WO2016119159A1 - Method for preparing monocrystalline - Google Patents

Abstract

A process method for inhibiting the crack formation and cracking of a manganese doped pyroelectric monocrystalline, wherein the chemical composition of the manganese doped pyroelectric monocrystalline is Mn-(1-x-y)Pb(In _1/2Nb _1/2)O ₃-yPb(Mg _1/3Nb _2/3)O ₃-xPbTiO ₃, wherein x＝0.35-0.42, y＝0.30-0.45, 1-x-y＝0.20-0.29, and the doping level of Mn is 0-5.0%. The preparation method for the material is an improved Bridgman method, comprising the processes of synthesizing a raw material, warming and melting, seeding with a crystal seed and crystal growing. The method overcomes the disadvantages of easy crack formation on a crystal and crystal cracking because of the Mn doping in the prior art, and provides an implementation method for preparing a large size pyroelectric monocrystalline with a high quality, and increasing the yield and performance reliability.

Description

Method for preparing single crystal Technical field

The invention relates to a method for suppressing crack initiation and cracking of a manganese-doped pyroelectric single crystal, in particular to a method for preparing a manganese-doped lead indium bismuth hydride-lead-magnesium titanate-titanate by a modified Bridgman method The method of lead ternary pyroelectric single crystal belongs to the field of crystal growth technology.

technical background

In the world today, countries are competing to develop infrared detection and imaging technology, which is used in many fields such as military, aerospace, scientific research, medical, industrial and so on. Infrared detectors are mainly divided into photon type infrared detectors and thermal infrared detectors. At present, the common photon-type infrared detector mainly uses a narrow band gap semiconductor material represented by mercury cadmium telluride and an optoelectronic semiconductor material represented by gallium arsenide. However, semiconductor infrared devices generally require low-temperature refrigeration, which is bulky, costly, and consumes a lot of power.

The pyroelectric infrared detector developed by the pyroelectric effect of the material has a flat spectral response in the ultraviolet, visible and infrared bands, and has no need for refrigeration, low power consumption, low noise bandwidth, compact structure and convenience. The advantages of carrying and low cost have become one of the most eye-catching focuses in the field of infrared technology. With the development of pyroelectric infrared detectors for low cost, low power consumption and miniaturization, pyroelectric infrared detectors are rapidly expanding from the military market to the civilian market, especially in human body detection, fire warning, gas analysis, infrared spectrometers. And the field of infrared thermal imaging has played an important role, while reflecting the huge market potential.

The materials currently used in pyroelectric infrared detectors mainly include lead zirconate titanate (PZT), barium titanate (BST) and lead citrate (PST), etc., and the main limitations of materials for pyroelectric unit detectors. Lithium niobate (LiTaO ₃ ), triglyceride sulfate (TGS), and the like. However, these traditional materials have shortcomings such as low pyroelectric coefficient, large dielectric loss, and unstable physical properties, which are difficult to meet the application requirements of high-performance pyroelectric infrared detectors and their extended products. For example, the more mature commercial LiTaO ₃ infrared detectors have a detection level of only 1 × 10 ⁸ cm (Hz) ^1/2 /W to 4 × 10 ⁸ cm (Hz) ^1/2 /W. Therefore, at the same time, overcoming the shortcomings of the above materials, exploring new pyroelectric materials with high detection value has become an urgent need for the development of uncooled infrared devices.

Beginning in 1996, Luo Haosu and others first succeeded in the growth of relaxed ferroelectric single crystal (1-x)Pb(Mg _1/3 Nb _2/3 )O ₃ -xPbTiO ₃铌magnesium titanium by Bridgman method. Lead acid (abbreviated as PMNT) (patent document 1). Since 2003, Luo Haosu and others have first discovered the excellent pyroelectric performance of PMNT, and carried out a large number of related pyroelectric performance optimization and material process research, and successively prepared a manganese-doped PMNT single crystal with lower loss and Manganese-doped PIMNT single crystal (diameter < two inches) with higher service temperature.

Crystals without cracks or microcracks are important guarantees for the preparation of high-performance pyroelectric detectors. On the one hand, cracks lead to the decrease in the availability of pyroelectric crystals and wafer yield, and on the other hand, pyroelectrics in practical applications. Cracks hidden in the wafer, resulting in cracking of crystal properties, poor performance under service conditions, and low stability. Mn-doped PMNT and PIMNT pyroelectric crystals are easy to form cracks and cracks, which is related to the formation of defects during crystal growth due to the ion distribution caused by the addition of Mn. To date, no publication has publicly reported a process for suppressing the generation and cracking of cracks in manganese-doped pyroelectric single crystals.

Patent literature:

Patent Document 1: Chinese patent CN 1080777C.

Summary of invention

The invention provides a good quality, non-cracking and crack-free manganese-doped PMNT, Mn-doped PIMNT pyroelectric single crystal prepared by the improved enthalpy drop method, to solve the prior art Mn-doped pyroelectricity The problem of internal cracks and crystal cracking due to Mn doping in single crystal growth.

In general, the present application reduces the temperature gradient and growth rate to improve uniformity compared to conventional preparation methods, while at the same time suppressing the resulting generation of segregation expansion by reducing the thickness of the crucible.

An aspect of the present application is to provide the following technical solutions:

A method for preparing a single crystal, the chemical composition of the single crystal is: Mn-(1-xy)Pb(In _1/2 Nb _1/2 )O ₃ -yPb(Mg _1/3 Nb _2/3 )O ₃ - xPbTiO ₃ , wherein x=0.35-0.42, y=0.30-0.45, 1-xy=0.20-0.29, and the doping amount of Mn is 0-5.0% (molar percentage), the method includes:

Step 1: Obtain high-purity Pb(Mn _1/3 Nb _2/3 )O ₃ , MgNb ₂ O ₆ and InNbO ₄ , PbO, TiO ₂ for 20 to 30 hours, and then pre-burn for 5 to 8 hours at 1100 to 1350 degrees Celsius. Starting material for crystal growth;

Step 2: Fixing the starting material with a crystal of PMNT (lead bismuth magnesium silicate-lead titanate) or PIMNT (lead bismuth indium hydride-lead bismuth magnesium silicate-lead titanate) as a seed crystal The crucible was closed and placed in a crystal growth furnace, and when the crucible began to fall, the temperature gradient in the descending direction was 30 to 70 ° C/cm, and the crystal growth rate was less than 0.5 mm/hr.

That is, the seed crystal and the starting material are enclosed in a crucible and then placed in a modified crystal growth furnace (Fig. 3), and the inoculation position is adjusted to a predetermined inoculation temperature and temperature gradient and then started to fall to achieve crystal growth. The temperature gradient of the solid-liquid interface is controlled to be 30 to 70 ° C / cm, and the rate of decline is less than 0.5 mm / hr.

Among them, a single layer or a double layer of ruthenium having a thickness of 0.8 to 2.0 mm, or a layer of ruthenium having a single layer thickness of 0.1 to 0.5 mm is used as a growth container, or a combination of two layers of different thicknesses is used.

Among them, the inoculation time of crystal inoculation is 6 to 10 hours.

The seed crystal has a length of 30 to 60 mm and a diameter smaller than or equal to the diameter of the grown crystal, and preferably has a seed crystal diameter of 20 to 50 mm.

Wherein, when the crystal structure of the crystal is a tetragonal phase, the crystallographic direction of the seed crystal is [001]. Among them, the furnace temperature is controlled at 1250 ~ 1500 °C.

Among them, the material of bismuth is platinum.

Among them, in order to ensure the growth of crystals, the purity requirements of Pb(Mn _1/3 Nb _2/3 )O ₃ , MgNb ₂ O ₆ , InNbO ₄ , PbO, and TiO ₂ are necessary. In general, its purity needs to reach 99.99%.

For PbO, TiO ₂ , it is generally commercially available, and for Pb(Mn _1/3 Nb _2/3 )O ₃ , MgNb ₂ O ₆ and InNbO ₄ , due to a process that is not mature on the market. Therefore, the second aspect of the present application is also a method for providing high purity Pb(Mn _1/3 Nb _2/3 )O ₃ , MgNb ₂ O ₆ and InNbO ₄ , as follows:

Step a, preparing InNbO ₄ : weighing 1:1 to weigh In ₂ O ₃ and Nb ₂ O ₅ , mixing for 20 to 30 hours, and then pre-burning at 1100 to 1350 degrees Celsius for 10 to 13 hours to obtain InNbO ₄ ,

Step b, preparing Pb(Mn _1/3 Nb _2/3 )O ₃ : molar ratio 1:1 weighs MnO ₂ and Nb ₂ O ₅ , mixes for 20-30 hours, and then in a vacuum atmosphere 900-1100 degrees Celsius The calcination was carried out for 10 to 13 hours to obtain MnNb ₂ O ₆ . The prepared MnNb ₂ O _{6 is} ground into a powder, and the MnNb ₂ O ₆ and PbO are accurately weighed by a molar ratio of 1:5 to 6, mixed for 20 to 30 hours, and then calcined at 1100 to 1300 degrees Celsius for 10 to 13 hours. Pb(Mn _1/3 Nb _2/3 )O ₃ .

Step c, preparing MgNb ₂ O ₆ : weighing 1:1 to weigh MgO and Nb ₂ O ₅ , mixing for 20-30 hours, and then calcining at 900-1100 degrees Celsius for 12-16 hours to obtain MgNb ₂ O ₆ .

In the above preparation method, the inventors of the present application specifically improve the following: through the step b, the Mn element can be present in the +2 valence state, thereby achieving the purpose of reducing the dielectric properties such as dielectric loss of the material; b, can make the Mn element occupy the B position of the perovskite structure ABO ₃ according to the material design requirements, and avoid the erosion of the free lead and manganese during the melting process of the raw material.

The improvement of the present invention is in addition to the prior art:

1) The raw material is prepared by the synthesis method of the present application, so that the growth precursor exists in the form of pure perovskite phase, especially Pb(Mn _1/3 Nb _2/3 )O ₃ , which avoids direct oxidation of the original raw material. Manganese is placed in a growth furnace, and the valence state of manganese ions in manganese oxide at high temperatures and the formation of hetero phases or inclusions in the crystal, resulting in the possibility of crystal cracking, greatly improving the crystal integrity of the crystal.

2) In order to reduce the mechanism of thermal stress during crystal growth to a large crystal pressure and easy to generate cracks, the present invention adopts a single layer or double layer of germanium having a thickness of 0.8 to 2.0 mm, or a thickness of 0.1 to More than 3 layers of 0.5 mm are used as growth vessels, or a combination of two layers of different thicknesses is used. The invention finds that the thickness of the germanium technology can match the stress generated by the growth process of the Mn-doped pyroelectric crystal, on the one hand, the more stress can be released, on the other hand, the stable control of the crystal shape can be realized, and the interface can be avoided. Fluctuations generate macroscopic defects from the place where the crystal is in contact with the crucible wall, and crystal cracks caused by expansion into the interior of the crystal.

3) The key point of the temperature field of the crystal growth furnace used in the present invention is that the temperature gradient of the temperature gradient in the descending direction when the crucible starts to fall is 30 to 70 ° C / cm, and the temperature gradient is too large, which may cause the crystal crystallization process to be easily cracked. Too small will cause polycrystals to appear and cause grain boundary defects.

4) The key point of the crystal growth rate employed in the present invention is that, corresponding to the above temperature gradient, the crystal growth rate used is less than 0.5 mm/hr, which is lower than that of the conventionally grown crystal, which is related to the Mn-doped pyrolysis. In the crystal, the kinetic effect of the manganese-octahedral element in the high-temperature melt is superimposed on the growth interface, thereby avoiding defects such as raw material encapsulation caused by excessive growth rate or cracks formed by unstable growth interface.

5) In the crystal growth process used in the present invention, the seed inoculation time of the crystal inoculation is 6 to 10 hours, thereby effectively eliminating the opportunity for the possible cracks in the seed crystal to diffuse into the newly solidified crystal.

DRAWINGS

1 is a photograph of a crack-free manganese-doped pyroelectric crystal prepared in Example 1, and b) a manganese-doped pyroelectric crystal prepared by a conventional method under strong light;

2 is a prepared crack-free manganese-doped pyroelectric crystal;

3 is a schematic view showing the structure of a melting zone of a Mn-doped relaxation ferroelectric single crystal growth furnace.

Summary of the invention

Example 1

In ₂ O ₃ and Nb ₂ O _{5 were} accurately weighed in a molar ratio of 1:1, and after mixing for 25 hours, they were calcined at 1250 degrees for 12 hours to obtain In NbO ₄ . (Step a)

MgO and Nb ₂ O _{5 were} accurately weighed according to a molar ratio of 1:1, and after mixing for 25 hours, calcination was carried out at 1050 degrees for 12 hours to obtain MgNb ₂ O ₆ . (Step c)

MnO ₂ and Nb ₂ O _{5 were} accurately weighed in a molar ratio of 1:1, mixed for 25 hours, and then calcined at 1000 degrees for 12 hours in a vacuum atmosphere to obtain MnNb ₂ O ₆ .

The MnNb ₂ O ₆ prepared as described above is ground into a powder, and the MnNb ₂ O ₆ and PbO are accurately weighed at a molar ratio of 1:5, mixed for 25 hours, and then calcined at 1250 degrees for 12 hours to obtain Pb (Mn _1/3 Nb _{2 ). /3} )O ₃ . (Step b)

According to Mn-(1-xy)Pb(In _1/2 Nb _1/2 )O ₃ -yPb(Mg _1/3 Nb _2/3 )O ₃ -xPbTiO ₃ , where x=0.38, y=0.42,1- Pt(Mn _1/3 Nb _2/3 )O ₃ , MgNb ₂ O ₆ and InNbO ₄ , PbO, TiO ₂ prepared by the above-mentioned preparation of xy=0.20, the doping amount of Mn is 1.0% by mole. After mixing for 25 hours, 1200 degrees was pre-fired for 7 hours as a starting material for crystal growth.

A crystal of PIMNT (length 50 mm, diameter 30 mm) in the direction of <001> is used as a seed crystal in a platinum crucible (the structure is shown in Fig. 3), and the diameter of the crystal growth portion is 75 mm and the thickness is 1 mm; The pre-fired starting material is charged and closed. Then, it was placed in a modified crystal growth furnace, the furnace temperature was controlled at 1400 ° C, the melting time was 5 hours, and the inoculation position was adjusted to reach a predetermined inoculation temperature and temperature gradient, and then began to fall to achieve crystal growth. The temperature gradient of the solid-liquid interface was controlled to be 45 ° C / cm, and the crystal growth rate was 0.4 mm / hr. Finally, a pyroelectric single crystal is produced, as shown in FIG.

1 is a photograph of a) crack-free manganese-doped pyroelectric crystal prepared in Example 1, and b) a manganese-doped pyroelectric crystal prepared by a conventional method under strong light. As can be seen from Fig. 1, the crystals prepared by the method provided by the present application avoid the problems of perforation, cracking and the like which may be caused by the conventional preparation method. As can be seen from the figures 1 and 2, the surface is smooth, crack-free, crack-like, and the like.

Claims (9)

1. A method for preparing a single crystal, the chemical composition of the single crystal is:

   Mn-(1-xy)Pb(In _1/2 Nb _1/2 )O ₃ -yPb(Mg _1/3 Nb _2/3 )O ₃ -xPbTiO ₃ , where x=0.35～0.42, y=0.30～0.45 , 1-xy=0.20-0.29, the doping amount of Mn is 0-5.0% (molar percentage), characterized in that the method comprises:

   Step 1: Obtain high-purity Pb(Mn _1/3 Nb _2/3 )O ₃ , MgNb ₂ O ₆ , InNbO ₄ , PbO, TiO ₂ for 20 to 30 hours and then pre-fire for 1 to 8 hours at 1100 to 1350 degrees Celsius. Starting material for crystal growth;

   Step 2: fixing the PMNT or PIMNT crystal or its Mn-doped crystal as a seed crystal to the bottom of the crucible, loading and closing the crucible, and placing the crucible into a crystal growth furnace, characterized in that ,

   When the crucible begins to fall, the temperature gradient along the descending direction is 30 to 70 ° C / cm, and the crystal growth rate is less than 0.5 mm / hr.
2. The production method according to claim 1, wherein the purity of the high-purity Pb(Mn _1/3 Nb _2/3 )O ₃ , MgNb ₂ O ₆ , InNbO ₄ , PbO, and TiO ₂ is 99.99%.
3. The production method according to claim 1, wherein the method of obtaining high purity In NbO ₄ , Pb(Mn _1/3 Nb _2/3 )O ₃ , and MgNb ₂ O ₆ in the step 1 is as follows:

   Step a, preparing InNbO ₄ : In ₂ O ₃ and Nb ₂ O _{5 are} weighed in a molar ratio of 1:1, and mixed for 20 to 30 hours, and then calcined at 1100 to 1350 ° C for 10 to 13 hours to obtain InNbO ₄ .

   Step b, preparing Pb(Mn _1/3 Nb _2/3 )O ₃ : molar ratio 1:1 weighs MnO ₂ and Nb ₂ O ₅ , mixes for 20-30 hours, and then in a vacuum atmosphere 900-1100 degrees Celsius The calcination was carried out for 10 to 13 hours to obtain MnNb ₂ O ₆ . The prepared MnNb ₂ O _{6 is} ground into a powder, and the MnNb ₂ O ₆ and PbO are weighed by a molar ratio of 1:5 to 6, mixed for 20 to 30 hours, and then calcined at 1100 to 1300 ° C for 10 to 13 hours to obtain Pb. (Mn _1/3 Nb _2/3 )O ₃ .

   Step c, preparing MgNb ₂ O ₆ : weighing 1:1 to weigh MgO and Nb ₂ O ₅ , mixing for 20-30 hours, and then calcining at 900-1100 degrees Celsius for 12-16 hours to obtain MgNb ₂ O ₆ .
4. The production method according to claim 1, wherein the total thickness of the crucible is 0.8 to 2.0 mm.
5. The production method according to claim 1, wherein the crystal inoculation has a melting time of 6 to 10 hours.
6. The production method according to claim 1, wherein the seed crystal has a length of 30 to 60 mm and a diameter smaller than or equal to a diameter of the grown crystal, and preferably has a seed crystal diameter of 20 to 50 mm.
7. The method according to claim 1, wherein when the crystal structure of the crystal is a tetragonal phase, the crystallographic direction of the seed crystal is [001].
8. The method of claim 1 wherein said furnace temperature is controlled between 1250 and 1500 °C.
9. The method of claim 1 wherein the material of the crucible is platinum.

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