Influence of divalent and monovalent doping on the ferroelectric and optical properties of RbKTiOPO₄

Coercive field (E_c) engineering based upon the monovalent Rb⁺ ion (Rb/K/Ba-exchange) and the divalent Ba²⁺ ion (Ba/K-exchange) has enabled the reliable periodic poling of RbKTiOPO₄ (RKTP) for quasi-phase-matching (QPM). Previously, there have been no systematic studies to understand and compare the changes in polarization-switching properties induced by these two families of exchanges. In this paper, we compare different compositions of Rb/K/Ba- and Ba/K-exchanges in terms of how they affect the polarization-switching time, t_s, and ionic conductivity in RKTP. We discuss the change in switching time, t_s, that is ascribed to the interplay between the monovalent and divalent cations in the exchange. Moreover, we propose exchange-induced strain as the cause of bulk phase-matching shift and show that exchanges containing lower amounts of Rb induce less strain. This is corroborated by strain-deformation measurements on the exchanged samples. Finally, we demonstrate highly efficient periodically poled RKTP crystals free of bulk changes, using two different high t_s - low strain exchanges.