Materiak Chemistry and Physics, 16 (1987) 189-195 189

PRELIMINARY NOTE

GROWTH OF Sb13 SINGLE CRYSTALS FROM VAPOUR BY THE TEMPERATURE

OSCILLATION METHOD

D. ARIVUOLI, F'.D. GNANAM and P. RAMASAMY

Crystal Growth Centre, Anna University, Madras-25 (India)

Received April 22, 1986; accepted June 5, 1986

ABSTRACT

Platelets of Sb13 were grown from vapour by the temperature oscillation

method. The surface features of the as grown crystals were found to depend

upon temperature gradients. The grown crystals were confirmed by chemical

and X-ray analysis.

INTRODUCTrON

The triiodides of antimony, arsenic and bismuth have semiconducting

properties which are retained even in the Liquid state [ll. They are

interesting due to the specific character of the chemical bond and the

associated crystal structure characteristics. These layered compounds SbI3

and Bi13 exist in several modifications or polytypes [21. These crystals

can be divided into two main types according to the type of spectrum of

the thermally stimulated depolarisation current (TSDCJ in photoelectret

state conditions. The first type crystals are obtained from the melt by

the Bridgman method or from the gas phase with high supersaturation. The

TSDC maxima for the first type crystals of BiI3 lie in the range 180 - 200 K

and for As1 3

and SbI 3

in the range 230 - 270 K 131. The second type of crystals

is obtained from gas phase with lower supersaturation. This type of

crystal does not show clear maxima.

Crystals of SbI3 were grown from the gas phase by the Bridgman method

[41 and from the vapour phase by Gasinets et al. [Sl. The present paper

describes the growth of SbI3 from vapour by the temperature oscillation

method and the surface features of the as grown platelets grown for different

temperature gradients.

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190

EXPERIMENTAL

The polycrystalline sample was prepared from organic solvents using

antimony (99.999%) and analar grade (99.9%) resublimed iodine. The prepared

compound was confirmed by wide angle X-ray analysis [61. Experiments were

carried out in a sealed point tipped glass ampoule of length 15 cm and

diameter 12 mm, vacuum sealed at a pressure of 10 -4

torr. Crystals were

grown from vapour for different growth zone temperatures by oscillating the

source zone temperature. The source zone was oscillated between 170°C and

190°c. The experiments were carried out for the growth zone temperature

160, 140 and 130°C. The time-temperature profile for the source zone

temperature is as shown in Fig. 1.

190

182

174

166 I I I I I .- _

0 120 240 360 480 600

TIME ( seconds 1

Fig. 1. The time-temperature profile for the source zone.

RESULTS AND DISCUSSION

When the growth period is about 3 to 4 days platelets of SbI3 of dimensions

8 mm x 4 mm x 0.2 mm were obtained. Surface studies were done on the as

grown crystals using a Leitz polarising microscope. Figure 2 shows the surface

of the SbI 3 platelet depicting the hexagonal morphology. In some of the

crystals grown for the growth temperature of 160°C, growth layers far separated

from each other as they reach the edge of the crystal were obtained.

191

Fig. 2. surface of the as grown SbI3 single crystal.

Fig. 3. Instability pattern obtained for the growth zone temperatures of 160'~.

Figure 3 shows the instability pattern obtained on the smooth face. The

lnstablllty appears through the roughening of the macrosteps which seem to

indicate a lateral layer spreading mechanism of growth, typlcal of atomically

smooth interfaces. In some of the platelets the ripple morphology with the

elevated part as shown in Fig. 3 is suppressed. Figure 4 is the bunch of

growth steps formed due to the bidimensional nucleation. Figure 5 shows

the special type of macrolayers obtained when the growth temperature is

150°c. The spreading of the layers is due to bidimensional nucleation and

the spreading occurs layer by layer over a perfect crystal surface and steps

Fig. 4. Bunch of growth steps formed on the surface of the as grown crystal.

Fig. 5. Peculiar type of layers obtained for the growth zone temperature

of 140°c.

when the bunches of macrosteps cease to progress. The higher magnification

of Fig. 5 clearly showed that each macrostep or layer is a collection of

interlaced layers and diminishes in size and step height as it spreads over

another due to two dimensional nucleation. Figure 6 shows the assembly of

many spiral steps originating from dislocations distributed along a straight

line.

193

Fig. 6. Assembly of many spiral steps.

Fig. I. FormatIon of the flat topped steps.

When the growth zone temperature was 13O'C interesting features were

obtained. Flat topped hexagonal pyramidal patterns as shown in the Fig. 7

were obtained after 1 or 2 days. When the experiment was carried out for

5 to 10 hours deposition of pyramidal hexagonal platelets (Fig. 8) was

Fig. 8. Pyramidal platelets deposited after 5 to 10 hours.

obtained. This c!an be explained as follows. Let there be a homogeneous

flat surface on which deposits a solution of iodine and Sb13. The Sb13 vapour

dissolves in the liquid saturating the solution. So SbI 3 condenses, due

to heat loss along the temperature gradient created by the substrate, in

the form of flat topped hexagonal pyramids and platelets confirming that

the growth takes place by a vapour-liquid-solid mechanism. At high tempe-

ratures, the overgrowth formed in the initial process evaporates, resulting

in layers. So in a vapour-liquid-solid mechanism, large pyramids and spirals

are formed in the initial process. At high temperatures well developed wave-

like central regions and rarely well formed edges were obtained. At tempe-

ratures 150 to 160°C flat topped layers with spirals appear. So a vapour-

liquid-solid mechanism plays an important role in the initial phase of the

process in the present case and its effect decreases in the process of layer

growth when the temperature rises.

The grown crystals were confirmed as single crystals by the Laue technique

and the lattice parameters were found to be a = 7.49 i and c = 20.87 i.

ACKNOWLEDGEMENT

One of the authors (D.A) is grateful to UGC for awarding the research

fellowship.

195

REFERENCES

1 G. Fisher, Helv. Phys. Acta., 34 (1961) 827.

2 R.F. Rolsten, Iodide metals and metal iodides, Wiley, New York, (1961).

3 A.A. Kikunesh, I.P. Mikhalko, D.G. Semak and I.D. Turyanitsa, Izv. Akad.

Nauk. SSSR. Neorg. Mater., 10 (1974) 559.

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5 S.M. Gasinets, G.M. Shpyrko, M.I. Golovei and T.N. Melnichenko, Inv. Akad.

Nauk. SSSR. Neorg. Mater., 13 (1977) 912.

6 Backer, Structure Reports, 11 (1947) 272.