CN1490243A

CN1490243A - Hot synthetic preparation of metastable rock salt phase nano gallium nitride in solvent

Info

Publication number: CN1490243A
Application number: CNA021384614A
Authority: CN
Inventors: 毅谢; 谢毅; 徐芬; 陆俊
Original assignee: University of Science and Technology of China USTC
Current assignee: University of Science and Technology of China USTC
Priority date: 2002-10-17
Filing date: 2002-10-17
Publication date: 2004-04-21
Anticipated expiration: 2022-10-17
Also published as: CN1291909C

Abstract

A process for preparing the nano-class gallium nitride in the substable halite phase includes such steps as loading organic solvent (benzene or toluene) in high-pressure reactor, proportionally adding gallium trihalide, amino sodium and iodine, reacting at 180-270 deg.c for 16-48 hr in sealing and no oxygen condition, washing the resultant, drying and vacuum calcining at 300-600 deg.C. Its advantages are small granularity and high output rate.

Description

Solvothermal synthesis preparation method of metastable rock salt phase nano gallium nitride

The technical field is as follows:

the invention belongs to the technical field of organic solvent thermal synthesis preparation methods, and particularly relates to a technology for preparing a metastable rock salt phase nano gallium nitride luminescent material by double decomposition reaction of gallium halide and sodium amide under the transportation catalysis of elemental iodine (I2).

Background art:

the nanometer gallium nitride has wide application in light emitting diode, optical filter, super ion material and semiconductor material. How to realize a preparation method which has simple process and high yield and can be produced in large batch is the first problem to be faced. The synthesis of group IIIA phosphide and transition metal nitride by Solid State Metathesis (SSM) is reported in the United states of America Inorganic Chemistry, 1993, 32 vol. 2745-2752 p and 1994, 33 vol. 5693-5700 p, but it needs to be carried out at high temperature (500-1000 ℃) and under the protection of specific atmosphere, the product has large particles, and it is difficult to separate the product with higher purity because the product and byproducts such as alkali metal halide form sintered body at high temperature, and the product does not have to be separated outThe method is suitable for mass production, is not generally used as a preparation method, and is only used for basic research; in particular, the SSM process is not capable of producing metastable rock salt phase gallium nitride. According to the reports of the United states of America of Materials Chemistry (1994, volume 6, pages 82-86), nano-nitride is usually prepared by using metal organic precursor, but the synthesis conditions of the metal organic precursor are very harsh, toxic and sensitive to air. The U.S. Chemistry of Materials (12 volume 1003-1010 pages 2000) reported that the ammonothermal method for preparing GaN is to decompose the organometallic precursor in liquid ammonia to obtain GaN, and the liquid ammonia is easy to explode although the reaction temperature is reduced (150 ℃ C.). The method is not limited to the above-mentioned method. The use of GaCl by solvothermal methods was reported in the United states of America of Materials Chemistry (Chemistry of Materials, 2001, Vol.13 4290-4296)₃And NaN₃The metathesis reaction in tetrahydrofuran or toluene solvent yields GaN, but since metal azides are very sensitive to heat and shock, the reaction can only be operated on a small scale in a special autoclave and is not suitable for mass production. Journal of Science (Science 1996, 272 1926-1927) reports lithium nitride (Li)₃N) as nitrogen source, and synthesizing GaN by a benzene thermal method at a high reaction temperature (up to 280 ℃), although a very small amount of rock salt phase GaN exists, due to Li in reactants₃N is not strong in ionicity, a catalyst is not used, most of the obtained products are GaN with a wurtzite structure, and relatively pure rock salt phase GaN cannot be obtained. The use of elemental iodine (I) was reported in the Rapid report of chemical and Physical (Chemistry of Physical letters, pp.351 vol.229-234 of 2002)₂) As the heat absorbing agent and the diluting agent, GaN with a wurtzite structure is synthesized, but sodium azide (NaN) is adopted as the reaction raw material₃) As a nitrogen source, and the reaction temperature exceeds 300 ℃, so that the GaN of the rock salt phase cannot be obtained; and NaN₃The reaction is sensitive to heat and vibration, and can only be operated in a small scale in a special autoclave and is only used for basic research.

The invention content is as follows:

the invention provides a method for preparing pure metastable rock salt phase nano gallium nitride at lower temperature and lower pressure in an organic solvent system, which overcomes the defects that the reaction temperature is higher, a virulent metal organic compound precursor and azide with poor stability are used, and pure rock salt phase GaN cannot be obtained in the existing method.

The invention relates to a solvothermal synthesis preparation method of metastable rock salt phase nano gallium nitride, which is characterized by comprising thefollowing steps: adding the reactant gallium trihalide (GaX) to an autoclave containing a suitable organic solvent in a molar ratio of 1: 3 to 1: 6₃) Sodium amide (NaNH)₂) And elemental iodine (I)₂) Carrying out the reaction at 180-270 ℃ for 16-48 hours under a closed oxygen-free condition to obtain a crude product; and washing and drying the crude product, and then calcining the crude product in vacuum at the temperature of 300-600 ℃ for 3-6 hours to obtain the product.

The halogen in the gallium halide is chlorine, bromine or iodine; the suitable organic solvent may be selected from thermally stable aromatic hydrocarbons including benzene or toluene; the oxygen-free condition can be realized by introducing inert gas or nitrogen into the solution to remove oxygen from the solution.

The product was characterized by using a rotating target X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Transmission Electron Microscope (TEM), High Resolution Transmission Electron Microscope (HRTEM), Electron Diffraction (ED) and photoluminescence spectroscopy (PL). XRD tests show that the phase of the prepared product is GaN of a metastable rock salt phase; XPS testing indicated the purity and composition of the material; the TEM picture shows that the particle size of the material is 30-100 nm; HRTEM pictures illustrate good crystallinity of rock salt phase GaN; the ED photograph further illustrates that it is GaN with a cubic structure; PL test shows that the material has excellent light emitting performance and is one excellent inorganic light emitting material.

The mechanism of the invention is as follows: in the presence of elemental iodine (I)₂) Under the catalytic action of transport of (2), gallium halide (GaX)₃) And sodium amide (NaNH)₂) The metastable rock salt phase, namely the nanometer gallium nitride (GaN) inorganic luminescentmaterial with the NaCl type face-centered cubic structure is generated by double decomposition reaction. By GaI₃For example, the reaction can be simply expressed as:

wherein E is an organic solvent, and comprises aromatic hydrocarbons with high thermal stability such as benzene or toluene.

The invention adopts elementary iodine (I)₂) As a transport catalyst for reaction, the method can effectively reduce the rigorous requirements of high temperature and ultrahigh pressure required in the preparation of rock salt phase GaN; the invention adopts NaNH₂As the nitrogen source, NaNH is used₂Loss of NH during heating₃To obtain highly active and ionic Na₃N, a strongly ionic reactant (Na)₃N) is favorable for obtaining products (GaN of rock salt phase) with strong ionic property and simultaneously releases NH rapidly₃But also is beneficial to increasing the pressure of the reaction system.

The reaction temperature, reaction time and molar ratio between reactants all have a great influence on the final product of the reaction. Generally, the larger the reactant concentration, the higher the reaction temperature, and the longer the reaction time, the larger the particle size of the product. The invention adopts the molar ratio of reactants GaX₃∶NaNH₂∶I₂1: 3 to 1: 6, and reacting at the temperature of 180-270 ℃, wherein the reaction time is usually within 16-48 hours, which can not only ensure that the reaction is relatively completely carried out, but also prevent the particle size of the obtained product from being too large; if the reaction temperature exceeds 270 ℃, the obtained product is wurtzite GaN or GaN formed by intergrowth of wurtzite and rock salt phase rather than purer rock salt phase GaN; if the reaction temperature is less than 180C, the desired product is not obtained. In addition, the calcination temperature of the post-treatment should be in a proper range, and the invention adopts calcination in the temperature range of 300-600 ℃ for 3-6 hours, because when the temperature is raised to be higher than 600 ℃, the GaN of the rock salt phase is converted into the GaN of the zinc blende; and when the temperature is lower than 300 ℃, the product still presents an amorphous state.

To prevent contamination of the reaction system with autoclave material and the introduction of impurities, an autoclave with a liner is generally used. When the reaction temperature is below 250 ℃, polytetrafluoroethylene and quartz are generally selected as lining materials; when the reaction temperature is higher than 250 ℃, noble metals such as platinum, gold or silver are selected as lining materials.

The method for preparing the nano gallium nitride has the following advantages:

the method of carrying out solid-liquid reaction in an organic solvent system is adopted, so that the preparation of the nitride can be realized at a temperature lower than that of an SSM method, the condition of high vacuum or specific protective atmosphere is avoided, and the defect that product particles are too large is avoided; the invention adopts gallium halide and sodium amide to directly react in a proper organic solvent to obtain the nano gallium nitride, thereby avoiding the use of expensive, highly toxic and difficultly synthesized metal organic compound precursors. In addition, compared with the methods in Science (Science, 1996, vol. 272 1926-1927) and Chemistry and physics promulgation (Chemistry of Physical letters, 2002, vol. 351, vol. 229-234), a nitrogen source (NaNH) with higher activity and stronger ionicity is used₂) The use of azides with poor stability is avoided; due to the introduction of elemental iodine (I)₂) The excellent transport catalyst can prepare pure metastable rock salt phase nano GaN while reducing temperature and pressure, has cheap and easily obtained raw materials, is relatively stable to air phase, has simple preparation process, is easy to amplify for batch production and has lower cost. By adopting the method, the particle size and the shape of the product can be controlled by adjusting the composition and the concentration of reactants, the type of a solvent, the temperature and the reaction time; because the reaction is realized at a lower temperature, the particle size of the obtained product is smaller, generally between 30 and 60nm, and the maximum particle size is not more than 100 nm; the particle size distribution range is narrow, and the particle size is relatively uniform; the yield is high and can reach more than 80 percent; the method of the invention has high purity of the product because the by-product can be removed by washing. The metastable rock salt phase nano gallium nitride prepared by the method is as stable as the gallium nitride of wurtzite or sphalerite prepared by a common method in air atmosphere.

Description of the drawings:

FIG. 1 is a spectrum obtained by XRD analysis of a product prepared according to the present invention;

FIG. 2 is the XPS spectrum of the product of the invention showing the 3d peak of elemental Ga;

FIG. 3 is the XPS spectrum of the product showing the 1s peak of element N;

FIG. 4 is a TEM photograph of the product;

FIG. 5 is a HRTEM photograph of the product;

FIG. 6 is an electron diffraction photograph of the product;

FIG. 7 is a photoluminescence spectrum of the product.

The specific implementation mode is as follows:

example 1:

an autoclave lined with polytetrafluoroethylene was charged with a freshly prepared autoclave containing 5mmol of gallium iodide (GaI)₃) 50mL of the benzene solution, and 30mmol of sodium amide (NaNH) was added₂) And 30mmol of elemental iodine (I)₂) Introducing argon into the solution for 10 minSealing the autoclave after removing oxygen, and keeping the temperature at 180 ℃ for 24 hours; washing the obtained product with ethanol for 2 times, then washing with distilled water for 2 times, placing in a vacuum drying oven for drying at 60 ℃ for 3 hours, and finally calcining the sample in vacuum at 400 ℃ for 5 hours to obtain product powder.

Example 2:

with GaBr₃Instead of GaI in example 1₃As gallium source, the solvent is changed into toluene, and GaBr is taken₃、NaNH₂、I₂The molar ratio of (A) to (B) is 1: 3; the procedure was as in example 1, the reaction was incubated at 240 ℃ for 16 hours; the crude product obtained was calcined in vacuo at 600 ℃ for 3 hours, and the product powder was likewise obtained.

Example 3:

adding GaCl₃In place of GaI₃Taking benzene as a solvent as a gallium source, adopting platinum as a lining material of the autoclave, and taking GaCl₃、NaNH₂、I₂In a molar ratio of 1: 4: 6, the reaction temperature was raised to 270 ℃ and kept constant for 48 hours, the operation of the reaction and the work-up were the same as in example 1, and the crude product was vacuum-calcined at 300 ℃ for 6 hours.

The products obtained in the above examples were characterized by means of transtargetted X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Transmission Electron Microscope (TEM), High Resolution Transmission Electron Microscope (HRTEM), Electron Diffraction (ED) and photoluminescence spectroscopy (PL).

The XRD pattern of the product powder given in FIG. 1 has 4 peaks corresponding to the four crystal faces (111), (002), (022) and (113) of the rock salt phase GaN, and the product is GaN of a metastable rock salt phase;

the XPS spectrogram 2 of the product is a 3d peak of the element Ga, the XPS spectrogram 3 is a 1s peak of the element N, and the areas of the two peaks are integrated to obtain the substance component Ga: N of 1.14: 1; XPS analysis shows that the product does not contain Na, I and H element impurities;

TEM photo 4 shows that the product gallium nitride powder consists of flaky particles with good dispersibility, and the average particle size is less than 100 nm; HRTEM micrograph FIG. 5 shows that the lattice fringe spacing is 2.36. ANG., corresponding to the (111) crystal plane of halite phase GaN, while indicating good crystallinity of the product gallium nitride; the electron diffraction spots shown in fig. 6 sequentially represent four crystal faces (111), (002), (022) and (113) of rock salt phase GaN from inside to outside, and the result is proved that the product gallium nitride is in a cubic rock salt phase structure, namely, has a NaCl type face-centered cubic structure.

The photoluminescence spectrum of the product in figure 7 has two peaks respectively at 330nm (3.76eV) and 348nm (3.56eV), which shows that the material has good luminescence property and is an excellent inorganic luminescent material.

Due to GaX₃The structures of (X ═ Cl, Br, I) are similarand belong to the homologous family, so GaCl can be used separately₃、GaBr₃、GaI₃Preparing rock salt phase GaN for a gallium source by using the method; but because of GaX₃Dimers are easily formed among molecules, and the binding force among the dimers is weakened in sequence according to Cl, Br and I, so that the dimers and NaNH are mixed₂The reaction temperature and reaction time are different from each other: when using GaCl₃When the gallium source is used, the reaction temperature is 250-270 ℃, and the reaction time is 24-48 hours; when using GaBr₃Or GaI₃The reaction temperature is 180 ℃ and 250 ℃, and the reaction time is 16-24 hours.

When the reaction temperature needs to be controlled between 250 ℃ and 270 ℃, the lining material in the high-pressure kettle can be selected from noble metals such as platinum, gold or silver; when the reaction temperature is below 250 ℃, the lining material can be selected from polytetrafluoroethylene or quartz.

Claims

1. A solvothermal synthesis preparation method of metastable rock salt phase nano gallium nitride is characterized by comprising the following steps: adding reactants of gallium trihalide, sodium amide and elementary iodine into an autoclave filled with organic solvent benzene or toluene according to the molar ratio of 1: 3 to 1: 6, and carrying out the reaction for 16-48 hours at the temperature of 270 ℃ under the closed oxygen-free condition to obtain a crude product; and washing and drying the crude product, and then calcining the crude product in vacuum at the temperature of 300-600 ℃ for 3-6 hours to obtain the product.

2. The solvothermal synthesis method for preparing metastable rock salt phase nano-gallium nitride according to claim 1, characterized in that the halogen in the reactant gallium trihalide is chlorine, bromine or iodine.

3. The method for preparing metastable rock salt phase nano gallium nitride by solvothermal synthesis according to claim 1, wherein the oxygen-free condition is realized by removing oxygen from the solution by introducing inert gas or nitrogen into the solution.