2022年7月14日星期四

Cadmium Tungstate Single Crystal Growth by Crucible Descent Method

Cadmium tungstate (CdWO4, CWO) single crystal is a scintillation crystal material with excellent comprehensive properties, which can be widely used in nuclear medicine imaging, safety inspection, industrial CT, oil logging, high energy physics and other technical fields, especially in medical X-CT, container inspection system. Up to now, it has been reported that the single crystal of cadmium tungstate has been grown by Czochralski method at home and abroad. It is very difficult to grow high-quality large-scale cadmium tungstate single crystal. The main problem is that the optical transmittance of the grown single crystals is not uniform at the beginning and the end, the repeatability of the single crystals grown in different batches is poor, and there are many crystal defects such as cracking, inclusions, color centers, etc. 

cadmium tungstate single crystal image

In view of the technical problems existing in the current Czochralski growth of cadmium tungstate single crystal, a transparent and complete CdWO4 single crystal with a size of φ 40mm x 70mm was successfully grown by the crucible descent method for the first time. The properties of the single crystal were characterized by X-ray diffraction, transmission spectrum and X-ray excitation emission spectrum.

In the experiment, CdWO4 polycrystal with theoretical stoichiometric composition was synthesized by using a special platinum crucible to grow cadmium tungstate single crystal. After the polycrystal was filled into the platinum crucible, the top of the crucible was completely welded and sealed to realize the growth of cadmium tungstate single crystal by the crucible drop method under the closed crucible. The results show that the platinum crucible can seal the vapor in the upper part of the melt reliably, and the component of the melt will not be volatilized. During the whole process of crystal growth, the toxic cadmium oxide vapor can be avoided to escape, the composition of the melt can keep constant, and almost all the melts grow into relatively uniform transparent single crystals.

The stoichiometric polycrystal was synthesized by high temperature solid-state reaction. The crystal growth was guided by oriented seed crystal. The temperature of the growth furnace was controlled at 1350-1400 ℃, the temperature gradient of the solid-liquid interface was adjusted to 30-40 ℃ / cm, and the large-scale transparent and complete cadmium tungstate single crystal was successfully grown by the crucible drop method under closed condition. The process avoids the volatilization of the melt components in the process of crystal growth, can maintain the uniformity of the melt components, and stable temperature field is conducive to reduce the crystal cracking. Therefore, the crucible drop method for the growth of cadmium tungstate single crystal is a valuable process for application and development.

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