Ferroelectric phase transition temperatures of self-flux-grown RbTiOPO ₄ crystals

A series of RTP crystals have been grown by the top-seeded solution growth method from self-fluxes containing different [Rb]/[P] atomic ratios (1.25-2) and solute concentrations (0.55-1.1 g-RTP/g-flux) covering a large portion of the RTP crystallization field in the Rb₂O-P₂O ₅-TiO₂ ternary system. The Curie points of as-grown crystals have been determined using the standard dielectric (capacitance) technique, and they show a spread from 770 to 800 °C. This indicates a clear correlation between the crystal stoichiometry and the flux chemical composition in similarity with KTP crystals. The major difference from the KTP case is that each growth sector (solidified simultaneously) in nominally pure RTP crystals exhibits its specific Curie temperature. Chemical analysis and intentional doping experiments show that trace impurities may have a very limited influence on this effect. The abrupt changes of the Curie temperatures along simultaneously grown surfaces are discussed in terms of the diverse incorporation mechanisms of the stoichiometric components or native defects into specific crystallographic faces during growth.