CA1054903A - Method and device for growing crystals - Google Patents
Method and device for growing crystalsInfo
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- CA1054903A CA1054903A CA207,461A CA207461A CA1054903A CA 1054903 A CA1054903 A CA 1054903A CA 207461 A CA207461 A CA 207461A CA 1054903 A CA1054903 A CA 1054903A
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Abstract
ABSTRACT
A method of growing crystals in a crystallisation vessel by the periodic deposition of the crystal material from a trans-porting phase of the material in the vessel and by the partial retransfer of crystal material deposited at the site of crystal growth to the transporting phase. During the periods of deposition and retransfer, a net amount of material is deposited at the site of the crystal growth and these periods are carried in such an alternation that the formation of parasitic seeds is suppressed.
The quantity of crystal material deposited on a perfect seed crystal at the site of crystal growth is larger in any period that the quantity of the crystal material retransferred to the transporting phase so long as the grown crystal is perfect. However, the quan-tity of the crystal material retransferred to the transporting phase is larger in any period than the quantity of deposited crystal material as soon as and as long as the crystal to be grown shows structural defects.
A method of growing crystals in a crystallisation vessel by the periodic deposition of the crystal material from a trans-porting phase of the material in the vessel and by the partial retransfer of crystal material deposited at the site of crystal growth to the transporting phase. During the periods of deposition and retransfer, a net amount of material is deposited at the site of the crystal growth and these periods are carried in such an alternation that the formation of parasitic seeds is suppressed.
The quantity of crystal material deposited on a perfect seed crystal at the site of crystal growth is larger in any period that the quantity of the crystal material retransferred to the transporting phase so long as the grown crystal is perfect. However, the quan-tity of the crystal material retransferred to the transporting phase is larger in any period than the quantity of deposited crystal material as soon as and as long as the crystal to be grown shows structural defects.
Description
~S~3 The invention relates to a method of growing crystals in a crystalli~ation vessel by the periodic deposition of the crystal material from a transporting phase of the crystal material present in said vessel and by the partial retransfer of crystal material de- -posited at the site of the crystal growth to said phase, in which said phase is separated from the deposition site and in which in the periods of deposition and retransfer ;
a net amount of material is deposited at the site of the crystal growth.
The method may be used in heterogeneous pro-cesses in which a finite temperature range for the crys-;~ tal growth is available, such as subliminations, chemical transport reactions in the gaseous phase and dissolving lS processes. It is recommendable, in particular with a view to~the growth of crystals o~ comparatively large dimensions, when the preferred range of applications l;es in the region of the gas-solid state reactions.
~ The transporting phase of the crystal material may consist, for example, of a vapour of the crystal material, possibly mixed with a carrier gas, of a solution of the crystal material in a liquid or a super- ;
critical gas or of decomposable compounds of the crystal ' '~', .,.:
: ,: ':: .
' ~ - 2 - ~ ~
~S~3 -material or the col~ponents thereof, for example, in the form of a gas or vapour, or of a solution of these ccm~
ponents in a liquid or a super-critical gas.
A problem occurring in such methods of manu-facturing crystals of comparati~ely large dLmensions is to cause onl~ one or a small nu~ber of seed crystals to grcw and to suppress the further formation and the growth of parasitic seed crystals or crystallites, respectively, so as to obtain in this manner only one crystal or a few crystal bod~es separated from each other.
It is suggested in our Canadian Patent 805,630, which issued on February 4, 1969/ to cause a seed crystal which has been gr3wn in any arbitrary manner and placed in a crystallisation vessel bo continue growing in such manner that crystal material is periodically deposited from a transporting phase of the crystal ma-terial and is p~rtially retransferred to the transporting phase so that the seed crystal can gnow bu~ smaller crystal parts ~ disapFear again. It is kncwn that in the presence of i 20 larger crys~als smaller crystals grow with more difficulty and, in the time in which crystal material is partly retransferred to the transporting phase, decrease even to ¦ a strcrlger e~tent than th~y can form in the time in w~Lich ~he deposition takes place of crystal material at the site of the grcwth, so that smaller crystals disappear entirely after a ew periods. ~ -. ~- ~ . .
The retransfer of a part of tb~ crystal material ` .
~' ; . , PHD. 73-092.
deposited at the site of the crystal growth to the trans-porting phase can be effected in various manners, ~or example, by periodically varying the concentration of the transporting phase or by building up a unipolar temperature field in -~he crystallisation vessel with a temp~rature gra~ient the dir~ction of which is period-:: .ically varied. m e temperature gradient in the crystalli- ..
sation vessel is adjusted in such manner that the b~mpe-rature of the circumference of ~he crystallisation vessel is periotically increased and decreased relative to the temperature of the centre or in that a rotationally~: .
symmetric crystallisation ~7essel is rotated in a tempera- .
ture drop which extends at riqht angles to the axis of the vessel and is co~stant with time~ The dNration of a . 15 period correspc~ds to ~he tim~! of rotation of the vessel.
In this method it can often not be est~blished whether the seed crystal was d.amaged or whether the ~ .
:. crystal is ~ree of structural defects to a sufficient ~ extent. In such cases the seed crystal has bo be dis-:, 20 solved again and the crystallisation vessel be provided ~ :. . : -with a new seed cryst~
Mbrec~7er, with the so far known methods of crystal growing and with the method described in our Canadian Patent 805,630 for reversing the temperature gradient in the crystallisation vesæ l it is oft~n not possible to ~orm large single crystals . , ~'.
, ~'' ,:, , _ 4 _ with -Few structural defects. Furthermore, it is not pos-sible with the known methods, in systems favourable for the nucleation to realise the nucleation of only one ; crystal in the previously determined site.
This holds, for example, for the sublimation system HgI2.
Especial'ly in the system HgI2 the extra dif-ficulty occurs that the material may be present in two modifications and that the probability of nucleation of a crystal of the red modification showing no twin forma- ' ' tion is very small. Moreover, with the compound HgI2 the surface nucleation above a given size of the crystal '' seems to occur with greater difficulty. The crysta1 then shows twin formation or forms a coarse mosaic structure. The result in both cases is that the material is hardly useful for certain technical applications, for example, for use as a spectrometer crystal.
It is the object of the invention to manufac-ture large perfect s;ngle crystals also from systems which are very favourable for the nucleation.
. ....................................................................... .
~ The invention is based on the recognition that .
' the formation in situ of a perfect seed crystal is also possible in systems which are very favourable for the 'nucleation when the seed selection is carried out so keenly that only the dynamically most stable seed -which is no doubt a readi'ly ordered no twin formation showing single crystal - has a possibility of survival.
, -~ PHD 73-092 ~5~9~3 The invention is furthermore based on the recog-nition that a perfect crystal structure, in which thus, `~ for example, twin formation and mosaic structure are avoided, can also be realized for orystals of compara-tively large dimensions when the selection does not ex-tend only to the potential parasitic seeds but also con-tinuously prevents that the growing crystal begins to show the said structural defects.
According to the invention this is achieved - ~ -in that the processes of the periodic deposition of the crystal material from the transporting phase and the . , .
retransfer to said phase are carried out in such an alternation that the formation of parasitic seeds is suppressed and that the quantity of the crystal material . ~ .
; 15 deposited on a per~ect seed crystal in a given site oF
the crystal growth is larger in any period than the amount of the crystal material retransferred to the transporting phase so long as the grown crystal is per-` fect and that the amount of the crystal material retrans-ferred to the transporting phase is larger in any period than the amount of the deposited crystal material as soon as and as long as the crystal to be grown shows - structural defects.
The seed crystal is preferably formed in the crystallisation vessel.
The advantages resulting from the method ac-cording to the invention consist in particular in that ' . . .
'~
~.
::
: .... ,~ , .
it is possible to stimulate a system having different modifications in the direction of the stable modifica-tion. It is possible in systems favourable for the nucleation to cause only one single crystal to nucleate in the previously determined site and to grow it. It is possible to suppress the development of crystal de-fects, such as twin structures and mosaic structures, in which as a further advantage it may be mentioned that also the size of the crystals grown by means of the method according to the invention can advantageously be influenced with respect to the crystals grown by means ~-of the known methods.
The method according to the invention naturally also presents the possibility in systems having different modifications to favour the unstable modification under certain growth kinetic conditions by an adaptation of the free parameters.
For the growth of HgI2 single crystals the method according to the ;nvention presents possibilities how the system ;s stimulated in the direction of the stable modification and structural defects such as formation of twin structures and mosaic structures can be suppressed.
The recognitions obtained for the system HgI2 - 25 may of course also be applîed to other systems.
The invention will now be described in greater detail with reference to the accompanying drawings which PHD 73-09~
~.~5~3 show various embodiments of a device for carrying out the method according to the invention, and in which:
Fig. 1 is a sectional view of a device for growing crystals by means of the method according to the invention, Figs. 2 and 3 are sectional views through va-riations of the device shown in Fig. 1, and Fig. 4 shows a diagrammatic temperature-time curve for the performance of the method according to the invention.
Fig. 1 shows a device with an axially symme-tric crystallisation vessel, which is rotatable and is present within an oven system consisting of two dome-shaped partsi the dome-shaped part 4 having a semi-spherical head and a cylindrical trunk may be heated by ~; means of a heating coil 9. The outer dome-shaped part 5 consisting of a glass which can withstand temperature variations serves to reduce thermal losses by convection.
By means of a wire loop 6 a bipolar temperature field is built up within the dome-shaped part 4 in which the crystallisation vessel 1 which is secured on a hollow tube can be rotated. Present in the hollow tube 13 are - ~:
a themocouple 10 and a tube 11 for cooling the centre of the crystaliization vessel. Within the circumference ; 25 of the crystallisation vessel 1 crystal starting ma-terial (source material) 2 is present. The quartz ~
glass dome-shaped part 4 is arranged on a temperature- :
resistent base plate 7; the glass dome-shaped part 5 is .. .. . . .. . . .. . . .
~1:35~3 present on a table 8 consisting of a temperature-resistent material. Below the bottom of the crystallisation vessel 1 are arranged two further thermo-couples lOi a radiation , , screen 12 is also present below the crystallisation ves-sel. The hollow tube 13 to which the crystallisation ' vessel 1 is rigidly connected can be rotated by a motor ,`~ not shown.
In this device, temperatures of 700C can be reached.
In the method according to the invention it deals with a process in which at least two defined re-gions of the circ,umference of the crystallisation ves-sel 1 are heated simultaneously and the temperature of -' the circumference is increased and decreased periodi-cally relative to the temperature of the centre by ro-tation of the crystallisation vessel 1, the temperature of the centre - of the site of the crystal growth - be ing kept not constant but being reduced intermittently.
The defined hot regions o~ the c;rcumference of the .~
crystallisation vessel 1 are formed by a locally fixed , ' heating by means of a wire loop 6.
When the rotationally symmetric crystallisa-- tion vessel 1 is rotated in the temperature drop which ~ -extends at right angles to the axis of the vessel and is constant with time, the starting crystal material ''~
a net amount of material is deposited at the site of the crystal growth.
The method may be used in heterogeneous pro-cesses in which a finite temperature range for the crys-;~ tal growth is available, such as subliminations, chemical transport reactions in the gaseous phase and dissolving lS processes. It is recommendable, in particular with a view to~the growth of crystals o~ comparatively large dimensions, when the preferred range of applications l;es in the region of the gas-solid state reactions.
~ The transporting phase of the crystal material may consist, for example, of a vapour of the crystal material, possibly mixed with a carrier gas, of a solution of the crystal material in a liquid or a super- ;
critical gas or of decomposable compounds of the crystal ' '~', .,.:
: ,: ':: .
' ~ - 2 - ~ ~
~S~3 -material or the col~ponents thereof, for example, in the form of a gas or vapour, or of a solution of these ccm~
ponents in a liquid or a super-critical gas.
A problem occurring in such methods of manu-facturing crystals of comparati~ely large dLmensions is to cause onl~ one or a small nu~ber of seed crystals to grcw and to suppress the further formation and the growth of parasitic seed crystals or crystallites, respectively, so as to obtain in this manner only one crystal or a few crystal bod~es separated from each other.
It is suggested in our Canadian Patent 805,630, which issued on February 4, 1969/ to cause a seed crystal which has been gr3wn in any arbitrary manner and placed in a crystallisation vessel bo continue growing in such manner that crystal material is periodically deposited from a transporting phase of the crystal ma-terial and is p~rtially retransferred to the transporting phase so that the seed crystal can gnow bu~ smaller crystal parts ~ disapFear again. It is kncwn that in the presence of i 20 larger crys~als smaller crystals grow with more difficulty and, in the time in which crystal material is partly retransferred to the transporting phase, decrease even to ¦ a strcrlger e~tent than th~y can form in the time in w~Lich ~he deposition takes place of crystal material at the site of the grcwth, so that smaller crystals disappear entirely after a ew periods. ~ -. ~- ~ . .
The retransfer of a part of tb~ crystal material ` .
~' ; . , PHD. 73-092.
deposited at the site of the crystal growth to the trans-porting phase can be effected in various manners, ~or example, by periodically varying the concentration of the transporting phase or by building up a unipolar temperature field in -~he crystallisation vessel with a temp~rature gra~ient the dir~ction of which is period-:: .ically varied. m e temperature gradient in the crystalli- ..
sation vessel is adjusted in such manner that the b~mpe-rature of the circumference of ~he crystallisation vessel is periotically increased and decreased relative to the temperature of the centre or in that a rotationally~: .
symmetric crystallisation ~7essel is rotated in a tempera- .
ture drop which extends at riqht angles to the axis of the vessel and is co~stant with time~ The dNration of a . 15 period correspc~ds to ~he tim~! of rotation of the vessel.
In this method it can often not be est~blished whether the seed crystal was d.amaged or whether the ~ .
:. crystal is ~ree of structural defects to a sufficient ~ extent. In such cases the seed crystal has bo be dis-:, 20 solved again and the crystallisation vessel be provided ~ :. . : -with a new seed cryst~
Mbrec~7er, with the so far known methods of crystal growing and with the method described in our Canadian Patent 805,630 for reversing the temperature gradient in the crystallisation vesæ l it is oft~n not possible to ~orm large single crystals . , ~'.
, ~'' ,:, , _ 4 _ with -Few structural defects. Furthermore, it is not pos-sible with the known methods, in systems favourable for the nucleation to realise the nucleation of only one ; crystal in the previously determined site.
This holds, for example, for the sublimation system HgI2.
Especial'ly in the system HgI2 the extra dif-ficulty occurs that the material may be present in two modifications and that the probability of nucleation of a crystal of the red modification showing no twin forma- ' ' tion is very small. Moreover, with the compound HgI2 the surface nucleation above a given size of the crystal '' seems to occur with greater difficulty. The crysta1 then shows twin formation or forms a coarse mosaic structure. The result in both cases is that the material is hardly useful for certain technical applications, for example, for use as a spectrometer crystal.
It is the object of the invention to manufac-ture large perfect s;ngle crystals also from systems which are very favourable for the nucleation.
. ....................................................................... .
~ The invention is based on the recognition that .
' the formation in situ of a perfect seed crystal is also possible in systems which are very favourable for the 'nucleation when the seed selection is carried out so keenly that only the dynamically most stable seed -which is no doubt a readi'ly ordered no twin formation showing single crystal - has a possibility of survival.
, -~ PHD 73-092 ~5~9~3 The invention is furthermore based on the recog-nition that a perfect crystal structure, in which thus, `~ for example, twin formation and mosaic structure are avoided, can also be realized for orystals of compara-tively large dimensions when the selection does not ex-tend only to the potential parasitic seeds but also con-tinuously prevents that the growing crystal begins to show the said structural defects.
According to the invention this is achieved - ~ -in that the processes of the periodic deposition of the crystal material from the transporting phase and the . , .
retransfer to said phase are carried out in such an alternation that the formation of parasitic seeds is suppressed and that the quantity of the crystal material . ~ .
; 15 deposited on a per~ect seed crystal in a given site oF
the crystal growth is larger in any period than the amount of the crystal material retransferred to the transporting phase so long as the grown crystal is per-` fect and that the amount of the crystal material retrans-ferred to the transporting phase is larger in any period than the amount of the deposited crystal material as soon as and as long as the crystal to be grown shows - structural defects.
The seed crystal is preferably formed in the crystallisation vessel.
The advantages resulting from the method ac-cording to the invention consist in particular in that ' . . .
'~
~.
::
: .... ,~ , .
it is possible to stimulate a system having different modifications in the direction of the stable modifica-tion. It is possible in systems favourable for the nucleation to cause only one single crystal to nucleate in the previously determined site and to grow it. It is possible to suppress the development of crystal de-fects, such as twin structures and mosaic structures, in which as a further advantage it may be mentioned that also the size of the crystals grown by means of the method according to the invention can advantageously be influenced with respect to the crystals grown by means ~-of the known methods.
The method according to the invention naturally also presents the possibility in systems having different modifications to favour the unstable modification under certain growth kinetic conditions by an adaptation of the free parameters.
For the growth of HgI2 single crystals the method according to the ;nvention presents possibilities how the system ;s stimulated in the direction of the stable modification and structural defects such as formation of twin structures and mosaic structures can be suppressed.
The recognitions obtained for the system HgI2 - 25 may of course also be applîed to other systems.
The invention will now be described in greater detail with reference to the accompanying drawings which PHD 73-09~
~.~5~3 show various embodiments of a device for carrying out the method according to the invention, and in which:
Fig. 1 is a sectional view of a device for growing crystals by means of the method according to the invention, Figs. 2 and 3 are sectional views through va-riations of the device shown in Fig. 1, and Fig. 4 shows a diagrammatic temperature-time curve for the performance of the method according to the invention.
Fig. 1 shows a device with an axially symme-tric crystallisation vessel, which is rotatable and is present within an oven system consisting of two dome-shaped partsi the dome-shaped part 4 having a semi-spherical head and a cylindrical trunk may be heated by ~; means of a heating coil 9. The outer dome-shaped part 5 consisting of a glass which can withstand temperature variations serves to reduce thermal losses by convection.
By means of a wire loop 6 a bipolar temperature field is built up within the dome-shaped part 4 in which the crystallisation vessel 1 which is secured on a hollow tube can be rotated. Present in the hollow tube 13 are - ~:
a themocouple 10 and a tube 11 for cooling the centre of the crystaliization vessel. Within the circumference ; 25 of the crystallisation vessel 1 crystal starting ma-terial (source material) 2 is present. The quartz ~
glass dome-shaped part 4 is arranged on a temperature- :
resistent base plate 7; the glass dome-shaped part 5 is .. .. . . .. . . .. . . .
~1:35~3 present on a table 8 consisting of a temperature-resistent material. Below the bottom of the crystallisation vessel 1 are arranged two further thermo-couples lOi a radiation , , screen 12 is also present below the crystallisation ves-sel. The hollow tube 13 to which the crystallisation ' vessel 1 is rigidly connected can be rotated by a motor ,`~ not shown.
In this device, temperatures of 700C can be reached.
In the method according to the invention it deals with a process in which at least two defined re-gions of the circ,umference of the crystallisation ves-sel 1 are heated simultaneously and the temperature of -' the circumference is increased and decreased periodi-cally relative to the temperature of the centre by ro-tation of the crystallisation vessel 1, the temperature of the centre - of the site of the crystal growth - be ing kept not constant but being reduced intermittently.
The defined hot regions o~ the c;rcumference of the .~
crystallisation vessel 1 are formed by a locally fixed , ' heating by means of a wire loop 6.
When the rotationally symmetric crystallisa-- tion vessel 1 is rotated in the temperature drop which ~ -extends at right angles to the axis of the vessel and is constant with time, the starting crystal material ''~
2(the source material) within the circumference of the crystallisation vessel 1 will pass alternately through _ g _ ~
'' ~
an undersaturated and a supersaturated region.
A material transport takes place when the average ; value of the temperature as a function of the time from ~ -all the circumferential points Tp is different from that of the temperature of the centre Tc. In this centre the dynamic saturation is reached for Tp = Tc, which means -; that just no material transport takes place. For Tp ~ Tc, the centre with an endothermal dissolving reaction is dynamically supersaturated, for Tp ~ Tc the centre is dynamically undersaturated.
For growing large perfect single crystals of systems which are favourable for nucleation the possi-bilities result herefrom to control the growth condi-; tions for the seed crystal present in the centre of the crystallisation vessel 1 in such manner that this can continue growing perfectly. By building up a bipolar temperature field by means of the wire loop 6 and with simultaneous interm1ttent cooling of the centre of the crystallisation vessel 1 - the site of the crystal growth - the transport of material within the crystal-lisation vessel 1 can be controlled in such manner that not only a selection of parasitic crystallites is pro- :
duced, but that it is also prevented periodically by evaporation or conversion of material that the growing crystal starts showing structural defects, such as, for example, twin formation or mosaic structures. The occurrence and disappearance of structural defects can ..
.. . .
- 10- ~ , ~.
often be established visually, for example, in the case of the growth of HgI2 crystals. The variables under ex- -perimental conditions, such as: variation of Tp and/or Tp , variation of Tc by variation of the period duration of the cooling and variation of the cool-ing temperature, variation of the speed of rotation of the crystallisation vessel and variation of the pola-rity of the temperature field in which the crystalli-sation vessel is present, should be adapted to the size of the growing crystal.
The nuclea-tion of a single crystal which is to serve as a seed crystal takes place inside the crys-tallisation vessel by carrying out the selection so sharply the only one and hence the thermodynamically lS most stable seed crystal is maintained. A suitable seed crystal formed in any site of the reaction vessel may also be loosened by mechanical pulse transfer or by local careful heating and be conveyed to the relative growth site in the centre of the crystallisation vessel 1. At the site9 the seed crystal 3 is first partially evapo rated before a transport of material from the circum- ;-ference to the centre is carried out, crystal material growing to the seed crystal 3. When the growing crystal proves to be not sufficiently perfect, the nucleation process may be repeated without the crystallisation vessel 1 being opened. However~ th;s procedure is not : so elegant as the direct nucleation in the relevant '' "'. "
- 11 - ' ' ' : : , , . . : ::
.
lOSA9g;1 3 growth site.
The experimental data of several HgI2 crystals manufactured by means of the method according to the in-vention are recorded in the Table below:
TABLE
All the crystals were nucleated in the reaction vessel. 1 cm3 corresponds to 6.3 g HgI2.
Introduced HgI2(g)Growth duration Crystal weight .
104.1 5 4.1 , 41.6 15 21.64 47.5 36 47 : .: . . .
52.2 46 52 1560.4 153 60.4 87.65 77 85 152.6 217 151 59.7 132 59.7 76.3 116 76.3 '~ 2050 60 50 ~
42 50 ;~ -` 56 25 56 ~578 16 70 - - , ., - . : ,: , , ' :' ' . -. - , : . ~ : . . ; ,: .
For the values of the sizes of the grown crys-tals recorded in the Table, a comparison with values for the larger HgI2 crystals described in literature is very instructive: for HgI2 crystals grown from solvents, values of approximately 100 mm3 are stated (Coleman, Journal of Crystal Growth, 1970, pp. 203-204)i for crystals grown by sublimation, values are mentioned of approximately 10 mm3 (Saura and Regolini, Journal of Crystal Growth 1972, pp. 307-308) Fig. 2 is a variation of the device shGwn in ~ ~ -Fig. 1, it may be advantageous to omit the quartz glass dome-shaped part 4 as an intermediate furnace. In this case it is to be preferred to construct the glass dome-shaped part 5 as a bolling point thermostat which screens the crystallisation vessel sufficiently from external ;~
temperature fluctuations, temperature fluctuations as a result o~ air pressure variations having substantially no influence on the crystal growth.
Fig. 3 shows a further favourable variation :
of the device shown in Fig. 1 in which the outer glass dome-shaped part 5 is constructed as a double-walled g~ass dome-shaped part 5 through which a coolant flows.
This device enables an easier adaptation of the tempe-rature field - and hence an increase of the possibili-ties to influencing the temperature difference between T and T - and of the selection sharpness to the Pmax Pmin -requ;rements of the crystal. With this device, particu- -~
: ::;
~5~
larly large crystals can be ob~ained.
A favourable embodiment of the method according to the invention having very favourable selection condi-tions is obtained when the speed of rotaticn of the crystallization vessel is systematically varied in a unipolar to multipolar temperature field, in which the speeds of rotation may be between 0.01 rpm and a few hundred rpm. It is simplest to stop the rotation perio-dically. -A modulation of the speed of rotatlon in a unipolar to mult;polar temperature field may be advan-.:
tageous for all the variations of the device shown in Fig. 1.
Fig. 4 shows diagrammatically the temperature variation for the crystal growth in a bipolar tempera-~ ture field with an intermittent cooling of the centre ,~ of the crystallisation vessel.
~, The total treatment dur;ng an experiment may be understood to be the sum of n partial steps in time `
intervals n ( ~ ~ j texperiment ; ~ < ~experiment)-:, 1 ..
For an endothermal d;ssolving reaction the thermal treatment must satisfy the equation ' . ' . .
~ .
' " ' '~
' ' ::
~ tj ~ tj P 1 ~i ~ r In ;ndividual periods rj the relation ~ may hold good instead of ~ . -Tp denotes the temperature at the circumference of the crystallisation vessel and need not be constant with time.
Tc denotes the temperature in the centre of the crystallisation vessel.
Admissible for Tp and Tc is:
PmaX Pn,jn ~ Cmax Cmin ' "' ~ .
For the red modification of the HgI2, T is < 127C.
Cmax It should be pointed out that all the parameters ~ should be adapted to the proceeding growth. The largest : selection sharpness is necessary at the beginning of the 15; nucleation process. ;
: :-.
: .:
, ', ' ' ' , . ': .' .' ,, ' . . . . . ., , - . . ,, ~'
'' ~
an undersaturated and a supersaturated region.
A material transport takes place when the average ; value of the temperature as a function of the time from ~ -all the circumferential points Tp is different from that of the temperature of the centre Tc. In this centre the dynamic saturation is reached for Tp = Tc, which means -; that just no material transport takes place. For Tp ~ Tc, the centre with an endothermal dissolving reaction is dynamically supersaturated, for Tp ~ Tc the centre is dynamically undersaturated.
For growing large perfect single crystals of systems which are favourable for nucleation the possi-bilities result herefrom to control the growth condi-; tions for the seed crystal present in the centre of the crystallisation vessel 1 in such manner that this can continue growing perfectly. By building up a bipolar temperature field by means of the wire loop 6 and with simultaneous interm1ttent cooling of the centre of the crystallisation vessel 1 - the site of the crystal growth - the transport of material within the crystal-lisation vessel 1 can be controlled in such manner that not only a selection of parasitic crystallites is pro- :
duced, but that it is also prevented periodically by evaporation or conversion of material that the growing crystal starts showing structural defects, such as, for example, twin formation or mosaic structures. The occurrence and disappearance of structural defects can ..
.. . .
- 10- ~ , ~.
often be established visually, for example, in the case of the growth of HgI2 crystals. The variables under ex- -perimental conditions, such as: variation of Tp and/or Tp , variation of Tc by variation of the period duration of the cooling and variation of the cool-ing temperature, variation of the speed of rotation of the crystallisation vessel and variation of the pola-rity of the temperature field in which the crystalli-sation vessel is present, should be adapted to the size of the growing crystal.
The nuclea-tion of a single crystal which is to serve as a seed crystal takes place inside the crys-tallisation vessel by carrying out the selection so sharply the only one and hence the thermodynamically lS most stable seed crystal is maintained. A suitable seed crystal formed in any site of the reaction vessel may also be loosened by mechanical pulse transfer or by local careful heating and be conveyed to the relative growth site in the centre of the crystallisation vessel 1. At the site9 the seed crystal 3 is first partially evapo rated before a transport of material from the circum- ;-ference to the centre is carried out, crystal material growing to the seed crystal 3. When the growing crystal proves to be not sufficiently perfect, the nucleation process may be repeated without the crystallisation vessel 1 being opened. However~ th;s procedure is not : so elegant as the direct nucleation in the relevant '' "'. "
- 11 - ' ' ' : : , , . . : ::
.
lOSA9g;1 3 growth site.
The experimental data of several HgI2 crystals manufactured by means of the method according to the in-vention are recorded in the Table below:
TABLE
All the crystals were nucleated in the reaction vessel. 1 cm3 corresponds to 6.3 g HgI2.
Introduced HgI2(g)Growth duration Crystal weight .
104.1 5 4.1 , 41.6 15 21.64 47.5 36 47 : .: . . .
52.2 46 52 1560.4 153 60.4 87.65 77 85 152.6 217 151 59.7 132 59.7 76.3 116 76.3 '~ 2050 60 50 ~
42 50 ;~ -` 56 25 56 ~578 16 70 - - , ., - . : ,: , , ' :' ' . -. - , : . ~ : . . ; ,: .
For the values of the sizes of the grown crys-tals recorded in the Table, a comparison with values for the larger HgI2 crystals described in literature is very instructive: for HgI2 crystals grown from solvents, values of approximately 100 mm3 are stated (Coleman, Journal of Crystal Growth, 1970, pp. 203-204)i for crystals grown by sublimation, values are mentioned of approximately 10 mm3 (Saura and Regolini, Journal of Crystal Growth 1972, pp. 307-308) Fig. 2 is a variation of the device shGwn in ~ ~ -Fig. 1, it may be advantageous to omit the quartz glass dome-shaped part 4 as an intermediate furnace. In this case it is to be preferred to construct the glass dome-shaped part 5 as a bolling point thermostat which screens the crystallisation vessel sufficiently from external ;~
temperature fluctuations, temperature fluctuations as a result o~ air pressure variations having substantially no influence on the crystal growth.
Fig. 3 shows a further favourable variation :
of the device shown in Fig. 1 in which the outer glass dome-shaped part 5 is constructed as a double-walled g~ass dome-shaped part 5 through which a coolant flows.
This device enables an easier adaptation of the tempe-rature field - and hence an increase of the possibili-ties to influencing the temperature difference between T and T - and of the selection sharpness to the Pmax Pmin -requ;rements of the crystal. With this device, particu- -~
: ::;
~5~
larly large crystals can be ob~ained.
A favourable embodiment of the method according to the invention having very favourable selection condi-tions is obtained when the speed of rotaticn of the crystallization vessel is systematically varied in a unipolar to multipolar temperature field, in which the speeds of rotation may be between 0.01 rpm and a few hundred rpm. It is simplest to stop the rotation perio-dically. -A modulation of the speed of rotatlon in a unipolar to mult;polar temperature field may be advan-.:
tageous for all the variations of the device shown in Fig. 1.
Fig. 4 shows diagrammatically the temperature variation for the crystal growth in a bipolar tempera-~ ture field with an intermittent cooling of the centre ,~ of the crystallisation vessel.
~, The total treatment dur;ng an experiment may be understood to be the sum of n partial steps in time `
intervals n ( ~ ~ j texperiment ; ~ < ~experiment)-:, 1 ..
For an endothermal d;ssolving reaction the thermal treatment must satisfy the equation ' . ' . .
~ .
' " ' '~
' ' ::
~ tj ~ tj P 1 ~i ~ r In ;ndividual periods rj the relation ~ may hold good instead of ~ . -Tp denotes the temperature at the circumference of the crystallisation vessel and need not be constant with time.
Tc denotes the temperature in the centre of the crystallisation vessel.
Admissible for Tp and Tc is:
PmaX Pn,jn ~ Cmax Cmin ' "' ~ .
For the red modification of the HgI2, T is < 127C.
Cmax It should be pointed out that all the parameters ~ should be adapted to the proceeding growth. The largest : selection sharpness is necessary at the beginning of the 15; nucleation process. ;
: :-.
: .:
, ', ' ' ' , . ': .' .' ,, ' . . . . . ., , - . . ,, ~'
Claims (19)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of growing crystals in a crystallisation vessel by the periodic deposition of the crystal material from a transporting phase of the crystal material present in said vessel and by the partial retransfer of crystal material deposited at the site of the crystal growth to said phase, in which said phase is separated from the deposition site and in which in the periods of de-position and retransfer a net amount of material is de-posited at the site of the crystal growth, characterized in that the processes of the periodic deposition of the crystal material from the transporting phase and the retransfer to said phase are carried out in such an alternation that the formation of parasitic seeds is suppressed and that the quantity of the crystal material deposited on a perfect seed crystal in a given site of the crystal growth is larger in any period than the quantity of the crystal material retransferred to the transporting phase so long as the grown crystal is per-fect and that the quantity of the crystal material re-transferred to the transporting phase is larger in any period then the quantity of deposited crystal material as soon as and as long as the crystal to be grown shows structural defects.
2. A method as claimed in Claim 1, characterized in that the periodic deposition of crystal material from the transporting phase and the partial retransfer of crystal material deposited at the site of the crystal growth to the transporting phase takes place in a temper-ature field in which at least two temperature gradients become operative.
3. A method as claimed in Claims 1 and 2, in which a relative movement takes place between the crystallisa-tion vessel and the temperature field, characterized in that the temperature field in the crystallisation vessel is built up by means of a furnace which produces a bipolar or multipolar temperature field.
4. A method as claimed in Claims 1 and 2, charac-terized in that the defined site of the crystal growth is periodically heated.
5. A method as claimed in Claims 1 and 2, charac-terized in that the defined site of the crystal growth is periodically cooled.
6. A method as claimed in Claims 1 and 2, charac-terized in that in at least one place in the crystalli-sation vessel a store of crystal starting material (source material) is present.
7. A method as claimed in Claims 1 and 2, charac-terized in that crystal material is led over by sublima-tion.
8. A method as claimed in Claims 1 and 2, charac-terized in that for leading over the crystal material a chemical transport reaction or dissolving reaction is used.
9. A method as claimed in Claim 1, characterized in that the seed crystal grown in the crystallisation vessel is conveyed to the defined site of the crystal growth by mechanical pulse transfer.
10. A method as claimed in Claim 1 or 2, charac-terized in that the seed crystal is formed in the crystallisation vessel.
11. A device for carrying out the method as claimed in Claim 1, characterized by a crystallisation vessel which is surrounded on the outside by a wire loop which is pro-vided in a furnace system which consists of at least one dome-shaped part surrounding the crystallisation vessel and the wire loop, the dome-shaped part being surrounded by a heating coil, a closing covering element with leadthroughs for thermocouples and for a hollow tube which is rotatable and is rigidly connected to the crystallisation vessel being present on the open side of said part with a thermo-couple and a tube for supplying coolants being provided in the hollow tube.
12. A device as claimed in Claim 11, characterized in that the furnace system comprises a further dome-shaped part provided between the dome-shaped part and the crystal-lisation vessel.
13. A device as claimed in Claim 11, characterized in that the dome-shaped parts consist of a material which can withstand temperature variations.
14. A device as claimed in Claim 13, characterized in that the dome-shaped parts consist of glass.
15. A device as claimed in Claim 11, characterized in that the dome-shaped part is double-walled.
16. A device as claimed in Claim 11, characterized in that the crystallisation vessel is axially symmetric.
17. A device as claimed in Claim 11, characterized in that the wire loop surrounds the crystallisation vessel under an inclination with the plane of rotation.
18. A device as claimed in Claim 11, characterized in that an axially symmetric vessel is used as a crystal-lisation vessel whose axis is at right angles to the direction of the temperature gradient of the furnace.
19. A device as claimed in Claim 11, characterized in that the crystallisation vessel has an axis of rotation at right angles to the direction of the temperature gradient.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19732341820 DE2341820A1 (en) | 1973-08-18 | 1973-08-18 | METHOD AND DEVICE FOR CULTIVATING CRYSTALS AND CRYSTALS PRODUCED BY THIS PROCESS |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1054903A true CA1054903A (en) | 1979-05-22 |
Family
ID=5890107
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA207,461A Expired CA1054903A (en) | 1973-08-18 | 1974-08-19 | Method and device for growing crystals |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS5051084A (en) |
| CA (1) | CA1054903A (en) |
| DE (1) | DE2341820A1 (en) |
| FR (1) | FR2245395B1 (en) |
| GB (1) | GB1464903A (en) |
| IT (1) | IT1019992B (en) |
| NL (1) | NL7410866A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102005003407B4 (en) * | 2005-01-25 | 2010-05-06 | Karlsruher Institut für Technologie | Process for the preparation of colloidal crystals or colloidal particle systems |
-
1973
- 1973-08-18 DE DE19732341820 patent/DE2341820A1/en not_active Withdrawn
-
1974
- 1974-08-14 NL NL7410866A patent/NL7410866A/en unknown
- 1974-08-14 FR FR7428187A patent/FR2245395B1/fr not_active Expired
- 1974-08-14 IT IT2636974A patent/IT1019992B/en active
- 1974-08-15 GB GB3598274A patent/GB1464903A/en not_active Expired
- 1974-08-16 JP JP9347874A patent/JPS5051084A/ja active Pending
- 1974-08-19 CA CA207,461A patent/CA1054903A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| IT1019992B (en) | 1977-11-30 |
| DE2341820A1 (en) | 1975-03-13 |
| JPS5051084A (en) | 1975-05-07 |
| NL7410866A (en) | 1975-02-20 |
| GB1464903A (en) | 1977-02-16 |
| FR2245395A1 (en) | 1975-04-25 |
| FR2245395B1 (en) | 1978-11-24 |
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