Roger F. Belt

Effect of crystal growth on Ti3+ centers in KTiOPO4

A series of Ti3+ centers have been formed in hydrothermally grown and flux‐grown potassium titanyl phosphate (KTiOPO4 or KTP). These 3d1 defects (S=1/2) were created with 60 kV x rays at 77 K, and electron paramagnetic resonance and electron‐nuclear double‐resonance (ENDOR) data were taken below 30 K. The ENDOR spectra show that the two Ti3+ centers having the largest concentrations in hydrothermally grown KTP have a neighboring proton, presumably in the form of an adjacent OH− ion. In contrast, ENDOR spectra show that neither of the two Ti3+ centers having the largest concentrations in flux‐grown KTP have a neighboring proton. These significant differences in the local environment of the Ti3+ centers may help explain why KTP crystals have shown differing susceptibilities to gray tracking.

Solubility and P-V-T relations and the growth of potassium titanyl phosphate

Abstract KTP, potassium titanyl phosphate (KTiOPO4) single crystals are the material of choice for frequency doubling Nd: YAG laser light to visible green. Solubility and P-V-T measurements were made at the conditions used in a new low temperature hydrothermal process for growth. P-V-T data show that in 2M K2HPO4 and 2M K2HPO4 +0.125M KNO3 saturated with KTP the pressures are not substantially different although they are greatly reduced from those of water. The data are used to show the temperature at which autoclaves fill with a single fluid phase as a function of various initial degrees of fill. This is of aid in crystal growth since better quality and reproducibility occur in the one fluid phase region. Solubility data in 2M K2HPO4 and 2M K2HPO4+KPO3 show that KTP is probably incongruently saturating and not the stable phase except when excess KPO3 is present. These results explain the long equilibrium times and scatter in apparent solubilities in K2HPO4 and the formation of solid TiO2 inclusions during the initial stages of KTP growth. The phase equilibrium and solubility measurements suggested that growth in a slight excess of KPO3 would improve perfection by repressing TiO2 formation. This was experimentally verified, but with some diminishing of growth rate on (011).

Top seeded solution growth of Cr3+: LiCaAlF6 in HF atmosphere

Abstract Single crystals of the tunable laser material, Cr 3+ : LiCaAlF 6. were grown via a top seeded solution method from LiF enriched melts. A weight sensing feedback system was used for diameter control. Boules were grown along [10 1 0] at 20 rpm and 0.75 mm/h in a flowing atmosphere of N 2 -HF. Cr 3+ was dispersed along the boule with a measured distribution coefficient ( k ) of 1.0. External quality was excellent with faceted growth in a flat solid-liquid interface. Internal quality was good but scattering defects, observed by He-Ne laser, were distributed primarily near the boule core. Traces of OH - were found in the boules by infrared spectroscopy. The scattering is related to defects, e.g. dislocations of particles, believed to arise from thr thermal conditions.

Infrared study of KTiOPO4 single crystals hydrothermally grown in H2O and D2O solutions

A detailed infrared study has identified the spectral features of potassium titanate orthophosphate, KTiOPO4 (KTP), between 4000 and 2200 cm−1. KTP single crystals grown by hydrothermal and flux methods were examined. By using ordinary and heavy water in separate runs to grow KTP crystals hydrothermally, features that depend on the presence of H2O or D2O in the growth process have been distinguished from features that do not. The effect of multiple OH sites in KTP has been linked with crystal quality and specific trace impurities, e.g., Fe+3.

Preparation of ZnO Thin‐Film Transducers by Vapor Transport

Thin films of ZnO were prepared for transducers and microwave acoustic delay lines. Preliminary results are reported for the latter devices. Vapor transport of ZnO in a sealed system was achieved at a source temperature of 700°C, a source‐substrate distance of 10 cm, a substrate temperature of 570°C, and 2 mm O2. On (0001) sapphire substrates, x‐ray diffraction proved ZnO (0002) planes were oriented parallel to the substrate. Methods were developed for the construction of predominantly longitudinal mode transducers. A one‐way conversion loss of 20 dB at 1.2 GHz was measured.

Hydrothermal growth of calcite in large autoclaves

Abstract An experimental and production program are reported for the hydrothermal growth of calcite from 6 m K 2 CO 3 solution at 1.7 kbar and 425 °C. Production growth runs in 20 cm diameter autoclaves attained growth rates of 50 μm/day. Regrown material 3 mm thick was obtained on 10–30 cm 2 of {10 1 1} surfaces.

Identification of point defects in hydrothermally grown KTiOPO4

Electron paramagnetic resonance has been used to investigate radiation‐induced point defects in hydrothermally grown single crystals of potassium titanyl phosphate ( KTiOPO4 or KTP). The crystals were irradiated at 77 K with 60–kV x rays. A trapped‐hole center, a Ti3+ center, and a Pt3+ center were observed between 10 and 30 K after the initial 77‐K irradiation. These defects become thermally unstable near 160 K. The trapped hole is localized on an oxygen ion adjacent to a potassium vacancy and has resolved hyperfine interactions with three phosphorus nuclei. The Ti3+ ion is the intrinsic self‐trapped electron center in KTP and has weak hyperfine interactions with four phosphorus nuclei.

Hydrothermal growth of potassium titanyl arsenate (KTA) in large autoclaves

Solubility and phase relations were investigated for selected K/As ratios in KH 2 AsO 4 -KOH solutions at 600°C and 2040 atm. All initial data were obtained with 5 mm diameter x 50 mm long platinum capsules in Tem-Pres type autoclaves. The most favorable results were repeated in Morey type autoclaves of 2.2 cm diameter. The P-V-T data were generated and extrapolated for use in gold liners and Rene 41 autoclaves with a pressure balancing method. Transfer to the 3.8 cm diameter x 46 cm long autoclaves with gold liners was achieved. Both nutrient and larger seed crystals were grown from a K 2 WO 4 -Li 2 WO 4 flux. The internal and external degrees of fill were adjusted to obtain a balance of pressure at 1700 atm and 590°C. Initial growth runs were made for 1–2 weeks under a gradient of 30°C with a 4 molar KH 2 AsO 4 mineralizer. Natural facet seeds were employed first while later runs utilized (011) cut and polished seeds.

The hydrothermal growth of zircon

Abstract Single crystals of zircon were grown hydrothermally at 700 °C and 25000 psi using a mineralizer of 2 m KF-1 m LiF and a thermal gradient of 20 °C. Under these conditions growth rates of up to 0.25 mm/day surface have been obtained on (100) seeds. Several mm of good crystal growth on 1 cm 2 seeds have been achieved. The growth quality may be limited by small inclusions of wadeite and OH impurity. Wadeite can be controlled by the amount of KF and OH incorporation is inhibited by Li. Large crystals require more extensive seed development.

Etching and X‐Ray Topography of Flux‐Grown Magnetic Garnets

Internal growth defects of high‐quality garnet crystals were studied by selective etchants and Lang x‐ray transmission topography. Terminal growth sections contained the fewest defects and dislocation densities were 102−104/cm2. Internal sections revealed both randomly dispersed etch pits and linear arrays. The latter were frequently found in the form of parallel grids. Results indicated that {100}, {111}, {411}, and {105} were the defective planes. X‐ray topographs verified that parallel linear faults are present in crystals on these same planes. The faults are not dislocation lines but tubular structural deviations caused by flux precipitation or other compositional changes. The origin and arrangement of the internal faults are related to fluctuations of the crystal growth rate. The rate changes can be initiated by small thermal gradients in the solution.