Post-spinel oxides and methods of making the same

Abstract

The present application provides a post-spinel oxide and a preparation method thereof. Specifically, the present application provides a post-spinel oxide having the following chemical formula: CaMFe2O5; wherein M is Cu, Co, Zn or Ni. The present application also provides a preparation method of the post-spinel oxide of the present application. The post-spinel oxide of the present application has new properties due to its unique structure, such as abnormal lattice distortion, low-dimensional magnetism, large coercive field and / or negative thermal expansion, etc. The present application provides a new way and new idea for the exploration and discovery of post-spinel oxide.

Description

Technical Field

[0001] This invention belongs to the field of materials. Specifically, this invention relates to a spinel oxide and its preparation method. Background Technology

[0002] Spinel is a widely studied group of minerals with the chemical formula AB₂O₄ or A₂BO₄. They are abundant in various geological structures, thus holding significant importance for Earth science research. Because the structure of spinel can accommodate trivalent and divalent cations, such as Fe... 2+ and Fe 3+ Therefore, transition metal spinel oxides not only exhibit rich physical properties, such as multiferroism, negative thermal expansion, and magnetic shape memory effect, but also have important application value in many fields, such as microwave devices and magnetic storage. Consequently, spinel has always been one of the important research areas in materials science and condensed matter physics.

[0003] Ordinary spinel has a cubic crystal system with space group Fd3m, and its crystal structure is similar to that of MgAl2O4. Each unit cell consists of eight molecular formulas. Oxygen ions with larger ionic radii are densely packed in space, forming a face-centered cubic lattice, while metal ions with smaller ionic radii fill the interstices between the oxygen ions. If the oxygen ions are taken as vertices, a set of oxygen tetrahedral sublattices and a set of oxygen octahedral sublattices can be constructed in space. The oxygen tetrahedral and oxygen octahedral sublattices are nested within each other, while the metal ions are located at the centers of the oxygen tetrahedrons (A-sites) and the oxygen octahedrons (B-sites).

[0004] Spinel also has another type of orthorhombic structure, similar to CaFe₂O₄, CaMn₂O₄, and CaTi₂O₄, called post-spinel. The most important characteristic of this type of spinel is its greater density compared to conventional spinel, with oxygen octahedra mostly connected by shared edges and fewer interstitial spaces. Due to its completely different structure, post-spinel in the orthorhombic system may exhibit entirely different physical properties. For example, theoretical predictions suggest that the migration rates of Li and Mg ions in the orthorhombic phases of LiMn₂O₄ and MgMn₂O₄ are greater than their migration rates in the cubic phase, thus holding promise for applications in Li-ion and Mg-ion batteries.

[0005] Currently, there is relatively little research on post-spinel and its oxides in academia. Due to their unique structure and novel properties, exploring new post-spinel and its oxides has important application value for the research of materials science and battery fields. Summary of the Invention

[0006] Therefore, the object of the present invention is to provide novel post-spinel oxides. The post-spinel oxides of the present invention possess novel properties due to their unique structure, such as anomalous lattice distortion, low-dimensional magnetism, large coercivity, and / or negative thermal expansion.

[0007] Another object of the present invention is to provide a method for preparing the spinel oxide of the present invention.

[0008] The objective of this invention is achieved through the following technical solutions.

[0009] In a first aspect, the present invention provides a spinel oxide having the following chemical formula: CaMFe2O5;

[0010] in,

[0011] M is Cu, Co, Zn, or Ni.

[0012] The inventors of this application unexpectedly synthesized four post-spinel oxides—CaCuFe2O5, CaCoFe2O5, CaZnFe2O5, and CaNiFe2O5—using a high-temperature, high-pressure synthesis method. The inventors characterized these post-spinel oxides of the present invention through numerous structural and physical property characterizations, including crystal structure, magnetism, electrical properties, and specific heat. They observed many novel characteristics, such as anomalous lattice distortion, low-dimensional magnetism, large coercive field, and / or negative thermal expansion—physical and chemical properties with potential application value.

[0013] Preferably, in the spinel oxide described in this invention, the space group of the spinel oxide is Cmcm.

[0014] Preferably, in the spinel oxide described in this invention, when M is Cu, the lattice constant of the spinel oxide CaCuFe2O5 is:

[0015] Preferably, in the spinel oxide described in this invention, when M is Co, the lattice constant of the spinel oxide CaCoFe2O5 is:

[0016] Preferably, in the spinel oxide described in this invention, when M is Zn, the lattice constant of the spinel oxide CaZnFe2O5 is:

[0017] Preferably, in the spinel oxide described in this invention, when M is Ni, the lattice constant of the spinel oxide CaNiFe2O5 is:

[0018] Preferably, in the spinel oxide described in this invention, when M is Cu, X-ray diffraction with a wavelength of 0.070 nm is used. The X-ray powder diffraction pattern of the spinel oxide CaCuFe2O5, expressed in terms of 2θ angle, has diffraction peaks at angles of 6.456°, 15.200°, 18.196°, and 19.049°, and the 2θ angle measurement error is ±0.006°.

[0019] Preferably, in the spinel oxide described in this invention, when M is Co, X-ray diffraction with a wavelength of 0.065 nm is used. The X-ray powder diffraction pattern of the spinel oxide CaCoFe2O5, expressed in 2θ angles, has diffraction peaks at angles of 5.872°, 13.946°, 17.030°, and 17.783°, and the 2θ angle measurement error is ±0.006°.

[0020] Preferably, in the spinel oxide described in this invention, when M is Zn, X-ray diffraction with a wavelength of 0.080 nm is used. The X-ray powder diffraction pattern of the spinel oxide CaZnFe2O5, expressed in 2θ angles, has diffraction peaks at angles of 7.241°, 17.176°, 20.876°, and 21.918°, and the 2θ angle measurement error is ±0.006°.

[0021] Preferably, in the spinel oxide described in this invention, when M is Ni, X-ray diffraction with a wavelength of 0.070 nm is used. The X-ray powder diffraction pattern of the spinel oxide CaNiFe2O5, expressed in terms of 2θ angle, has diffraction peaks at angles of 6.324°, 15.052°, 18.144°, and 19.052°, and the 2θ angle measurement error is ±0.006°.

[0022] In a second aspect, the present invention provides a method for preparing the spinel oxide of the present invention, which includes the following steps:

[0023] (1) CaO, MO and Fe2O3 are thoroughly ground and mixed in a protective gas atmosphere to obtain a mixture;

[0024] (2) After sealing and wrapping the mixture, heat and pressurize it.

[0025] (3) Cool and depressurize the processed product obtained in step (2);

[0026] Where M is Cu, Co, Zn or Ni.

[0027] Preferably, in the method described in this invention, the molar ratio of CaO, MO and Fe2O3 in step (1) is CaO:MO:Fe2O3 = 1:1:1.

[0028] Preferably, in the method described in this invention, the protective gas is selected from one or more of nitrogen, helium, and argon.

[0029] Preferably, in the method described in this invention, the particle size of the mixture is 100-1000 mesh, more preferably 200-600 mesh. In step (1) of this invention, grinding makes the materials uniformly mixed, while reducing the particle size of each material, which in turn facilitates uniform mixing. In step (1) of this invention, the grinding includes grinding in an agate mortar for 30 minutes to 2 hours, preferably 1 hour. The particle size of the ground mixture is in the micrometer range.

[0030] Preferably, in the method described in this invention, the treatment in step (2) is carried out under the following conditions: temperature of 1100-1200°C and pressure of 5-10 GPa.

[0031] Preferably, in the method of the present invention, the longer the processing in step (2) lasts, the more complete the reaction; more preferably, the processing in step (2) lasts for more than 20 minutes, and even more preferably 30 to 60 minutes.

[0032] Preferably, in the method described in this invention, the sealing and wrapping in step (2) is performed using a gold capsule or a platinum capsule; more preferably, the thickness of the gold capsule or platinum capsule is 0.05 to 1.00 mm.

[0033] Preferably, in the method described in this invention, the processing in step (2) is carried out in a six-sided anvil press or a two-stage push press of type DIA, Walker, or Kawai.

[0034] Preferably, in the method of the present invention, the cooling in step (3) is carried out by cooling the product to room temperature within 1 minute.

[0035] Preferably, in the method of the present invention, the depressurization in step (3) is carried out by reducing the product to ambient pressure within 2 to 10 hours.

[0036] The present invention has the following beneficial effects:

[0037] (1) This invention utilizes a high-temperature, high-pressure synthesis method to prepare stable post-spinel oxides CaCuFe2O5, CaCoFe2O5, CaZnFe2O5, and CaNiFe2O5. It is noteworthy that the materials of this invention cannot be synthesized under normal pressure. This invention provides a new approach and new ideas for the exploration and discovery of post-spinel oxides. By studying the microstructure and interactions of these novel post-spinel oxide materials, theoretical support is provided for the design of novel functional materials for social applications.

[0038] (2) The spinel oxides CaCuFe2O5, CaCoFe2O5, CaZnFe2O5 and CaNiFe2O5 of the present invention are rare complete material systems that can be replaced by a variety of transition metal ions in the same type of fault-blocking system, and have significant research and application value.

[0039] (3) The novel material CaCuFe2O5 of this invention is the first spinel oxide with a CuO6 octahedral structure exhibiting compression distortion.

[0040] (4) The novel material CaZnFe2O5 of this invention is the first post-spinel oxide material to exhibit two-dimensional magnetism. The novel material CaZnFe2O5 of this invention has application value in fields such as information storage, sensors, and spintronics.

[0041] (5) The novel material CaCoFe2O5 of this invention is the first material to generate a coercive field as high as 18 Tesla solely induced by 3d transition metal ions, indicating that the novel material CaCoFe2O5 possesses excellent hard magnetic properties. The novel material CaCoFe2O5 of this invention has potential application value in the fields of permanent magnet materials and magnetic storage devices.

[0042] (6) The novel material CaNiFe2O5 of this invention is the first polar spinel material with uniaxial negative thermal expansion properties, and has broad application prospects in thermomechanical engineering, nanodevice manufacturing, aerospace and other fields. Attached Figure Description

[0043] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0044] Figure 1 The X-ray diffraction pattern of CaCuFe2O5 obtained in Example 1 of this invention;

[0045] Figure 2 The X-ray diffraction pattern of CaCoFe2O5 obtained in Example 2 of this invention;

[0046] Figure 3 The X-ray diffraction pattern of CaZnFe2O5 obtained in Example 3 of this invention;

[0047] Figure 4 The X-ray diffraction pattern of CaNiFe2O5 obtained in Example 4 of this invention;

[0048] Figure 5 This is a schematic diagram of the CuO6 octahedron with anomalous compression distortion of CaCuFe2O5 obtained in Example 1 of the present invention.

[0049] Figure 6 This is a schematic diagram of the low-dimensional magnetic structure of CaZnFe2O5 obtained in Example 3 of the present invention;

[0050] Figure 7 The curve showing the change of lattice constant of CaNiFe2O5 prepared in Example 4 of this invention as a function of temperature;

[0051] Figure 8 The curve showing the change in magnetic susceptibility of CaZnFe2O5 prepared in Example 3 of this invention as a function of temperature;

[0052] Figure 9 The curve showing the change of magnetization intensity of CaZnFe2O5 prepared in Example 3 of this invention with magnetic field strength is shown.

[0053] Figure 10 The curve showing the change of magnetization intensity of CaCoFe2O5 prepared in Example 2 of this invention with steady-state magnetic field strength is shown.

[0054] Figure 11 The curve showing the change of magnetization intensity of CaCoFe2O5 prepared in Example 2 of this invention with pulsed magnetic field intensity is shown.

[0055] Figure 12 The second harmonic signal of CaNiFe2O5 obtained in Example 4 of this invention;

[0056] Figure 13 The curve showing the specific heat capacity of CaZnFe2O5 prepared in Example 3 of this invention as a function of temperature. Detailed Implementation

[0057] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0058] Example 1

[0059] First, 0.5g of high-purity calcium carbonate (CaCO3) was placed in an alumina crucible. Then, the crucible was placed in a muffle furnace and held at 1000℃ for 24 hours. Afterward, the crucible was cooled to approximately 300℃ with the furnace. Next, using heat-resistant gloves, the product was removed and quickly placed in an argon-filled glove box to obtain high-purity calcium oxide (CaO). CaO, CuO, and Fe2O3 with purities higher than 99.9% were mixed in a molar ratio of 1:1:1, resulting in a total powder mass of 0.5g. The mixed powder was then ground for 1 hour in an argon-filled glove box to obtain a mixture with a particle size of 200 mesh. The mixture was filled into platinum capsules and sealed, with a wall thickness of 0.1mm. The platinum capsules were placed in a six-sided anvil press and the raw materials inside were reacted for 30 minutes at a pressure of 8GPa and a temperature of 1150℃. Then, the heating power was directly cut off, allowing the temperature to drop to room temperature within 1 minute, followed by 5 hours to reduce the pressure to atmospheric pressure. The reaction product was then removed from the platinum capsule, yielding CaCuFe2O5.

[0060] Example 2

[0061] First, 0.5g of high-purity calcium carbonate (CaCO3) was placed in an alumina crucible. Then, the crucible was placed in a muffle furnace and held at 1100℃ for 24 hours. Afterward, the crucible was cooled to approximately 200℃ with the furnace. Next, using heat-resistant gloves, the product was removed and quickly placed in an argon-filled glove box to obtain high-purity calcium oxide (CaO). CaO, CoO, and Fe2O3 with purities higher than 99.9% were mixed in a molar ratio of 1:1:1, resulting in a total powder mass of 1g. The mixed powder was then ground in an argon-filled glove box for half an hour to obtain a mixture with a particle size of 200 mesh. The mixture was filled into platinum capsules and sealed, with the capsule walls having a thickness of 0.1mm. The platinum capsules were placed in a six-sided anvil press and the reactants were subjected to a pressure of 7GPa and a temperature of 1200℃ for 60 minutes. Then, the heating power was directly cut off, allowing the temperature to drop to room temperature within 1 minute, followed by a pressure reduction to atmospheric pressure over 3 hours. The reaction product was then removed from the platinum capsule, yielding CaCoFe2O5.

[0062] Example 3

[0063] First, 0.5g of high-purity calcium carbonate (CaCO3) was placed in an alumina crucible. Then, the crucible was placed in a muffle furnace and held at 1000℃ for 24 hours. Afterward, the crucible was cooled to approximately 300℃ with the furnace. Next, using heat-resistant gloves, the product was removed and quickly placed in an argon-filled glove box to obtain high-purity calcium oxide (CaO). CaO, ZnO, and Fe2O3 with a purity higher than 99.9% were mixed in a molar ratio of 1:1:1, resulting in a total powder mass of 0.5g. The mixed powder was then ground for 1 hour in an argon-filled glove box to obtain a mixture with a particle size of 100 mesh. The mixture was filled into platinum capsules and sealed, with the capsule walls having a thickness of 0.1mm. The platinum capsules were placed in a six-sided anvil press and the reactants inside were subjected to a pressure of 9GPa and a temperature of 1180℃ for 30 minutes. Then, the heating power was directly cut off, allowing the temperature to drop to room temperature within 1 minute, followed by 8 hours of pressure reduction to atmospheric pressure. The reaction product was then removed from the platinum capsule, yielding CaZnFe2O5.

[0064] Example 4

[0065] First, 0.5g of high-purity calcium carbonate (CaCO3) was placed in an alumina crucible. Then, the crucible was placed in a muffle furnace and held at 1000℃ for 24 hours. Afterward, the crucible was cooled to approximately 300℃ with the furnace. Next, using heat-resistant gloves, the product was removed and quickly placed in an argon-filled glove box to obtain high-purity calcium oxide (CaO). CaO, NiO, and Fe2O3 with purities higher than 99.9% were mixed in a molar ratio of 1:1:1, resulting in a total powder mass of 0.5g. The mixed powder was then ground for 1 hour in an argon-filled glove box to obtain a mixture with a particle size of 100 mesh. The mixture was filled into platinum capsules and sealed, with a wall thickness of 0.1mm. The platinum capsules were placed in a six-sided anvil press and the raw materials inside were reacted for 30 minutes at a pressure of 9GPa and a temperature of 1180℃. Then, the heating power was directly cut off, allowing the temperature to drop to room temperature within 1 minute, followed by 8 hours of pressure reduction to atmospheric pressure. The reaction product was then removed from the platinum capsule, yielding CaNiFe2O5.

[0066] Performance testing

[0067] 1. Room temperature X-ray diffraction measurement

[0068] The room-temperature crystal structure of the samples was characterized using synchrotron X-rays of different wavelengths generated by the BL02B2 beamline of the Spring-8 synchrotron radiation source in Japan.

[0069] Figure 1The X-ray diffraction pattern of CaCuFe2O5 prepared in Example 1 is shown. (Fitting...) Figure 1 Based on the positions and intensities of the diffraction peaks, the crystal space group of CaCuFe2O5 prepared in Example 1 is Cmcm, and the lattice constant is . The lengths of the six Cu-O bonds in the CuO6 octahedron observed in the crystal structure are as follows: This indicates the presence of compressed CuO6 octahedra in the crystal structure, a feature observed for the first time in a spinel material system.

[0070] Figure 2 The X-ray diffraction pattern of CaCoFe2O5 prepared in Example 2 is shown. (Fitting...) Figure 2 Based on the positions and intensities of the diffraction peaks, the crystal space group of CaCoFe2O5 prepared in Example 2 is Cmcm, and the lattice constant is .

[0071] Figure 3 The X-ray diffraction pattern of CaZnFe2O5 prepared in Example 3 is shown. (Fitting...) Figure 3 Based on the positions and intensities of the diffraction peaks, the crystal space group of CaZnFe2O5 prepared in Example 3 is Cmcm, and the lattice constant is .

[0072] Figure 4 The X-ray diffraction pattern of CaNiFe2O5 prepared in Example 4 is shown. (Fitting...) Figure 4 Based on the positions and intensities of the diffraction peaks, the crystal space group of CaNiFe2O5 prepared in Example 4 is Cmcm, and the lattice constant is .

[0073] 2. Crystal structure diagram

[0074] Figure 5 This shows a schematic diagram of the CuO6 octahedron in the CaCuFe2O5 structure prepared in Example 1, with the lengths of the two shorter Cu-O bonds in the longitudinal direction being... The lengths of the four long Cu-O bonds in the transverse direction are Compression distortion occurred.

[0075] Figure 6 A schematic diagram of the crystal structure of CaZnFe2O5 prepared in Example 3 is shown; in the b-axis direction, the magnetic Fe is separated by the non-magnetic Zn and Ca, exhibiting obvious low-dimensional (two-dimensional) magnetism.

[0076] 3. Variable-temperature X-ray diffraction measurement

[0077] Synchrotron X-rays generated by the BL02B2 beamline of the Spring-8 synchrotron radiation source in Japan were used to characterize the crystal structure of the sample at different temperatures.

[0078] Figure 7 The graph shows the variation trend of the cell parameters of CaNiFe2O5 prepared in Example 4 from 120K to 300K with temperature. The results show that the cell parameters of the a-axis and c-axis decrease with decreasing temperature, while the cell parameter of the b-axis increases with decreasing temperature in the range of 260K to 200K, indicating a significant negative thermal expansion phenomenon.

[0079] 4. Magnetic susceptibility measurement

[0080] The magnetic property measurement system (MPMS) from Quantum Design, USA, was used to measure the change in magnetic susceptibility of CaZnFe2O5 prepared in Example 3 as a function of temperature. In zero-field cooling (ZFC), no external magnetic field was applied, and the measurement was performed by cooling the temperature from room temperature to 2K. In field cooling (FC), an external magnetic field of 0.1T was applied, and the measurement was performed by heating the temperature from 2K to 300K. The temperature rise and fall rate was 2K per minute.

[0081] Figure 8 The curve showing the change in magnetic susceptibility of CaZnFe2O5 prepared in Example 3 as a function of temperature, obtained by ZFC-FC measurement, is shown. Figure 8 As shown, the magnetic susceptibility of CaZnFe2O5 prepared in Example 3 increases when the temperature is close to 180K to 150K, but the upward trend is not significant, which is consistent with the characteristics of low-dimensional magnetism.

[0082] 5. Magnetization Measurement

[0083] The magnetization of CaZnFe2O5 prepared in Example 3 was measured at 300 K and 2 K using a Magnetic Property Measurement System (MPMS) from Quantum Design, USA. The applied magnetic field varied at a rate of 0.01 T per second, and the magnetic field ranged from -7 T to 7 T. At each temperature point, the applied magnetic field decreased from its positive maximum value to its negative maximum value, and then increased back to its positive maximum value.

[0084] Figure 9The curves showing the magnetization of CaZnFe2O5 prepared in Example 3 as a function of magnetic field are displayed. The results show that at a temperature of 300 K, which is above its short-range magnetic correlation formation temperature, the magnetization of the sample is very small and increases linearly with the increase of the applied magnetic field, exhibiting paramagnetism; at a temperature of 2 K, which is below its short-range magnetic correlation formation temperature, the magnetization of the sample exhibits hysteresis, showing short-range magnetic correlation characteristics.

[0085] The magnetization of CaCoFe2O5 prepared in Example 2 was characterized using a steady-state strong magnetic field generated by the High Magnetic Field Laboratory of the Hefei Institutes of Physical Science. The applied magnetic field changed at a rate of 0.015 T per second, and the magnetic field ranged from -35 T to 35 T. At each temperature point, the applied magnetic field decreased from its positive maximum value to its negative maximum value, and then increased back to its positive maximum value.

[0086] Figure 10 The magnetization of CaCoFe2O5 prepared in Example 2 at 300 K and 2 K is shown as a function of magnetic field. The results show that at 300 K, which is above its tilted antiferromagnetic transition temperature, the magnetization of the sample is very small and increases linearly with the increase of the applied magnetic field, exhibiting paramagnetism; at 2 K, the magnetization of the sample exhibits hysteresis, and the coercive field of the ferromagnetic component reaches 18 T.

[0087] The magnetization of CaCoFe2O5 prepared in Example 2 was characterized using a pulsed high magnetic field generated by the National Pulsed High Magnetic Field Center. The magnetic field ranged from 0 to 55 T, and only a positive pulsed magnetic field was applied.

[0088] Figure 11 The magnetization of CaCoFe2O5 prepared in Example 2 at 2K is shown as a function of magnetic field. The results indicate that the coercive field of the ferromagnetic component of the sample reaches 18T at 2K.

[0089] 6. Measurement of Second Harmonic Signal

[0090] The second harmonic signal of the sample was tested using a WITec alpha300R instrument manufactured by WITec GmbH, Germany. The emission wavelength used in the test was 800 nm, and the power was 10 mW. The test temperatures were 300 K, 200 K, and 100 K. The sample needed to be polished before testing.

[0091] Figure 12 The results show the second harmonic signals of the CaNiFe2O5 prepared in Example 4 at three test temperatures: 300K, 200K, and 100K. The results indicate that the sample showed no signal at 300K and 200K, while it reflected a second harmonic signal at 100K, suggesting the presence of a non-centrosymmetric polar structure at this temperature.

[0092] 7. Specific heat measurement

[0093] The specific heat data of CaZnFe2O5 prepared in Example 3 were measured using a Physical Property Measurement System (PPMS) from Quantum Design, Inc., USA.

[0094] Figure 13 The specific heat of CaZnFe2O5 prepared in Example 3 is shown as a function of temperature. The results show that the specific heat of the sample did not show significant anomalies throughout the entire measurement temperature range, indicating that the material has no obvious long-range magnetic order and exhibits low-dimensional magnetic characteristics.

Claims

1. A spinel oxide having the following chemical formula: CaMFe2O5; in, M is Cu, Co, Zn, or Ni.

2. The spinel oxide according to claim 1, wherein, The space group of the spinel oxide is Cmcm.

3. The spinel oxide according to claim 1, wherein, When M is Cu, the lattice constant of the spinel oxide CaCuFe2O5 is:

4. The spinel oxide according to claim 1, wherein, When M is Co, the lattice constant of the spinel oxide CaCoFe2O5 is:

5. The spinel oxide according to claim 1, wherein, When M is Zn, the lattice constant of the spinel oxide CaZnFe2O5 is:

6. The spinel oxide according to claim 1, wherein, When M is Ni, the lattice constant of the spinel oxide CaNiFe2O5 is:

7. The spinel oxide according to claim 1, wherein, When M is Cu, using synchrotron X-ray diffraction with a wavelength of 0.070 nm, the X-ray powder diffraction pattern of spinel oxide CaCuFe2O5 expressed in 2θ angles shows diffraction peaks at 6.456°, 15.200°, 18.196°, and 19.049°, with a 2θ angle measurement error of ±0.006°. Preferably, when M is Co, synchrotron X-ray diffraction with a wavelength of 0.065 nm is used. The X-ray powder diffraction pattern of spinel oxide CaCoFe2O5, expressed in terms of 2θ angle, shows diffraction peaks at 5.872°, 13.946°, 17.030°, and 17.783°, with a 2θ angle measurement error of ±0.006°. Preferably, when M is Zn, synchrotron X-ray diffraction with a wavelength of 0.080 nm is used. The X-ray powder diffraction pattern of spinel oxide CaZnFe2O5, expressed in terms of 2θ angle, shows diffraction peaks at 7.241°, 17.176°, 20.876°, and 21.918°, with a 2θ angle measurement error of ±0.006°. Preferably, when M is Ni, synchrotron X-ray diffraction with a wavelength of 0.070 nm is used. The X-ray powder diffraction pattern of spinel oxide CaNiFe2O5, expressed in 2θ angle, has diffraction peaks at 6.324°, 15.052°, 18.144°, and 19.052°, and the 2θ angle measurement error is ±0.006°.

8. A method for preparing the spinel oxide according to any one of claims 1-7, comprising the following steps: (1) CaO, MO and Fe2O3 are thoroughly ground and mixed in a protective gas atmosphere to obtain a mixture; (2) After sealing and wrapping the mixture, heat and pressurize it. (3) Cool and depressurize the processed product obtained in step (2); Where M is Cu, Co, Zn or Ni.

9. The method according to claim 8, wherein, The molar ratio of CaO, MO and Fe2O3 in step (1) is CaO:MO:Fe2O3 = 1:1:1; Preferably, the protective gas is selected from one or more of nitrogen, helium, and argon; Preferably, the particle size of the mixture is 100-1000 mesh, more preferably 200-600 mesh; Preferably, the treatment in step (2) is carried out under the following conditions: temperature of 1100-1200°C and pressure of 5-10 GPa; Preferably, the processing in step (2) is carried out for more than 20 minutes, more preferably 30 to 60 minutes; Preferably, the sealing and wrapping in step (2) is done with a gold capsule or a platinum capsule; more preferably, the thickness of the gold capsule or platinum capsule is 0.05 to 1.00 mm.

10. The method according to claim 8, wherein, The processing in step (2) is carried out in a six-sided anvil press or a two-stage push press of type DIA, Walker, or Kawai. Preferably, the cooling in step (3) is performed by reducing the product to room temperature within 1 minute; Preferably, the depressurization in step (3) is carried out by reducing the product to ambient pressure over 2 to 10 hours.

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