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Seeded growth of garnet from molten salts
458
Journal of Crystal Growth 3, 4 (1968) 458—462 © North-Holland Publishing Co., Amsterdam
SEEDED GROWTH OF GARNET FROM MOLTEN SALTS
G. A. BENNETT Department of Electrical Engineering, University of Glasgow, Glasgow, Great Britain
In an effort to try and reduce some of the limitations associated with the molten salt technique a modification to the system has been developed which permits: seeded growth; removal of the excess solution from the crystals on growth termination without damaging the crucible or removing the crucible from the furnace at elevated temperatures; eliminates nucleation created by the growth of a second phase crystallising during the earlier stages of cooling; permits economical use ofthe excess solution remaining
after growth; and provides a system for possible growth of composite crystals. Results are given on the growth of yttrium iron garnet (YIG) and crystal from the system, Bi 3 - 2~Ca2,~Fe5 _~V~O12 (CVB) utilising this modified technique. In conjunction with this type of seeding a number of YIG crystals were pulled from barium borate melts using YIG and yttrium aluminium garnet (YAG) seeds, with a view to producing a composite structure suitable for magnetoacoustic delay line applications.
1. Introduction
becomes the predominant nucleation site as the cooling
A reduction in some of the limitations associated with molten salt growth systems has been achieved by a modification to the technique which permits:
cycle is continued. On completion of the slow cooling the rotation procedure was repeated, this action separates the excess solution from the crystals deposited on the lid. Details of the seed position with respect to the solution are shown in fig. 2.
(i)
Seeded growth.
Removal of the excess solution without thermally shocking the crystals. (iii) Economical use of the remaining solution. (iv) A reduction in nucleation sites created by a second phase. (ii)
REFRACTORY BRICK
A number of garnets have also been pulled from the melt to evaluate the possibility of growing a composite YIG—YAG—YIG single crystal system. 2. Experimental procedure
~IMS1I~T~RAME
A garnet seed was attached 3toplatinum the crucible lid, which crucible conwas then welded to a 700 cm taming the premelted oxides. The crucible was evacuated, refilled with oxygen to a pressure which promoted equilibrium conditions at the “soak” temperature, and sealed. During the initial heating, soaking and cooling cycle the crucible was located at the base of the furnace shown in fig. 1. When the required temperature was reached the crucible was raised into the position shown, rotated through 180° and lowered to the base of the furnace. The seed thus XI
PLATINUM CRUCIBLE
0 0 0
0 0
ALUMINA
0
0
SILICON ELEMENTS
II’tONIC SHAFT & SUPPORT
Fig. 1.
Schematic arrangement of the furnace and reversal facilities used in seeding molten salts.
—
5
459
SEEDED GROWTH OF GARNET FROM MOLTEN SALTS TABLE
I
Results of garnet growth using the reversal technique Melt No. composition (g)
Soak temperature (°C)
Initial rotation temperature (°C)
Final rotation temperature (°C/hr)
Cooling rate (°C/hr)
Y
203320 Fe203—480
Comments
No evidence of seeding
1
PbO—845 PbF2—750 B203—52
1280
1245
1045
0.5
No growth on the base of the crucible
2
As above
1280
1230
1070
0.65
3
As above
1280
1210
1070
0.5
No evidence of seeding, neglible growth on base Seeding occurred
4
As above
1280
1210
1070
1.0
1200
1070
1000
0.5
Bi203—750 Fe2O3—530 5
CaCo3—310 V205—l 15 PbO—290
YAG seed dissolved aluminium doped YIG obtained No seeding attempted Ferrite phase restricted to crucible base 25 g garnet crystal obtained
3. Results Seeded YIG was obtained with the conditions as shown in No. 3 of table 1. During the initial heating and slow cooling period, which permits the earlier stages of growth to be deposited on the base of the crucible, the seed was located as shown in fig. 2a. At 1210 °Cthe crucible was rotated to position 2b, cooled to 1070 °C,rotated to position 2c and cooled to room temperature. Figs. 3a andrespectively. 3b show theAs12indicated g seed and the resulting 57 g crystal in No. 4, table 1, which was an attempted composite growth, the YAG seed dissolved resulting in aluminium substituted YIG crystals. The result of run No. 5 demonstrated the effectiveness of this technique in reducing the number of nucleation sites created by calcium ferrite during CVB growth. The ferrite crystals deposited in the region 1200—1080 °Cwere almost cornpletely restricted to the crucible base and the garnet yield to the lid, 4. Experimental procedure
A number of YIG crystals have been pulled from the melt using the apparatus shown in fig. 4, this system
3). was developed by Linaresi ~2) and later Kestigian Pulling rates, which were monitored by by a linear potentiometer, as low as 0.002 inch per hour were achieved from the difference in linear movement produced by the action of the gears on the threaded columns shown in the figure. The YIG seeds were cut from crystals grown from PbO—PbF 2 melts and the YAG seeds from Czochralski-grown boules. The melt composition and temperatures were similar to those described by Kesti3). gian 5. Results A section of a <110> pulled crystal is shown in fig.5. The sample which demonstrates the differences in domain pattern, consists of three regions; (a) the left hand section, which is reddish-brown in colour, is the seed; (b) an intermediate yellow band adjacent to the (110) interface, is the material deposited during the necking period and (c) the right hand green coloured region is the pulled material. The variation in colour from the yellow to red may be indicative of Fe2 + content associated with increasing silicon content as shown by Lefever and Chase4). The result of pulling YIG from a <111> YAG seed is shown in fig. 6. Unlike
XI-5
460
G. A. BENNETT
NIMONIC FRAME
SA ~ SOLUTION
PLATINUM CRUCIBLE WITH WELDED LID (~Q)
Fig. 2.
ALUMINA SUPPORT CRUCIBLE
(b)
AXIS
(~c)
Location of the garnet seed relative to the melt during the growth cycle.
mini
iiui~ WORM WHEEL DRIVEN FROM FLEXIBLE DRIVES
‘~
PULLING MECHANISM
J
~
——---j!j!J~ ~
ROTATION (a)
_____________________
MECHANISM
4F~
PLATINUM ROD & __________ CRUCIBLE \\\
I
~
V77//
LfJ
y///A\
Li u
~-LINEAR POTENTIOMETER TORECORDER
f”j—~ II \~s\~\’
CRUCIBLE SUPPORT
FIREBRICK
(b) Fig. 3.
j
!IHlI~
Photograph of before (a) and after (b) seeded growth ofYIG.
XI
Fig. 4.
—
5
Mechanical gear arrangement and furnace used to pull crystals from the melt.
SEEDED GROWTH OF GARNET FROM MOLTEN SALTS
Fig. 5.
461
Photomicrograph of a YIG crystal illustrating the junction of the seed and pulled material, with growth parallel to the (110) interface.
the YIG—YIG system where little or no material was dissolved from the seed by the flux, the YAG was preferentially etched giving rise to large grained polycrystalline growth. Recent experiments have shown that annealing the YAG prior to growth, eliminates the cracking which can be seen in fig. 6. The etching of the seed created a 25 pm junction at the interface which consists of a transition from YAG through aluminium doped YIG to pure YIG.
______
______
6. Conclusion
Fig. 6.
The rotation technique eliminates thermal shocking of the crystals and permits economical use of the remaining solution. Seeding the melt offers the operator some means of control over the nucleation process which would be relevant with high purity melts. The
Photograph of a pulled YIG crystal from a YAG seed,
XI
—
5
462
G. A. BENNETT
initial results obtained on the composite structure indicate that such a system may be realised within the near future.
the Science Research Council for their financial support of this project. References
Acknowledgment The author would like to express his appreciation to
1) 2) 3) 4)
XI-5
R. C. Linares, J. Am. Ceram. Soc. 45 (1962) 307. R. C. Linares, J. App!. Phys. 35 (1964) 433. M. Kestigian, J. Am. Ceram. Soc. 50 (1967) 165. R. A. Lefever and A. B. Chase, J. Chem. Phys. 32(1960)1575.
Journal of Crystal Growth 3, 4 (1968) 458—462 © North-Holland Publishing Co., Amsterdam
SEEDED GROWTH OF GARNET FROM MOLTEN SALTS
G. A. BENNETT Department of Electrical Engineering, University of Glasgow, Glasgow, Great Britain
In an effort to try and reduce some of the limitations associated with the molten salt technique a modification to the system has been developed which permits: seeded growth; removal of the excess solution from the crystals on growth termination without damaging the crucible or removing the crucible from the furnace at elevated temperatures; eliminates nucleation created by the growth of a second phase crystallising during the earlier stages of cooling; permits economical use ofthe excess solution remaining
after growth; and provides a system for possible growth of composite crystals. Results are given on the growth of yttrium iron garnet (YIG) and crystal from the system, Bi 3 - 2~Ca2,~Fe5 _~V~O12 (CVB) utilising this modified technique. In conjunction with this type of seeding a number of YIG crystals were pulled from barium borate melts using YIG and yttrium aluminium garnet (YAG) seeds, with a view to producing a composite structure suitable for magnetoacoustic delay line applications.
1. Introduction
becomes the predominant nucleation site as the cooling
A reduction in some of the limitations associated with molten salt growth systems has been achieved by a modification to the technique which permits:
cycle is continued. On completion of the slow cooling the rotation procedure was repeated, this action separates the excess solution from the crystals deposited on the lid. Details of the seed position with respect to the solution are shown in fig. 2.
(i)
Seeded growth.
Removal of the excess solution without thermally shocking the crystals. (iii) Economical use of the remaining solution. (iv) A reduction in nucleation sites created by a second phase. (ii)
REFRACTORY BRICK
A number of garnets have also been pulled from the melt to evaluate the possibility of growing a composite YIG—YAG—YIG single crystal system. 2. Experimental procedure
~IMS1I~T~RAME
A garnet seed was attached 3toplatinum the crucible lid, which crucible conwas then welded to a 700 cm taming the premelted oxides. The crucible was evacuated, refilled with oxygen to a pressure which promoted equilibrium conditions at the “soak” temperature, and sealed. During the initial heating, soaking and cooling cycle the crucible was located at the base of the furnace shown in fig. 1. When the required temperature was reached the crucible was raised into the position shown, rotated through 180° and lowered to the base of the furnace. The seed thus XI
PLATINUM CRUCIBLE
0 0 0
0 0
ALUMINA
0
0
SILICON ELEMENTS
II’tONIC SHAFT & SUPPORT
Fig. 1.
Schematic arrangement of the furnace and reversal facilities used in seeding molten salts.
—
5
459
SEEDED GROWTH OF GARNET FROM MOLTEN SALTS TABLE
I
Results of garnet growth using the reversal technique Melt No. composition (g)
Soak temperature (°C)
Initial rotation temperature (°C)
Final rotation temperature (°C/hr)
Cooling rate (°C/hr)
Y
203320 Fe203—480
Comments
No evidence of seeding
1
PbO—845 PbF2—750 B203—52
1280
1245
1045
0.5
No growth on the base of the crucible
2
As above
1280
1230
1070
0.65
3
As above
1280
1210
1070
0.5
No evidence of seeding, neglible growth on base Seeding occurred
4
As above
1280
1210
1070
1.0
1200
1070
1000
0.5
Bi203—750 Fe2O3—530 5
CaCo3—310 V205—l 15 PbO—290
YAG seed dissolved aluminium doped YIG obtained No seeding attempted Ferrite phase restricted to crucible base 25 g garnet crystal obtained
3. Results Seeded YIG was obtained with the conditions as shown in No. 3 of table 1. During the initial heating and slow cooling period, which permits the earlier stages of growth to be deposited on the base of the crucible, the seed was located as shown in fig. 2a. At 1210 °Cthe crucible was rotated to position 2b, cooled to 1070 °C,rotated to position 2c and cooled to room temperature. Figs. 3a andrespectively. 3b show theAs12indicated g seed and the resulting 57 g crystal in No. 4, table 1, which was an attempted composite growth, the YAG seed dissolved resulting in aluminium substituted YIG crystals. The result of run No. 5 demonstrated the effectiveness of this technique in reducing the number of nucleation sites created by calcium ferrite during CVB growth. The ferrite crystals deposited in the region 1200—1080 °Cwere almost cornpletely restricted to the crucible base and the garnet yield to the lid, 4. Experimental procedure
A number of YIG crystals have been pulled from the melt using the apparatus shown in fig. 4, this system
3). was developed by Linaresi ~2) and later Kestigian Pulling rates, which were monitored by by a linear potentiometer, as low as 0.002 inch per hour were achieved from the difference in linear movement produced by the action of the gears on the threaded columns shown in the figure. The YIG seeds were cut from crystals grown from PbO—PbF 2 melts and the YAG seeds from Czochralski-grown boules. The melt composition and temperatures were similar to those described by Kesti3). gian 5. Results A section of a <110> pulled crystal is shown in fig.5. The sample which demonstrates the differences in domain pattern, consists of three regions; (a) the left hand section, which is reddish-brown in colour, is the seed; (b) an intermediate yellow band adjacent to the (110) interface, is the material deposited during the necking period and (c) the right hand green coloured region is the pulled material. The variation in colour from the yellow to red may be indicative of Fe2 + content associated with increasing silicon content as shown by Lefever and Chase4). The result of pulling YIG from a <111> YAG seed is shown in fig. 6. Unlike
XI-5
460
G. A. BENNETT
NIMONIC FRAME
SA ~ SOLUTION
PLATINUM CRUCIBLE WITH WELDED LID (~Q)
Fig. 2.
ALUMINA SUPPORT CRUCIBLE
(b)
AXIS
(~c)
Location of the garnet seed relative to the melt during the growth cycle.
mini
iiui~ WORM WHEEL DRIVEN FROM FLEXIBLE DRIVES
‘~
PULLING MECHANISM
J
~
——---j!j!J~ ~
ROTATION (a)
_____________________
MECHANISM
4F~
PLATINUM ROD & __________ CRUCIBLE \\\
I
~
V77//
LfJ
y///A\
Li u
~-LINEAR POTENTIOMETER TORECORDER
f”j—~ II \~s\~\’
CRUCIBLE SUPPORT
FIREBRICK
(b) Fig. 3.
j
!IHlI~
Photograph of before (a) and after (b) seeded growth ofYIG.
XI
Fig. 4.
—
5
Mechanical gear arrangement and furnace used to pull crystals from the melt.
SEEDED GROWTH OF GARNET FROM MOLTEN SALTS
Fig. 5.
461
Photomicrograph of a YIG crystal illustrating the junction of the seed and pulled material, with growth parallel to the (110) interface.
the YIG—YIG system where little or no material was dissolved from the seed by the flux, the YAG was preferentially etched giving rise to large grained polycrystalline growth. Recent experiments have shown that annealing the YAG prior to growth, eliminates the cracking which can be seen in fig. 6. The etching of the seed created a 25 pm junction at the interface which consists of a transition from YAG through aluminium doped YIG to pure YIG.
______
______
6. Conclusion
Fig. 6.
The rotation technique eliminates thermal shocking of the crystals and permits economical use of the remaining solution. Seeding the melt offers the operator some means of control over the nucleation process which would be relevant with high purity melts. The
Photograph of a pulled YIG crystal from a YAG seed,
XI
—
5
462
G. A. BENNETT
initial results obtained on the composite structure indicate that such a system may be realised within the near future.
the Science Research Council for their financial support of this project. References
Acknowledgment The author would like to express his appreciation to
1) 2) 3) 4)
XI-5
R. C. Linares, J. Am. Ceram. Soc. 45 (1962) 307. R. C. Linares, J. App!. Phys. 35 (1964) 433. M. Kestigian, J. Am. Ceram. Soc. 50 (1967) 165. R. A. Lefever and A. B. Chase, J. Chem. Phys. 32(1960)1575.