Investigation on the dislocation, thermal and mechanical properties, and crystal growth stress of Zr:GdTaO4 scintillator

The dislocation, thermal and mechanical properties, and crystal growth stress of the new heavy scintillator Zr:GdTaO4 (Zr:GTO) grown by the Czochralski method were systematically studied. The chemical etching experiment exhibits that the dislocation morphology of Zr:GTO is quadrilateral, whose causes were explained by the surface energy of the crystal faces calculated with the first principle. The thermal diffusivities of Zr:GTO along <1 0 0> and <0 0 1> directions are similar to each other and larger than that along <0 1 0> direction. The thermal expansion coefficient of Zr:GTO crystal along the crystalline axis presents a large anisotropic feature. And the thermal expansion curves demonstrate that the phase of Zr:GTO is transformed at 1650 K, which suggests that its annealing temperature should be lower than 1650 K to avoid crystal cracking. The thermal and mechanical properties are anisotropic, which causes the crystal to crack during growth and cooling. The thermal stress of Zr:GTO crystal during the growth and cooling stages was studied by numerical simulation for the first time. The results indicate that the thermal stress results in seed bending and cracking near the interface of the iridium rod and the crystal seed, and the crystal seed should be as short as possible to reduce thermal stress. Meanwhile, the cooling rate after crystal growth was optimized numerically. For Zr:GTO crystal with a size of Ø25 mm × 30 mm, uniform cooling for 48 h may be optimal. All the obtained results are of great significance for the growth and applications of high-quality Zr:GTO scintillator.