A method of growing single crystals of lithium ferrospinel life5o8

 

(57) Abstract:

Usage: devices based on magnetic excitations. The invention - alloy (wt.%) 17,1oC 18,0 oxide of boron IN2O3, 52,0oC53,5 oxide of bismuth Bi2O317,2oC18,0 lithium carbonate Li2CO3the iron oxide - rest. The solution-melt heated to 980 - 1000oC. Establish a temperature gradient with the vertical component (1oC3)o(Temperature decreases with distance from the bottom of the crucible). Stand 20oC 24 hour, 4oC6 hour with stirring. At a temperature of 5oC10oWith higher saturation temperature is brought into contact with a solution-melt horizontally oriented surface of the seed. Kristalose with the blades rotate at a speed of 40 - 60/min After 20 to 30 minutes the temperature is reduced by 5 - 7oC below saturation temperature and next on the program with increasing cooling rate from 1 to 5oWith a day when the temperature 759 - 800oWith crystallochemical raise and the crystals out of the solution-melt is cooled to room temperature at a speed of 40 - 50oWith in the hour. Manufactured samples for magnetoacoustic research on low from solutions-melts and can be used in obtaining single crystals of lithium ferrospinel LiFe5O8for devices based on magnetic excitations.

In a known solution-melt method of growing single crystals of lithium ferrospinel iron oxide Fe2O3and lithium carbonate Li2CO3was fused with boron oxide IN2O3and lead oxide PbO. Melt a few hours overheat at temperatures of 1025oC 1060oC, then cooled with a speed of 0.8oC 2 deg/hour up to temperatures of 300 to 600oC. the crystals were separated from the hardened solution-melt by dissolving the latter in a hot nitric acid solution.

These methods with spontaneous nucleation does not allow to reproducibly obtain high-quality single crystals for applied research and technical applications.

The method described in [1] which were obtained the largest crystals selected for the prototype. According to this method, the iron oxide Fe2O3and lithium carbonate Li2CO3was fused with boron oxide B2O3and lead oxide PbO in the following proportions, they say.

IN2O3to 20.28 (8,9 wt.)

PbO 44,32 (62,2 wt.)

Fe2O323,09 (23,2 wt.)

Li2CO312,31 (5.7 wt.)

The solution-melt prepared in a 500 mloS/cm (the temperature in the solution-melt increases as the distance from the bottom of the crucible), kept for 12 hours. After this, the solution-melt was cooled with a speed of 0.8oC/h to 600oWith, and then turned off oven. From the hardened mass by dissolving it in a hot aqueous solution of nitric acid was separated 6 crystals up to 1 cm and one with a maximum size up to 2 cm

The main drawback of this method is that it does not provide reproducible growing high quality single crystals of lithium ferrospinel with the size needed for microwave devices for magnetoelastic and magnetostatic waves. Because of microdefects in the form of inclusions solution-melt only parts of the grown crystals were suitable for the manufacture of the samples. Quality share in the largest block crystal was less. However, with increasing size of the crystals was observed growing role of poloschatosti". In crystals fractures caused by cooling in a hardening solution-melt. In this way the spontaneous emergence of both the number and the size of the crystals and their quality vary significantly from experiment to experiment.

The purpose of izobreteny the tsya fact, in the known method, including the alloying of iron oxide Fe2O3and lithium carbonate Li2CO3double oxide mixture containing an oxide of boron IN2O3, overheating and subsequent crystallization by cooling, the second component of the mixture is injected oxide of bismuth Bi2O3at the next General ratio in wt.

B2O317,1 18,0

Bi2O352,0 53,5

Li2CO317,2 18,0

Fe2O3else,

the resulting solution is heated to melt 980 1000oWith and by setting the temperature gradient with the vertical component (1 3)oC/cm (temperature decreases with distance from the bottom of the crucible), aged 20 to 24 hours 4 6 hours with stirring, and then at a temperature of 5 to 10oWith higher saturation temperature Tushorizontally oriented surface (III) m is brought into contact with a solution-melt and rotating crystallochemical with a speed of 40 to 60 rpm, 20 to 30 minutes the temperature is reduced by 5 7oWith the below Tusand next on the program with increasing cooling rate from 1 to 5oC/d, and at a temperature of 750 800oWith crystallochemical raise, and the crystals out of the solution-melt-Ahmadzai on the filing date is not known to the inventive method of growing single crystals of lithium ferrospinel LiFe5O8, from which it follows that the invention is new.

In the present method at the specified ratio of the components of the solution-melt lithium ferrospinel is a high temperature phase, crystallizing in the temperature range from 900 950oWith up to 740 - 750oC. the density of the solution-melt is less than its density, which eliminates the possibility of stable long-term development of freely floating parasitic crystals. Overheating of such a solution-melt at 980 1000o(I.e., at temperatures of 50 to 80oWith higher saturation temperature) in an inhomogeneous field with temperature, decreasing with distance from the bottom of the crucible, and the mixing is complete homogeneity regardless of the initial state. The introduction of nucleating fixed initial number of crystallization centers and surface growth. Temperature field, hydrodynamic conditions and the cooling mode after the introduction of nucleating agreed so that is preferential crystallization on blades rotating in the surface layer of the solution-melt. The crystal growth proceeds under conditions close to equilibrium with intensive wash their faces with a solution-melt, and the probability of formation of macro defects t is our solution-melt eliminates stresses and cracks.

Deviations from the ratio of components, as well as from thermal and hydrodynamic parameters specified in the present method, accompanied by replenishment of the factors that lead ultimately or decrease the size of the obtained crystals, or reducing their quality and reproducibility. So with the increase in the content of B2O3and Bi2O3(respectively decrease in Li2CO3) beyond these much narrower temperature interval of crystallization ferrospinel, and with some excess of the generally high temperature phase becomes hematite. Narrowing the interval of crystallization ferrospinel with subsequent replacement of the high temperature phase occurs when the decrease IN2O3and Bi2O3(accordingly, the increase in Li2CO3) beyond these. However, in this case the competing phase will be Li2O containing compound. Along with this should indicate that the depletion of solution-melt components with low density (B2O3and Li2CO3) is unacceptable because of the danger of the growth of "parasitic" floating crystals. At the same enrichment such components increases the difference in the densities of ferrospinel the temperature gradients, and this will inevitably lead to a rise of temperature fluctuations and the narrowing of the metastable zone. The concentration of Fe2O3cannot be increased (with its growth on one Mac. the saturation temperature is increased by 20 25oC), otherwise the operating temperature exceeds 1000oWith that will cause uncontrollable changes of the conditions of crystallization due to intensive evaporation. The lowering of the same concentration of Fe2O3directly means reducing the size of the grown crystals.

The decrease of the temperature in the solution-melt at a distance from the bottom of the crucible at the stage of overheating promotes homogenization, and when cooling is necessary for preferential crystallization on blades, rotating in the surface layer. When the magnitude of the vertical component of the gradient is less than 1oS/cm significantly reduced the percentage of substance crystallized on the seed, while when the gradients of more than 3oS/cm due to the growth temperature fluctuations decreases the quality of the crystals.

20 30-minute extract of the seeds at temperatures of 5 to 10oWith higher saturation temperature allows to dissolve only the surface of the disturbed layer of the seed and thus avoid inheritance Chris it is also possible and separazione".

The initial growth temperature TbegTus(5 7)oWith is selected in the middle zone of metastability, and the rate of further cooling corresponds to an increase of 1 4 crystals with speeds of 0.5 to 0.7 mm/day. The rotation of the crystals at a speed of 40 to 60 rpm practically eliminated the possibility of nucleation of the solution-melt. Growth is complete at temperatures of 750 - 800oWith as due to the lower concentration of crystalloblastic oxides and increased viscosity of the solution-melt the development of crystals slows down, increasing the likelihood of macro defects types of inclusions solution-melt.

Thus, in the proposed method of growing physico-chemical properties of the solution-melt, temperature and hydrodynamic conditions agreed so that the main part of the substance crystallizes on the seed in conditions close to equilibrium, and this can significantly increase the size of the crystals and the reproducibility of their properties.

Example 1. The solution-melt weight 1900 g was prepared in 800 ml platinum cylindrical glass (D= 100 mm) by fusing at a temperature of 980oWith iron oxide and lithium carbonate with a mixture of boron oxide and bismuth oxide in the ratio, wt.


Qualification of all reagents "OFS". The necessary temperature distribution in the solution-melt with a vertical component (1 3)oS/cm was established by regulation of the heat capacity given vertically-arranged main and bottom horizontal silicon carbide heaters crystallization furnace. In this heterogeneous field at a temperature of 980o(Here and hereinafter specified timing by regulating thermocouple located at the level of the surface of the solution-melt on the outside of the glass) solution-melt is kept for 24 hours, with the last 6 hours with stirring (=60 rpm).

Temperature equilibrium crystal lithium ferrospinel with a solution-melt in the center of the surface (Tus) recorded with an accuracy of 2oWith 900oC.

After overheating the furnace was introduced crystallochemical with two seed crystals, each of which faces (III), oriented horizontally, facing toward the surface of the solution-melt and were in the same plane. These faces in the form of right triangles had a square respectively 0.15 cm2and 0.1 cm2. At T=Tus- 10oC=910oWith the CG/min). After 30 min the temperature is lowered to Tbeg=Tus< / BR>
6oC= 894oC, and then cooling was carried out according to the program shown in the table.1:

At TKON= 782oWith crystallochemical raised to break contact grown crystals with a solution-melt and the furnace was cooled to room temperature 40 50oWith/hour.

One of the grown crystals had the weight of 38.2 g and a size of 32 mm, the second crystal had weight to 29.8 g and a size of 30 mm Faces of the crystals were mirrored and free from macro defects, dislocation density is not more than 10 cm-2. Crystal samples were made in the form of disks (D 5 7 mm h 2 4 mm), cylinder (D 3 4 mm, l 10-12 mm) for magnetoacoustic research and areas for FMR. Minimum line width at a frequency of 9.1 GHz at room temperature (N 1,8 2 e) correspond to the best values found in the literature.

Example 2. The solution-melt weight 1900 g was prepared in 800 ml platinum cylindrical glass (D=100 ml) by fusing at 980oWith iron oxide and lithium carbonate with a mixture of boron oxide and bismuth oxide at a ratio of wt.

B2O317,2

Bi2O352,1

Li2O317,4

Fe2O313,3

Kaliveli crystallization furnace, described in example 1. Overheating was carried out at T=1000oC for 24 hours in the last 4 hours with stirring (w=60 rpm). After overheating the furnace was introduced crystallochemical with four seed crystals, each having a horizontally oriented face (III) facing toward the surface of the solution-melt and were in the same plane. These faces in the form of right triangles had a square 0.1 cm2, 0,13 cm2, 0.15 cm2, 0,17 cm2. At T= Tus+5oC= 951oWith the seed crystal is brought into contact with the solution-melt and included the rotation of Kristallografiya (w=40 rpm). After 20 min the temperature is lowered to Tbeg=Tus- 7oC=939oWith further cooling led on the program table.2:

At TKON=770oWith crystallochemical raised to break the contact of the crystals with a solution-melt and the furnace was cooled to room temperature 40 50oC/hour. The total weight of the obtained crystals 117 g, maximum size (31 mm, 30.5 mm, 28 mm, 25 mm). The dislocation density on the mirror faces does not exceed 102cm-2, the faces of the crystals had no macro defects. From crystals were produced samples for mA is 1,8 2 e, which corresponds best to the values given for lithium ferrospinel in the literature.

Data from other experiments conducted according to the same scheme, but with different ratios of components that are listed in the table.3.

A method of growing single crystals of lithium ferrospinel LiFe5O8that includes the fusion of iron oxide Fe2O3and lithium carbonate Li2CO3double oxide mixture containing an oxide of boron B2O3, overheating and subsequent crystallization when cooled, characterized in that the second component of the oxide mixture is injected oxide of bismuth Bi2O3in the following ratio, wt.

B2O317,1 18,0

Bi2O352,0 53,5

Li2CO317,2 18,0

Fe2O3Else

the resulting solution is heated to melt 980 1000oC establish a vertical temperature gradient 1 3oC/cm when the temperature reduces in the direction from the bottom of the crucible can withstand 20 24 h 4 6 h under stirring, and then at a temperature of 5 to 10oC above the saturation temperature is brought into contact with the solution-melt horizontally oriented towards the surface of the seed, size>C below saturation temperature, and then cooling is carried out to 750 800oC, gradually increasing the cooling rate from 1 to 5oC/d, then crystallochemical raise and the crystals are cooled by the outside solution-melt to room temperature at a speed of 40 - 50oC/H.

 

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