llustration of the atomic scale mechanism of piezoelectricity in Iβ-NC.
Right panels are reduced regions representing the larger NC slab. The left side depicts schemes for the smallest unit needed to explain the molecular mechanism of the piezoelectric response. (a) The distance between equivalent atoms of each chain is represented by ‘l’. (b) The model units are held along the b-axis direction by HB, whereas the covalent chains are oriented in the c-axis direction. The CB tightens the system constraining electromechanical responses in c-axis direction. ‘L’ denotes the length of the crystal in the b-axis. (c) Effect of an E-field in the b-direction. The variation in ‘L’ due to an external field is represented by a finite Δli value in this direction. (d) Such atomic-scale effect is extended along the bc plane in the b-direction of the NC crystal. Then, in terms of collective effects we predict stretching and compression behaviour in this direction.