WO2016119157A1 - Method for preparing pyroelectric single crystal - Google Patents

Abstract

Disclosed is a method for preparing a large-size high-homogeneity manganese-doped pyroelectric single crystal. The chemical composition of the manganese-doped pyroelectric single crystal is as follows: Mn-(1-x-y)Pb(In_1/2Nb_1/2)O₃-yPb(Mg_1/3Nb_2/3)O₃-xPbTiO₃, wherein x＝0.35-0.42, y＝0.30-0.45, and 1-x-y＝0.20-0.29. The doping amount of Mn is 0-5%. The preparation method for the material is an improved Bridgman method, which comprises raw material synthesis, seed crystal selection, growth process control, defect regulation and control, etc. The present invention overcomes the disadvantages in the prior art that it is difficult to dope the Mn element, the crucible easily leaks, and a defect is easily generated in the [001] direction, and provides an implementation method for the industrial growth of large-size pyroelectric single crystals.

Description

Method for preparing pyroelectric single crystal Technical field

The invention relates to a preparation method of a large-sized manganese-doped novel pyroelectric single crystal, in particular to a method for preparing a large-sized (diameter ≥ three inches) manganese-doped lead indium bismuth-bismuth by a modified Bridgman method. The method of lead magnesium titanate-titanate lead ternary pyroelectric single crystal belongs to the technical field of crystal growth.

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 infrared thermal imaging, etc. The field plays an important role and at the same time reflects 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 A manganese-doped PIMNT single crystal having a higher use temperature.

However, by the prior art, the size of the single crystals prepared using the Bridgman method is less than 2 inches. In order to reduce the cost of the device, detector design and other factors, more and more larger wafers are needed.

As mentioned earlier, large-size wafers are an important way and trend to reduce device costs. Pyroelectric detector arrays also impose requirements on the size of the wafer. However, the increase in size and the addition of Mn make it necessary for the raw material to be melted for a longer period of time before crystal growth, which makes the platinum crucible more likely to leak and cause crystal growth failure. In the art, the existing solution is to increase the thickness of the crucible to avoid the occurrence of leakage.

However, increasing the thickness of the crucible can improve the leakage, but at the same time brings two new problems. First, the increase in the thickness of the crucible causes the internal stress of the crystal to increase, causing the crystal to crack, so that the crystal can not be subsequently applied, and the preparation cost is further Also greatly increased.

Therefore, so far, there is no suitable solution for industrial application in the industry for how to improve the size of the Mn pyroelectric single crystal.

Patent literature:

Patent Document 1: Chinese patent CN 1080777C;

Summary of invention

The present invention provides a large-sized manganese-doped pyroelectric single crystal prepared by the modified Bridgman method to solve the defects in the prior art that large-sized Mn-doped pyroelectric single crystals are difficult to grow in batches.

The chemical composition of a single crystal suitable for use in the method of the present invention 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 to 0.42, y = 0.30 to 0.45, 1-xy = 0.20 to 0.29, and the doping amount of Mn is 0 to 5.0% by mole.

An aspect of the present invention provides a method for preparing a single crystal, which is an improved method. The Bridgman method includes the following specific steps:

Step 1: Obtain high-purity Pb(Mn _1/3 Nb _2/3 )O ₃ , MgNb ₂ O ₆ , InNbO ₄ , TiO ₂ and PbO for 20 to 30 hours, then pre-burn at 6 to 1300 ° C for 6 to 10 Hour as the starting material for crystal growth;

Step 2: Fixing the bottom of the crucible with PMNT (lead magnesium niobate-lead titanate) or PIMNT (lead antimony lead indium niobate-lead magnesium niobate-lead titanate) or its Mn-doped crystal as a seed crystal The starting material is charged and closed, and the crucible is placed in a crystal growth furnace, and the crystal growth furnace adopts a melting zone width of 10 to 25 mm, and the crucible is used for storing the original material. The diameter is greater than three inches.

Among them, the ruthenium material is platinum, and the ruthenium has a thickness of 0.6 to 1.5 mm.

Wherein, the seed crystal has a length of 50 to 70 mm, and the seed crystal diameter is less than or equal to the diameter of the grown crystal, and preferably the seed crystal diameter is 30 to 40 mm.

Wherein, when the crystal structure of the crystal is a tetragonal phase, the crystallographic direction of the seed crystal is [001].

Wherein, the furnace temperature is controlled at 1350 to 1400 °C.

Wherein, the solid-liquid interface temperature gradient is 50 to 100 ° C / cm.

Wherein, the falling speed is 7.0 to 10. mm/day.

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 ,} Pb(Mn _1/3 Nb _2/3 )O ₆ , TiO ₂ and PbO are necessary. of. In general, its purity needs to reach 99.99%.

For TiO ₂ , PbO is generally commercially available, and for Pb(Mn _1/3 Nb _2/3 )O ₃ , MgNb ₂ O ₆ and InNbO ₄ , due to the unprepared preparation process on the market, the present application The second aspect 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 Pb(Mn _1/3 Nb _2/3 )O ₃ : mass ratio 1:1 weighs MnO ₂ and Nb ₂ O ₅ , mixes for 20-30 hours, and then in a vacuum atmosphere 900-1000 degrees Celsius The calcination was carried out for 12 to 16 hours to obtain MnNb ₂ O ₆ .

Preparation of Pb(Mn _1/3 Nb _2/3 )O ₃ : The MnNb ₂ O ₆ prepared in the step a is ground into a powder, and the MnNb ₂ O ₆ and PbO are weighed at a molar ratio of 1:5, and mixed 20-30. After an hour, it is pre-fired at 1100 to 1300 ° C for 12 to 16 hours to obtain Pb(Mg _1/3 Nb _2/3 )O ₃ .

In step b, MgNb ₂ O _{6 is} prepared: MgO and Nb ₂ O _{5 are} weighed in a molar ratio of 1:1, and after mixing for 20 to 30 hours, calcination is carried out at 900 to 1100 ° C for 12 to 16 hours to obtain MgNb ₂ O ₆ .

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

In the above preparation method, the inventors of the present application specifically improve that through the step a, the Mn element can exist in the +2 valence state, thereby achieving the purpose of reducing the dielectric properties such as dielectric loss of the material; b, may be such that Mn element occupies a perovskite structure ABO B bit ₃ of the material according to the design requirements, to avoid lead and manganese free state of erosion of the crucible material during melting; preparation of starting materials combined step b and step 1 Can avoid free lead and manganese.

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 Mn element occupies the B position of the perovskite structure ABO ₃ according to the material design requirement, and exists in the +2 valence state, thereby achieving the purpose of reducing the dielectric property loss and the like. In addition, the raw material is completely present in the form of a pure perovskite phase, which avoids the erosion of free lead and manganese during the melting of the raw material.

2) Different from the prior art method of increasing the thickness of the crucible to prevent leakage, thereby achieving an increase in growth size. The inventors of the present application selected a narrow melting zone to achieve the effect of increasing the crystal size. The inventors of the present application have found that setting the width of the melt zone to 10 to 25 mm can prevent leakage and obtain a temperature gradient required for a large-sized crystal to achieve an effect of increasing the crystal size.

3) At the same time, the inventors of the present application found that another advantage of selecting a narrow melting zone is that it can increase the temperature gradient of the growth interface, since Mn needs to be bonded to the Mg, Ti, and Nb of the B site. More heat is released, so the narrow melting zone, that is, the large temperature gradient, facilitates the Mn ions to bond to the solid-liquid interface and enter the crystal, thereby avoiding the erosion of the free manganese during the melting of the raw material.

4) The conventional helium-down method growth relaxation ferroelectric crystal adopts the [111] direction seed crystal. This method uses the [001] direction seed crystal growth tetragonal phase relaxation ferroelectric single crystal. The optimal pyroelectric performance direction of the tetragonal phase relaxation ferroelectric single crystal for pyroelectric devices is the [001] direction, and the seed crystal growth in this direction can obtain large wafer uniformity, and the heat of the tetragonal phase large-sized crystal. The application of electricity is necessary.

5) Use Mn doping to eliminate defects caused by [001] direction growth and improve crystal integrity. Although crystal growth in the [001] direction is advantageous for obtaining a wafer having uniform performance, point defects are generated to cause blackening of the crystal as compared with the conventional growth in the [111] direction. The Mn doping regulates the dot defect structure in the crystal, inhibits crystal blackening, and improves wafer integrity.

DRAWINGS

1 is an absorption edge of Mn element in a Mn-doped relaxed ferroelectric single crystal, thereby indicating a synchrotron radiation X-ray absorption spectrum for measuring a valence state of Mn in a Mn-doped PMNT single crystal;

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

3 is a photograph of a three-inch manganese-doped pyroelectric crystal prepared in Example 1;

4 is a graph showing the relationship between the dielectric constant ε _r of the <001> oriented single crystal prepared in Example 1 after the polarization treatment at 1, 10, and 100 kHz, respectively.

Summary of the invention

Example 1:

MnO ₂ and Nb ₂ O _{5 were} weighed at a molar ratio of 1:1, and after mixing for 20 hours, they were calcined at 1000 ° C for 12 hours in a vacuum atmosphere (step a). The obtained agglomerated MnNb ₂ O _{6 was} ground into a powder, and MnNb ₂ O ₆ and PbO were weighed at a molar ratio of 1:5, mixed for 20 hours, and then calcined at 1200 ° C for 15 hours to obtain Pb (Mn _1/3 Nb). _2/3 ) O ₃ (step a). MgO and Nb ₂ O _{5 were} weighed in a molar ratio of 1:1, and after mixing for 20 hours, calcination was carried out at 1000 ° C for 15 hours to obtain MgNb ₂ O ₆ (step b). In ₂ O ₃ and Nb ₂ O _{5 were} weighed in a molar ratio of 1:1, mixed for 20 hours, and then calcined at 1200 ° C for 12 hours to obtain InNbO ₄ (step c). Finally, 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=0.42, y=0.29, 1-xy=0.29, a chemical formula of Mn doping amount of 1.0% is mixed with MgNb ₂ O ₆ , InNbO ₄ , PbO, TiO ₂ and Pb(Mn _1/3 Nb _2/3 )O ₃ for 24 hours. It was calcined at 1100 degrees for 10 hours as a starting material for crystal growth.

A PMNT crystal having a diameter of 40 mm and a length of 50 mm in the [001] direction is used as a seed crystal, and is placed in a platinum crucible. The crystal growth portion has a crucible diameter of 77 mm and a thickness of 1 mm; and the pre-fired starting material is further used. Load and close the 坩埚. Then, it is placed in a crystal growth furnace as shown in Fig. 2, the furnace temperature is controlled at 1350 to 1400 ° C, and the melting zone width is 15 mm. Crystal growth is achieved by adjusting the inoculation position to a predetermined inoculation temperature and temperature gradient and then starting to fall. The temperature gradient of the solid-liquid interface was controlled to be 60 ° C / cm, and the rate of decline was 0.7 mm / hr. The crystal shown in Figure 3 is finally obtained.

Line 4 in Figure 1 represents the valence state of the crystal prepared in Example 1 of the present application, and lines 1, 2, 3, and 5 are the valence states of the material containing Mn element known in the prior art, wherein the line 1 is the absorption edge of Mn in (Sr _0.97 Mn _0.03 )TiO ₃ , lines 2, 3 are absorption edges of Mn in Sr(Ti _0.97 Mn _0.03 )O ₃ purchased from different companies, and line 5 is Pb (Mn _1/2 Mn in Nb _1/2 )O ₃ . Line 4 is the absorption edge of Mn in the Mn-doped relaxed ferroelectric crystal obtained by the present method. As can be seen from FIG. 1, the structure of the crystal prepared by the present application is a pure perovskite structure in which the doped Mn is +2 valence and occupies the B site of the perovskite structure ABO ₃ .

Figure 4 is a graph showing the dielectric constant ε _r of a Mn-doped PIMNT 29/29/42 single crystal at a frequency of 0.1 kHz, 1.0 kHz, and 10.0 kHz as a function of temperature. The inner point is 258 degrees Celsius and the crystal is a tetragonal phase crystal. The average dielectric constant of the same film is 240, and the dielectric constant fluctuation of different parts is <4.0%, indicating that the crystal has high uniformity.

Claims (9)

1. A method for preparing a pyroelectric single crystal, wherein 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 molar percentage of the doping amount of Mn is 0-5.0%, 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 , TiO ₂ , PbO, mix for 20 to 30 hours, and pre-fire at 1100 to 1300 ° C for 6~ 10 hours as the starting material for crystal growth;

   Step 2: Fixing the PMNT or PIMNT 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, wherein The crystal growth has a melt zone width of 10 to 25 mm, and the diameter of the crucible for storing the original material is greater than or equal to three inches.
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 , TiO ₂ , and PbO was 99.99%.
3. The production method according to claim 1, wherein

   The method for obtaining high-purity Pb(Mn _1/3 Nb _2/3 )O ₃ , MgNb ₂ O ₆ , and InNbO ₄ in the step 1 is divided into the following steps:

   Step a, preparing Pb(Mn _1/3 Nb _2/3 )O ₃ : mass ratio 1:1 weighs MnO ₂ and Nb ₂ O ₅ , mixes for 20-30 hours, and then in a vacuum atmosphere 900-1000 degrees Celsius The calcination was carried out for 12 to 16 hours to obtain MnNb ₂ O ₆ . Then, Pb(Mn _1/3 Nb _2/3 )O _{3 is} prepared, and the MnNb ₂ O ₆ prepared above is ground into a powder, and then MnNb ₂ O ₆ and PbO are weighed by a molar ratio of 1:5 to 6, and mixed 20~. After 30 hours, it was pre-fired at 1100 to 1300 ° C for 12 to 16 hours to obtain Pb(Mn _1/3 Nb _2/3 )O ₃ .

   In step b, MgNb ₂ O _{6 is} prepared: MgO and Nb ₂ O _{5 are} weighed in a molar ratio of 1:1, and after mixing for 20 to 30 hours, calcination is carried out at 900 to 1100 ° C for 12 to 16 hours to obtain MgNb ₂ O ₆ .

   Step c, preparing InNbO ₄ : In ₂ O ₃ and Nb ₂ O _{5 are} weighed in a molar ratio of 1:1, mixed for 20 to 30 hours, and then calcined at 1100 to 1350 ° C for 10 to 13 hours to obtain InNbO ₄ .
4. The method of claim 1 wherein said niobium material is platinum and the total thickness of tantalum is from 0.6 to 1.5 mm.
5. The method of claim 1, wherein the seed crystal has a length of 50 to 70 mm and the seed crystal diameter is less than or equal to the diameter of the grown crystal, preferably 30 to 40 mm.
6. 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].
7. The method of claim 1 wherein said furnace temperature is controlled between 1350 and 1400 degrees Celsius.
8. The method of claim 1 wherein said solid-liquid interface temperature gradient is from 50 to 100 ° C/cm.
9. The method of claim 1 wherein said descending speed is from 7.0 to 10.0 mm/day.

Images