ZnWO4 Crystals Research Articles

The temperature distribution in ZnWO4 crystal during growth from the melt

Abstract The temperature distribution in Czochralski pulled zinc tungstate crystals has been predicted and measured for pure and cobalt doped specimens. The results indicate a uniform temperature gradient in the crystal from the melt interface up to the level of the top of the crucible walls, thereafter the temperature of the crystal drops exponentially with increasing distance from the melt interface. Only in this latter region does the temperature depend on the cobalt doping and hence radiative properties of the crystal. The temperature distribution in the melt and the surrounding air space has also been measured.

Spin—Lattice Relaxation of Rh(II) in Single Crystals of ZnWO4

The spin-lattice relaxation time T1 of Rh(II) in a single crystal of ZnWO4 has been measured in the temperature range 1.5°—110°K. In the region 56°—110°K relaxation occurs by an Orbach process. From the temperature dependence of this process, the separation of the first excited Kramers doublet E′ from the ground doublet E″ is found to be 320 cm−1, and the lifetime of the excited state 1.7×10−11 sec. At low temperatures, the relaxation times are relatively short and depend upon the direction of the applied magnetic field H. With H aligned along the a, b, or c crystalline axes an anomalously strong dependence of T1 on temperature is observed.

Electron Spin Resonance of Cu2+ Ion in CdWO4, ZnWO4, and MgWO4 Single Crystals

Paramagnetic resonance measurements have been carried out at 78° and at 4°K on Cu2+ ions diluted in single crystals of CdWO4, ZnWO4, and MgWO4. The g factors and the hyperfine interaction with the copper nucleus have been determined. From this experimental data the ground-state wavefunction of the Cu2+ ion has been constructed. It has also been possible to calculate the relevant l=2 terms of the low-symmetry crystal-field components. Then in the framework of a simple g-factor theory the g-factor anisotropy has been calculated and compared with the measured anisotropy. The role of the distortion of the covalent π bonds has also been examined. In the case of MgWO4 and ZnWO4 a distinct temperature-dependent g-factor shift and a temperature-dependent change of hyperfine interaction constants have been observed.

Dislocation Arrangements in Zinc Tungstate

Dislocations in low dislocation density (∼102 cm−2) single crystals of ZnWO4 have been analyzed by the application of standard etching techniques and by Borrmann and Berg-Barrett x-ray diffraction techniques. The majority of dislocations lying on the (010) slip planes were found to have [100] Burgers vectors, while the remainder had [001] Burgers vectors. Dislocations lying on the (100) plane had predominantly [001] Burgers vectors; dislocations with [010] Burgers vectors were present, but uncommon. In Borrmann photographs dislocations which were close to the exit surface of the crystal gave images of increased, rather than decreased, intensity. The effect of the oxygen atom positions on the intensities of the anomalously transmitted x-ray beams was shown to be significant in ZnWO4. Also, impurity segregation, which was revealed in both transmission optical and in x-ray photographs, indicates that facetting occurred on a convex growth interface.