Zone refining method for growing cdi2 crystals and studying their polytypism by x-ray diffraction

Abstract EN

Purification involves repeated passage of a narrow molten zone through the boat of the material to be purified.

Impurities which are more soluble in the melt than in the solid are carried along the direction of the movement of the molten zone.

Impurities which are less soluble in the melt than the host solid tend to solidify first as it progresses, and thus move in a direction opposite to that of the molten movement in steps whose maximum length is equal to that of the molten zone.

The boat containing powdered cadmium iodide was placed in the central portion of the growth chamber.

The argon gas was made to flow slowly through the system to prevent oxidation of the material during heating.

This flow was begun after half an hour before the actual operation of the zone refining to ensure that an inert atmosphere is provided inside the growth chamber before heating.

The voltage was regulated through the variac so that the temperature inside the growth was lightly higher than the melting point of CdI2 (3880C).

It is required to maintain 65v potential.

The movement of heating trolley was started 10 minutes after switching on the heater.

At the end of each zone pass, the heater was quickly returned to their initial position by manual operation so that the process of zone refining could be started all over again.

A structure of CdI2 and typical impurity distribution along the length of the one refined rod is shown in figs (1), (2), (3) and (4).

A satisfactory good single crystal could be grown in about 8 to 10 zone passes.

In the present experiment, 8 passes were made.

After the passes are over, the crystal is allowed to cool down slowly.

Since the single crystals of CdI2 are known to be very soft, the ingot had to be handled very carefully.

Since CdI2 crystals have a platy nature, the faces were suspected to be ab-planes.

As shown in fig (5).

The intermediate section of the crystal was chosen for the study of the crystal by x-ray diffraction since it is purest part.

For the sake of convenience in mounting and adjustment of the x-ray diffraction camera, the crystals with thickness ranging between 0.6 and 0.8 mm were cleaved from the ingot and were finally cut into pieces of length ranging between 5 and 8 mm.