Crystal engineering of doped pyroelectric crystals decoupled from piezoelectricity

The physical and chemical properties of crystals are dictated by their symmetry. Polar crystals display pyroelectricity upon temperature change with two primary and secondary contributions.[1] Primary pyroelectricity, arises directly from the anharmonicity of chemical bonds, leading, upon heating or cooling, to changes of the relative positions of the atoms without changing the overall volume of the crystal. The secondary pyroelelctricity arises from the thermal expansion or contraction of the crystal, i.e. a piezoelectric contribution. Both contributions are always present along the same polar direction, and the secondary effect is often quite comparable to the primary one. Because the piezoelectric and pyroelectric effects provide the backbone for a wide range of technologies, from sensors and actuators to energy harvesters, controlling pyroelectricity and piezoelectricity independently of such crystals is not only a topic of scientific curiosity but is also technologically advantageous. This is because devices exploiting pyroelectricity are affected by unavoidable piezoelectricity, which is a source of mechanical noise interfering with the device operation. Therefore, it is a challenging quest to develop synthetic methods to design pyroelelctric materials decoupled from piezoelelctricity. Here we report the design of a synthetic method, for the preparation of co-doped crystals, where pyroelectricity is decoupled from piezoelectricity. The method based on the reduction of symmetry of centrosymmetric crystals (α-glycine), delineated by enantiotopic faces, by doping with “tailor made”, chiral dopants (alanine, serine and threonine), which converts centrosymmetric crystals into polar pyroelectric crystals.[2, 3] By the selection of appropriate combination of chiral dopants, we designed pyroelelctric materials with minimal or no piezoelelctricity. This approach will be illustrated with several examples*.

*Dishon Ben Ami et al, Angew. Chem. Int. Ed.2022, e202213955
[1] S. B. Lang, Phys Today 2005, 58, 31. [2] M. Vaida et al, Science, 1988, 241, 1475 [3] E. Meirzadeh et al., Nat Commun 2017, 8.