A perovskite manganite magnetic refrigeration material and its application

Abstract

The present invention discloses a perovskite manganese oxide magnetic refrigeration material with variable components and its application. The perovskite manganese oxide is La 0.66‑x Ca 0.33‑y Mn 1+x+y O3 porous nanospheres, wherein the molar ratios of La:Ca:Mn are 0.66:0.33:1, 0.61:0.33:1.05, 0.56:0.33:1.1, 0.66:0.28:1.05, and 0.66:0.23:1.1 respectively. The perovskite manganese oxide porous nanospheres of the present invention have a large surface area and flexible phase transition temperature regulation. The material of the present invention is used for magnetic refrigeration, has excellent magnetic entropy change and relative refrigeration capacity, and the relatively wide entropy change temperature range makes the refrigeration temperature range more flexible.

Description

Technical Field

[0001] The present invention relates to the field of magnetic refrigeration materials, and particularly to the composition of La 0.66-x Ca 0.33-y Mn 1+x+y O3 perovskite manganese oxide porous nanospheres and the application of magnetic refrigeration materials. Background Art

[0002] With the increasing attention to environmental problems such as global warming, energy crisis, environmental pollution, and ecological protection, people are eager to find efficient and energy-saving alternative solutions in various fields. The discovery of the magnetocaloric effect has attracted the favor of the refrigeration field due to its unique physical properties. Compared with traditional air compression refrigeration methods, magnetic refrigeration has advantages such as high theoretical efficiency, simple structure, and adaptability to extreme environments. MCE is an inherent property of magnetic materials. The temperature change (ΔTad) during the adiabatic process and the entropy change (ΔST) during the isothermal process are important indicators for evaluating its performance. Therefore, people have been committed to finding new materials with large magnetic entropy change |-ΔSM| and wide working temperature. Medium-bandwidth La-Ca-Mn-O perovskite manganese oxides have large magnetic entropy changes, small thermal hysteresis, phase transition temperatures close to room temperature, and relatively low costs, and have been a research hotspot for refrigeration materials for many years. Summary of the Invention

[0003] The purpose of the present invention is to design a magnetic refrigeration material of La 0.66-x Ca 0.33-y Mn 1+x+y O3 perovskite manganese oxide porous nanospheres. The complex precursor is synthesized by the solvothermal method under high temperature and high pressure, and the Mn-doped porous nanospheres are obtained after calcination. By adjusting the composition, the phase transition temperature is increased to obtain a magnetic refrigeration material more suitable for room temperature.

[0004] A perovskite manganese oxide magnetic refrigeration material of the present invention is characterized in that the perovskite manganese oxide is La 0.66-x Ca 0.33-y Mn 1+x+y O3 porous nanospheres, wherein the molar ratios of La:Ca:Mn are 0.66:0.33:1, 0.61:0.33:1.05, 0.56:0.33:1.1, 0.66:0.28:1.05, and 0.66:0.23:1.1 respectively.

[0005] A perovskite manganese oxide magnetic refrigeration material of the present invention specifically comprises the following preparation steps:

[0006] 1) Adding lanthanum nitrate hexahydrate, calcium nitrate tetrahydrate, manganese nitrate, and PVP into a mixed solution of glycerol and isopropanol in a certain proportion;

[0007] 2) Ultrasonicate the mixed solution for 15 min, and then stir for 50 min until completely dissolved; the ultrasonic frequency is 40 ± 2 kHz, and the time is 0.5 h;

[0008] 3) Transfer the mixed solution obtained in 2) to the inner lining of a 200 ml polytetrafluoroethylene reaction kettle, tighten the high-pressure reaction kettle, and place the reaction kettle in a forced-air drying oven at 180 °C for heat preservation for 6 h;

[0009] 4) After the reaction kettle cools down, centrifuge the product in it at 8000 r / min for five minutes. After discarding the supernatant, wash it with anhydrous ethanol and then centrifuge it, repeat twice, and dry the obtained precipitate in a forced-air drying oven for 12 h;

[0010] 5) Put the dried precursor into a muffle furnace and calcine it at 750 °C for 6 h.

[0011] The application of a perovskite manganese oxide magnetic refrigeration material of the present invention is characterized in that it specifically includes:

[0012] Apply the La 0.66-x Ca 0.33-y Mn 1+x+y O3 porous nanospheres obtained after calcination to the magnetic refrigeration direction, place the material near its magnetic phase transition temperature, and measure the magnetic induction intensity data of the material under the magnetic field change of 0 - 5 T at every 2 K temperature test. Calculate the magnetic entropy change data under a certain magnetic field and temperature environment according to formula 1 by integration.

[0013]

[0014] According to the maximum magnetic entropy change, obtain the full width at half maximum temperature range of the maximum magnetic entropy change, and use formula 2 to obtain the relative refrigeration capacity of the material.

[0015]

[0016] T1 and T2 represent the temperature points where the full width at half maximum of the magnetic entropy change is located.

[0017] The beneficial effects of the present invention:

[0018] The present invention has low preparation energy consumption, is simple, and is environmentally friendly; 2) The present invention prepares La 0.66-x Ca 0.33-y Mn 1+x+y O3 porous nanospheres doped with A-site defective Mn by adjusting the ratio of ions. The doping process is simple and efficient, and no additional ions are added; 3) The A-site doping of Mn brings multiple double exchange effects, changes the crystal structure of the product, etc., resulting in changes in magnetic interactions and bringing magnetic disorder during the phase transition. Thus, without reducing the entropy change, the La 0.66-x Ca0.33-y Mn 1+x+ y The phase transition temperature of MnO3 porous nanospheres makes the material have better prospects for practical utilization. Description of the Drawings

[0019] Figure 1 is the XRD (X-ray diffraction) of the present invention according to its diffraction pattern.

[0020] Figure 2 is a scanning electron microscope, a transmission electron microscope and a Mapping element distribution map of the present invention; (a, b) Example 1, (c, d) Example 2, (e, f) Example 3, (g, h) Example 4, (i, j) Example 5. (k, l, m) High-resolution transmission of Example 3; (n) Mapping element distribution map.

[0021] Figure 3 is La of the present invention 0.66-x Ca 0.33-y Mn 1+x+y Magnetic entropy change diagram of LaCaMnO3. The x-axis is the temperature unit K, the y-axis is the magnetic field strength unit Oe, and the z-axis is the absolute value unit of magnetic entropy change J / kg.K. (a - e) respectively represent the magnetic entropy change diagrams of Example 1 to Example 5.

[0022] Figure 4 is La of the present invention 0.66-x Ca 0.33-y Mn 1+x+y FORC diagram of LaCaMnO3 in three temperature ranges. Illustrate the manifestation of the change in material composition in terms of magnetic interaction. (a - e) respectively represent the FORC of Example 1 to Example 5 at 10K temperature; (f - j) respectively represent the FORC of Example 1 to Example 5 at T C temperature; (k - o) respectively represent the FORC of Example 1 to Example 5 at 300K temperature. Detailed Embodiments

[0023] The following is to further elaborate the present invention in combination with specific embodiments. These embodiments are only used to illustrate the present invention, but not to limit the scope of the present invention.

[0024] Example 1

[0025] 1) Dissolve 1.666 mmol of lanthanum nitrate hexahydrate, 0.833 mmol of calcium nitrate tetrahydrate, and 2.5 mmol of manganese nitrate in a mixed solution of 65 ml of isopropanol and 36 ml of glycerol (glycerol), and add 1 g of PVP;

[0026] 2) Ultrasonic the mixed solution for 15 min, and then stir for 50 min until completely dissolved;

[0027] 3) Transfer the mixed solution obtained in 2) into a 200 ml Teflon reactor liner, and tighten the high-pressure reactor. Place the reactor in a forced-air drying oven and keep it at 180 °C for 6 h;

[0028] 4) After the reactor cools down, centrifuge the product in it at 8000 r / min for five minutes. Discard the supernatant, wash it with absolute ethanol and then centrifuge it, repeating this twice. Dry the obtained precursor precipitate in a drying oven for 12 h;

[0029] 5) Put the dried precursor into a muffle furnace and calcine it at 750 °C for 6 h.

[0030] The magnetocaloric entropy changes of the perovskite-type manganese oxide nanospheres obtained in Example 1 are equal to 1.10 J / kg·K and 3.76 J / kg·K under 1 T and 5 T magnetic fields respectively, and the relative cooling capacities under 1 T and 5 T magnetic fields are equal to 41.80 J / kg and 226.61 J / kg respectively.

[0031] Example 2

[0032] 1) Dissolve 1.525 mmol of lanthanum nitrate hexahydrate, 0.833 mmol of calcium nitrate tetrahydrate, and 2.641 mmol of manganese nitrate in a mixed solution of 65 ml of isopropanol and 36 ml of glycerol (glycerin), and add 1 g of PVP;

[0033] 2) Ultrasonic the mixed solution for 15 min, and then stir it for 50 min until it is completely dissolved;

[0034] 3) Transfer the mixed solution obtained in 2) into a 200 ml Teflon reactor liner, tighten the high-pressure reactor, and place the reactor in a forced-air drying oven and keep it at 180 °C for 6 h;

[0035] 4) After the reactor cools down, centrifuge the product in it at 8000 r / min for five minutes. Discard the supernatant, wash it with absolute ethanol and then centrifuge it, repeating this twice. Dry the obtained precursor precipitate in a drying oven for 12 h;

[0036] 5) Put the dried precursor into a muffle furnace and calcine it at 750 °C for 6 h.

[0037] The magnetocaloric entropy changes of the perovskite-type manganese oxide nanospheres obtained in Example 2 are equal to 1.09 J / kg·K and 3.61 J / kg·K under 1 T and 5 T magnetic fields respectively, and the relative cooling capacities under 1 T and 5 T magnetic fields are equal to 37.57 J / kg and 210.51 J / kg respectively.

[0038] Example 3

[0039] 1) Dissolve 1.416 mmol of lanthanum nitrate hexahydrate, 0.833 mmol of calcium nitrate tetrahydrate, and 2.75 mmol of manganese nitrate in a mixed solution of 65 ml of isopropanol and 36 ml of glycerol (propanetriol), and add 1 g of PVP;

[0040] 2) Ultrasonicate the mixed solution for 15 min, and then stir for 50 min until completely dissolved;

[0041] 3) Transfer the mixed solution obtained in 2) to a 200-ml Teflon reactor liner, tighten the high-pressure reactor, and place the reactor in a forced-air drying oven at 180 °C for 6 h;

[0042] 4) After the reactor cools down, centrifuge the product in it at 8000 r / min for five minutes. Discard the supernatant, wash it with absolute ethanol and then centrifuge, repeat twice, and dry the obtained precursor precipitate in a drying oven for 12 h;

[0043] 5) Put the dried precursor into a muffle furnace and calcine it at 750 °C for 6 h.

[0044] The magnetocaloric entropy changes of the perovskite-type manganese oxide nanospheres obtained in Example 3 are equal to 0.89 J / kg·K and 3.08 J / kg·K under magnetic fields of 1 T and 5 T, respectively, and the relative cooling powers under magnetic fields of 1 T and 5 T are equal to 33.54 J / kg and 183.57 J / kg, respectively.

[0045] Example 4

[0046] 1) Dissolve 1.666 mmol of lanthanum nitrate hexahydrate, 0.708 mmol of calcium nitrate tetrahydrate, and 2.625 mmol of manganese nitrate in a mixed solution of 65 ml of isopropanol and 36 ml of glycerol (propanetriol), and add 1 g of PVP;

[0047] 2) Ultrasonicate the mixed solution for 15 min, and then stir for 50 min until completely dissolved;

[0048] 3) Transfer the mixed solution obtained in 2) to a 200-ml Teflon reactor liner, tighten the high-pressure reactor, and place the reactor in a forced-air drying oven at 180 °C for 6 h;

[0049] 4) After the reactor cools down, centrifuge the product in it at 8000 r / min for five minutes. Discard the supernatant, wash it with absolute ethanol and then centrifuge, repeat twice, and dry the obtained precursor precipitate in a drying oven for 12 h;

[0050] 5) Put the dried precursor into a muffle furnace and calcine it at 750 °C for 6 h.

[0051] The magnetocaloric entropy changes of the perovskite manganite nanospheres obtained in Example 4 are equal to 1.10 J / kg.K and 3.67 J / kg.K under magnetic fields of 1 T and 5 T, respectively, and the relative refrigeration capacities under magnetic fields of 1 T and 5 T are equal to 38.75 J / kg and 233.45 J / kg, respectively.

[0052] Example 5

[0053] 1) Dissolve 1.666 mmol of lanthanum nitrate hexahydrate, 0.583 mmol of calcium nitrate tetrahydrate, and 2.75 mmol of manganese nitrate in a mixed solution of 65 ml of isopropanol and 36 ml of glycerol (propanetriol), and add 1 g of PVP.

[0054] 2) Ultrasonicate the mixed solution for 15 min, and then stir for 50 min until completely dissolved.

[0055] 3) Transfer the mixed solution obtained in 2) to a 200-ml polytetrafluoroethylene reaction kettle liner, tighten the high-pressure reaction kettle, and place the reaction kettle in a forced-air drying oven at 180 °C for 6 h.

[0056] 4) After the reaction kettle cools down, centrifuge the product in it at 8000 r / min for five minutes. After discarding the supernatant, wash it with anhydrous ethanol and then centrifuge it. Repeat this process twice, and dry the obtained precursor precipitate in a drying oven for 12 h.

[0057] 5) Put the dried precursor into a muffle furnace and calcine it at 750 °C for 6 h.

[0058] The magnetocaloric entropy changes of the perovskite manganite nanospheres obtained in Example 5 are equal to 0.82 J / kg.K and 2.99 J / kg.K under magnetic fields of 1 T and 5 T, respectively, and the relative refrigeration capacities under magnetic fields of 1 T and 5 T are equal to 35.51 J / kg and 195.71 J / kg, respectively.

Claims

1. A perovskite manganite magnetic refrigeration material, characterized in that, The perovskite manganese oxide described is La 0.66- x Ca 0.33-y Mn 1+x+y O3 porous nanospheres, where the molar ratios of La:Ca:Mn are 0.61:0.33:1.05, 0.56:0.33:1.1, 0.66:0.28:1.05, and 0.66:0.23:1.1, respectively.

2. The perovskite manganese oxide magnetic refrigeration material according to claim 1, characterized in that, The preparation method comprises the following steps: 1) Add lanthanum nitrate hexahydrate, calcium nitrate tetrahydrate, manganese nitrate, and PVP into a mixed solution of glycerol and isopropanol in a certain proportion; 2) Ultrasonic the mixed solution for 15 min, and then stir for 50 min until completely dissolved; the ultrasonic frequency is 40 ± 2 kHz and the time is 0.5 h; 3) Transfer the mixed solution obtained in 2) to a 200 ml polytetrafluoroethylene reaction kettle liner, tighten the high-pressure reaction kettle, and place the reaction kettle in a forced-air drying oven at 180 °C for heat preservation for 6 h; 4) After the reaction kettle cools down, centrifuge the product in it at 8000 r / min for five minutes. After discarding the supernatant, wash it with absolute ethanol and then centrifuge, repeat twice, and dry the obtained precipitate in a forced-air drying oven for 12 h; 5) Put the dried precursor into a muffle furnace and calcine it at 750 °C for 6 h.

3. The application of the perovskite manganite magnetic refrigeration material according to claim 1, characterized in that, Specifically, it includes: Place the material near its magnetic phase transition temperature and measure the magnetic induction intensity data of the material under the magnetic field change of 0 - 5 T at every 2 K temperature; calculate the magnetic entropy change data under a certain magnetic field and temperature environment by integrating according to the magnetic entropy change formula; obtain the half-width temperature range of the maximum magnetic entropy change according to the maximum magnetic entropy change, and obtain the relative refrigeration capacity of the material by using the relative refrigeration capacity formula.

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