Defects in KTiOPO₄

Abstract

KTiOPO4 (KTP) is a nonlinear optical crystal presently used for second harmonic generation and electro-optic applications. The properties (ionic conductivity and damage susceptibility) of KTP crystals can vary depending on the specific technique and conditions used for growth. Consistent defect mechanisms have been determined to explain the observed AC conductivity and damage results of KTP grown by the flux and high and low temperature hydrothermal techniques. The presence of nonstoichiometry on the K and 0 sublattices in KTP, increasing in magnitude with temperature, is proposed. Using these defect mechanisms, the predominant defects compensating for the formation of vacant potassium sites (VK's) in flux and hydrothermal materials are vacant oxygen sites (VO's) and OH-'s, respectively. The presence of a more varied distribution of OH-sites at room temperature in high temperature hydrothermal material with higher AC conductivity indicates the importance of specific OH-sites in the lattice that may enhance the mobility of ionic carriers. The correlation of higher AC conductivity to increased average current and damage in electric field treated KTP is explained on the basis of the proposed compensating defects (Vo's and OH-'s) which set the [VK] and [Ti 3 +]. The similarity of the linear optical properties of KTP grown by the various techniques is confirmed by the insensitivity of the absorption edge to the nonstoichiometry or defects present.

Proton Effects in KTiOPO4

“…Some variability is observed between samples containing slightly different OH-distributions. The trends in the activation energies of the different materials are similar to those reported in [12], but the use of bulk ionic conductivity values in the present case yields a more accurate determination of the actual activation energies than the single frequency values previously reported there and by other researchers. [ 19,20] The carrier concentrations, [VK], calculated for high temperature hydrothermal KTP using the activation energy of 0.3 eV are consistent with previously estimated OH-concentrations, in the range of a hundred ppm [17].…”

“…[ 12] In this study, a mechanism supported by the correlation of the OH-sites represented by the infrared bands at 3428 and 3490 cm-1 in high temperature hydrothermal KTP crystals is proposed. Polarized infrared spectra at 10 K (Crawford et al, found in this proceedings) of these sites indicate that the 3428 cm-1 band is polarized in the Y-direction but contains an appreciable X-component, while the 3490 cm-1 band is strongly polarized in the X-direction.…”

“…The total [OH-] in good quality high temperature hydrothermal KTP crystals has previously been estimated to be in the range of a hundred ppm. [17] The OH-distributions in KTP crystals as a function of the growth technique are shown at room temperature and 10 K in [12] and in a Crawford et al (found elsewhere in this proceedings). The distribution of OH-sites in KTP is clearly a function of the growth technique and conditions.…”

“…This is calculated from the bulk ionic conductivity data shown in Figure 1 for KTP crystals grown by the flux technique over a range of temperatures. A previously reported value was calculated from data at a single frequency [12], the limitations of which are discussed below.…”

“…The effects of protons on the ionic conductivity in KTP was first proposed in [12]. Previous work on the low frequency dielectric loss in the Z-direction in KTP was done on flux grown crystals only.…”