A method for synthesizing and modifying the magnetic properties of PrFeO3 rare earth ferrite

Abstract

The present invention discloses a method for synthesizing and changing the magnetic properties of PrFeO3 rare-earth ferrite. First, praseodymium nitrate and iron nitrate are used as the ion sources of Pr and Fe, and samples are weighed and prepared according to the chemical stoichiometry of PrFeO3. The samples are dissolved in deionized water, and citric acid is added after stirring evenly. Then, the solution is titrated to neutral with ammonia water. The neutral solution is stirred and dried in a constant-temperature water bath to obtain a wet gel. The wet gel is dried and then subjected to a self-propagating reaction on an electric resistance furnace to obtain a precursor powder. The precursor powder is ground and then annealed in a muffle furnace at 800 °C to obtain an antiferromagnetic PrFeO3 rare-earth ferrite material. Finally, it is annealed at 1300 °C to obtain a PrFeO3 rare-earth ferrite magnetic material. The samples prepared by annealing at a low temperature for a short time are in an antiferromagnetic state. The present invention makes the grains and magnetic domains larger by increasing the temperature and prolonging the time, thereby changing the change of the PrFeO3 sample from antiferromagnetism to ferromagnetism.

Description

Technical Field

[0001] The present invention relates to rare earth ferrite magnetic materials, and specifically to a PrFeO3 rare earth ferrite magnetic material and a method for synthesizing and changing the magnetic properties of PrFeO3 rare earth ferrite. Background Art

[0002] Magnetic ceramics mainly refer to ferrite ceramics. Ferrite is a composite oxide with iron oxide and other iron group or rare earth group oxides as the main components. Most ferrites are semiconductors, with a resistivity much greater than that of general metal magnetic materials, and have the advantage of small eddy current losses. They have been widely used in high-frequency and microwave technology fields, such as radar technology, communication technology, space technology, electronic computers, etc.

[0003] Rare earth permanent magnet materials are the most popular rare earth application fields today. Praseodymium alone does not have outstanding performance as a permanent magnet material, but it is an excellent synergistic element that can improve magnetic properties. Whether it is the first-generation rare earth permanent magnet material samarium-cobalt permanent magnet alloy or the third-generation rare earth permanent magnet material neodymium iron boron, adding an appropriate amount of praseodymium can effectively improve and enhance the performance of permanent magnet materials. Adding praseodymium can also improve the antioxidant performance (resistance to air corrosion) and mechanical properties of magnets, and has been widely used in various electronic devices and motors.

[0004] Since rare earth ferrites have always been the focus of attention, the research on rare earth ferrites with perovskite structure is also very meaningful. However, there is very little research on PrFeO3 in existing references and experiments. Therefore, this application selects it as the research object, synthesizes samples using different preparation processes and different preparation conditions, and conducts magnetic property tests and comparisons, which has important guiding significance for the design and production of new high-performance permanent ferrite materials. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for synthesizing and changing the magnetic properties of PrFeO3 rare earth ferrite. By changing the annealing temperature and annealing duration, the grain growth and magnetic domains of the sample become larger, thereby changing the magnetic properties of PrFeO3 and obtaining a sudden change from antiferromagnetic to ferromagnetic properties.

[0006] The technical solution for achieving the purpose of the present invention is as follows:

[0007] A method for synthesizing and changing the magnetic properties of PrFeO3 rare earth ferrite, the method comprising the following steps:

[0008] (1) Using praseodymium nitrate and iron nitrate as the ion sources of Pr and Fe, weighing and preparing samples according to the chemical stoichiometry of PrFeO3. Dissolve the weighed samples in deionized water, stir evenly, and then add citric acid and continue stirring. The molar ratio of citric acid to the sum of the two metal ions is 2-3:1;

[0009] (2) Titrate the solution obtained in step (1) with ammonia water to make the solution neutral, with a pH of 5 - 7;

[0010] (3) Place the neutral solution obtained in step (2) in a constant temperature water bath at 70 - 90 °C and stir it with a magnetic stirrer. After stirring, dry it to obtain a cyan transparent wet gel;

[0011] (4) Dry the wet gel obtained in step (3) at 80 - 100 °C, and then carry out a self-propagating reaction on an electric resistance furnace to obtain a precursor powder;

[0012] (5) Grind the precursor powder obtained in step (4), and then anneal it in a muffle furnace at 700 - 1000 °C to obtain an antiferromagnetic PrFeO₃ rare earth ferrite material;

[0013] (6) It can be seen from observing the preparation of the Pr₂O₃ - Fe₂O₃ binary phase diagram that the melting point of PrFeO₃ is very high. In order to make PrFeO₃ have better crystallinity, anneal the antiferromagnetic PrFeO₃ rare earth ferrite material obtained in step (5) at 1200 - 1700 °C to obtain a PrFeO₃ rare earth ferrite magnetic material.

[0014] Further, in step (3), the stirring time is 4 - 6 hours.

[0015] Further, in step (4), the wet gel is dried in a drying oven, and the drying time is 8 - 12 hours.

[0016] Further, in step (5), the annealing time is 4 - 10 hours, and the annealing temperature is preferably 800 °C.

[0017] Further, in step (6), the annealing time is 14 - 21 days, and the annealing temperature is preferably 1300 °C.

[0018] The present invention also provides a PrFeO₃ rare earth ferrite magnetic material, which is obtained by the above synthesis method. This magnetic material belongs to a single-phase perovskite rare earth oxide with a Pbnm space structure, and its unit cell parameters are a = 5.4815 (Å), b = 5.5773 (Å), c = 7.7848 (Å), V = 238.00 (Å 3 )

[0019] For the PrFeO₃ rare earth ferrite magnetic material synthesized by the synthesis method of the present invention, the key to the ferromagnetic property transformation of its samples lies in annealing for 14 - 21 days at a temperature of 1200 - 1700 °C. The synthesis method is not limited to the sol-gel method and includes any one of the daily sample synthesis methods.

[0020] The PrFeO3 rare-earth ferrite magnetic material of the present invention and its synthesis method solve the problems of complex preparation and single performance of existing samples, and have the following advantages:

[0021] (1) For the PrFeO3 rare-earth ferrite magnetic transformation material of the present invention, as the temperature and annealing time increase, the crystallinity of its samples is enhanced, and the sample grains and magnetic domains correspondingly increase. When the magnetic domain area is larger than the grain size, the magnetism cannot be easily reversed, causing the samples to transform from antiferromagnetism to ferromagnetism, thus achieving a good experimental direction for regulating the temperature transformation performance. Taking this as the process conditions, it guides the production of PrFeO3 ceramic samples. PrFeO3 of the present invention has wide applications in the fields of optoelectronics, fuel cells, etc.;

[0022] (2) For the synthesis method of the present invention, the sol-gel wet chemical method is used to successfully prepare the nano rare-earth ferrite magnetic transformation material. The product has high uniformity and purity. Compared with other preparation methods, it is simple to prepare and has a high cost performance. This method can improve the production efficiency of permanent magnet ferrites, meet the performance and structure requirements of ferrites, greatly reduce the R & D cycle and cost of new ferrite designs, and has important guiding value for the design and production of new high-performance permanent magnet ferrite materials. Description of the Drawings

[0023] Figure 1 It is a flowchart of the synthesis method of the PrFeO3 rare-earth ferrite magnetic material of the present invention.

[0024] Figure 2 It is the Pr2O3-Fe2O3 binary phase diagram referred to in the present invention.

[0025] Figure 3 It is the XRD pattern and refinement result diagram of the low-temperature and high-temperature samples of the PrFeO3 rare-earth ferrite material synthesized by the sol-gel method in Example 1 and the samples prepared by the solid-phase method;

[0026] Among them, Figure 3 a is the XRD pattern of the comparison between the low-temperature and high-temperature samples of the PrFeO3 rare-earth ferrite material synthesized by the sol-gel method in Example 1 and the samples prepared by the solid-phase method;

[0027] Figure 3 b is the refinement result diagram of the comparison between the low-temperature and high-temperature samples of the PrFeO3 rare-earth ferrite material synthesized by the sol-gel method in Example 1 and the samples prepared by the solid-phase method.

[0028] Figure 4 It is the selected area electron diffraction and high-resolution result diagram in the transmission electron microscope of the low-temperature and high-temperature samples of the PrFeO3 rare-earth ferrite material synthesized by the sol-gel method in Example 1 and the samples prepared by the solid-phase method;

[0029] Among them, Figure 4a is the selected electron diffraction pattern of the sample prepared by the sol-gel method in Example 1 annealed at 800 °C for 4 hours;

[0030] Figure 4 a1 is the high-resolution image of the sample prepared by the sol-gel method in Example 1 annealed at 800 °C for 4 hours;

[0031] Figure 4 b is the selected electron diffraction pattern of the sample prepared by the sol-gel method in Example 1 annealed at 1300 °C for 21 days;

[0032] Figure 4 b1 is the high-resolution image of the sample prepared by the sol-gel method in Example 1 annealed at 1300 °C for 21 days;

[0033] Figure 4 c is the selected electron diffraction pattern of the sample prepared by the solid-phase method in Example 1 annealed at 1300 °C for 21 days;

[0034] Figure 4 c1 is the high-resolution image of the sample prepared by the solid-phase method in Example 1 annealed at 1300 °C for 21 days.

[0035] Figure 5 is the magnetic property test result diagram of the PrFeO3 rare-earth ferrite material low-high temperature samples prepared by the sol-gel method and the samples prepared by the solid-phase method in Example 1. Detailed implementation mode

[0036] Next, the technical solutions in the embodiments of the present invention will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0037] Example 1

[0038] A method for synthesizing and changing the magnetic properties of PrFeO3 rare-earth ferrite, the process is as Figure 1 shown, and the specific steps are as follows:

[0039] (1) Take analytical pure ferric nitrate nonahydrate (Fe(NO3)3·9H2O) and praseodymium nitrate hexahydrate (Pr(NO3)3·6H2O) as the ion sources of Pr and Fe, weigh and prepare according to the chemical stoichiometry of PrFeO3, dissolve the weighed samples in 40 ml of deionized water, stir evenly and then add citric acid and continue to stir. The molar ratio of citric acid to the sum of the two metal ions is 3:1;

[0040] (2) Titrate the solution obtained in step (1) with ammonia water to make the solution neutral, and the pH value reaches 5-7.

[0041] (3) Stir and dry the neutral solution obtained in step (2) in a constant temperature water bath at 80 °C, and stir with a magnetic stirrer for 4 - 6 hours to finally obtain a cyan transparent wet gel;

[0042] (4) Place the wet gel obtained in step (3) in an oven at 80 - 100 °C and dry for 12 hours, then carry out a self-propagating reaction on an electric resistance furnace to remove organic substances and obtain a precursor powder;

[0043] (5) Grind the precursor powder obtained in step (4), and then anneal it in a muffle furnace at 800 °C for 4 hours to obtain an antiferromagnetic PrFeO₃ rare earth ferrite material.

[0044] (6) It can be seen from observing the preparation of the Pr₂O₃ - Fe₂O₃ binary phase diagram that the melting point of PrFeO₃ is very high. In order to make PrFeO₃ have better crystallinity, anneal the PrFeO₃ sample obtained in step (5) at 1300 °C for 21 days to obtain a PrFeO₃ rare earth ferrite magnetic material.

[0045] The annealing interval can be seen by using the binary phase diagram. As Figure 2 shown, refer to the Pr₂O₃ - Fe₂O₃ binary phase diagram to better select the annealing temperature, which provides a prerequisite for sample production.

[0046] Product detection: For the prepared PrFeO₃ rare earth ferrite magnetic material powder sample, use a powder X-ray diffractometer (Smart Lab 9kw) with a Cu target (Kα, wavelength λ = 1.54178 Å) to detect the prepared powder sample.

[0047] Figure 3 a is the XRD pattern of the PrFeO₃ rare earth ferrite material low and high temperature samples synthesized by the sol - gel method in Example 1 compared with the samples prepared by the commonly used solid - phase method in the art. It can be observed from the XRD diffraction pattern that there are no any impurity phases except PrFeO₃. The upper right corner shows that the increase in temperature and time makes the full width at half maximum become smaller and the crystallinity become larger.

[0048] The samples prepared by the sol - gel method at 800 °C for 4 hours of annealing, the samples prepared by the sol - gel method at 1300 °C for 21 days of annealing, and the samples prepared by the solid - phase method at 1300 °C for 21 days of annealing in the examples are compared, and they correspond to the PrFeO₃ standard PDF card in Jade 6.0 software. As Figure 3 shown in a, the peak position at 32.4° is shown in the figure. It can be clearly seen that the full width at half maximum becomes narrower with the increase of time and temperature. Using Jade 6.0 software, it can be calculated that the crystallinity of the samples prepared by the low - temperature sol - gel method is lower, and the crystallinity of the high - temperature sol - gel method and the solid - phase method is higher and similar.

[0049] The crystal structure refinement was carried out using FullProf software, and it was found that the samples prepared under the three conditions had no any impurity phases except PrFeO3, as Figure 3 shown in b. It can be seen from the refinement results that PrFeO3 belongs to the single-phase perovskite rare-earth oxide with the Pbnm space structure, and its unit cell parameters are a = 5.4815 (Å), b = 5.5773 (Å), c = 7.7848 (Å), V = 238.00 (Å 3 ), and the refinement result diagram is consistent with the XRD diffraction pattern conclusion without any impurity phases and the structure remains unchanged.

[0050] Figure 4 Figure 10 shows the selected area electron diffraction and high-resolution results in the transmission electron microscope for the low-temperature and high-temperature samples of the PrFeO3 rare-earth ferrite material synthesized by the sol-gel method in Example 1 and the samples prepared by the solid-phase method; from Figure 4 it can be seen that for the sample PrFeO3, whether it is prepared by the sol-gel method at low temperature and high temperature or by the solid-phase method, no any impurity phases can be seen except PrFeO3 in the selected electron diffraction pictures. Figure 4 Figs. 4a, 4b, and 4c show different crystal plane indices seen from different zone axes, and no any impurity phases and structural transformations can be observed therein; Figure 4 Figs. 4a1, 4b1, and 4c1 show the high-resolution images of different preparation processes, and the crystal plane spacings of each sample are shown in the figures.

[0051] Figure 4 Fig. 4a is the selected area electron diffraction pattern of the sample prepared by annealing the sol-gel method in Example 1 at 800 °C for 4 hours, Figure 4 and the Fourier transform pattern is at the lower right corner of Fig. 4a. The crystal planes (001), (201), and (200) can be observed through the (002) zone axis; Figure 4 Fig. 4a1 is the high-resolution image of the sample prepared by annealing the sol-gel method in Example 1 at 800 °C for 4 hours, Figure 4 and the high-resolution enlarged image is at the lower right corner of Fig. 4a1. The crystal plane shown in the figure is the (002) crystal plane, and the crystal plane spacing d = 0.389 nm; Figure 4 Fig. 4b is the selected area electron diffraction pattern of the sample prepared by annealing the sol-gel method in Example 1 at 1300 °C for 21 days, Figure 4 and the Fourier transform pattern is at the lower right corner of Fig. 4b. The crystal planes (10-1), (00-2), and (-10-1) can be observed through the (010) zone axis; Figure 4 Fig. 4b1 is the high-resolution image of the sample prepared by annealing the sol-gel method in Example 1 at 1300 °C for 21 days, Figure 4 and the high-resolution enlarged image is at the lower right corner of Fig. 4b1. The crystal plane shown in the figure is the (101) crystal plane, and the crystal plane spacing d = 0.4485 nm; Figure 4c is the selected electron diffraction pattern of the sample prepared by the solid-phase method in Example 1 annealed at 1300 °C for 21 days. Figure 4 The lower right corner of b is the Fourier transform pattern. The crystal planes (-100), (-11-2), and (01-2) can be observed through the (021) zone axis. Figure 4 c1 is the high-resolution image of the sample prepared by the solid-phase method in Example 1 annealed at 1300 °C for 21 days. Figure 4 The lower right corner of c1 is the high-resolution enlarged pattern. The crystal plane shown in the figure is the (200) crystal plane, and the interplanar spacing d = 0.272 nm. It can be clearly seen from the figure that the grain size of the sample at 800 °C is much smaller than that at 1300 °C. It can be concluded from this that there is no structural transformation, and the growth of grains and the enlargement of magnetic domains are the reasons for the transformation of magnetic properties.

[0052] The magnetic properties were measured using a vibrating sample magnetometer (VSM). The coercivity of the sample prepared by the sol-gel method at 800 °C was 0.145 KOe; the coercivity of the sample prepared by the sol-gel method at 1300 °C was 5.269 KOe; the coercivity of the sample prepared by the solid-phase method at 1300 °C was 7.023 KOe; within the test range of ±2 T magnetic field, the magnetic property test results are as Figure 5 shown. The remanent magnetic induction intensity of the solid-phase method and the sol-gel method at 1300 °C is similar, and the remanent magnetic induction intensity of the sample prepared by the sol-gel method at 800 °C is much smaller than that of the sample at 1300 °C.

[0053] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be recognized that the above description should not be considered as a limitation of the present invention. After those skilled in the art have read the above content, various modifications and substitutions of the present invention will be obvious. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims

1. A method for synthesizing and modifying the magnetic properties of PrFeO3 rare-earth ferrite, characterized in that, The method comprises the following steps: (1) Using praseodymium nitrate and iron nitrate as the ion sources of Pr and Fe, weighing and preparing samples according to the stoichiometric ratio of PrFeO3, dissolving the weighed samples in deionized water, stirring evenly, and then adding citric acid and continuing to stir. The molar ratio of citric acid to the sum of the two metal ions is 2-3:1; (2) Titrating the solution obtained in step (1) with ammonia water to make the solution neutral, with a pH of 5-7; (3) Placing the neutral solution obtained in step (2) in a constant temperature water bath at 70-90 °C and stirring with a magnetic stirrer, and drying after stirring to obtain a cyan transparent wet gel; (4) Drying the wet gel obtained in step (3) at 80-100 °C, and then carrying out a self-propagating reaction on an electric resistance furnace to obtain a precursor powder; (5) Grinding the precursor powder obtained in step (4), and then annealing it in a muffle furnace at 700-1000 °C for 4-10 hours to obtain an antiferromagnetic PrFeO3 rare earth ferrite material; (6) Annealing the antiferromagnetic PrFeO3 rare earth ferrite material obtained in step (5) at 1200-1700 °C for 14-21 days to obtain a PrFeO3 rare earth ferrite magnetic material.

2. The method according to claim 1, characterized in that: In step (3), the stirring time is 4-6 hours.

3. The method according to claim 1, wherein: In step (4), the wet gel is dried in an oven, and the drying time is 8-12 hours.

4. The method according to claim 1, wherein: In step (5), the annealing temperature is 800 °C.

5. The method according to claim 1, characterized in that: In step (6), the annealing temperature is 1300 °C.

6. The PrFeO3 rare earth ferrite magnetic material obtained by the synthesis method according to any one of claims 1-5, characterized in that: This magnetic material belongs to a single-phase perovskite rare-earth oxide with a Pbnm space structure, and its unit cell parameters are a = 5.4815 (Å), b = 5.5773 (Å), c = 7.7848 (Å), V = 238.00 (Å 3 )

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