Crystallization by Amorphous Particle Attachment: On the Evolution of Texture

Abstract

Crystallization by particle attachment (CPA) is a gradual process where each step has its own thermodynamic and kinetic constrains defining a unique pathway of crystal growth. An important example is biomineralization of calcium carbonate through amorphous precursors that are morphed into shapes and textural patterns that cannot be envisioned by the classical monomer-by-monomer approach. Here, a mechanistic link between the collective kinetics of mineral deposition and the emergence of crystallographic texture is established. Using the prismatic ultrastructure in bivalve shells as a model, a fundamental leap is made in the ability to analytically describe the evolution of form and texture of biological mineralized tissues and to design the structure and crystallographic properties of synthetic materials formed by CPA.

Keywords: amorphous particle attachment; biomineralization; calcite; crystal growth; dislocations; lattice twist; texture.

Figure 1

Textural evolution of the prismatic ultrastructure in bivalve shells. A) The bivalve shell of P. nobilis. B) Fracture of the prismatic architecture in P. nobilis imaged parallel to the direction of growth. C) Electron backscatter diffraction (EBSD) map of the prismatic architecture in P. nobilis obtained parallel to the direction of growth. The corresponding color‐coded inverse pole figure of calcite, with the reference direction normal to the image plane, is depicted in (H). (0001)‐pole figures describe the overall texture of the entire assembly at the beginning and at the end of growth. D) The bivalve shell of P. nigra. E) Fracture of the prismatic architecture in P. nigra imaged parallel to the direction of growth. F) EBSD map of the prismatic architecture in P. nigra obtained parallel to the direction of growth. The corresponding color‐coded inverse pole figure of calcite, with the reference direction normal to the image plane, is depicted in (H). Prisms that have their crystallographic c‐axis of calcite parallel to the direction of growth and do not rotate are marked by black dots. (0001)‐pole figures describe the overall texture of the prismatic assembly at the beginning and at the end of growth. G) A 3D‐EBSD series of two prisms from P. nigra obtained perpendicular to the direction of growth taken with approximately 15 µm steps along the direction of growth. (0001)‐pole figures describe the overall texture of the prisms at different stages of formation. H) Color‐coded inverse pole figure of calcite, with the reference direction normal to the image plane.

Figure 2

Dislocation analysis using a high resolution transmission electron microscopy (HRTEM). A,C) Dark‐field images of TEM lamella taken from the prisms of P. nobilis and P. nigra, respectively. Scale bars are 1 µm; and B,D) are the corresponding large area electron diffraction patterns, respectively. E,F) HRTEM images of P. nobilis and P. nigra using the samples in (A) and (C), respectively. Indicated crystal planes were extracted from the corresponding Fourier transforms. Zone axes are indicated in the upper right corner. G) Schematic representation of slip‐systems and basal lattice rotation axes in calcite. H) Misorientation map displaying the change in lattice orientation in P. nigra relative to the area marked by a red rectangle obtained using 4D scanning electron nano‐diffraction microscopy (4D‐STEM) analysis. I) Scanning transmission electron microscopy (STEM) image of the TEM lamella investigated with 4D‐STEM in (H). Red rectangle indicates the area further studied using the two‐beam condition. J) Electron diffraction pattern of the area indicated in (I). K) Bright field image with $\overline{g}=0003$. L) Dark field image with $\overline{g}=0003$. M) Dark field image with $\overline{g}=\overline{2}110$.

Figure 3

Crystal growth pathways by amorphous particles attachment. Bleached surface of the prisms in P. nobilis at the beginning of their formation imaged using: A,B) scanning electron microscopy (SEM); and C,D) atomic force microscopy (AFM). The pyramid in (B) reveals {101–4} planes of calcite. Bleached surface of the prisms in P. nigra at the beginning of their formation imaged using: E,F) SEM; and G,H) AFM. The lines in (F) designate the faceted circular patterns formed around what we assume to be the nucleus marked by an arrow and highlighted in the insert.

Figure 4

Schematic representation of the suggested mechanisms of textural evolution during prism biomineralization. A) High growth rate by amorphous particle attachment as observed in P. nobilis. The large influx of amorphous particles is accommodated by the rough surface of the growing prism. B) Low growth rate by amorphous particle attachment as observed in P. nigra. The ACC particles first arrive at the surface and then diffuse until integration. C,D) Cross‐sectional and longitudinal view of prism recrystallization process induced by dislocations formed during the amorphous‐to‐crystalline phase transformation in P. nigra, respectively. Initially, they form dislocation structures that rotate the prisms. When rotation is no longer possible the stored elastic energy is released by recrystallization. Each prism rotates following an activation of a specific slip‐system that depends on the initial orientation of the prism. Dislocations are marked in green. E) Longitudinal view on textural evolution of the entire prismatic assembly in P. nigra. Gray arrows indicate the [0001] direction of the lattice.