Abstract

This paper reports a suppressed ionic conductivity in a KTiOPO4 (KTP) crystal grown from a potassium-rich K4P2O7 flux. Potassium-rich KTP is shown to have an ionic conductivity, which is reduced by one order of magnitude relative to normal flux-grown KTP and is explained by an improved potassium–oxygen stoichiometry. However, it is found that the frequency dispersion of the conductivity is almost identical in form to that of conventional KTP, showing that the fundamental Debye-like origin of the conductivity is unchanged as the number of potassium vacancies is decreased. This behaviour is contrasted with that of Rb-doped KTP, in which the conductivity is reduced by a factor of more than 100 and the dispersion is drastically changed to resemble a disordered system rather than a Debye-like relaxor. Potassium-rich KTP is also found to have a reduced low-frequency dielectric constant, a contracted Cole–Cole plot and a lowered ferroelectric coercive electric field of only 3.0(±0.1) kV mm−1 at room temperature. Successful periodic poling of a potassium-rich KTP crystal to produce a grating of 60 μm period is demonstrated at room temperature for the first time. X-ray topographs proving the existence of periodic domains throughout the bulk of potassium-rich KTP in both the usual [100] grating orientation and the unconventional [010] orientation are presented.

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