A method for preparing lanthanum-based hypernitrogen polymers

Abstract

The application relates to a method for preparing a lanthanum-based super-nitrogen polymer and belongs to the technical field of high-energy material preparation. A new lanthanum-based super-nitrogen polymer LaN8 is synthesized under the pressure of ten million atmospheres by directly reacting laser heating of lanthanum and nitrogen in a diamond anvil cell through magnetron sputtering or vacuum evaporation and high-pressure gas loading technology. The lanthanum-based super-nitrogen polymer prepared by the application has cage type N8 polymerization units which are different from the known multi-nitrogen structure. The lanthanum-based super-nitrogen polymer has the longest nitrogen-nitrogen bond length among all the multi-nitrogen polymers and is a potential high-energy density material. The research opens up a new and promising way for discovering new super-nitrogen compounds with unique nitrogen structures through high-temperature and high-pressure experimental means.

Description

Technical Field

[0001] This invention belongs to the field of high-energy material preparation technology, and specifically relates to a method for preparing lanthanum-based supernitrogen polymer materials. Background Technology

[0002] The conversion of triple-bonded nitrogen molecules into single-bonded polymers has been a research hotspot for decades. This interconversion is typically accompanied by extremely significant energy changes, which have a range of potential applications, such as energy storage, propellants, and high explosives. Using high-temperature, high-pressure synthesis techniques, various solid nitrogen single-bonded polymer structures, such as cg-N, LP-N, HLP-N, and BP-N, can now be created. However, the synthesis of these polymers still requires pressures exceeding one million atmospheres. To reduce synthesis pressure and increase the product's stable pressure range, "chemical pre-compression" has been widely used in numerous high-pressure polymer synthesis experiments. Theoretical studies have shown that this method can stabilize various polymer networks at lower pressures, such as K2N6 with pseudobenzene "N6" molecules and N6 with pentazocine anions. 5- The results showed that the type of metal significantly affects the bonding mode between two adjacent nitrogen atoms. Lanthanum (La), with its abundant valence electrons, is an important element for synthesizing novel compounds. In particular, lanthanum can react with hydrogen to form the high-temperature superconductor LaH₂. 10 This has caused quite a stir, but currently, the predicted or synthesized La-N compounds are limited to those with low nitrogen atom content and simple nitrogen configuration. Therefore, the search for a lanthanum-nitrogen compound with a high nitrogen atom ratio has remained a blank. Such compounds not only possess excellent physicochemical properties and potential applications, but can also provide technical guidance for subsequent research on other transition metal and rare earth metal nitrides. Summary of the Invention

[0003] The technical problem to be solved by this invention is to provide a new method for preparing metal polymeric nitrogen materials with excellent energy properties through a simple, purely physical means.

[0004] This method prepares a lanthanum-based supernitrogen polymer, LaN8, using magnetron sputtering or vacuum evaporation to prepare a La metal sample. A high-pressure nitrogen gas is loaded using a gas loading system (GLS), and a diamond anvil cell (DAC) is employed to achieve the target pressure. An infrared laser is then used to perform in-situ laser heating of the sample under the target pressure, thereby preparing LaN8. The sample is subsequently quenched to 22 GPa. This method exhibits good reproducibility.

[0005] The specific technical solution of the present invention is as follows:

[0006] A method for preparing lanthanum-based supernitrogen polymers involves first preparing an initial metallic La film on a diamond surface using magnetron sputtering or vacuum evaporation; then loading and encapsulating high-purity nitrogen gas at 180 MPa using a GLS system; subsequently, slowly pressurizing the loaded nitrogen gas and La film to 110 GPa using a DAC; then uniformly subjecting the sample to high-pressure in-situ laser heating using a 1070 nm infrared laser for 3–5 minutes at a temperature of 2000 K; finally, rapidly annealing with the laser off to obtain LaN8 material with a lanthanum:nitrogen ratio of 1:8.

[0007] Preferably, the initial La metal film has a thickness of 1 to 2 micrometers and a size of 1 / 4 the size of a diamond anvil.

[0008] Preferably, the purity of the high-purity nitrogen gas is 99.999%.

[0009] Preferably, the pressurization rate for slowly increasing the pressure to 110 GPa is 30 GPa / day; and the annealing rate for rapid annealing is 1000 °C / second.

[0010] Preferably, the experimental method has good repeatability.

[0011] Beneficial effects:

[0012] This invention first utilizes magnetron sputtering or vacuum evaporation to prepare a thin metal sample layer, which facilitates complete reaction and testing. Using GLS (Gas Lamination System) provides ample nitrogen for the reaction, which is beneficial for synthesizing metal nitrides with high nitrogen ratios. The sample prepared by this invention has a polymer network of nitrogen atoms forming covalent single bonds within its structure. Its average nitrogen-nitrogen bond length surpasses that of all currently disclosed nitrides, exhibiting high energy content and making it suitable as a high-energy storage material. Attached Figure Description

[0013] Figure 1 This is the X-ray diffraction pattern of the initial sample in Example 1 under a pressure of 97 GPa before the reaction.

[0014] Figure 2 These are photomicrographs of the raw materials before and the products after the reaction in the DAC, which are identical in all conditions except for the volume of the raw materials used in Example 2.

[0015] Figure 3 This is the X-ray diffraction pattern of Example 3 under a pressure of 110 GPa after the reaction.

[0016] Figure 4 This is the crystal structure of the product P4 / n LaN8 prepared in Example 3.

[0017] Figure 5 This is the curve showing the relationship between the volume of the product LaN8 prepared in Example 3 and pressure.

[0018] Figure 6 This is a comparison of the average bond length of the product LaN8 prepared in Example 3 with other nitrides. Detailed Implementation

[0019] The present invention will now be described in more detail with reference to the following embodiments. Unless otherwise specified, all reagents used are commercially available products and have not been further purified before use.

[0020] Example 1: Preparation of the initial product of the reaction

[0021] First, regardless of whether magnetron sputtering or vacuum evaporation is used, a mask shaped like a 5mm × 5mm × 50μm W metal sheet must be fabricated before sample preparation. The mask is pre-pressed to 30 GPa using a DAC device. Then, according to the target sample size, a corresponding hole is drilled at the center of the indentation using a laser drill. The sheet is then placed in the exact center of the diamond substrate. This sheet is then fixed as the mask using vacuum sealing (magnetron sputtering) or AB glue (vacuum evaporation). If magnetron sputtering is used, the lanthanum target (99.9% purity) must first be loaded into the magnetron sputtering apparatus and sputtered onto the diamond substrate covering the mask using DC under an argon atmosphere of 0.5 Pa for 12 minutes. The sputtering time can be appropriately increased if the sample is thinner. It is worth noting that a 3-5 minute pre-sputtering is required before the actual sputtering to remove oxides from the target surface. If vacuum evaporation is used, the diamond substrate covered with a mask should be suspended upside down in the evaporation equipment. An appropriate amount of metallic La powder should be loaded into the lower molybdenum boat. The current is then gradually increased until it reaches 30 amperes. When the molybdenum boat becomes bright, it indicates that the sample has been successfully evaporated, and the current can be disconnected and the substrate removed. After the metal thin film is prepared, the entire DAC device is placed in the GLS system, and high-pressure nitrogen gas (180 MPa) is applied. The DAC device is then removed, and the pressure is slowly increased to the target pressure of 110 GPa. During pressurization, the purity of the initial sample is determined by X-ray diffraction. Figure 1 As shown.

[0022] Example 2: Preparation of Lanthanum-based Supernitrogen Polymer

[0023] The preparation of lanthanum-based supernitrogen polymers requires a symmetric DAC (Digital Amplifier Diameter), which can easily achieve laser heating and sample synthesis under pressures of up to one million atmospheres. This experiment used two sets of Boheler diamond lasers paired with a standard DAC. The two sets of experiments differed only in the initial sample size; all other experimental conditions were identical. The diamond pressure standard method was used to determine the pressure applied to the sample during pressure loading. The sample was slowly pressurized (30 GPa / day) to 110 GPa to minimize the internal pressure gradient. Subsequently, a micro-focused infrared laser was used to uniformly heat the entire sample for 3-5 minutes at 2000 K. After heating, the laser was quickly shut off, and the sample was quenched to room temperature. Images of the sample cavity before and after laser heating are shown below. Figure 2 As shown.

[0024] Example 3: Structural Characterization of Lanthanum-based Supernitrogen Polymers

[0025] After the sample reaction is complete, the crystal structure properties of the sample can be characterized by (synchrotron radiation) X-ray diffraction. Figure 3 The image shows the X-ray diffraction pattern of the sample collected at the BL15U1 beamline of the synchrotron radiation source. The pattern reveals numerous newly generated, unknown X-ray diffraction signals (later identified as the target product LaN8 and the byproduct LaN) in addition to the peaks for the reactant La and the metal capping W. Based on theoretical calculations, the new product was determined to be the lanthanum-based supernitrogen polymer LaN8. The nitrogen atoms exhibit a cage-like arrangement, and the three-dimensional structure is as follows: Figure 4 . Figure 5 The relationship between sample volume and pressure is shown for the new samples in the two DAC groups. Even with different initial sample volumes, the physical properties of the products remain highly consistent. This indicates that the method has excellent reproducibility. Decompression quenching experiments on this sample show that it can be stabilized at a pressure of 22 GPa, lower than the 46 GPa of conventional polymeric nitrogen. This further confirms that the introduction of metal atoms plays a crucial role in the synthesis and stabilization of the polymeric nitrogen structure. The average nitrogen-nitrogen bond length of this structure is calculated as follows: Figure 6 It can be seen that the bond length of the nitrogen atom in this structure is higher than that of almost all other polymeric nitrides. This indicates that the nitrogen atom in this structure releases more energy during the transformation from a single bond to a triple bond, and has the potential to be a high-energy material.

Claims

1. A method for preparing lanthanum-based supernitrogen polymers, comprising: firstly, preparing an initial metallic La film on a diamond surface using magnetron sputtering or vacuum evaporation; then, loading high-purity nitrogen gas at 180 MPa using a high-pressure gas loading device and encapsulating it; subsequently, slowly pressurizing the loaded nitrogen gas and La film to 110 GPa using a diamond anvil cell; then uniformly subjecting the sample to high-pressure in-situ laser heating using a 1070 nm infrared laser for 3-5 minutes at a temperature of 2000 K; and finally, rapidly annealing the sample after turning off the laser to obtain LaN8 material with a lanthanum:nitrogen ratio of 1:

8.

2. The method for preparing lanthanum-based supernitrogen polymer according to claim 1, characterized in that, The initial La metal film has a thickness of 1-2 micrometers and a size of 1 / 4 the size of a diamond anvil.

3. The method for preparing lanthanum-based supernitrogen polymer according to claim 1, characterized in that, The purity of the high-purity nitrogen gas is 99.999%.

4. The method for preparing lanthanum-based supernitrogen polymer according to claim 1, characterized in that, The pressurization rate for slowly increasing the pressure to 110 GPa is 30 GPa / day; the annealing rate for rapid annealing is 1000 °C / second.

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