, L.M. Anovitz1, S.S. Lee2, A. Suzana2, P. Fenter1, A.G. Stack1, “Mechanistic insights into defect-mediated crystallization revealed by lattice strain evolution,” J. Am. Chem. Soc. 2026, 148, 2, 2206-2219 (2026) https://doi.org/10.1021/jacs.5c11233
Author affiliations: 1Oak Ridge National Laboratory; 2Argonne National Laboratory
This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, Geosciences Program. K.Y., J.W., N.R., J.Y., R.Z., L.M.A., and A.G.S. were supported by the Geosciences Program, FWP #EKRCC72, at Oak Ridge National Laboratory. S.S.L., A.S., and P.F. were supported by the Geosciences Program, FWP #57814, at Argonne National Laboratory. S.S.L., A.S., and P.F. assisted with the interpretation of the data. The BCDI experiment was done at Beamline 34-ID-C at the Advanced Photon Source, Argonne National Laboratory. This research used resources of the Advanced Photon Source, a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. TEM characterization was conducted as part of a user project at the Center for Nanophase Materials Sciences (CNMS), which is a U.S. Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory. This research used resources of the Compute and Data Environment for Science (CADES) at Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. This research used resources from the ORNL Research Cloud Infrastructure at Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725.
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