Polar crystals display pyroelectricity upon temperature change with two primary and secondary contributions. 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 pyroelectricity 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 there is a quest to develop synthetic methods to design pyroelectric materials decoupled from piezoelectricity. 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, delineated by enantiotopic faces, by doping with “tailor made”, chiral dopants, which converts centrosymmetric crystals into polar pyroelectric crystals. By the selection of appropriate combination of chiral dopants, we designed pyroelectric materials with minimal or no piezoelectricity. This approach will be illustrated with several examples.
Igor Lubomirsky completed his undergraduate studies (B.Sc.) in Chemical Engineering, Kharkov Polytechnic Institute (Ukraine, 1990) and earned a Ph.D. in Solid State Chemistry at the Weizmann Institute of Science (1997). After two postdoctoral appointments- in Electrical Engineering at UCLA, and at the Max Planck Institute for Solid State Research (Stuttgart, Germany) - he returned to the Weizmann Institute in Dec. 1999 as a faculty member and currently serves as a full professor in the Department of Materials and Interfaces. To date, I.L. has supervised more than 30 M.Sc. and Ph.D. students. Concomitantly, he serves as an Editor of the Solid State Ionics journal (Elsevier) and also as a member of the Editorial Board of the Materials Research Society Bulletin. I.L. holds the Rowland and Sylvia Schaefer Chair in Energy Research (since 2017) and received Best Solid State Ionic Paper award in 2014. I.L. studies local symmetry reduction leading to anelastic and electrostrictive effects in inorganic solids with a large concentration of point defects, in general, and in ion conductors in particular. Among his most important achievements are the development if quasi-amorphous (non-crystalline but polar) phases; the discovery of nanocrystalline polar domains in self-supported films of ferroelectrics; non-classical electrostriction in Gd-doped ceria; and the experimental demonstration that positive surface charge promotes ice nucleation while negative charge suppresses it.