Chemical Switching of Ferroaxial and Nonferroaxial Structures Based on Second-Order Jahn-Teller Activity in (Na,K)2Hf(BO3)2

Ferroaxial order, which is characterized by a vortex of electric dipole moments, is attracting more attention in terms of a new category of ferroic order. Here we propose that the disodium hafnium borate, Na2Hf(BO3)2, shows ferroaxial order that is stabilized by the second-order Jahn-Teller (SOJT) effect. Furthermore, the dipotassium hafnium borate, K2Hf(BO3)2, the synthesis of which has never been reported previously, is predicted to have a nonferroaxial ground state from the perspective of the SOJT effect. This prediction is demonstrated through our structural refinements on polycrystalline samples and our firstprinciples calculations with representation theory. This study offers a chemical perspective for developing new ferroaxial materials and controlling their ferroaxial order.