DE2418711A1 - Single crystals of bismuth rare-earth garnets - lead-free bismuth gadolinium iron garnets with high faraday effect - Google Patents

Abstract

A mixt. of oxides is used in the desired proportions, except that more bismuth oxide or boric oxide is used than the theoretical amt. required to form the single crystal; the mixt. is melted and cooled at a rate of 0.1-10 degrees C./hour to 950 degrees C., then cooled to room temp. Alternatively, the melt temp. can be reduced below the saturation temp. and a garnet inoculant used. Bismuth doped, rare-earth-iron garnet single crystals can be crystallised from their own melts within area (ABCD) of a pseudo-ternary diagram where B2O3 can be used in place of Bi2O3 up to concn. of 0.5 mol. per mol. of Bi2O3. The compsns. (all in mol.%) are (A) 30 Bi2O3, 69.5 Fe2O3, 0.5 R2O3 (R is a rare-earth metal); (B) 30 Bi2O3, 43.75 Fe2O3, 26.5 R2O3; (D) 57.5 Bi2O3, 26.6 Fe2O3, 15.9 R2O3; and (C) 57.5 Bi2O3, 42 Fe2O3, 0.5 R2O3. By using a starting mixt. of 45.8 Bi2O3, 9.7 Gd2O3, 38.8 Fe2O3, 5.7 B2O3 the garnets produced amounted to 95% of all the crystals obtd. Both homoepitactic and heteroepitactic single crystals can be made, heteroepitactic meaning that the inoculant crystal has a different chemical compsn. to the crystal being grown.

Description

Process for the production of bismuth-doped iron aranate single crystals The invention relates to a method for producing bismuth-doped iron garnet single crystals. In particular, the invention relates to a method of making lead-free with Bismuth-doped rare earth iron ranate single crystals from the melt.

A rare earth iron garnet doped with bismuth (hereinafter BiRIG) can be represented by the general formula R3-xBixFe5-yAyO12. In of this formula, O <x # 1.5, O # - y <5, R is one or more of the rare earth elements and A at least one element that can be substituted for iron.

The collective name "rare earth metal" does not include the usual one Nomenclature including the elements Sc, Y and La to Lu. The BiRIG is through Replacement of some of the rare earth elements in the rare earth iron garnet (im following RIG). The BiRIG is characterized by a particularly high Faraday rotation, i.e.

by a particularly strong rotation of the plane of polarized light in transmission off.

So far, however, the BiRIG could only be obtained in polycrystalline form. In polycrystalline material, however, incident light is reflected at the grain boundaries and diffusely scattered. This makes the effective absorption coefficient a noticeable elevated. Correspondingly, the figure of merit F / a of the magnetic rotation is decreased. In this figure of merit, F is the angle of rotation of the plane of polarization for a sample layer thickness, in which the intensity of the transmitted light is reduced by 1 dB. The figure of merit the Faraday rotation, as described in the description for the BiRIG single crystals is used, so has the dimension degree / dB. To improve the Gtite number are High quality single crystals required.

When mixing an oxide mixture in proportions that are stable Composition in the phase diagram of the BiRIG correspond, and heating to one Temperature below the melting point of the mixture and cooling is indeed the BiRIG is formed in a single phase by solid-state reaction, but it is only polycrystalline Material received.

If you heat the same weighed in according to the target composition Oxide mixture up to above the melting point and then allows the melt to cool down gradually, in this way, the desired garnet phase is not obtained on cooling. Rather, part First off a foreign phase.

Flawless BiRIG single crystals cannot be obtained in this way will. It is particularly important when using Bi 203 in the starting oxide mixture impossible to obtain technically useful BiRIG single crystals in useful yield.

Crystallization is an ideal way of overcoming these difficulties from flux melts. In the manufacture of bismuth-free RIG, PbO, PbO-PbF2, PbO-B2O3, PbO-PbP2-B203, BaO-B203 and other flux mixtures used. When using Bi203 as a flux for growing garnet single crystals must have the disadvantage of an uncontrolled and uncontrollable incorporation of bismuth must be accepted into the garnet phase. In practice, they are single crystals grown from a PbO or PbF2 melt, however, there will also be significant Lots of lead built into the garnet single crystal. It can't do it this way pure BiRIG single crystals can be obtained.

By incorporating the bivalent lead into the growing Garnet crystal also occurs primarily in reloading of iron (III). For example Fe4 + ions formed. This makes the absorption coefficient of the single crystal noticeable elevated. By growing BiRIG single crystals from PbO or PbF2 or others Melts containing lead salts are therefore only crystals with markedly poorer properties Quality number received.

The invention is therefore based on the object of a method for To create lead-free BiRIG single crystals that work economically, allows low deposition temperatures and high quality crystals supplies.

To solve this problem, according to the invention, a method of Proposed type mentioned at the beginning, which is characterized in that the Weighing in oxides in the desired cation ratio of the garnet Weighs in bismuth oxide or a mixture of bismuth oxide and boron oxide in an amount that is above the target amount intended for the single crystal that the oxides mixes and melts by controlling the melt at 0.1-10 ° C./h up to 950 ° C. cools down and then cools down to room temperature.

The invention therefore relates to the production of lead-free BiRIG single crystals by mixing the corresponding oxides in the desired cation ratio Soll composition of the garnet, the bismuth, which is preferably weighed as Bi203 is weighed in an amount greater than the target amount of the garnet composition lies. The oxide mixture weighed in this way is then melted. The melt is cooled with a specified and monitored cooling rate until the single crystal grows in the way you want. Alternatively, the melt can be up to a temperature be cooled below the saturation temperature. In the melt that has cooled down in this way a seed crystal is then immersed. This seed crystal is preferably a garnet, the one crystal structure as similar as possible to the garnet to be grown, but one has a different chemical composition than this.

By adding B203 as a flux to the starting oxide mixture the deposition temperature can be lowered.

The main advantage of the method of the invention is that BiRIG single crystals of high crystallographic and optical quality can be obtained. Above all, the single crystals thus obtained are free from any impurity, for example of lead, which impair the optical quality of the garnet.

If the oxide mixture or the melt B203 in an amount of not More than 0.5 mol per mol of Bi203 is added, garnet single crystals with excellent optical properties are retained even when extremely low proportions of Boron are incorporated in the BiRIG single crystal thus obtained. However, since the boron is called B3 + is installed, there is above all no charge reversal of the iron ions.

The absorption coefficient of the BiRIG single crystal is determined by the presence small amounts of boron incorporated in this way are not affected.

By the preferred embodiment of the invention, according to the starting oxide mixture Boron oxide is added, the deposition temperature for the BiRIG single crystal growth can optionally be shifted and set in the range between 700 and 1200 OC. Because the solid solubility of bismuth in the RIG single crystal decreases with decreasing precipitation temperature increases, you have to achieve the highest possible bismuth content in the garnet Lower the deposition temperature as much as possible when growing single crystals. Such a lowering of the deposition temperature can be achieved by adding a compound the melting point of which is below the melting point of Bi203. These Compound or this mixture of compounds must be capable of producing of the RIG required starting oxides, namely the rare earth metal oxides (hereinafter R203), Fe203, A1203 and others to solve well. The connection is allowed continue not to be incorporated into the garnet crystal in such a way that they to noticeable deviations from the nominal composition of the garnet, i.e. to a Displacement of the desired cations from the lattice structure, leads. Among the connections which meet these requirements, B203 occupies an excellent special position. By adding B203 to the starting oxide mixture for the production of the BiRIG the absorption coefficient of the obtained single crystal becomes equal to one Crystal that was grown without the addition of boron was not altered in any way.

The reason for this is seen in the fact that the bcrions are practical cannot be built into the grenade grille.

If such an installation takes place at all, then only in traces. Besides that the boron is in the form of boron (III) ions, which have the absorption coefficient in do not affect it in any way, and in particular do not trigger any recharging of the iron (III) ions.

Albeit also the use of B203 to lower the deposition temperature The garnet single crystal is preferred, but other compounds can also be used can be used for the same purpose as long as they exceed the deposition temperature of the RIG single crystals can degrade without reducing the absorption coefficient of the obtained To increase single crystals significantly.

The maximum amount of bismuth that can be incorporated into BiRIG single crystals can, passes through as a function of the ionic radius of the rare earth element or of the rare earth elements (hereinafter R) is a maximum. This maximum is R = Gd. The phase boundary for the bismuth doping of the gadolinium-iron-garnet lies at x = 1.5, corresponding to a garnet Gd115Bi115Fe5012.

If the Gd is replaced by other rare earth elements, no over x = 1.5 lying value can be obtained.

The invention is illustrated in the following on the basis of exemplary embodiments Connection described in more detail with the drawing.

It shows: FIG. 1 a three-component diagram for the pseudoternary System R203-Bi203-Fe203 or R203- (Bi203 + B203) -Fe203.

Example 1 With an oxide mixture, which in the diagram of FIG. 1 within of the rectilinear square delimited by the corner points ABCD lies, BiRIG single crystals of the pseudo-ternary system R203-Bi 203 -Fe 203 by letting it crystallize out of your own melt. The point A corresponds to a composition of 30 mol% Bi203, 69.5 mol% Fe203 and 0.5 mol% R2O3, the point B corresponds a composition of 30 mol% Bi203, 43.75 mol% Fe203 and 26.5 mol% R2O3, point D corresponds to a composition of 57.5 mol% Bi2O3, 26.6 mol% Fe2O3 and 15.9 mol% R2O3, while point C has a composition of 57.5 mol% Bi203, Corresponds to 42 mol% Fe203 and 0.5 mol% R203. The single crystals can be used without of seed crystals are obtained through their own nucleation from their own melt.

Oxide mixtures having a composition similar to that described above Field ABCD of the pseudo-ternary system R203-Bi2O3-Fe2O3 falls are melted on and cooled to 950 ° C. at cooling rates of 10 to 0.1 ° C./h.

No single crystals are formed at a cooling rate of over 10 ° C / h obtain. At cooling rates of less than 0.1 ° C./h, the for growth of the crystal required so long that they are dated economic and dated Industrial production is no longer justifiable.

With a Bi 203 content below the line AB, i.e. with less than 30 mol% Bi203 in the starting oxide mixture, this mixture is no longer at temperatures of not more than 1300 ° C completely melted. With an Fe203 content, the lower is than it corresponds to the line BD, separates instead of the desired garnet crystal exclusively from the orthoferrite phase.

If the proportion of Bi203 in the starting oxide mixture is higher than that Line CD corresponds, so is over 58 mol%, another also separates than the desired garnet phase. If the R2O3 content in the starting oxide mixture is below the line CA, i.e. below 0.5 mol%, only very small amounts separate Garnet off.

Table I shows the influence of the composition of the starting oxide mixture on the single crystals obtained for the bismuth-substituted gadolinium-iron-garnet Gd3-xBixFe5O12 shown in the range 0 c x - 1.5. The quantities of the oxides are in mol%. The sample numbers given in the first column of Table I correspond the reference numerals of the composition points entered in the diagram of FIG.

Table I Samples of starting oxide mixture (mol%) properties of the obtained No. BiRIG single crystals or the Bi2O3 Gd2O3 Gd2O3 Fe2O3 B2O3 system 1 50 0.3 49.7 0 Garnet content: 1% of all precipitated crystals 2 50 4 46 0 Garnet content: 25 % of all precipitated crystals 3 45.8 5.0 46.3 0 Garnet content: 60% of all precipitated Crystals 4 45.8 9.7 38.8 5.7 Garnet content: 95% of all separated crystals 5 50 18 32 0 Garnet content: 20% of all precipitated crystals 6 50 21 29 0 es Orthoferrite is now excreted 7 59 8.0 33 0 Garnet content: 1% of all excreted Crystals 8 56 8.5 35.5 0 Garnet content: 8% of all precipitated crystals 9 32 13.3 54.7 0 crystals with a small grain size are precipitated 10 29 14 57 0 the starting material is not completely melted Of the Bismuth content in each of the garnet single crystals thus produced was lower than the bismuth content in the starting oxide mixture. The absorption coefficients of each one of the BiRIG single crystals obtained was much deeper than that of single crystals using fluxes which essentially consist of PbO and / or PbF2 passed. The figures of merit F / a of the BiRIG single crystals obtained in this way were significantly above the figures of merit of corresponding single crystals made from lead-containing Melts were grown.

The aforementioned starting mixtures are modified in such a way that that part of the Bi is replaced by B203. The oxide mixtures are at higher Temperatures melted and then gradually cooled to 750 ° C at 10 to 0.1 ° C / h. In each of the garnet single crystals thus obtained, the bismuth content was below the bismuth content of the starting oxide mixture. The absorption coefficient of the obtained BiRIG single crystals was significantly below the absorption coefficient of the corresponding RIG single crystals, that were grown from lead-containing melts. The quality figures were accordingly F / for the BiRIG monocrystals obtained in this way is significantly higher than the figure of merit RIG single crystals consisting essentially of PbO or PbF2 melts were obtained.

Example 2 With starting oxide mixtures, the composition of which is included in the rectilinear quadrangle CDEF falls in the composition diagram of FIG. 1, BiRIG single crystals can can be grown homoepitaxially and heteroepitaxially on substrate crystals. "Homoepitactic" means that the substrate crystal or the seed crystal the same chemical composition as the epitaxially grown single crystal has, while "heteroepitaxial" means that seed crystal and seed crystal different chemical compositions, but the same crystal structures to have. For heteroepitaxial crystal growth it is necessary that the seed crystal is not a magnetically coupled garnet, in particular a ferromagnetic garnet.

If the Bi203 content in the starting oxide mixture is below the line CD, the deposition temperature is so high that the substrate crystal melts. if In the starting oxide mixture the R203 content is above the line DF, germs form the orthoferrite structure, which inhibits the growth of the garnet single crystals. In one Starting oxide mixture, the Bi 203 content of which is above the line EF, becomes the growth rate of the garnet extremely slowed down. If the R203 content in the starting oxide mixture is below the line EC, the garnet crystals are only in very small quantities obtain.

Table II shows the influences of the composition of the starting oxide mixture on the system and on the T n crystals obtained. It becomes the garnet single crystal systems Gd3-xBixFe5O12 and Yb3-xBixFe5O12 with O of x = 1.5 examined. Each of the crystals was at a temperature below the corresponding saturation temperature of the Garnet bred. The temperature at which the crystals are grown 1 respectively.

at which they grow is referred to in the following description as Denotes 'professional temperature'. The growth temperature of the foregoing Gadolinium and ytterbium garnets are in the range from 800 to 1000 ° C., preferably in the range of 850 to 950 OC Table II Samples of the starting oxide mixture (Mol-%) Properties of the single crystals No. or the systems Bi2O3 Gd2O3 Fe2O3 B2O3 11 58 0.3 34.7 7 no detectable crystal growth 12 58 4 31 7 no detectable Crystal growth 13 58 12 23 7 limited loose adhesion of orthoferrite to garnet 14 58 14 21 7 Orthoferrite adheres to the garnet single crystal 15 82 2.0 9 7 Growth rate below 1 µm / h 16 84 2.0 7 7 growth rate below 1 µm / h Bi2O3 Yb2O3 Fe2O3 B2O3 17 78 1.7 20.3 0 growth of a shiny epitaxial layer 18 75 1.9 23.1 0 growth of a shiny epitaxial layer The growing temperatures for epitaxial growth are in the range of preferably 800 to 1000 OC chosen. In each of the obtained single crystals, the bismuth content is lower than the bismuth content in the starting oxide mixture. The absorption coefficient of each of the obtained BiRIG single crystals is much lower than the absorption coefficient in corresponding RIG single crystals consisting essentially of PbO and / or PbF2 containing Melts are grown.

The cultivations described above are repeated in such a way that that a part, as in Example 1, preferably up to 0.5 mol per 1 mol Bi203, Bi203 is replaced by B203. The epitaxial growth is in the temperature range preferably carried out from 700 to 900 ° C.

In each of the single crystals grown in this way, the bismuth content is lower than the bismuth content in the corresponding starting oxide mixture. The absorption coefficient of the BiRIG single crystals obtained in this way are lower than the corresponding absorption coefficients of RIG single crystals grown from lead-containing fluxes.

The single crystals of Example 2 are in that through the rectilinear Quadrilateral CDEF delimited composition field, with points C and D in the example 1 correspond to the specified compositions and point F of the composition 90 mol% Bi203, 6.25 mol% Fe203 and 3.75 mol% R203 and the point E of the composition 90 mol% Bs203, 9.5 mol% Fe203 and 0.5 mol% R203 in the pseudo-ternary system of Fig. 1 correspond.

Example 3 The procedures described in Examples 1 and 2 are followed with the amendment repeated that part of the Fe203 through Ga 203 is replaced. These starting oxide mixtures are used in the examples 1 and 2 by letting it crystallize out without a seed crystal, homoepitaxial and heteroepitaxial bismuth doped rare earth iron gallium garnet single crystals manufactured.

The absorption coefficients of each of the garnet single crystals thus produced is much lower than the absorption coefficient of the corresponding rare earth metal ice en-gallium garnet single crystals made from lead-containing fluxes according to the state of the art Technique to be bred.

Example 4 The procedures described in Examples 1 and 2 are followed with the modification that part of the Fe203 in the starting oxide mixture is repeated A1203 is replaced. The three methods described will be of excellent quality obtained with bismuth substituted rare earth metal iron aluminum garnet single crystals. The bismuth content in all single crystals was lower than the bismuth content in the corresponding starting oxide mixtures. The absorption coefficient of each of the so garnet single crystals obtained were significantly lower than the absorption coefficients of the corresponding rare-earth-iron-aluminum garnet single crystals, which are made from im essential from PbO and resp.

or PbF2 existing melts.

Example 5 The procedure described in Examples 1 and 2 is followed in the modification that part of the Fe203 in the starting oxide mixture is repeated In 203 is replaced. After the three process variants described, allow to crystallize out without a seed crystal, homoepitaxial and heteroepitaxial, are doped with bismuth Rare earth indium iron garnet single crystals grown. In each of the so obtained single crystals, the bismuth content is lower than the bismuth content in the corresponding starting oxide mixture.

Likewise are the absorption coefficients of all so obtained with bismuth doped single crystals were significantly lower than the absorption coefficient of the corresponding rare-metal-iron-indium-garnet single crystals, which are made of lead-containing Melts are grown.

Example 6 The procedures described in Examples 1 and 2 are followed in the modification repeats that part of the Fe 2 O 3 of the starting oxide mixture is replaced by Cr203. The after all three of the process variants described manufactured with bismuth doped rare earth metal-iron-chromium-garnet single crystals have a lower bismuth content than the corresponding starting oxide mixtures on.

The absorption coefficient of those grown in the manner described Crystals is much lower than the corresponding absorption coefficient Rare-earth-iron-chromium-garnet single crystals, consisting essentially of a PbO existing flux can be grown.

Example 7 The procedures described in Examples 1 and 2 are followed in the amendment repeats that part of the 203 in the starting oxide mixture through Cm 203 is replaced. Those obtained by the three process variants described Rare earth iron cobalt garnet single crystals doped with bismuth have a lower bismuth content than the starting oxide mixture. Compared to the corresponding undoped single crystals of the rare earth metal-iron-cobalt garnet system, which consist of melts consisting essentially of PbO are bred, the bismuth-doped garnet single crystals of the invention have much lower ones optical absorption coefficients.

The BiRIG single crystals obtained according to the examples described above are so produced in such a way that one of the cation ratio of the to The starting oxide mixture corresponding to the growing crystal, but its bismuth content larger than is intended for the single crystal to be grown, melts and the Single crystals from the melt obtained in this way through self-nucleation without a seed crystal or breeds homoepitaxially or heteroepitactically. To carry out the procedure According to the invention, in principle all processes known per se for growing crystals can be used can be used. The deposition temperature of the single crystals of the desired The composition can be reduced by adding suitable amounts of B203. the depending on the desired lowering of the deposition temperature in the individual case The amount of B203 to be added can be determined by the person skilled in the art in individual cases without any inventive step determine yourself effortlessly.

Claims (5)

Claims 1. Process for the production of bismuth-doped iron garnet single crystals, d u r c h e k e n n n z e i c h n e t that the oxides are in the desired cation ratio of the garnet weighed in, but using the bismuth oxide or a mixture of bismuth oxide and boron oxide in an amount greater than that intended for the single crystal The target amount is that the oxides are mixed and melted, that the melt is also mixed 0.1 - 10 OC / h down to 950 OC controlled and that one then on room temperature cools down. 2. The method according to claim 1, d a d u r c h g e k e n n -z e i c h n e t that the temperature of the melt can be reduced to below the saturation temperature the target composition of the doped garnet lowers and that one then goes to cultivation of the garnet single crystal of the target composition is the same as a garnet seed crystal Crystal structure, but with different compositions, is immersed in the melt. 3. The method according to claim 2, d a d u r c h g e k e n n -z e i c h n e t that the garnet seed crystal has the same composition as that to be grown crystal Has. 4. The method according to claim 1, d a d u r c h g e k e n n -z e i c h n e t that the starting oxide mixture has a composition in the pseudo-ternary Three-component diagram within a straight rectangle with the corner points (A) 30 mol% Bi203, 69.5 mol% Fe203 and 0.5 mol% R203, where R203 is a rare earth metal oxide means (B) 30 mol% Bi203, 43.75 mol% Fe203 and 26.5 mol% R203, (D) 57.5 mol% Bi203, 26.6 mol% Fe203 and 15.9 mol% R203 and (C) 57.5 mol% Bi203, 42 mol% Fe203 and 0.5 mol% of R203, with a mixture of Bi 0 and 23 instead of Bi203 2 and B203 can be used, the B203 portion in this mixture being 0.5 mol per mole of Bi203 does not exceed. 5. The method according to any one of claims 2 or 3, d a d u r c h g e it is not indicated that the composition of the starting oxide mixture in a pseudo-ternary three-component diagram within a straight quadrangle forming composition area lies with the vertices (C) 57.5 mol% Bi203, 42 mol% Fe 2 O 3 and 0.5 mol% R 2 O 3, (D) 57.5 mol% Bi 2 O 3, 26.6 mol% Fe 2 O 3 and 15.9 Mol% R203, (F) 90 mol% Bi203, 6.25 mol% Fe203 and 3.75 mol% R203 and (E) 90 Mol% Bi203, 9.5 mol% Fe203 and 0.5 mol% R203, the Bi203 can be replaced by a mixture of Bi203 and B203, in which the B203 in a Amount of not more than 0.5 mol per mol of Bi203 is present.