Crystal orientation, toughening mechanisms and a mimic of nacre

Gradual Ordering in Red Abalone Nacre

“…Others report that nacre tablets are misoriented in the ab plane 8, [23][24][25][26][27] or that c axes have a spread at the macroscopic scale, 8,27,28 but to our knowledge our recent observations reported here and elsewhere 5,6 provide the first evidence of c axis orientation variations in immediately adjacent nacre tablets. The experimental data shown in Figure 2B demonstrate that the PIC contrast arises from misorientation of the c axes with respect to each other and to the polarization vector, while tablet rotation around the c axes, or crystal With the polar angle fixed at θ ) 32°, the sample was rotated in the ab plane around the c axis.…”

Order-Disorder Transition of Aragonite Nanoparticles in Nacre

“…Nacre has attracted widespread interest, because its unique hierarchical structure assembled with brittle aragonite (a polymorph of CaCO 3 ) and organic biopolymer leads to several orders of improvement in fracture toughness (in energy terms) compared with its primary counterparts [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Extensive work has hitherto revealed that nacre is a self-assembled nanocomposite, consisting primarily of highly organized polygonal aragonite platelets with a thickness ranging from 200 to 500 nm and an edge length of about 5 m sandwiched with 5-20 nm thick organic biopolymer interlayers.…”

“…For instance, is an individual platelet made of a single crystal or assembled with nanoparticles? Previous work showed that individual platelets are single crystals and form via epitaxial nucleation [3,4], resulting in a highly stacking sequence layer by layer. Selected area diffraction pattern from TEM further confirmed single-crystal appearance from the crystallographic relationship within single and/or multiple layers [4].…”

Unveiling the Formation Mechanism of Pseudo-Single-Crystal Aragonite Platelets in Nacre

“…This material has a brick-and-mortar-like structure with highly organized polygonal aragonite platelets of a thickness ranging from 200 to 500 nm and an edge length of about 5 m sandwiched with a 5-20 nm thick organic biopolymer interlayer, which assembles the aragonite platelets together [3]. Previous transmission electron microscopy (TEM) studies showed that the electron diffraction patterns of individual aragonite platelets have characteristics of single-crystal electron diffraction [4][5][6]. It has long been thought that aragonite platelets are brittle single crystals.…”