Method of growing single crystals of lithium triborate

 

(57) Abstract:

The invention relates to the production of nonlinear optical single crystal triborate lithium (LBO). The method comprises the cultivation of the solution-melt, the composition of which is defined by the area ABCD of the ternary diagram of the system Li2O - B2O3- MoO3coordinates system, mol. share: A: Li2O - 0,18; B2O3- 0,51; MoO3- 0,31; B: Li2O - 0,17; B2O3- 0,83; MoO3- 0; C: Li2O - 0,04; B2O3to 0.21; MoO3- 0,75; D: Li2O - 0,28; B2O3- 0,07; MoO3- 0,65. The growing crystal is pulled from the melt with a speed of 0.3 - 1.3 mm/day at low melt temperature from 750 - 790 up to 690 - 720oWith speeds of 1 to 2oC/day. The solvent MoO3low viscosity, as well as conducting growth by pulling the crystal provides the possibility of obtaining large single crystals LBO size 49 x 52 x 45 mm3high optical quality: the change in the refractive index < 10-3; adsorption loss < 10-3cm-1; radiation resistance of > 10 GW/cm2when = 1.06 µm and = 1 NS, which enables to produce optical elements up to size (5 - onocrotalus of triborate lithium (LBO), having nonlinear optical properties and intended for frequency conversion of laser radiation, create parametric light generators.

Known methods of growing single-crystal LBO of the solution in the melt method of reducing the temperature of the melt, producing crystals suitable for fabrication of these optical elements. For example, a method of obtaining crystals LBO in the system Li2O-B2O3at which stoichiometric amounts of starting materials in Li2CO3H3BO3, Li2O, B2O3, LiOH are mixed, the mixture is melted at a temperature above 900oC and hold growth or original synthesize connection LBO, then melt it together with the solvent B2O3and spending growth on a seed crystal by the method of lowering the temperature from 834 750oC at a rate of 0.2-2oC/day at pulling speeds of 1 mm/day with or without stretching. You get crystals HH mm3.

Also known is a method of growing crystal LBO of the solution-melt in the system Li2O - B2O3by displacement of a homogeneous mixture of starting materials in Li2CO3and H3oC at a rate of 0.5oC/day with subsequent cooling of the crystal at a speed of 40oC/H. thus receive transparent crystals up to HH mm3. However, using as solvent B2O3leads to the appearance of inclusions in the crystals, due to the high viscosity of this solvent, and does not allow to grow large crystals.

Closest to the invention is a method of obtaining a crystal LBO of the solution-melt in the system Li2O-B2O3-MoO3comprising dissolving the source materials of Li2CO3H3BO3in MoO3and the growth method of reducing the temperature from 670 to 580oC with a speed of 5oC/h for obtaining the melt in the system Li2O-B2O3-MoO3occurs through the well-known decomposition reaction of the source reagents: Li2CO3(46.6 g), H3BO3(the amount of 203.9 g) and MoO3(158,3 g), which corresponds to the ratio of Li2O: B2O3: MoO30,17: 0,5:0,33 mol.share. The grown crystal is removed from the melt and cooled to room temperature at a rate of 100oC/H. In this way the obtained transparent crystals HH mm3.

However, PRA, which leads to the deterioration of the natural convection in the melt and changes in growth conditions, which complicates the regulation process. In combination with a large anisotropy of crystal properties, including the growth rates of different faces, this leads to the formation of stagnant zones and inclusions solvents in the direction 111 and 201.

To improve the optical quality and size of the crystals triborate lithium proposed to obtain LBO crystals from a solution-melt on a seed crystal by reducing the melt temperature of the growing hold of the melt, the composition of which is defined by the area ABCD of the ternary diagram of the system Li2O-B2O3-MoO3when the crystal pulling speed of 0.3 - 1.3 mm/day, while the temperature of the melt is reduced from 750 - 790 up to 690 - 720oC with a speed of 1 to 2oC/day. This coordinate system is defined by the following points, mol.share:

A: Li2O - 0,18; B2O3- 0,51; MoO3- 0,31;

B: Li2O - 0,17; B2O3- 0,83; MoO3- 0;

C: Li2O - 0,04; B2O3to 0.21; MoO3- 0,75;

D: Li2O - 0,28; B2O3- 0,07; MoO3- 0,65.

The drawing shows a diagram of the composition of the ternary system is N the prototype.

The diagram was studied using solid-phase synthesis, quenching of melts and spontaneous crystallization.

The results show that the crystallization outside the specified area leads to cocrystallization borates another part.

The inventive compositions can be used in various methods of growing LBO crystals from the melt by the method of reduction temperature on seed and preferred in the present method of cultivation by pulling the seed crystal in the growth process.

Holding growth at pulling the growing crystal from the melt provides the location of the front growth near the surface of the partition, a good mixing of the water without ponding, while not changing the growth conditions during the whole time and simplifies the regulation of the growth process.

The use of a solvent with low viscosity (MoO3), as well as pulling the growing crystal provide LBO crystals, the maximum dimensions of which are HH mm high optical quality: the change in the refractive index < 10-3, adsorption loss < 10-3cm-1, l is ω to (5-15) x (5-15) x (5-30) mm3.

Thus, the proposed solution meets the condition of inventive step, because the achievement of the technical result is an improvement of the optical quality and the larger crystals triborate lithium based both on the choice of the composition of the solvent, and the establishment of the optimal growth modes. The fame of the individual operating parameters do not destroy the novelty of causality distinctive features - technical result.

Example. To obtain the LBO crystal is used the solution-melt, the composition of which is within the area ABCD and contains Li2O - 0,2; B2O3- 0,36; MoO3to 0.44 mol. share. Sample source reagents Li2CO3OFS - 156,35 g, B2O3OFS - 265,46 g, MoO3analytical grade - 671,24 g mechanically stirred in glass containers, the mixture is loaded into a platinum crucible of 800 cm3and placed in an oven at a temperature of 830oC to obtain a melt. The solution-melt is heated above the melting temperature 100oC and cooled down to 775oC, 5oC above the temperature of crystallization. After stabilization of the temperature in the melt contribute to the platinum rod seed of single-crystal LBO and begin the growth of a crystal from a melt with a speed of 0.03 mm/H. 40 days (1000 hours) crystal reaches 49 size:52:45 mm x: y:z, respectively, after which it raise above the surface of the melt. Lowering the temperature to room carried out with a speed of 20oC/H.

A method of growing single crystal triborate lithium from the solution-melt in the system Li2O - B2O3- MoO3to whet your appetite by lowering the temperature of the melt, characterized in that the cultivation of lead from the melt, the composition of which is defined by the area ABCD of the ternary diagram of the system Li2O - B2O3- MoO3when the crystal pulling speed of 0.3 - 1.3 mm/day and the temperature drops from 750 - 790 up to 690 - 720oC with a speed of 1 to 2oC/d, with coordinates system defined by the following points, mol.share:

 

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