| dc.description.abstract | The crystal growth of KTP (Potassium Titanyl Phosphate) from K?P?O?? solvent has been carried out by spontaneous crystallization as well as the top-seeded solution growth (TSSG) technique. For TSSG, a crystal growth system was developed and fabricated.
Dislocation etching and X-ray topographic studies on these crystals revealed their high quality in terms of defect content. Optical transmission in these crystals was found to be more than 80%. The room-temperature IR spectrum of KTP showed absorption bands in the 3000 cm?¹ and 2400–1800 cm?¹ regions, in agreement with literature.
Microhardness studies on the (100) plane showed sub-surface cracking, which could be due to the presence of cleavage planes parallel to (100) faces. Finally, second harmonic generation (SHG) was demonstrated in this crystal.
Ferroelectric Domains and Domain Engineering
The ferroelectric domains in flux-grown single crystals were studied by selective domain etching and synchrotron X-ray topography. It was observed that when grown by TSSG, growth above a certain temperature produced multidomain crystals, while growth below that temperature always produced single-domain crystals.
On the other hand, crystals grown by self-nucleation exhibited complicated domain patterns. The dependence of such domain patterns on growth parameters was investigated, and stress was found to play a role in domain structure modification.
Subsequently, thermal annealing of multidomain crystals was found to be a simple and efficient method to convert them into monodomain crystals without the necessity of poling the crystal in the conventional way.
Dielectric Properties and Annealing Effects
It is observed that the low-frequency dielectric constant of KTP is dependent on the sample thickness. This behavior is attributed to the existence of surface layers. Upon annealing the KTP samples, the low-frequency dielectric constant shows drastic changes in magnitude, whereas no change is observed in the high-frequency region.
These changes in the low-frequency dielectric constant are attributed to the annealing of space-charge-related defects in the crystal. Prolonged annealing leads to surface degradation, resulting in the formation of a surface layer of lower dielectric constant. However, degradation is least when annealed in the presence of dry oxygen.
Modulus plots show that the relaxation phenomena associated with KTP is of non-Debye type, with a distribution of relaxation times. The parameter ?? shows an increase in its value in all cases after annealing, indicating an increase in the distribution of relaxation times.
Grey-Track Formation and Optical Properties
Several conclusions can be drawn from these studies. Grey-tracks induced by DC field in KTP reveal that the electronic levels associated with Ti?? get modified in the grey-tracked region. There is no evidence of a major structural change or disorder in this region. Nevertheless, the X-ray topograph indicated that a remnant strain persists along the grey-tracks.
The electrical properties of grey-tracked KTP crystals showed a decrease in the dielectric constant, loss tangent, and ionic conductivity. Photoluminescence studies indicated that a broadband luminescence is observed in the grey-tracked samples in the 700–900 nm region.
An analogy between grey-tracked KTP and other Ti³?-doped oxides showed that the luminescence observed in grey-tracked samples can be attributed to a transition from the ²T? to ²T? states of the Ti³? levels. By virtue of creating a defect center with luminescence in the 1.4 eV region by grey-tracking, it has been possible to record the cathodoluminescence (CL) images of the underlying defect structure of KTP crystals. | |
