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PbTe-SnTe mutual diffusion coefficient at just above the Pb0.8Sn0.2Te solidus temperature
Journal of Crystal Growth 67 (1984) 375—379 North-Holland, Amsterdam
375
PbTe-SnTe MUTUAL DIFFUSION COEFFICIENT AT JUST ABOVE THE Pb08Sn02Te SOLIDUS TEMPERATURE Kyoichi KINOSHITA and Kiyomasa SUGII Musashino Electrical Communication Laboratory, Nippon Telegraph and Telephone Public Corporation, Midori - cho, Musashino - shi. Tokyo 180, Japan Received 20 April 1984
The PbTe—SnTe mutual diffusion coefficient at just above the Pb0 8Sn02Te solidus temperature is measured using a directional solidification 2/s. method, with a capillary used to suppress convective flows. The diffusion coefficient is determined to be (5.3 ±0.3)>< 10 cm
I. Introduction
a constant solute concentration region except for in the initial and terminal transient regions.
Pb 1 - ~ ~Te is a useful material for infrared detectors and tunable diode lasers. Efforts have focused on the growth of Ph0 8Sn02Te crystals, since the band gap for this composition corresponds to an electromagnetic radiation energy of 10 p.m, which falls within the atmospheric window range of 8 to 14 ~tm. One of the difficulties in Pb1 — ~Sn5Te crystal growth is to obtain compositionally homogeneous crystals. It can easily be seen from a PbTe—SnTe pseudo-binary phase diagram [1] that the SnTe component is rejected from a solid—liquid (S/L) interface when solidification occurs, thus, forming a piled-up SnTe layer on the liquid side of the S/L interface. In an earth gravity environment, the piled-up SnTe layer disappears rapidly through convective flows in the melt, and crystals grow from the melt containing a gradually enriched SnTe component. This results in a monotonic increase in SnTe with the fraction solidified, obeying the normal freezing law [2]. One possible way to improve homogeneity is to carry out crystal growth in a microgravity environment [3]. In this environment, convective flow can be suppressed and diffusion-controlled steady-state (DCSS) growth will be realized. Characteristic of crystals grown under DCSS growth conditions is that these crystals have
Tiller et al. and Smith et al. analyzed diffusioncontrolled crystal growth and showed that the solute concentration profiles along the growth axes are dependent on the solidification rate (R), the segregation coefficient (k) and the mutual diffu~,ion coefficient (D) in the melt [4,5]. The mutual diffusion coefficient at just above the solidus ternperature should be known for a precise analysis of concentration profiles. This is because this coefficient depends heavily on the temperature near the freezing point of the melt. The mutual diffusion coefficient of a PbTe—SnTe system was first measured by Clark et a!. at 990°C [6]. This is about 100°C higher than the Pb0 8Sn02Te solidus temperature. However, the mutual diffusion coeffident at just above the solidus temperature has not been reported on. This paper reports the results of the PbTe—SnTe mutual diffusion coefficient measurement at just above the Pb0 8Sn0 2Te solidus temperature.
2. Experimental The mutual diffusion coefficient was measured by the directional solidification method. The experimental arrangement is shown in fig. 1, and is
0022-0248/84/$03.00 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
376
K. Kinoshita, K. Sugo
/
PhTe— SnTe mutual diffusion (os’Ifislent
Motor dive
mm/h. The temperature gradient in the melt (G) was about 40°C/cm. tinder this temperature Canillarv tube
000000
L
0~0 0~ 0
~
gradient, crystals containing no cellular substructure were grown at an R) of less than 5 mm/h.
~
d2mm
—
000000000
Heater 00000000
0 0~0
0 0000000
000
~
10
The mutual was SnTe determined in such diffusion a way thatcoefficient the measured distribution best fitted the theoretical diffusioncontrolled growth curve for given parameters k and R [4,5]. The solidification rate (R) does not
~ 8
Solidus Temp.
0
10
20 30 40 Distance (cm)
50
Fig. 1. Experimental arrangement of directional solidification
method.
the same configuration as that used in the horizontal Bridgman method. The main procedures for obtaining the coefficient are as follows; First, the critical ampoule bore necessary to suppress convective flows in the melt is determined. Reducing the ampoule bore is effective in suppressing convection. This is because the fluid flow is suppressed in the capillary tube owing to large kinematic viscosity. Then, the coefficient is obtained on the basis of two kinds of SnTe distribution measurements: one is a measurement along the axial length of the directionally solidified crystal and the other is a measurement in front of the S/L interface of the crystal quenched in the course of directional solidification. Whether the convective flows are suppressed or not is determined from the SnTe axial distributions of directionally solidified crystals. SnTe is distributed in accordance with the diffusion-controlled growth theory when there exist no convective flows, while SnTe is distributed in accordance with the normal freezing law when convective flows exist, In the experiments, polycrystalline Pb0 8Sn0 2Te was sealed in a capillary tube at about 5 x i0~ Torr. The solidification rate was almost the same as the furnace translation rate (R0) in the steadystate, where R0 was varied in the range of 1—lO
coincide with the furnace translation rate (R() in the initial and terminal transient regions because the solute concentration at the S/L interface changes as crystal growth proceeds. True solidification rates were estimated from the furnace translation rates in accordance with the procedure proposed by Lehoczky and Szofran [7]. The SnTe concentration was measured using an EPMA (Electron Probe Microanalyzer). Conversion from the X-ray intensity to the SnTe concentration was carried out based on a calibration curve, obtained by using six samples with known SnTe concentrations.
3. Results and discussion 3.1. Determination of critical bore Directional solidification of the Pb~
5Sn~Te melt in an ampoule with various bores was carried out to determine the critical bore for suppressing convective flows. The bores used in the experiments were 10, 5, 4, 3, 2, and 1.5 mm. The critical bore was experimentally determined to be between 2 and 3 mm. In fig. 2, SnTe distributions along the solidification direction are shown for 2 and 3 mm bores. It is noted that DCSS growth, resulting in a constant SnTe region, is realized when the bore is reduced to 2 mm. while normal freezing. which indicates the existence of convective flows, occurs when the bore is 3 mm. The furnace translation rate should be chosen to be higher than the mass transport rate due to mutual diffusion. It was set at 5 mm/h in the present critical bore determination. If the bore is too small, it becomes difficult to handle the sample. Therefore, in the following experiments, all crystals were grown in capillary tubes with bores of 2 mm.
K. Kinoshita, K. Sugii
/
PhTe
—
Sn Te mutual diffusion coefficient
377
0.5 0.5 translation
rate
5mm/h
5cm2lsec.
R.~10mm/h
0.4
0.6
D~3.0x1Q D~5.5xl0icm2/Sec.
—.—.—
9
D~S.0x105cm2/sec.
U .~
0.3 ~easu
± 0 E 0.2 ~02
-
red
S IC
a)
Bore=3mm
Theoretical
0.1
0.1 0
I
0
1
0_ I
2 Distance (cm)
1
2
3
Distance
Fig. 2. SnTe distribution along the solidification direction for
0.5
I
two different ampoule bores.
—
3.2. Determination of the mutual diffusion coefficient from the Sn Te distribution along the crystal length
4
5
1cm)
I
~ 0.4 2 03
a I
0
I
D~3~ cm2/sec D ~5.3xl~.5C m2/ Sec.
O 80x10~Scm2/sec, ~•~smm/hMeaS:;~~)
E 0.2
The measured compositional profiles were cornpared with the theoretical curves. Calculations were based on the following equation [5]: in the initial transient region,
Theoretical
-
Ij1
b 0
5
Distance (cm)
C
5(x)
=
~ /1 + erf(~~ 2k
R r3mm/h
2
+(2k— 1) exp[—k(1 —k)(Rx/D)]
_D~30xl0Scm2/Sec.
0.4
5cm2/Sec. O 5 5x10
Scm2/sec
0.3 S
x erfc{( 2k 2— 1
(1)
C
0.2
C
‘°
in the terminal transient,
Theoretical
0.1
C
C 5(x)
0
I
0 =
co{i
+ ~ n=1
(2n
+
1) (1— k)(2 (1
+
k)(2
—
+
k)...(n k). . .(n
—
+
k) k)
o.~— ~
xexp[_n(n+1)R(L_x)/D]}~
(2)
1
2
3
4
5
Distance (cm) R,~1mm/h
0.4 03
a,
where C5 is solute concentration in the crystal, C0 is the original solute concentration in the melt, x is the distance measured from the starting end of the crystal, and L is the entire crystal length. The results of the theoretical fitting to the experimental data are shown in figs. 3a—3d for several furnace translation rates. Although the solidification rate in eqs. (1) and (2) is different from the furnace translation rate, it was found that these
E
0.2
Theoretical
C
(
Normal freezing)
d 0 I
0
1
2
3
Distance (cm)
4
5
Fig. 3. Comparisons between measured and theoretical cornpositional profiles for various furnace translation rates R0 (in mm/h): (a) 10. (b) 5, (c) 3, (d) 1.
378
K. Kinoshita. K. Sugii / PhTe — Sn Te mutual diffusion soe/jicienl
Table I Mutual diffusion coefficients obtained from axial SnTe distrihutions for various furnace translation rates
penetrates deeply into the remaining melt as a result of mutual diffusion.
Diffusion coefficient 2/s) _____ (10 cm 5.0 5.6 5.5 4.8 5.3 5.5
(mm/h) 1.0 2.5 3.0 4.0 5.0 10.0
as shown in fig. 3d. This is hecatise the S/L interface translation rate (~I mm/h) is too slow and the piled-up SnTe at the S/L interface
In the Bridgman method, G/R ratio is known to be an important parameter for growing good single crystals [4]. Using the present diffusion coefficient, the G/R value required to prevent constitutional supercooling in the melt for Ph 55 5Sn ~Te under steady-state growth conditions is obtained as
2.
two ratesthegave almost between the samethe results. Thisandis because separation liquidus solidus lines in the PhTe—SnTe system is quite small [3,71. The mutual diffusion coefficients obtained are listed in table 1, where coefficients are selected to explain the experimental data in the steady-state growth region. From these results, a mutual diffusion coefficient just above the Pb 55 8Sn02Te solidus temperature (892°C) is averaged to be (5.3 ±0.3) >< 10~ cm~/s.This value is about three fourths the value obtained at 990°C [61. Figs. 3a—3d shows that DCSS growth is realized at furnace translation rates of faster than 4—S mm/h. This is in agreement with the calculated diffusion length, /bt, of 4.4 mm in an hour, where denotes time. When the furnace translation rate is reduced to I mm/h, the SnTe concentration profile becomes similar to that for normal freezing
0.5 I
R~5mm/h sore 2mm
.~
3.3. Determination of the mutual diffusion coe//icient from the SnTe distribution in front of the solid--liquid
The diffusion coefficient can also be derived from the solute distribution in the melt. During steady-state growth, solute distribution in the melt is approximately given as follows [4],
c
=
c0 [I
+
I—k
~
exp(
R —
-~
1
1
(3)
where C~is the solute concentration in the liquid. and I is the distance measured from the S/L interface. Fig. 4 shows the SnTe distribution around the S/L interface in the case where the solidification rate is 5 mm/h. This was obtained by quenching a sample in the midst of directional solidification. Fitting eq. (3) to the results shown in fig. 4, the diffusion2/s, coefficient is obtained as which agrees with the D = (5 ±1) x 10 cm value obtained from the solute distribution in the solid. Since the dendritic growth in the quenched
_______
c 0.4
G/R mm(/ [(k slope — 1 )/kJ /1) liquidus = 6)~K h/cm where is the of the line.
~
D 5x105cm2/sec ~ D4xlOScm2/sec
U 0
0.3
melt causes local inhornogeneity in the concentra-
0
C U)
0.1
data tion, isa obtained scatteringasinshown the measured in fig. 4. concentration
~~~~oOoO
0.2
S/L interface
_________
0
__________
4. Conclusion
________
_....c........ i
0
1
2
3
4
5
Distance (cm) Fig. 4. Comparison between measured and theoretical SnTe distributions around the S/L interface; bore 2 mm and
just above the Pb
R0 = 5 mm/h.
has
The PbTe—SnTe mutual diffusion coefficient at 55 5Sn02Te solidus temperature been determined to be (5.3 ±0.3) X 10--
K. Kinoshita, K. Sugii
/
PbTe— SnTe mutual diffusion coefficient
2/s, from an analysis of the SnTe distributions cm in the crystals and the quenched melt in the absence of convective flows,
Acknowledgments
379
References [1] AR. T.C.242 Harman, M. Finn and P. Youtz, Trans. Met. Calawa. Soc. AIME (1968) 374. [2] W.C. Pfann. Zone Melting (Wiley, New York, 1966) p. 11. [3] R.K. Crouch, AL. Fripp, W.J. Debnarn, 1.0. Clark and F.M. Carlson, Ground Based Studies for the Space Process-
ing of Lead—Tin—Telluride, in: Materials Processing in the
Reduced Gravity Environment of Space. Ed. G.E. Rindone
The authors wish to thank Drs. N. Kuroyanagi, Y. Suemune, H. Okamoto, T. Yamada and S. Miyazawa for their valuable discussions and continued encouragement throughout this work.
(North-Holland, New York, 1982) p. 611. [4] WA. Tiller, K.A. Jackson, 3W. Rutter and R. Chalmers, Acta Met. 1 (1953) 428. [5] V.G. Smith, WA. Tiller and J.W. Rutter, Can. J. Phys. 33 (1955) 723.
[6] 1.0. Clark, AL. Fripp, W.J. Debnam, Jr., R.K. Crouch and W.D. Brewer, J. Electrochem. Soc. 130 (1983) 164. [7] S.L. Lehoczky and FR. Szofran, Directional Solidification and Characterization of Hg 1 — ~Cd~Te alloys, in: Materials Processing in the Reduced Gravity Environment of Space, Ed. G.E. Rindone (North-Holland. New York, 1982) P. 409.
375
PbTe-SnTe MUTUAL DIFFUSION COEFFICIENT AT JUST ABOVE THE Pb08Sn02Te SOLIDUS TEMPERATURE Kyoichi KINOSHITA and Kiyomasa SUGII Musashino Electrical Communication Laboratory, Nippon Telegraph and Telephone Public Corporation, Midori - cho, Musashino - shi. Tokyo 180, Japan Received 20 April 1984
The PbTe—SnTe mutual diffusion coefficient at just above the Pb0 8Sn02Te solidus temperature is measured using a directional solidification 2/s. method, with a capillary used to suppress convective flows. The diffusion coefficient is determined to be (5.3 ±0.3)>< 10 cm
I. Introduction
a constant solute concentration region except for in the initial and terminal transient regions.
Pb 1 - ~ ~Te is a useful material for infrared detectors and tunable diode lasers. Efforts have focused on the growth of Ph0 8Sn02Te crystals, since the band gap for this composition corresponds to an electromagnetic radiation energy of 10 p.m, which falls within the atmospheric window range of 8 to 14 ~tm. One of the difficulties in Pb1 — ~Sn5Te crystal growth is to obtain compositionally homogeneous crystals. It can easily be seen from a PbTe—SnTe pseudo-binary phase diagram [1] that the SnTe component is rejected from a solid—liquid (S/L) interface when solidification occurs, thus, forming a piled-up SnTe layer on the liquid side of the S/L interface. In an earth gravity environment, the piled-up SnTe layer disappears rapidly through convective flows in the melt, and crystals grow from the melt containing a gradually enriched SnTe component. This results in a monotonic increase in SnTe with the fraction solidified, obeying the normal freezing law [2]. One possible way to improve homogeneity is to carry out crystal growth in a microgravity environment [3]. In this environment, convective flow can be suppressed and diffusion-controlled steady-state (DCSS) growth will be realized. Characteristic of crystals grown under DCSS growth conditions is that these crystals have
Tiller et al. and Smith et al. analyzed diffusioncontrolled crystal growth and showed that the solute concentration profiles along the growth axes are dependent on the solidification rate (R), the segregation coefficient (k) and the mutual diffu~,ion coefficient (D) in the melt [4,5]. The mutual diffusion coefficient at just above the solidus ternperature should be known for a precise analysis of concentration profiles. This is because this coefficient depends heavily on the temperature near the freezing point of the melt. The mutual diffusion coefficient of a PbTe—SnTe system was first measured by Clark et a!. at 990°C [6]. This is about 100°C higher than the Pb0 8Sn02Te solidus temperature. However, the mutual diffusion coeffident at just above the solidus temperature has not been reported on. This paper reports the results of the PbTe—SnTe mutual diffusion coefficient measurement at just above the Pb0 8Sn0 2Te solidus temperature.
2. Experimental The mutual diffusion coefficient was measured by the directional solidification method. The experimental arrangement is shown in fig. 1, and is
0022-0248/84/$03.00 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
376
K. Kinoshita, K. Sugo
/
PhTe— SnTe mutual diffusion (os’Ifislent
Motor dive
mm/h. The temperature gradient in the melt (G) was about 40°C/cm. tinder this temperature Canillarv tube
000000
L
0~0 0~ 0
~
gradient, crystals containing no cellular substructure were grown at an R) of less than 5 mm/h.
~
d2mm
—
000000000
Heater 00000000
0 0~0
0 0000000
000
~
10
The mutual was SnTe determined in such diffusion a way thatcoefficient the measured distribution best fitted the theoretical diffusioncontrolled growth curve for given parameters k and R [4,5]. The solidification rate (R) does not
~ 8
Solidus Temp.
0
10
20 30 40 Distance (cm)
50
Fig. 1. Experimental arrangement of directional solidification
method.
the same configuration as that used in the horizontal Bridgman method. The main procedures for obtaining the coefficient are as follows; First, the critical ampoule bore necessary to suppress convective flows in the melt is determined. Reducing the ampoule bore is effective in suppressing convection. This is because the fluid flow is suppressed in the capillary tube owing to large kinematic viscosity. Then, the coefficient is obtained on the basis of two kinds of SnTe distribution measurements: one is a measurement along the axial length of the directionally solidified crystal and the other is a measurement in front of the S/L interface of the crystal quenched in the course of directional solidification. Whether the convective flows are suppressed or not is determined from the SnTe axial distributions of directionally solidified crystals. SnTe is distributed in accordance with the diffusion-controlled growth theory when there exist no convective flows, while SnTe is distributed in accordance with the normal freezing law when convective flows exist, In the experiments, polycrystalline Pb0 8Sn0 2Te was sealed in a capillary tube at about 5 x i0~ Torr. The solidification rate was almost the same as the furnace translation rate (R0) in the steadystate, where R0 was varied in the range of 1—lO
coincide with the furnace translation rate (R() in the initial and terminal transient regions because the solute concentration at the S/L interface changes as crystal growth proceeds. True solidification rates were estimated from the furnace translation rates in accordance with the procedure proposed by Lehoczky and Szofran [7]. The SnTe concentration was measured using an EPMA (Electron Probe Microanalyzer). Conversion from the X-ray intensity to the SnTe concentration was carried out based on a calibration curve, obtained by using six samples with known SnTe concentrations.
3. Results and discussion 3.1. Determination of critical bore Directional solidification of the Pb~
5Sn~Te melt in an ampoule with various bores was carried out to determine the critical bore for suppressing convective flows. The bores used in the experiments were 10, 5, 4, 3, 2, and 1.5 mm. The critical bore was experimentally determined to be between 2 and 3 mm. In fig. 2, SnTe distributions along the solidification direction are shown for 2 and 3 mm bores. It is noted that DCSS growth, resulting in a constant SnTe region, is realized when the bore is reduced to 2 mm. while normal freezing. which indicates the existence of convective flows, occurs when the bore is 3 mm. The furnace translation rate should be chosen to be higher than the mass transport rate due to mutual diffusion. It was set at 5 mm/h in the present critical bore determination. If the bore is too small, it becomes difficult to handle the sample. Therefore, in the following experiments, all crystals were grown in capillary tubes with bores of 2 mm.
K. Kinoshita, K. Sugii
/
PhTe
—
Sn Te mutual diffusion coefficient
377
0.5 0.5 translation
rate
5mm/h
5cm2lsec.
R.~10mm/h
0.4
0.6
D~3.0x1Q D~5.5xl0icm2/Sec.
—.—.—
9
D~S.0x105cm2/sec.
U .~
0.3 ~easu
± 0 E 0.2 ~02
-
red
S IC
a)
Bore=3mm
Theoretical
0.1
0.1 0
I
0
1
0_ I
2 Distance (cm)
1
2
3
Distance
Fig. 2. SnTe distribution along the solidification direction for
0.5
I
two different ampoule bores.
—
3.2. Determination of the mutual diffusion coefficient from the Sn Te distribution along the crystal length
4
5
1cm)
I
~ 0.4 2 03
a I
0
I
D~3~ cm2/sec D ~5.3xl~.5C m2/ Sec.
O 80x10~Scm2/sec, ~•~smm/hMeaS:;~~)
E 0.2
The measured compositional profiles were cornpared with the theoretical curves. Calculations were based on the following equation [5]: in the initial transient region,
Theoretical
-
Ij1
b 0
5
Distance (cm)
C
5(x)
=
~ /1 + erf(~~ 2k
R r3mm/h
2
+(2k— 1) exp[—k(1 —k)(Rx/D)]
_D~30xl0Scm2/Sec.
0.4
5cm2/Sec. O 5 5x10
Scm2/sec
0.3 S
x erfc{( 2k 2— 1
(1)
C
0.2
C
‘°
in the terminal transient,
Theoretical
0.1
C
C 5(x)
0
I
0 =
co{i
+ ~ n=1
(2n
+
1) (1— k)(2 (1
+
k)(2
—
+
k)...(n k). . .(n
—
+
k) k)
o.~— ~
xexp[_n(n+1)R(L_x)/D]}~
(2)
1
2
3
4
5
Distance (cm) R,~1mm/h
0.4 03
a,
where C5 is solute concentration in the crystal, C0 is the original solute concentration in the melt, x is the distance measured from the starting end of the crystal, and L is the entire crystal length. The results of the theoretical fitting to the experimental data are shown in figs. 3a—3d for several furnace translation rates. Although the solidification rate in eqs. (1) and (2) is different from the furnace translation rate, it was found that these
E
0.2
Theoretical
C
(
Normal freezing)
d 0 I
0
1
2
3
Distance (cm)
4
5
Fig. 3. Comparisons between measured and theoretical cornpositional profiles for various furnace translation rates R0 (in mm/h): (a) 10. (b) 5, (c) 3, (d) 1.
378
K. Kinoshita. K. Sugii / PhTe — Sn Te mutual diffusion soe/jicienl
Table I Mutual diffusion coefficients obtained from axial SnTe distrihutions for various furnace translation rates
penetrates deeply into the remaining melt as a result of mutual diffusion.
Diffusion coefficient 2/s) _____ (10 cm 5.0 5.6 5.5 4.8 5.3 5.5
(mm/h) 1.0 2.5 3.0 4.0 5.0 10.0
as shown in fig. 3d. This is hecatise the S/L interface translation rate (~I mm/h) is too slow and the piled-up SnTe at the S/L interface
In the Bridgman method, G/R ratio is known to be an important parameter for growing good single crystals [4]. Using the present diffusion coefficient, the G/R value required to prevent constitutional supercooling in the melt for Ph 55 5Sn ~Te under steady-state growth conditions is obtained as
2.
two ratesthegave almost between the samethe results. Thisandis because separation liquidus solidus lines in the PhTe—SnTe system is quite small [3,71. The mutual diffusion coefficients obtained are listed in table 1, where coefficients are selected to explain the experimental data in the steady-state growth region. From these results, a mutual diffusion coefficient just above the Pb 55 8Sn02Te solidus temperature (892°C) is averaged to be (5.3 ±0.3) >< 10~ cm~/s.This value is about three fourths the value obtained at 990°C [61. Figs. 3a—3d shows that DCSS growth is realized at furnace translation rates of faster than 4—S mm/h. This is in agreement with the calculated diffusion length, /bt, of 4.4 mm in an hour, where denotes time. When the furnace translation rate is reduced to I mm/h, the SnTe concentration profile becomes similar to that for normal freezing
0.5 I
R~5mm/h sore 2mm
.~
3.3. Determination of the mutual diffusion coe//icient from the SnTe distribution in front of the solid--liquid
The diffusion coefficient can also be derived from the solute distribution in the melt. During steady-state growth, solute distribution in the melt is approximately given as follows [4],
c
=
c0 [I
+
I—k
~
exp(
R —
-~
1
1
(3)
where C~is the solute concentration in the liquid. and I is the distance measured from the S/L interface. Fig. 4 shows the SnTe distribution around the S/L interface in the case where the solidification rate is 5 mm/h. This was obtained by quenching a sample in the midst of directional solidification. Fitting eq. (3) to the results shown in fig. 4, the diffusion2/s, coefficient is obtained as which agrees with the D = (5 ±1) x 10 cm value obtained from the solute distribution in the solid. Since the dendritic growth in the quenched
_______
c 0.4
G/R mm(/ [(k slope — 1 )/kJ /1) liquidus = 6)~K h/cm where is the of the line.
~
D 5x105cm2/sec ~ D4xlOScm2/sec
U 0
0.3
melt causes local inhornogeneity in the concentra-
0
C U)
0.1
data tion, isa obtained scatteringasinshown the measured in fig. 4. concentration
~~~~oOoO
0.2
S/L interface
_________
0
__________
4. Conclusion
________
_....c........ i
0
1
2
3
4
5
Distance (cm) Fig. 4. Comparison between measured and theoretical SnTe distributions around the S/L interface; bore 2 mm and
just above the Pb
R0 = 5 mm/h.
has
The PbTe—SnTe mutual diffusion coefficient at 55 5Sn02Te solidus temperature been determined to be (5.3 ±0.3) X 10--
K. Kinoshita, K. Sugii
/
PbTe— SnTe mutual diffusion coefficient
2/s, from an analysis of the SnTe distributions cm in the crystals and the quenched melt in the absence of convective flows,
Acknowledgments
379
References [1] AR. T.C.242 Harman, M. Finn and P. Youtz, Trans. Met. Calawa. Soc. AIME (1968) 374. [2] W.C. Pfann. Zone Melting (Wiley, New York, 1966) p. 11. [3] R.K. Crouch, AL. Fripp, W.J. Debnarn, 1.0. Clark and F.M. Carlson, Ground Based Studies for the Space Process-
ing of Lead—Tin—Telluride, in: Materials Processing in the
Reduced Gravity Environment of Space. Ed. G.E. Rindone
The authors wish to thank Drs. N. Kuroyanagi, Y. Suemune, H. Okamoto, T. Yamada and S. Miyazawa for their valuable discussions and continued encouragement throughout this work.
(North-Holland, New York, 1982) p. 611. [4] WA. Tiller, K.A. Jackson, 3W. Rutter and R. Chalmers, Acta Met. 1 (1953) 428. [5] V.G. Smith, WA. Tiller and J.W. Rutter, Can. J. Phys. 33 (1955) 723.
[6] 1.0. Clark, AL. Fripp, W.J. Debnam, Jr., R.K. Crouch and W.D. Brewer, J. Electrochem. Soc. 130 (1983) 164. [7] S.L. Lehoczky and FR. Szofran, Directional Solidification and Characterization of Hg 1 — ~Cd~Te alloys, in: Materials Processing in the Reduced Gravity Environment of Space, Ed. G.E. Rindone (North-Holland. New York, 1982) P. 409.