US3051656A

US3051656A - Method of preparing magnetic garnet crystals

Info

Publication number: US3051656A
Application number: US811807A
Authority: US
Inventors: Kramarsky Bernhard
Original assignee: Individual
Current assignee: Individual
Priority date: 1959-05-08
Filing date: 1959-05-08
Publication date: 1962-08-28
Anticipated expiration: 1979-08-28

Description

United States Patent 3,051,656 METHOD OF PREPARING MAGNETIC GARNET CRYSTALS Bernhard Krarnarsky, Microwave Chem. Lab. Inc. 282 7th Ave., New York, N.Y. No Drawing. Filed May 8, 1959, Ser. No. 811,807 7 Claims. (Cl. 252-625) This invention is concerned with methods of growing magnetic garnet crystals.

More specifically, this invention has to do with a significant improvement in method whereby single crystals of certain rare-earth iron garnets may be produced which are considerably larger in average size and in far greater yield.

The identity of these ferrimagnetic garnets, whose general formula is M Fe O (M=rare earth, e.g. yttrium, gadolinium, erbium, Samarium) was first reported in 1956. (F. Bertaut and F. Forrat: Comptes Rendus 242, 382, 1956; S. Geller and M. A. Gilleo; Acta Cryst. 10, 239, 1957.) The first efforts to prepare these compounds resulted in polycrystalline products. Interest in the physical properties of these garnets and their potential use in microwave systems indicated the desirability of growing single crystals of these compounds of maximum size. At present, single magnetic garnet crystals have found important use in parametric amplifiers for radar systems; and because they have the property of transparency to infra-red, their use as infra-red transmission modulators is projected. I. P. Rerneika (J. Amer. Chem. Soc. 78, 4259, 1956) first reported single crystals. J. W. Nielsen and E. F. Dearborn (J. Phys. Chem. Solids 5, 202-207, 1958) have investigated and outlined the general methods of producing these magnetic garnets as single crystals from three-component systems, i.e. iron oxide, Fe O with lead oxide, PbO, as flux.

Nielsen has defined the composition range in which magnetic garnets will grow and the conditions favorable to their growth. However, his methods have produced at best crystals of generally small size and poor yield, with only an occasional large crystal.

The present invention departs from Nielsens method by adding a fourth component to the system, which suppresses the formation of many nuclei for multiple crystal growth, and encourages the formation of few, larger in dividual crystals. It has been found that the addition of suitable quantities of bon'c anhydride, B to the threecomponent system of Nielsen provides a remarkable increase in the size and yield of magnetic garnet crystals.

The following table of typical experimental results clearly shows the eifect of the addition of boric anhydride:

Percent Average Total Expt Composition B203 Yield of Size Wt. of No, of Bulk Added Yttrium- (Diarn) Y,I. G. Material (In iron of Y.I.G. Single (In Mole Mole Garnet Single Crystals Percent) Percent) Single Crystals (Grams) Crystals PbO:52.5 1 FezOaz44 0 6. 04 0. 09 1. 92

YzO325.25--

1 Better crystal faces than in 1.

lQQ

The typical procedure employed in the above experimental batches comprised the following steps: A thorough mixture of the oxide powders in the proportion indicated was made, and a weighed portion thereof placed in a 375 ml. platinum crucible so as to fill it. (The average batch weight was 400 gms.) The crucible was covered tightly with a platinum lid and placed in a furnace. The furnace temperature was raised to 1325 and maintained at that point for 10 hours to insure complete solution of the ingredients. The temperature was then lowered at a steady rate of l.9 per hour, to allow for optimum crystal growth, until 925 C. was reached.

The crucible and its contents were then cooled rapidly to room temperature, and the resultant mass repeatedly boiled in dilute nitric acid and washed until the matrix was sufficiently reduced to permit dislodgement of the crystals within. Separation of the garnet from the non-garnet crystals was accomplished magnetically in the usual manner, taking advantage of the difference in Curie temperatures of the aforesaid crystals.

The magnetic garnet crystals formed in the above manner are well-developed in crystal structure and quite pure, the total impurities running less than 0.2%, and the quantity of boric anhydride in the crystals less than 0.09% determined spectroscopically. The weight of these crystals ranges from mg. to 2.0 gms. when prepared as above. It should be noted here that while the crystal sizes and yields in these experimental batches are comparable among themselves, better yields and larger crystals are to be expected from using larger crucibles and bigger batches.

Returning to consideration of the experimental results shown in the table above, it is evident that the range of effectiveness of the B 0 additive is clearly marked and quite specific. A significant influence is shown when 5 mole percent is added; the optimum amount appears to be in the range of 10 mole percent; and over 15 mole percent, no garnet crystals form, since new phases appear and glassy products result.

The function of the boric anhydride additive is evidently that of nucleus suppression, similar to that of mineralizers, so that a few large crystals, rather than many small crystals, are encouraged to grow. Variation of the other three components, namely, lead oxide, iron oxide, and rare-earth oxide will influence the formation of garnet crystals as indicated in the phase diagrams of Nielsen, as will modifications of temperature, batch size, etc. However, as indicated in Experiment 6 in the table above, under conditions Where garnet crystals Will form at all in the three-component system, the addition of boric anhydride in the indicated range will enhance the yield and quality of said crystals.

Suitable ranges within the contemplation of the invention are as follows:

Iron oxide, F6 0,, from 25 to 70 mole percent Lead oxide, PbO, from 30 to 70 mole percent Rare-earth oxide, M 0 from 0.1 to 10 mole percent Boric anhydride, B 0 from 2 to 15 mole percent The letter M in the foregoing is intended to represent a rare-earth selected from the group comprising yttrium, gadolinimum, erbium and samarium.

The foregoing mixtures in the ranges given may be heated to a temperature in the range of 1315 to 1345 degrees centrigrade. The most effective temperature, however, is 1325 degrees centigrade. It will be understood that the material should be maintained at said elevated temperature for a minimum of 8 to 10 hours under standard pressure. The cooling rate ranges from 0.5 degrees centigrade per hour, the most eifective rate being 1.9 degrees per hour. Cooling should continue until optimum or maximum crystal growth is attained. It will be found that this will occur by the time the temperature is reduced to approximately 925 degrees.

I claim:

1. The method of growing magnetic iron rare-earth garnet crystals, comprising the steps of providing a mixture of iron oxide, lead oxide, rare-earth oxide and boric anhydride from 2 to 15 mole percent, heating said mixture to an elevated temperature suflicient to cause it to go into solution, and then cooling said heated mixture at a controlled, sufficiently slow rate to produce crystals.

2. The method of growing magnetic iron rare-earth garnet crystals, comprising the steps of providing a mixture of iron oxide, from 25 to 70 mole percent, lead oxide, from 30 to 70 mole percent, rare-earth oxide, from 0.1 to 10 mole percent, the rare earth being selected from the group consisting of yttrium, gadolinium, erbium and Samarium, and boric anhydride, from 2 to 15 mole percent, heating said mixture to a temperature in the range of 1315 to 1345 degrees centigrade, and then cooling said heated mixture at a controlled rate in the range of 0.5 to 5 degrees centigrade per hour to allow for proper crystal growth.

3. The method of growing magnetic iron rare-earth garnet crystals, comprising the steps of providing a mixture of iron oxide, from 25 to 70 mole percent, lead oxide, from 30 to 70 mole percent, yttrium oxide, from 0.1 to mole percent, and boric anhydride, from 2 to mole percent, heating said mixture to a temperature in the range of 1315 to 1345 degrees centigrade, and then cooling said heated mixture at a controlled rate in the range of 0.5 to 5 degrees centigrade per hour to allow for proper crystal growth.

4. The method of growing magnetic iron rare-earth garnet crystals, comprising the steps of providing a mixture of iron oxide, approximately 44 mole percent, lead oxide, approximately 52.5 mole percent, yttrium oxide, approximately 3.5 mole percent, and boric anhydride, approximately 10.34 mole percent, heating said mixture to a temperature in the range of 1315 to 1345 degrees centigrade, and then cooling said heated mixture at a controlled rate in the range of 0.5 to 5 degrees centigrade per hour to allow for proper crystal growth.

5. The method of growing magnetic iron rare-earth garnet crystals, comprising the steps of providing a mixture of iron oxide, approximately 43.75 mole percent, lead oxide, approximately 51.5 mole percent, yttrium oxide, approximately 5.25 mole percent, and boric anhydride, approximately 10.34 mole percent, heating said mixture to a temperature in the range of 1315 to 1345 degrees centigrade, and then cooling said heated mixture at a controlled rate in the range of 0.5 to 5 degrees centigrade per hour to allow for proper crystal growth.

6. The method of growing magnetic iron rare-earth garnet crystals, comprising the steps of providing a mixture of iron oxide, approximately 44 mole percent, lead oxide, approximately 52.5 mole percent, yttrium oxide, approximately 3.5 mole percent, and boric anhydride, approximately 10.34 mole percent, heating said mixture to a temperature of approximately 1325 degrees centigrade, maintaining it at said temperature for approximately 10 hours, and then cooling said heated mixture at the rate of 1.9 degrees centigrade per hour until a temperature of approximately 925 degrees centigrade is reached in order to allow for proper crystal growth.

7. The method of growing magnetic iron rare-earth garnet crystals of claim 1, wherein the iron oxide is in a range from 25 to mole percent, the lead oxide ranging from 30 to 70 mole percent and the rare-earth oxide ranging from 0.1 to 10 mole percent.

References Cited in the file of this patent UNITED STATES PATENTS 2,736,708 Crowley Feb. 28, 1956 2,848,310 Remeika Aug. 19, 1958 2,886,530 Greger May 12, 1959 2,938,183 Dillon May 24, 1960 2,957,827 Nielsen Oct. 25, 1960 OTHER REFERENCES J. Amer. Ceram. Soc., Bauer et al., vol. 33, pp. -143.

Comptes Rendus, Aleonard et al., vol. 242, pp. 2531- 2533, May 23, 1956.

Comptes Rendus, Pauthenet et al., vol. 243, pp. 1499- 1501, Nov. 12, 1956.

Claims

2. THE METHOD OF GROWING MAGNETIC IRON RARE-EARTH GARNET CRYSTALS, COMPRISING THE STEPS OF PROVIDING A MIXTURE OF IRON OXIDE, FROM 25 TO 70 MOLE PERCENT, LEAD OXIDE, FROM 30 TO 70 MOLE, PERCENT, RARE-EARTH OXIDE, FROM 0.1 TO 10 MOLE PERCENT, THE RARE EARTH BEING SELECTED FROM THE GROUP CONSISTING OF YTTRIUM, GADOLINIUM, ERBIUM AND SAMARIUM, AND BORIC ANHYDRIDE, FROM 2 TO 15 MOLE PERCENT, HEATING SAID MIXTURE TO A TEMPERATURE IN THE RANGE OF 1315 TO 1345 DEGREES CENTIGRADE, AND THEN COOLING, SAID HEATED MIXTURE AT A COMTROLLED, RATE IN THE RANGE OF 0.5 TO 5 DEGREES CENTIGRADE PER HOUR TO ALLOW FOR PROPER CRYSTAL GROWTH.