Pyroelectricity from Non-Polar Crystals Enables Understanding Features of Crystal Growth and Design

Pyroelectricity, a property of certain crystalline materials, is the creation of a temporary surface charge upon temperature change, resulting in an external electric current. Thermal movement of the molecules alters their average positions, leading to changes in their dipole moments. As a consequence of this property, spontaneous polarization was constricted to the polar directions of the ten polar crystal classes, when exposed to temperature change, resulting in the creation of two oppositely charged faces, which engender pyroelectricity. With the emergence of modern analytical instruments for measuring electric currents, it became possible, however, to probe the structures of polar defects and imperfections, and near surface polar layers that outline non-polar crystals. In spite of their slight amounts, those architectures play indispensible role for the understanding of the different features that control the macroscopic properties of crystals and provide perceptiveness on the mechanisms of crystal growth.

The following sub-topics will be presented.

a) Deciphering the riddle of polarity found in the growth of the centrosymmetric crystals of glycine.^1-2

b) Enantiomeric disorder within the crystals of D,L alanine not detectable by diffraction.³

c) Solvent molecules as “tailor-made” auxiliary in the control of crystal polymorphism, as illustrated with the three polymorphs of glycine.⁴

d) Pyroelectricity combined with theoretical simulations as a new analytical method for the structure determination of polar tiny-doped domains in crystals at the molecular level.⁵

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(2) Piperno, S. et al. Angew Chem Int Ed 2013, 52, 6513.

(3) Mishuk, E. et al. Cryst Growth Des 2014, 14, 3839.

(4) Meirzadeh, E.: Dishon, S work in progress.

(5) Meirzadeh, E.; Azuri, I. et al.; Nature Com. 2016, 7, 13354.