Nanoscale structural and polar behavior in abalone and clamshell probed by scanning probe microscopy.

Nanoscale structural and polar behavior in abalone and clamshell have been studied using the scanning probe techniques. Untreated pristine sample surfaces were probed to realize their intrinsic electrical properties. While prominent polarization switching under opposite bias field is observed in the clusters of nanograins of the abalone shell, the piezoelectric phase contrasts remained confined mostly at the grain-grain boundary regions in the clamshell. These shells mostly comprised of centrosymmetric CaCO₃, the observed polar responses is attributed to the structural distortion initiated by the intra-granular organic phase of the biopolymers. The biopolymer-nanocrystalline layered (as found in abalone shell) or 3:1 composite structure (as found in clamshell) bear an analogy with the piezoelectric composites, where due to the stretching/twisting of the biopolymers under external mechanical stress, the piezoelectric responses get originated owing to the intrinsic electromechanical coupling. [ABSTRACT FROM AUTHOR]