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The effect of local cooling and accelerated crucible rotation on the quality of garnet crystals
566
Journal of Crystal Growth 13114 (1972) 566-570 © North-Holland Publishinc Co.
THE EFFECT OF LOCAL C O O L I N G A N D ACCELERATED CRUCIBLE R O T A T )N ON THE QUALITY OF GARNET CRYSTALS
W. TOLKSDORF and F. WELZ Philips Forschungslaboratorimn Hamburg GmbH, 2 Hamburg 54, Germany
To characterize growth and properties of yttrium iron garnet single crystals a detailed description of gr wth conditionsis given includingtemperature distribution in the fluxed melt in terms of isotherms. The inflt nee of local cooling and the accelerated crucible-rotation technique, recently published by Scheel and St ulzDuBois, are described. Growth features on crystal faces are discussed, and analytical data about impu ities are summarized.
1. Introduction In a paper recently published by Van Uitert et al. t) the following statement can be read: "The dynamics of growth of rare earth iron garnets are somewhat unusual. It is quite possible to obtain orthoferrite where garnet is expected and vice versa. Nucleation conditions and growth rates are of major importance... It is of interest that there is only a 50-50 chance that pure ,,ttrium iron garnet (YIG) will form in the course of ~t~ual flux run.'" \Ve mu~t underline this statement. Sometimes we lind ,ingle crystah of magnetopl ttmbite (PbFe~.~Ot ,~) or yttrium oxyttuoride (Y.~oO~6F28) besides or instead of YIG IY3Fe O~_,). Because of this uncertainty it is the aim of this contribution to carefully describe growth conditmns ar d properties of YIG single crystals. 2. Experimental Our standart composition of the melt similar to the composition us~.d by Grodkiewicz et al. 2) is: PbO 36.3; PbF, 27.0: BzG j 5.4: CaO 0.1; Fe20 3 3.4 and Fe20 3 17.38 and Y203 10.42 ¢in mole?;i). The procedure we use has been described already by Tolksdorf3). A crucible in a top heated chamber furnace can be turned around its horizontal axis to separate the bottom grown crystals from the flux. Temperature stability is of the order of +0.01 ~C at the bottom of the platinum crucible which is thermally isolat.d l-,y an aluminasilicate ceramic fibre aed an alumina ceramic support cru:ible. To local!ze nu:leation an ali..iRa ceramic XI!
pipe cooled by a pressure stabilized air stream is pressed on to the center of the bottom of the platinum crucible. To apply the accelerated crucible-rotati0n technique (ACRT) described by Scheel et al.4), the support crucible is mounted on an alumina shaft. As long as the crucible is rotated around this vertical axis, the horizontal axis has to be withdrawn. The temperature distribution was measured inside the melt in steps of 5 mm with three thermocouples: m he centre, in 16 mm and 32 mm distance from the centre, respectively. During the measurements the crucible could not be rotated. The isotherms obtained arc given in tig. I assuming a symmetrical and steady dhtribution. The shape of the isotherm is very sensiti,.e to the form of the crucible and its surroundings. Th, ,e is no evidence of convection within the flux, beca~ ~e a filling with alumina granulate shows a similar te~ ~erature distribution. No temperature oscillations ~ -ger than the temperature stability o f t h e order of +0. 'C could be detected. The effect of the cooling fin: : at the bottom of the platinum crucible is limited an area with a radius of about 15 mm around the c tre Outside of this zone there is still competitive n :cation. Fig. 2 shows a typical result of a I I00,,. un Note that nucleation is essentially o f o n e crystal the cooling finger. Nucleation occurs at Ii00 + 10 a~ has been measured by many runs around this tc :~erature; the undercooling is less than the given tc :~erature range of + 10 "C. The cooling rate was t .'/h. the cooling air stream was 160 l/h. At 1010 _+ ,I 'C the crystal was taken out of the flux by turni~ the -
3
EFFECT
OF COOLING
AND CRUCIBLE
ROTATION
ON QUALITY
OF G A R N E T
CRYSTALS
/ ,1172o
/
1 :::::~: ~ :::'-~ ~ ~: ~1.':1::~:::1,. : ..:::k::::::;:;* ::ii :;;::::::: ::i::i:::~:::;::':':: / •< . ' . ~ :::::::::::::::'~:: ~ ! ~ i :~:~:~.-':':~:: ~i~..'.":~.':'-~'.:~!:i~ ~ ~~!~;~! ~.:.-'i~!: /
/
~~~!:i:i:i:~!:!:~::'::::::::::::":':':':':':'~':"" : i :i~:.:' : i : i'!~'iii:'i::.'i.:!i::: :..:::::::::, '::.:-"" .: ~:~:!:~:i:~:. '.:!:!:!:~./:.!:?: i'~: :":'~:i:i:!~i . . . . ;.:.::::~:~: :i:!:~:i:~::::-"....:!: ::~'-::-::i:i?-:::::~~~~ ~:k":~::: I / ~.:!:~ ~ ' : : ~ ~ : : I • ~:i::-.'.',,-..""''~:.'.! ''~ ~ ~ ' ~ : ~ ~ " ? ? . ~ ~ I/
F IIII II ' = '' . . . . . . . . .
a)
--~
T:1150°
c)
Scale 1:1 J
l'. ~~:: iiili gi ::iiiiii:::: ....
air 170 I I h Fig. I.
/
air O l l h
~.1172°
.....::::::::::::::::::::::::::" •".'.:',. ....
,"I
b)
Temperature (>C) distribution in the melt. (a, b) standard mountilg, (c, d) mounting for ACRT'~).
XII - 3
567
~68
W. T O L K S D O R F A N D F. W E L Z
Fig. 2.
Central YIG crystal (scale in ram).
Fig. 4. Growth centre on a (110) face of YIG. Magnilicati0n > 1000.
Fig. 3,
Yield of YIG crystals grown by A C R T "t) (scale in mm).
crucible around its horizontal axis. In many runs with the given composition YIG was the only phase to crystaUize in the temperature range mentioned. In one ,:ase, one magnetoplumbite single crystal of substantial size grew at the center of the bottom, while the other crystal~ ~ ere YIG. Sometimes surface crystals were present. Thi~ indicates that there is not always equilibrium in the melt as a ~hole without stirring. After cooling with ~pced of 50 C/h (this is normal speed after finishir.g crxstal growth) an analysis of the solidified melt had shown different zones of composition. To apply a stirring effect by A('=?,T '*) the crucible x~a~ ahcrnately rotated (50 rpm) ~.no .~topped around the vertical axis. In this case there i~ ~ .','.rong tendency
for nucleation at the edge of the bottom of the crucible, as shown in tig. 3, when no cooling air stream i~ applied. The crystals had fewer inclusiops, the yield ~vas larger (up to 45 wt ~/~ of the input) by this method, and no surface crystals or crystals of other phases vere present.
3. Characterization The growth features on the crystal faces are tht as in the ur, qtirred case. As reported by Lefew ChaseS), Komatsu and Sunagawa 6) and others, g spirals can be seen on (110) and (21 I) faces ,~; crystals. Under our standard conditions often x.c spirals, sometimes only one, cover (I 10) facc~ than 1 cm 2. The centre of such a growth figure i, in fig. 4 on a photomicrograph with differential fere,ce contrast like that used by Nomarski= height of the steps varied between 50 and 150 A regular were the growth features found on (I 10 of rare earth orthoferrite crystals (R.E.FeO~)
XII - 3
itue tnd ~vth IG fe~ gcr ~e~ tcrIhe 10rc aces hich
E F F E C T OF C O O L I N G
AND CRUCIBLE
ROTATION
ON QUALITY
OF G A R N E T
CRYSTALS
569
9 G H z ) we normally find the following impurities given in formula units (,t~lll
~11-'~
lit
!11
~
II~'IV,.'~
¥ 3 -a-bl"O at'-abue5 - c - d U e c~3ld ~'.Jl 2 - e - xFe)
Pb: a = 0.012 to 0.019; Ca: b = 0.0008 and less; Fe 2+ : c = 0.005 to 0.01 ; Si: d = 0.001 to 0.003; F: e = 0.010 to 0.016. F o r analysis only optically clear specimens were used. The molar concentrations of lead and fluorine were in the same range. Fe2+-values were measured by cerimetric analysis. Less than 0.00001 platinum per formula unit was found in the crystals. Values of Pb and Fe 2÷ decrease slightly after high temperature annealing (13 hr, 1300 ='C in O2) of small pieces (diameter ~. I m m l o f Y I G . The lattice constant ao for YIG was determined by a method described by Winkler et ai. t o). with an accuracy of 4- 3 × 10 -4 ,~, at 22 ~'C. The values varied from run to run from 12.3745 A to 12.3776 .&. After high temperature annealing of powdered crystals we found for all samples ao = 12.3763 4- 0.0005 A and the Fe 2~ content dropped under the detection limit of 0.002 per Fig. 5. Growth centre on a (llO) face of (Smo.ssTbo..~sFeOa). formula unit. Magnili~;ation ,: 180. 4. C o n c l u s i o n were grown by the same technique (fig. 5) where the hei,_,ht of the steps varied from 250 A near the centre to 15() ~, near the edge o f the face. The measurement wa, carried out by multibeam interferometry after To ~,nskiS). Very often the center of the growth spiral is : 'at the edge of the face. This may be due to the fac that the slip direction of the dislocation diffe~ ln, ly within about 5 ° from the normal of the face as w~ ~und by a photoelastic method in agreement with th -suits of Prescott and Basterfield 9) on G d 3 G a 5Or 2 an Sm3GasO~: garnets which were grown by the ~a ' technique as YIG. By etching it could be proved d~ there is always a dislocation - or a cluster of di cations - in the center of the growth feature. !) ~cation density was often fotmd to he less than I( .,t -2 aaracterization of YIG-crystals often is only given b.,, qe low linewidth value of the magnetic resonance. In ur crystals which have a very low linewidth (AH le, than 0 . 5 0 e , AH~: less than 0.16 Oe measured at
With A C R T equilibriunl ,~ithin the whole melt can be achieved, a,ad no competitive phase crystallizes. Crystallization can be localized within a certain area by applying an air cooler. The influence of the cooler is diminished by the size of the growing crystal. Crystals grown by A C R T have very few flux inclusions and cracks. Cubes with (I ! I), (110) and (211) faces as large as 12 x 12 x 12 mm free of cracks and inclusions could be produced. There is no significant difference of growth featm-es and impurities between crystals grown with and without ACRT. The low numbers of groxvth centers and the regular form of growth features on crystal faces indicate constant growth conditions.
References I) L. G. Van Uitert, W. A. Bonnet', W. H. Grodkiex~icz, L. Pietroski and G..1. Zydzik, Mater. Rcs. Bull. 5 (;970'J 825. 2) W. H. Grodkiexvicz, E. F. Dearborn and t.. G. V:m Uitcrt. in: Crystal Growth, Ed. H. S. Peiscr (Pergamon, Oxford, 1967) p. 441.
Xil - 3
570
w.
~OLXSDORF
3) W. Tolksdorf, J. Crystal Gro~th 3, 4 (1968) 463. 4) H. J. Scheel and E. O. Schulz-DuBois, J. Crystal Growth 8 (1971) 304. 5) R. A. Lefex~r and A. B. Chase, J. Am. Ceram. $oc. 45 (1962) 32. 6~ H. Komatsu and J. Sunagawa, Miner. J. (Tokyo)4(1964)203.
ASD
V,
... W I / L•. .Z
~
•
:
7) W. Lang, Zeissinformationen 70 (1968,) 114. 8) W. Miiller, Leitz, Mitteilungen aus dem Labor, Anwen~ ang Mikro, Nr. 27, 1968. 9) M.J. Prescott and J. Basterfi¢ld, J. Mater. Sci. 2 (1967) ;83. 10) G. Winkler, P. Hansen and P. Hoist, to be publish, i ~ Philips Res. Rept: (1972).
Xll - 3
Journal of Crystal Growth 13114 (1972) 566-570 © North-Holland Publishinc Co.
THE EFFECT OF LOCAL C O O L I N G A N D ACCELERATED CRUCIBLE R O T A T )N ON THE QUALITY OF GARNET CRYSTALS
W. TOLKSDORF and F. WELZ Philips Forschungslaboratorimn Hamburg GmbH, 2 Hamburg 54, Germany
To characterize growth and properties of yttrium iron garnet single crystals a detailed description of gr wth conditionsis given includingtemperature distribution in the fluxed melt in terms of isotherms. The inflt nee of local cooling and the accelerated crucible-rotation technique, recently published by Scheel and St ulzDuBois, are described. Growth features on crystal faces are discussed, and analytical data about impu ities are summarized.
1. Introduction In a paper recently published by Van Uitert et al. t) the following statement can be read: "The dynamics of growth of rare earth iron garnets are somewhat unusual. It is quite possible to obtain orthoferrite where garnet is expected and vice versa. Nucleation conditions and growth rates are of major importance... It is of interest that there is only a 50-50 chance that pure ,,ttrium iron garnet (YIG) will form in the course of ~t~ual flux run.'" \Ve mu~t underline this statement. Sometimes we lind ,ingle crystah of magnetopl ttmbite (PbFe~.~Ot ,~) or yttrium oxyttuoride (Y.~oO~6F28) besides or instead of YIG IY3Fe O~_,). Because of this uncertainty it is the aim of this contribution to carefully describe growth conditmns ar d properties of YIG single crystals. 2. Experimental Our standart composition of the melt similar to the composition us~.d by Grodkiewicz et al. 2) is: PbO 36.3; PbF, 27.0: BzG j 5.4: CaO 0.1; Fe20 3 3.4 and Fe20 3 17.38 and Y203 10.42 ¢in mole?;i). The procedure we use has been described already by Tolksdorf3). A crucible in a top heated chamber furnace can be turned around its horizontal axis to separate the bottom grown crystals from the flux. Temperature stability is of the order of +0.01 ~C at the bottom of the platinum crucible which is thermally isolat.d l-,y an aluminasilicate ceramic fibre aed an alumina ceramic support cru:ible. To local!ze nu:leation an ali..iRa ceramic XI!
pipe cooled by a pressure stabilized air stream is pressed on to the center of the bottom of the platinum crucible. To apply the accelerated crucible-rotati0n technique (ACRT) described by Scheel et al.4), the support crucible is mounted on an alumina shaft. As long as the crucible is rotated around this vertical axis, the horizontal axis has to be withdrawn. The temperature distribution was measured inside the melt in steps of 5 mm with three thermocouples: m he centre, in 16 mm and 32 mm distance from the centre, respectively. During the measurements the crucible could not be rotated. The isotherms obtained arc given in tig. I assuming a symmetrical and steady dhtribution. The shape of the isotherm is very sensiti,.e to the form of the crucible and its surroundings. Th, ,e is no evidence of convection within the flux, beca~ ~e a filling with alumina granulate shows a similar te~ ~erature distribution. No temperature oscillations ~ -ger than the temperature stability o f t h e order of +0. 'C could be detected. The effect of the cooling fin: : at the bottom of the platinum crucible is limited an area with a radius of about 15 mm around the c tre Outside of this zone there is still competitive n :cation. Fig. 2 shows a typical result of a I I00,,. un Note that nucleation is essentially o f o n e crystal the cooling finger. Nucleation occurs at Ii00 + 10 a~ has been measured by many runs around this tc :~erature; the undercooling is less than the given tc :~erature range of + 10 "C. The cooling rate was t .'/h. the cooling air stream was 160 l/h. At 1010 _+ ,I 'C the crystal was taken out of the flux by turni~ the -
3
EFFECT
OF COOLING
AND CRUCIBLE
ROTATION
ON QUALITY
OF G A R N E T
CRYSTALS
/ ,1172o
/
1 :::::~: ~ :::'-~ ~ ~: ~1.':1::~:::1,. : ..:::k::::::;:;* ::ii :;;::::::: ::i::i:::~:::;::':':: / •< . ' . ~ :::::::::::::::'~:: ~ ! ~ i :~:~:~.-':':~:: ~i~..'.":~.':'-~'.:~!:i~ ~ ~~!~;~! ~.:.-'i~!: /
/
~~~!:i:i:i:~!:!:~::'::::::::::::":':':':':':'~':"" : i :i~:.:' : i : i'!~'iii:'i::.'i.:!i::: :..:::::::::, '::.:-"" .: ~:~:!:~:i:~:. '.:!:!:!:~./:.!:?: i'~: :":'~:i:i:!~i . . . . ;.:.::::~:~: :i:!:~:i:~::::-"....:!: ::~'-::-::i:i?-:::::~~~~ ~:k":~::: I / ~.:!:~ ~ ' : : ~ ~ : : I • ~:i::-.'.',,-..""''~:.'.! ''~ ~ ~ ' ~ : ~ ~ " ? ? . ~ ~ I/
F IIII II ' = '' . . . . . . . . .
a)
--~
T:1150°
c)
Scale 1:1 J
l'. ~~:: iiili gi ::iiiiii:::: ....
air 170 I I h Fig. I.
/
air O l l h
~.1172°
.....::::::::::::::::::::::::::" •".'.:',. ....
,"I
b)
Temperature (>C) distribution in the melt. (a, b) standard mountilg, (c, d) mounting for ACRT'~).
XII - 3
567
~68
W. T O L K S D O R F A N D F. W E L Z
Fig. 2.
Central YIG crystal (scale in ram).
Fig. 4. Growth centre on a (110) face of YIG. Magnilicati0n > 1000.
Fig. 3,
Yield of YIG crystals grown by A C R T "t) (scale in mm).
crucible around its horizontal axis. In many runs with the given composition YIG was the only phase to crystaUize in the temperature range mentioned. In one ,:ase, one magnetoplumbite single crystal of substantial size grew at the center of the bottom, while the other crystal~ ~ ere YIG. Sometimes surface crystals were present. Thi~ indicates that there is not always equilibrium in the melt as a ~hole without stirring. After cooling with ~pced of 50 C/h (this is normal speed after finishir.g crxstal growth) an analysis of the solidified melt had shown different zones of composition. To apply a stirring effect by A('=?,T '*) the crucible x~a~ ahcrnately rotated (50 rpm) ~.no .~topped around the vertical axis. In this case there i~ ~ .','.rong tendency
for nucleation at the edge of the bottom of the crucible, as shown in tig. 3, when no cooling air stream i~ applied. The crystals had fewer inclusiops, the yield ~vas larger (up to 45 wt ~/~ of the input) by this method, and no surface crystals or crystals of other phases vere present.
3. Characterization The growth features on the crystal faces are tht as in the ur, qtirred case. As reported by Lefew ChaseS), Komatsu and Sunagawa 6) and others, g spirals can be seen on (110) and (21 I) faces ,~; crystals. Under our standard conditions often x.c spirals, sometimes only one, cover (I 10) facc~ than 1 cm 2. The centre of such a growth figure i, in fig. 4 on a photomicrograph with differential fere,ce contrast like that used by Nomarski= height of the steps varied between 50 and 150 A regular were the growth features found on (I 10 of rare earth orthoferrite crystals (R.E.FeO~)
XII - 3
itue tnd ~vth IG fe~ gcr ~e~ tcrIhe 10rc aces hich
E F F E C T OF C O O L I N G
AND CRUCIBLE
ROTATION
ON QUALITY
OF G A R N E T
CRYSTALS
569
9 G H z ) we normally find the following impurities given in formula units (,t~lll
~11-'~
lit
!11
~
II~'IV,.'~
¥ 3 -a-bl"O at'-abue5 - c - d U e c~3ld ~'.Jl 2 - e - xFe)
Pb: a = 0.012 to 0.019; Ca: b = 0.0008 and less; Fe 2+ : c = 0.005 to 0.01 ; Si: d = 0.001 to 0.003; F: e = 0.010 to 0.016. F o r analysis only optically clear specimens were used. The molar concentrations of lead and fluorine were in the same range. Fe2+-values were measured by cerimetric analysis. Less than 0.00001 platinum per formula unit was found in the crystals. Values of Pb and Fe 2÷ decrease slightly after high temperature annealing (13 hr, 1300 ='C in O2) of small pieces (diameter ~. I m m l o f Y I G . The lattice constant ao for YIG was determined by a method described by Winkler et ai. t o). with an accuracy of 4- 3 × 10 -4 ,~, at 22 ~'C. The values varied from run to run from 12.3745 A to 12.3776 .&. After high temperature annealing of powdered crystals we found for all samples ao = 12.3763 4- 0.0005 A and the Fe 2~ content dropped under the detection limit of 0.002 per Fig. 5. Growth centre on a (llO) face of (Smo.ssTbo..~sFeOa). formula unit. Magnili~;ation ,: 180. 4. C o n c l u s i o n were grown by the same technique (fig. 5) where the hei,_,ht of the steps varied from 250 A near the centre to 15() ~, near the edge o f the face. The measurement wa, carried out by multibeam interferometry after To ~,nskiS). Very often the center of the growth spiral is : 'at the edge of the face. This may be due to the fac that the slip direction of the dislocation diffe~ ln, ly within about 5 ° from the normal of the face as w~ ~und by a photoelastic method in agreement with th -suits of Prescott and Basterfield 9) on G d 3 G a 5Or 2 an Sm3GasO~: garnets which were grown by the ~a ' technique as YIG. By etching it could be proved d~ there is always a dislocation - or a cluster of di cations - in the center of the growth feature. !) ~cation density was often fotmd to he less than I( .,t -2 aaracterization of YIG-crystals often is only given b.,, qe low linewidth value of the magnetic resonance. In ur crystals which have a very low linewidth (AH le, than 0 . 5 0 e , AH~: less than 0.16 Oe measured at
With A C R T equilibriunl ,~ithin the whole melt can be achieved, a,ad no competitive phase crystallizes. Crystallization can be localized within a certain area by applying an air cooler. The influence of the cooler is diminished by the size of the growing crystal. Crystals grown by A C R T have very few flux inclusions and cracks. Cubes with (I ! I), (110) and (211) faces as large as 12 x 12 x 12 mm free of cracks and inclusions could be produced. There is no significant difference of growth featm-es and impurities between crystals grown with and without ACRT. The low numbers of groxvth centers and the regular form of growth features on crystal faces indicate constant growth conditions.
References I) L. G. Van Uitert, W. A. Bonnet', W. H. Grodkiex~icz, L. Pietroski and G..1. Zydzik, Mater. Rcs. Bull. 5 (;970'J 825. 2) W. H. Grodkiexvicz, E. F. Dearborn and t.. G. V:m Uitcrt. in: Crystal Growth, Ed. H. S. Peiscr (Pergamon, Oxford, 1967) p. 441.
Xil - 3
570
w.
~OLXSDORF
3) W. Tolksdorf, J. Crystal Gro~th 3, 4 (1968) 463. 4) H. J. Scheel and E. O. Schulz-DuBois, J. Crystal Growth 8 (1971) 304. 5) R. A. Lefex~r and A. B. Chase, J. Am. Ceram. $oc. 45 (1962) 32. 6~ H. Komatsu and J. Sunagawa, Miner. J. (Tokyo)4(1964)203.
ASD
V,
... W I / L•. .Z
~
•
:
7) W. Lang, Zeissinformationen 70 (1968,) 114. 8) W. Miiller, Leitz, Mitteilungen aus dem Labor, Anwen~ ang Mikro, Nr. 27, 1968. 9) M.J. Prescott and J. Basterfi¢ld, J. Mater. Sci. 2 (1967) ;83. 10) G. Winkler, P. Hansen and P. Hoist, to be publish, i ~ Philips Res. Rept: (1972).
Xll - 3