CN111379014A - A kind of flux for crystal growth and crystal growth method - Google Patents

Abstract

The invention discloses a flux for crystal growth and a crystal growth method. The crystal is Pb ₁₇ O ₈ Cl ₁₈ , and the system of the flux includes at least one of PbO, metal halide M′X, metal halide M″X ₂ and Bi ₂ O ₃ ; M′ is Li, Na or K, M" is Mg, Ca, Ba, Sr or Pb, and X is F or Cl. The crystal growth method is: mix and melt the polycrystalline raw material with the flux; start seeding above the saturation point of the melt temperature, the melt temperature is stabilized at the saturation point, and the crystal growth begins; the crystal grows to the required size, and the seed rod crystal is raised After leaving the liquid surface, annealing is performed in a weakly oxidizing atmosphere. The invention fully takes care of the orientation of crystal growth, effectively improves the stability of crystal growth, reduces the volatilization of the solution and the viscosity of the system during the growth process, solves the problems of needle-like development of the crystal and the easy cracking and discoloration of the grown crystal, and the size of the grown crystal is large. , High optical quality.

Description

A kind of flux for crystal growth and crystal growth method

technical field

The invention relates to a single crystal growth method, in particular to a flux and a crystal growth method for mid-infrared nonlinear optical Pb ₁₇ O ₈ Cl ₁₈ crystal growth.

Background technique

每个晶胞中包含3个Pb₁₇O₈Cl₁₈化学式。由于Pb₁₇O₈Cl₁₈晶体是同成分熔融化合物，先前的报道是采用自发成核的方法进行晶体生长，但生长出的晶体都是部分透明，并且晶体内有大量的宏观包裹体，生长的晶体易开裂，难以能满足物性测试。因此本发明优选新的合适的助熔剂采用熔盐顶部籽晶法来进行中红外非线性光学晶体Pb₁₇O₈Cl₁₈的生长。Pb ₁₇ O ₈ Cl ₁₈ crystal is a new type of mid-infrared nonlinear optical crystal with high laser damage threshold discovered in 2015. It has the advantages of large nonlinear optical coefficient, high laser damage threshold, wide light transmission range, and stable physical and chemical properties. Compared with other mid-infrared nonlinear optical crystals, the Pb ₁₇ O ₈ Cl ₁₈ crystal has a better growth habit and can be grown in an open system, which greatly reduces the difficulty of growing traditional infrared frequency-doubling crystals in a closed system. Pb ₁₇ O ₈ Cl ₁₈ crystal can realize mid- and far-infrared laser output for visible light or near-infrared laser through laser frequency conversion. Due to the high light damage resistance threshold of this crystal, the crystal has broad application prospects in the field of high-power laser frequency conversion. The American Journal of the American Chemical Society [J.Am.Chem.Soc.2015, 137, 8360-8363] reported the structure of the Pb ₁₇ O ₈ Cl ₁₈ crystal, which belongs to the orthorhombic system, the space group is Fmm2, is a biaxial crystal whose unit cell parameters

Each unit cell contains 3 chemical formulas of Pb ₁₇ O ₈ Cl ₁₈ . Since the Pb ₁₇ O ₈ Cl ₁₈ crystal is a molten compound of the same composition, the previous report used the method of spontaneous nucleation for crystal growth, but the grown crystals were all partially transparent, and there were a large number of macroscopic inclusions in the crystals. The crystal is easy to crack, and it is difficult to meet the physical property test. Therefore, the present invention preferably uses a new and suitable flux for the growth of the mid-infrared nonlinear optical crystal Pb ₁₇ O ₈ Cl ₁₈ by using the molten salt top seeding method.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a flux and a crystal growth method for Pb ₁₇ O ₈ Cl ₁₈ crystal growth, so as to improve the stability of the crystal growth system, increase the crystallization temperature range for crystal growth, and reduce the high temperature solution. Viscosity and volatility, improve crystal acicular growth habit, and obtain larger size and high quality Pb ₁₇ O ₈ Cl ₁₈ crystals.

In order to solve the above problems, the present invention adopts the following technical solutions:

A flux for Pb ₁₇ O ₈ Cl ₁₈ crystal growth, characterized in that the system of the flux comprises at least one of PbO, metal halide M'X, metal halide M'X ₂ and Bi ₂ O ₃ In the metal halide M′X and metal halide M″X ₂ , M′ is Li, Na or K, M″ is Mg, Ca, Ba, Sr or Pb, and X is F or Cl.

Preferably, the Pb ₁₇ O ₈ Cl ₁₈ is prepared by reacting a Pb-containing compound, an O-containing compound and a Cl-containing compound.

The present invention also provides a crystal growth method using the above-mentioned Pb ₁₇ O ₈ Cl ₁₈ crystal growth flux, which is characterized in that the growth by using a molten salt top seed crystal method includes the following steps:

Step 1): pre-synthesize Pb ₁₇ O ₈ Cl ₁₈ polycrystalline raw material;

Step 2): using a platinum crucible or an alumina ceramic as a container, mixing the pre-synthesized Pb ₁₇ O ₈ Cl ₁₈ polycrystalline raw material with the fluxing agent uniformly, heating up until the raw material is completely melted, and maintaining at a constant temperature;

Step 3): start seeding at 1-10°C above the melt temperature saturation point, keep the temperature constant for 5-300 minutes, the melt temperature is stabilized at the saturation point, and crystal growth begins;

Step 4): the crystal is grown to the required size, the seed rod crystal is lifted out of the liquid surface, lowered to room temperature at a rate of less than 50°C/h, and annealed in a weakly oxidizing atmosphere to obtain a Pb ₁₇ O ₈ Cl ₁₈ crystal .

Preferably, the amount of the fluxing agent in the step 2) is 5-75 mol% of the Pb ₁₇ O ₈ Cl ₁₈ polycrystalline raw material; the temperature at which the Pb ₁₇ O ₈ Cl ₁₈ polycrystalline raw material is completely melted into a high-temperature solution is 515-600° C. ; The time of constant temperature is 24h.

Preferably, in the step 3), the temperature saturation point of the melt is 510-550°C.

Preferably, the process parameters for crystal growth in the step 4) are: the cooling rate is 0.01-2°C/day, the rotational speed is 1-50 rpm/min, the pulling speed is 0-100mm/day,

Preferably, the weak oxidizing atmosphere in the step 4) is air, or a mixture of any one or more of nitrogen, hydrogen, carbon monoxide gas, carbon dioxide gas and alkane gas, or the aforementioned gas and oxygen and/or A mixture of inert gases.

The invention also provides the application of the Pb ₁₇ O ₈ Cl ₁₈ crystal prepared by the above crystal growth method in an infrared nonlinear optical crystal.

Preferably, the Pb ₁₇ O ₈ Cl ₁₈ crystal converts visible light or near-infrared laser light through laser frequency down-conversion to generate mid- and far-infrared laser output in the 3-8 μm and 8-14 μm bands.

The molten salt top seeding method of the Pb ₁₇ O ₈ Cl ₁₈ crystal provided by the present invention uses a cosolvent system of metal halides M′X, M″X ₂ , PbO and Bi ₂ O ₃ . Compared with the prior art , the beneficial effects of this method are:

1) It can effectively reduce the volatilization of the melt, improve the stability of the system during the crystal growth process, prevent the formation of miscellaneous crystals and dendrites, and improve the growth rate of the crystal.

2) The viscosity of the solution can be significantly reduced, and the lower viscosity is beneficial to the transport of solutes and is conducive to the growth of high-quality crystals.

3) In this flux system, the crystallization temperature range of Pb ₁₇ O ₈ Cl ₁₈ crystal is wider, which is convenient to find a suitable saturation point, avoid the formation of miscellaneous crystals and dendrites, and easily grow large-sized crystals.

Detailed ways

In order to make the present invention more obvious and easy to understand, preferred embodiments are hereby described in detail as follows.

Example 1

Weigh PbO and PbCl ₂ according to the stoichiometric ratio, fully grind and mix them, and then transfer them to an alumina ceramic crucible. In a muffle furnace, it was first sintered at 420°C for 24 hours. After cooling to room temperature, the obtained product was ground again, transferred to an alumina ceramic crucible, and sintered in a muffle furnace at 480° C. for 24 hours. After being naturally cooled to room temperature, it was taken out to obtain Pb ₁₇ O ₈ Cl ₁₈ polycrystalline raw material. Mix the Pb ₁₇ O ₈ Cl ₁₈ polycrystalline raw materials with the fluxes PbCl ₂ and LiF ₂ according to the molar ratio of 65:35. After grinding and mixing the weighed raw materials, they are directly melted in a platinum crucible of Φ100mm×75mm. The above-mentioned crucible containing the molten material is put into the molten salt furnace, the opening at the top of the furnace is sealed with a heat insulating material, and a small hole for the seed rod to enter and exit is left on the top of the furnace and the center of the crucible corresponding to the position, and the temperature rises. At 530°C, the above melt is completely melted, and the temperature is kept for 24 hours to make the melt fully melt and uniform. Use the crystal washing test method to find that the saturation temperature of crystal growth is 521°C, cool the above-mentioned high temperature solution to 526°C (5°C higher than the saturation temperature), and fix the Pb ₁₇ O ₈ Cl ₁₈ seed crystal on the seed rod with platinum wire At the lower end, slowly introduce the seed crystal into the growth furnace from the small hole at the top of the furnace, so that the lower end of the seed crystal protrudes into the liquid surface about 1mm, the seed crystal rotates at a rate of 25 rpm, and after 240 minutes of constant temperature, it is immediately cooled to 521 ℃, and then The temperature was lowered at a rate of 0.3°C/day for crystal growth. During the growth process, the rotational speed of the seed crystal slows down with the gradual growth of the crystal. After the crystal growth was completed, the crystal was removed from the liquid surface, lowered to room temperature at a rate of 15°C/h, and annealed in air to obtain a Pb ₁₇ O ₈ Cl ₁₈ crystal.

Example 2

Mix evenly with stoichiometric ratio of PbO and PbCl ₂ powder, put it into an alumina ceramic crucible, put it in a muffle furnace with a cover, keep it at 470 ° C for 48 hours, naturally cool it to room temperature, take it out, and fully grind it After that, the polycrystalline raw material of Pb ₁₇ O ₈ Cl ₁₈ was obtained. Mix the Pb ₁₇ O ₈ Cl ₁₈ polycrystalline raw material with PbF ₂ and PbCl ₂ in a molar ratio of 55:45. After the weighed raw materials are ground and mixed uniformly, the ground POC polycrystalline material is placed in a Φ100mm×75mm platinum crucible. , place the loaded crucible in a molten salt furnace, put the crucible cover on the top of the crucible, control the furnace temperature to 575°C, melt the raw materials completely, and keep the temperature constant for 18 hours to make the high-temperature solution completely uniform. Use the crystal washing test method to find that the saturation temperature of crystal growth is 512 ° C, the above high temperature solution is cooled to 520 ° C (8 ° C higher than the saturation temperature), and the Pb ₁₇ O ₈ Cl ₁₈ seed crystal is fixed on the seed rod with platinum wire. At the lower end, slowly introduce the seed crystal into the growth furnace from the small hole at the top of the furnace, so that the lower end of the seed crystal protrudes into the liquid surface by about 1mm, the seed crystal rotates at a rate of 45 rpm, and after 120 minutes of constant temperature, the temperature is immediately lowered to 512 ° C, and then The temperature was lowered at a rate of 0.3°C/day, and the crystal growth was carried out at a pulling rate of 0.1 mm/day. During the growth process, the rotational speed of the seed crystal slows down with the gradual growth of the crystal. After the crystal growth was completed, the crystal was pulled away from the liquid surface, lowered to room temperature at a rate of 40° C./h, and annealed in an air atmosphere to obtain a Pb ₁₇ O ₈ Cl ₁₈ crystal.

Claims (9)

1. A flux for crystal growth, the crystal is Pb ₁₇ O ₈ Cl ₁₈ , wherein the system of the flux comprises PbO, metal halide M′X, metal halide M″X ₂ and Bi At least one of ₂ O ₃ ; in the metal halide M'X, metal halide M'X ₂ , M' is Li, Na or K, M'' is Mg, Ca, Ba, Sr or Pb, X is F or Cl. 2 . The flux for crystal growth according to claim 1 , wherein the Pb ₁₇ O ₈ Cl ₁₈ is prepared by reacting a Pb-containing compound, an O-containing compound and a Cl-containing compound. 3 . 3. a crystal growth method utilizing the fluxing agent of claim 1 or 2, characterized in that, adopting molten salt top seed crystal growth, comprising the following steps: Step 1): pre-synthesize Pb ₁₇ O ₈ Cl ₁₈ polycrystalline raw material; Step 2): using a platinum crucible or an alumina ceramic as a container, mixing the pre-synthesized Pb ₁₇ O ₈ Cl ₁₈ polycrystalline raw material with the fluxing agent uniformly, heating up until the raw material is completely melted, and maintaining at a constant temperature; Step 3): start seeding at 1-10°C above the melt temperature saturation point, keep the temperature constant for 5-300 minutes, the melt temperature is stabilized at the saturation point, and crystal growth begins; Step 4): the crystal is grown to the required size, the seed rod crystal is lifted out of the liquid surface, lowered to room temperature at a rate of less than 50°C/h, and annealed in a weakly oxidizing atmosphere to obtain a Pb ₁₇ O ₈ Cl ₁₈ crystal . 4. The crystal growth method according to claim 3, wherein the amount of _the flux in the step ₂ ) is 5-75 mol% of _the Pb ₁₇ O ₈ Cl ₁₈ polycrystalline raw material; The temperature at which the crystal raw material is completely melted into a high-temperature solution is 515-600° C.; the constant temperature is 24 hours. 5 . The crystal growth method according to claim 3 , wherein the temperature saturation point of the melt in the step 3) is 510-550° C. 6 . 6. The crystal growth method according to claim 3, wherein the process parameters of the crystal growth in the step 4) are: a cooling rate of 0.01～2°C/day, a rotating speed of 1～50 rev/min, a pulling speed of 0～100mm/day. 7. crystal growth method as claimed in claim 3 is characterized in that, the weak oxidizing atmosphere in described step 4) is air, or any one in nitrogen, hydrogen, carbon monoxide gas, carbon dioxide gas and alkane gas Or a mixture of several, or a mixture of the aforementioned gases and oxygen and/or inert gases. 8. Application of the Pb ₁₇ O ₈ Cl ₁₈ crystal prepared by the crystal growth method according to any one of claims 3 to 7 in infrared nonlinear optical crystals. 9 . The application according to claim 8 , wherein the Pb ₁₇ O ₈ Cl ₁₈ crystal converts visible light or near-infrared laser light through laser frequency down-conversion to generate mid- and far-infrared laser output in 3-8 μm and 8-14 μm wavebands. 10 .