Multi-step high-entropy high-enthalpy phase change hybrid double perovskite material and preparation method thereof

Abstract

This invention discloses a multi-step high-entropy high-enthalpy phase transition hybrid double perovskite material and its preparation method. The preparation method includes the following steps: 1) Weigh at least one of 1,3-propanediamine, N-methyl-1,3-propanediamine, 1,3-diamino-2-propanol, ethylenediamine, N-ethylethylenediamine, and N-(2-hydroxyethyl)ethylenediamine, as well as a salt containing M1, a salt containing M2, and formic acid as raw materials according to stoichiometric ratio; 2) Add the above raw materials to a reaction vessel lined with polytetrafluoroethylene and mix evenly; 3) Seal the reaction vessel and heat it at a constant temperature of 80-110℃ for 36-72h; 4) Cool naturally to room temperature, collect the product, wash and dry it to obtain a material with the chemical formula [A]2[M1M2(HCOO)6]. This material achieves multi-step reversible high-entropy and high-enthalpy phase transitions through heterovalent bimetallic synergy and flexible cyclic ammonium cation design. It also features dielectric response and low-temperature photoluminescence. The phase transition temperature can be tuned to room temperature and near room temperature range, effectively solving the problems of limited phase transition steps, low entropy and enthalpy changes, and poor performance synergy of existing materials.

Description

Technical Field

[0001] This invention relates to the field of organic-inorganic hybrid perovskite materials, and more particularly to multi-step high-entropy high-enthalpy phase transition hybrid double perovskite materials and their preparation methods. Background Technology

[0002] Organic-inorganic hybrid perovskite materials, due to their tunable structure, rich phase transition behavior, and diverse functional properties, have significant application value in fields such as dielectric switches, temperature sensors, green refrigeration, phase change energy storage, and optoelectronic functional devices, and have become a research hotspot in the field of functional materials. However, existing perovskite phase change materials still have significant limitations in terms of structural design, performance regulation, and functional integration, specifically in the following aspects:

[0003] 1. The phase transition behavior is simple and the entropy change and enthalpy change values ​​are relatively low. The traditional single metal perovskite structure has high symmetry, making it difficult to achieve multi-step phase transitions. Moreover, the A-site cations of existing materials are mostly linear ammonium salts, which have limited hydrogen bonding interaction modes, conformational flexibility and structural induction ability, and cannot drive complex structural phase transitions with multi-step, high enthalpy change and high entropy change.

[0004] 2. The phase change temperature control range is narrow, and there is a lack of multi-step phase change materials suitable for room temperature and near-room temperature range, which seriously limits their practical application scenarios;

[0005] 3. The synergy between optical properties and phase transition properties is poor, and material systems that combine excellent photoluminescence properties and multi-step phase transition behavior are relatively scarce;

[0006] 4. Most studies on heterovalent bimetallic perovskites focus on cyanide and halide systems, while there are few studies on formic acid-based organic-inorganic hybrid biperovskites. Their equivalent heterometallic construction strategies, phase transition mechanisms, and performance regulation rules are still unclear. Summary of the Invention

[0007] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide a multi-step high-entropy high-enthalpy phase transition hybrid double perovskite material and its preparation method. This material achieves multi-step reversible high-entropy high-enthalpy phase transition through heterovalent bimetallic synergy and flexible cyclic ammonium cation design, and has both dielectric response and low-temperature photoluminescence. The phase transition temperature can be tuned to the room temperature and near room temperature range, effectively solving the problems of low phase transition steps, low entropy and enthalpy change, and poor performance synergy of existing materials.

[0008] The multi-step high-entropy, high-enthalpy phase transition hybrid double perovskite material provided by this invention has the chemical formula [A]2[M1M2(HCOO)6];

[0009] Wherein, A is a five / hexacyclic ammonium cation, which is generated by in-situ reaction of at least one of 1,3-propanediamine, N-methyl-1,3-propanediamine, 1,3-diamino-2-propanol, ethylenediamine, N-ethylethylenediamine, and N-(2-hydroxyethyl)ethylenediamine with formic acid;

[0010] M1 is a trivalent transition metal ion, which is selected from Cr. 3+ Al 3+ In 3+ Bi 3+ Ga 3+ Fe 3 + ,Sc 3+ Y 3+ La 3+ Ce 3+ Pr 3+ 、Nd 3+ Pm 3+ 、Sm 3+ Eu 3+ Gd 3+ 、Tb 3+ Dy 3+ Ho 3+ Er 3+ Tm 3+ Yb 3+ Lu 3+ At least one of them;

[0011] M2 is selected from Li + Na + K + 、Rb + Cs + Ag + NH4 + At least one of them;

[0012] The [A]2[M1M2(HCOO)6] does not include [(C4H9N2)2][Cr] III Na I [(HCOO)6]、[(C4H9N2)2][Cr III K I Any one of (HCOO)6].

[0013] Furthermore, the five / six-membered ring ammonium cation is at least one selected from 1,4,5,6-tetrahydropyrimidineonium, N-methyl-1,4,5,6-tetrahydropyrimidineonium, 5-hydroxy-1,4,5,6-tetrahydropyrimidineonium, 2-imidazolineonium, N-ethyl-2-imidazolineonium, and N-hydroxyethyl-2-imidazolineonium.

[0014] Furthermore, this invention also provides a method for preparing the multi-step high-entropy high-enthalpy phase transition hybrid double perovskite material as described above, comprising the following steps:

[0015] 1) Weigh out organic amine, salt containing M1, salt containing M2, and formic acid according to stoichiometric ratio as raw materials;

[0016] 2) Add the above raw materials to a polytetrafluoroethylene-lined reactor and mix thoroughly;

[0017] 3) After sealing the above-mentioned reaction vessel, heat it at a constant temperature of 80-110℃ for 36-72 hours;

[0018] 4) After naturally cooling to room temperature, the product was collected, washed, and dried to obtain a material with the chemical formula [A]2[M1M2(HCOO)6].

[0019] Further, in step 1), the salt containing M1 is (Cr(NO3)3, AlCl3, InCl3, In(NO3)3, BiCl3, Bi(NO3)3, Ga(NO3)3, Fe(NO3)3, FeCl3, Fe2(C2O4)3, Sc(NO3)3, Y(NO3)3, La(NO3)3, Ce(NO3)3, Pr(NO3)3, Nd(NO3)3, Pm(NO3)3, etc.). 3) At least one of Sm(NO3)3, Eu(NO3)3, Gd(NO3)3, Tb(NO3)3, Dy(NO3)3, Ho(NO3)3, Er(NO3)3, Tm(NO3)3, Yb(NO3)3, and Lu(NO3)3; the salt containing M2 is at least one of HCOOLi, LiNO3, HCOONa, KNO3, RbNO3, Cs2CO3, AgNO3, and ammonia water.

[0020] Further, in step 1), the volume ratio of the formic acid to the organic amine is 1.1:1-1.8:1; the organic amine is at least one of 1,3-propanediamine, N-methyl-1,3-propanediamine, 1,3-diamino-2-propanol, ethylenediamine, N-ethylethylenediamine, and N-(2-hydroxyethyl)ethylenediamine.

[0021] Furthermore, in step 4), methanol is used for washing, the drying temperature is 70-90℃, and the drying time is 20-40 min.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1) The material of this invention achieves one to three independent thermally driven reversible phase transitions (all first-order phase transitions) within the range of 80-500K, exhibiting rich phase transition behavior and solving the problem of limited phase transition steps in existing materials. The phase transition process is accompanied by significant changes in structural symmetry, gradually transforming from a low-symmetry triclinic / monoclinic crystal system to a high-symmetry cubic crystal system, providing a structural basis for multi-state control devices; [(C4H9N2)2][Al III Rb I [HCOO]6] The entropy change of a single-step phase transition reaches 51.37 J·mol⁻¹. -1 ·K -1 ,[(C4H9N2)2][Al III Na I The total entropy change of the three-step phase transition [(HCOO)6] is as high as 69.38 J·mol⁻¹. -1 ·K -1 The thermal effect is significant.

[0024] 2) This invention contains Cr 3+ Several examples of materials exhibit strong deep red luminescence at low temperatures, with their laser spectra showing two distinct peaks at 417 and 571 nm, corresponding to Cr, respectively. 3+ of 4 A2→ 4 T1 and 4 A2→ 4 T2 transition. Under optimal excitation at 571 nm, the intense, deep red, narrow emission peak at 685 nm is attributed to Cr. 3+ Located in CrO6 octahedron 2 E→ 4 The radiative transition of A2 exhibits high temperature sensitivity to luminescence intensity, achieving synergy between phase transition and luminescence performance, resulting in a higher degree of functional integration than existing single-function materials.

[0025] 3) When the material of this invention approaches its phase transition point, changes in its microstructure significantly affect its dielectric properties, thus exhibiting a pronounced dielectric response on a macroscopic scale. During the heating-cooling cycle, the real part of the dielectric constant ( The numerical curves of the material exhibit a significant step-like dielectric anomaly near the phase transition point, and a hysteresis phenomenon was observed in the step-like dielectric anomaly of the heating and cooling curves, which is highly consistent with the DSC observations. After multiple consecutive heating and cooling cycles, the dielectric constant remained unchanged. These clear step-like dielectric anomaly curves not only verify the material's reversible phase transition behavior but also reveal its potential as a dielectric switching material.

[0026] 4) The material of the present invention has high crystallinity, no impurities adhering to the surface, no cracks, and good stability. It can be sealed and stored for 12 months at 25℃ / 60% RH without any change in crystal phase. X-ray powder diffraction has verified that the phase purity is high.

[0027] 5) The material of the present invention has multiple phase transition, temperature-responsive luminescence, dielectric switching and pressure-clamping effect, and can be applied to a variety of application scenarios such as dielectric switching devices, green refrigeration, low temperature sensors, red light emitting devices, magnetic storage devices and phase change energy storage materials. Its application scenarios are more extensive than those of existing single-function perovskite materials.

[0028] It should be understood that the description in the Summary of the Invention is not intended to limit the key or essential features of the embodiments of the present invention, nor is it intended to restrict the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0029] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0030] Figure 1 [(C4H9N2)2][Al] Ⅲ Na Ⅰ (HCOO)6] DSC curves of the three-step phase transition and schematic diagrams of their enthalpy change and entropy change;

[0031] Figure 2 [(C4H9N2)2][Cr Ⅲ Cs Ⅰ (HCOO)6] DSC curve of phase transition and schematic diagram of enthalpy change and entropy change curves;

[0032] Figure 3 [(C4H9N2)2][Cr Ⅲ Rb Ⅰ Photoluminescence spectra of (HCOO)6]: (a) excitation and emission spectra at 80 K; (b) temperature-varying emission spectra in fluorescence mode; (c) temperature-varying emission spectra in phosphorescence mode; (d) CIE coordinates at 80 K;

[0033] Figure 4 In the diagram, (a) represents [(C4H9N2)2][Al] at different frequencies. Ⅲ Na Ⅰ (b) is a schematic diagram of the temperature-induced dielectric constant change of [(HCOO)6], and shows the curves of [(C4H9N2)2][Al] at different frequencies. Ⅲ Na Ⅰ A schematic diagram of the change in dielectric constant of [HCOO] upon cooling;

[0034] Figure 5 In the example, (a) is [(C4H9N2)2][Cr Ⅲ Rb Ⅰ (b) is a schematic diagram of the thermogravimetric curve of [(HCOO)6], and [(C4H9N2)2][Cr] is a schematic diagram of the thermogravimetric curve of [(HCOO)6]. Ⅲ Schematic diagram of the thermogravimetric curve of [NH4)(HCOO)6];

[0035] Figure 6 In the example, (a) is [(C4H9N2)2][Cr Ⅲ Rb Ⅰ XRD pattern of [(HCOO)6], (b) is [(C4H9N2)2][Cr Ⅲ Cs Ⅰ XRD pattern of [(HCOO)6], (c) is [(C4H9N2)2][Cr Ⅲ XRD pattern of [(NH4)(HCOO)6], (d) is [(C4H9N2)2][Al] Ⅲ K Ⅰ XRD pattern of (HCOO)6; Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0037] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0038] Please refer to Figures 1-6 The embodiments of the present invention provide a multi-step high-entropy high-enthalpy phase transition hybrid double perovskite material, the chemical formula of which is [A]2[M1M2(HCOO)6];

[0039] Wherein, A is a five / hexacyclic ammonium cation, which is generated by in-situ reaction of at least one of 1,3-propanediamine, N-methyl-1,3-propanediamine, 1,3-diamino-2-propanol, ethylenediamine, N-ethylethylenediamine, and N-(2-hydroxyethyl)ethylenediamine with formic acid;

[0040] M1 is a trivalent transition metal ion, which is selected from Cr. 3+ Al 3+ In 3+ Bi 3+ Ga 3+ Fe3 + ,Sc 3+ Y 3+ La 3+ Ce 3+ Pr 3+ 、Nd 3+ Pm 3+ 、Sm 3+ Eu 3+ Gd 3+ 、Tb 3+ Dy 3+ Ho 3+ Er 3+ Tm 3+ Yb 3+ Lu 3+ At least one of them;

[0041] M2 is selected from Li + Na + K + 、Rb + Cs + Ag + NH4 + At least one of them;

[0042] The [A]2[M1M2(HCOO)6] does not include [(C4H9N2)2][Cr] III Na I [(HCOO)6]、[(C4H9N2)2][Cr III K I Any one of (HCOO)6].

[0043] The five / six-membered cyclic ammonium cation is at least one selected from 1,4,5,6-tetrahydropyrimidineonium, N-methyl-1,4,5,6-tetrahydropyrimidineonium, 5-hydroxy-1,4,5,6-tetrahydropyrimidineonium, 2-imidazolineonium, N-ethyl-2-imidazolineonium, and N-hydroxyethyl-2-imidazolineonium.

[0044] Furthermore, this invention also provides a method for preparing the multi-step high-entropy high-enthalpy phase transition hybrid double perovskite material as described above, comprising the following steps:

[0045] 1) Weigh out organic amine, salt containing M1, salt containing M2, and formic acid according to stoichiometric ratio as raw materials;

[0046] 2) Add the above raw materials to a polytetrafluoroethylene-lined reactor and mix thoroughly;

[0047] 3) After sealing the above-mentioned reaction vessel, heat it at a constant temperature of 80-110℃ for 36-72 hours;

[0048] 4) After naturally cooling to room temperature, the product was collected, washed, and dried to obtain a material with the chemical formula [A]2[M1M2(HCOO)6].

[0049] In step 1), the salt containing M1 is (Cr(NO3)3 (chromium nitrate), AlCl3 (aluminum chloride), InCl3 (indium chloride), In(NO3)3 (indium nitrate), BiCl3 (bismuth chloride), Bi(NO3)3 (bismuth nitrate), Ga(NO3)3 (gallium nitrate), Fe(NO3)3 (ferric nitrate), FeCl3 (ferric chloride), Fe2(C2O4)3 (ferric oxalate), Sc(NO3)3 (scandium nitrate), Y(NO3)3 (yttrium nitrate), La(NO3)3 (lanthanum nitrate), Ce(NO3)3 (cerium nitrate), Pr(NO3)3 (praseodymium nitrate), Nd(NO3)3 (neodymium nitrate), Pm(NO3)3 (promethium nitrate). The salt containing M2 is at least one of the following: Sm(NO3)3 (samarium nitrate), Eu(NO3)3 (europium nitrate), Gd(NO3)3 (gadolinium nitrate), Tb(NO3)3 (terbium nitrate), Dy(NO3)3 (dysprosium nitrate), Ho(NO3)3 (holmium nitrate), Er(NO3)3 (erbium nitrate), Tm(NO3)3 (thulium nitrate), Yb(NO3)3 (ytterbium nitrate), and Lu(NO3)3 (lutetium nitrate); the salt containing M2 is at least one of HCOOLi (lithium formate), LiNO3 (lithium nitrate), HCOONa (sodium formate), KNO3 (potassium nitrate), RbNO3 (rubidium nitrate), Cs2CO3 (cesium carbonate), AgNO3 (silver nitrate), and ammonia water.

[0050] In step 1), the volume ratio of formic acid to organic amine is 1.1:1-1.8:1; the organic amine is at least one of 1,3-propanediamine, N-methyl-1,3-propanediamine, 1,3-diamino-2-propanol, ethylenediamine, N-ethylethylenediamine, and N-(2-hydroxyethyl)ethylenediamine.

[0051] In step 4), methanol is used for washing, the drying temperature is 70-90℃, and the drying time is 20-40 min.

[0052] The material of this invention achieves one to three independent thermally driven reversible phase transitions (all first-order phase transitions) within the range of 80-500K, exhibiting rich phase transition behavior and solving the problem of limited phase transition steps in existing materials. The phase transition process is accompanied by a significant change in structural symmetry, gradually transforming from a low-symmetry triclinic / monoclinic crystal system to a high-symmetry cubic crystal system, providing a structural basis for multi-state control devices. [(C4H9N2)2][Al] III Rb I [HCOO]6] The entropy change of a single-step phase transition reaches 51.37 J·mol⁻¹. -1 ·K-1 ,[(C4H9N2)2][Al III Na I The total entropy change of the three-step phase transition [(HCOO)6] is as high as 69.38 J·mol⁻¹. -1 ·K -1 The thermal effect is significant.

[0053] This invention contains Cr 3+ Several examples of materials exhibit strong deep red luminescence at low temperatures, with their laser spectra showing two distinct peaks at 417 and 571 nm, corresponding to Cr, respectively. 3+ of 4 A2→ 4 T1 and 4 A2→ 4 T2 transition. Under optimal excitation at 571 nm, the intense, deep red, narrow emission peak at 685 nm is attributed to Cr. 3+ Located in CrO6 octahedron 2 E→ 4 The radiative transition of A2 exhibits high temperature sensitivity to luminescence intensity, achieving synergy between phase transition and luminescence performance, resulting in a higher degree of functional integration than existing single-function materials.

[0054] The microstructure of the material of this invention, as it approaches its phase transition point, significantly affects its dielectric properties, thus exhibiting a pronounced dielectric response on a macroscopic scale. During the heating-cooling cycle, the real part of the dielectric constant (…) The numerical curves of the material exhibit a significant step-like dielectric anomaly near the phase transition point, and a hysteresis phenomenon was observed in the step-like dielectric anomaly of the heating and cooling curves, which is highly consistent with the DSC observations. After multiple consecutive heating and cooling cycles, the dielectric constant remained unchanged. These clear step-like dielectric anomaly curves not only verify the material's reversible phase transition behavior but also reveal its potential as a dielectric switching material.

[0055] The material of this invention has high crystallinity, no impurities adhering to the surface, no cracks, and good stability. It can be sealed and stored for 12 months at 25℃ / 60% RH without any change in crystal phase. X-ray powder diffraction has verified that the phase purity is high.

[0056] The material of this invention combines multi-step phase transition, temperature-responsive luminescence, dielectric switching, and pressure-clamping effect, and can be applied to a variety of application scenarios such as dielectric switching devices, green refrigeration, low-temperature temperature sensors, red light emitting devices, magnetic storage devices, and phase change energy storage materials. Its application scenarios are more extensive than those of existing single-function perovskite materials.

[0057] In this invention, the in-situ reaction equation for the organic ammonium at site A is as follows:

[0058] (1) 1,4,5,6-Tetrahydropyrimidineonium:

[0059]

[0060] (2) N-methyl-1,4,5,6-tetrahydropyrimidineonium:

[0061]

[0062] (3) 5-Hydroxy-1,4,5,6-Tetrahydropyrimidineonium:

[0063]

[0064] (4) 2-Imidazolinium:

[0065]

[0066] (5) N-ethyl-2-imidazolinium:

[0067]

[0068] (6) N-hydroxyethyl-2-imidazolinium:

[0069]

[0070] Example 1

[0071] Weigh 1 mL of at least one of 1,3-propanediamine, N-methyl-1,3-propanediamine, 1,3-diamino-2-propanol, ethylenediamine, N-ethylethylenediamine, and N-(2-hydroxyethyl)ethylenediamine, and 3.5 mmol of a salt containing M1, 1.5 mmol of a salt containing M2, and 1.5 mL of formic acid as raw materials; add the above raw materials sequentially to a polytetrafluoroethylene-lined reactor and mix thoroughly; seal the reactor and place it in an oven, heating it at 110°C for 72 h; after the reaction is complete, allow it to cool naturally to room temperature, collect the product, wash the surface impurities three times with methanol, and then dry it in an oven at 80°C for 30 min to obtain the target double perovskite material, the general chemical formula of which is [A]2[M1M2(HCOO)6].

[0072] Example 2

[0073] The reaction temperature in step 2) can be adjusted within the range of 80-110℃. The reaction time can be extended to obtain larger crystals. Appropriately shortening the reaction time can yield high-quality single crystals with better crystallinity. There is no significant difference in the structure and properties of the product.

[0074] Example 3

[0075] By replacing the salt containing M1 and the salt containing M2 with other soluble salts in equal molar amounts, while keeping other raw materials and steps unchanged, the target material with the same structure can be obtained.

[0076] Example 4

[0077] By adjusting the volume ratio of formic acid to organic amine to 1.1:1-1.8:1, while keeping other conditions unchanged, the target material can be successfully prepared with no significant difference in performance.

[0078] Example 5

[0079] Adding 5-10 μL of methanol, ethyl acetate, or methyl tert-butyl ether as a co-solvent during raw material mixing, while keeping other conditions unchanged, can shorten the reaction time to 30-40 h and slightly increase the yield.

[0080] Example 6

[0081] Small amounts of other metal ions (such as Mn) can be introduced at the B site. 2+ Ni 2+ Co 2+ Zn 2+ Doping can be performed to finely control the phase transition temperature or optical properties.

[0082] Example 7

[0083] Other synthesis methods, such as solvent evaporation, diffusion, or ultrasound-assisted synthesis, can be used to prepare this series of crystals.

[0084] In the description of this specification, the terms "one embodiment," "some embodiments," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0085] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A multi-step high-entropy, high-enthalpy phase transition hybrid double perovskite material, characterized in that, The general chemical formula of the material is [A]2[M1M2(HCOO)6]; Wherein, A is a five / hexacyclic ammonium cation, which is generated by in-situ reaction of at least one of 1,3-propanediamine, N-methyl-1,3-propanediamine, 1,3-diamino-2-propanol, ethylenediamine, N-ethylethylenediamine, and N-(2-hydroxyethyl)ethylenediamine with formic acid; M1 is a trivalent transition metal ion, which is selected from Cr. 3+ Al 3+ In 3+ Bi 3+ Ga 3+ Fe 3+ ,Sc 3 + Y 3+ La 3+ Ce 3+ Pr 3+ 、Nd 3+ Pm 3+ 、Sm 3+ Eu 3+ Gd 3+ 、Tb 3+ Dy 3+ Ho 3+ Er 3+ Tm 3+ Yb 3+ Lu 3+ At least one of them; M2 is selected from Li + Na + K + 、Rb + Cs + Ag + NH4 + At least one of them; The [A]2[M1M2(HCOO)6] does not include [(C4H9N2)2][Cr] III Na I [(HCOO)6]、[(C4H9N2)2][Cr III K I Any one of (HCOO)6].

2. The multi-step high-entropy high-enthalpy phase transition hybrid double perovskite material according to claim 1, characterized in that, The five / six-membered cyclic ammonium cation is at least one selected from 1,4,5,6-tetrahydropyrimidineonium, N-methyl-1,4,5,6-tetrahydropyrimidineonium, 5-hydroxy-1,4,5,6-tetrahydropyrimidineonium, 2-imidazolineonium, N-ethyl-2-imidazolineonium, and N-hydroxyethyl-2-imidazolineonium.

3. A method for preparing a multi-step high-entropy, high-enthalpy phase transition hybrid double perovskite material as described in any one of claims 1-2, characterized in that, Includes the following steps: 1) Weigh out organic amine, salt containing M1, salt containing M2, and formic acid according to stoichiometric ratio as raw materials; 2) Add the above raw materials to a polytetrafluoroethylene-lined reactor and mix thoroughly; 3) After sealing the above-mentioned reaction vessel, heat it at a constant temperature of 80-110℃ for 36-72 hours; 4) After naturally cooling to room temperature, the product was collected, washed, and dried to obtain a material with the chemical formula [A]2[M1M2(HCOO)6].

4. The method for preparing multi-step high-entropy high-enthalpy phase transition hybrid double perovskite material according to claim 3, characterized in that, In step 1), the salt containing M1 is Cr(NO3)3, AlCl3, InCl3, In(NO3)3, BiCl3, Bi(NO3)3, Ga(NO3)3, Fe(NO3)3, FeCl3, Fe2(C2O4)3, Sc(NO3)3, Y(NO3)3, La(NO3)3, Ce(NO3)3, Pr(NO3)3, Nd(NO3)3, or Pm(NO3)3. At least one of Sm(NO3)3, Eu(NO3)3, Gd(NO3)3, Tb(NO3)3, Dy(NO3)3, Ho(NO3)3, Er(NO3)3, Tm(NO3)3, Yb(NO3)3, and Lu(NO3)3; the salt containing M2 is at least one of HCOOLi, LiNO3, HCOONa, KNO3, RbNO3, Cs2CO3, AgNO3, and ammonia water.

5. The method for preparing multi-step high-entropy high-enthalpy phase transition hybrid double perovskite material according to claim 3, characterized in that, In step 1), the volume ratio of formic acid to organic amine is 1.1:1-1.8:1; the organic amine is at least one of 1,3-propanediamine, N-methyl-1,3-propanediamine, 1,3-diamino-2-propanol, ethylenediamine, N-ethylethylenediamine, and N-(2-hydroxyethyl)ethylenediamine.

6. The method for preparing multi-step high-entropy high-enthalpy phase transition hybrid double perovskite material according to claim 3, characterized in that, In step 4), methanol is used for washing, the drying temperature is 70-90℃, and the drying time is 20-40 min.

Images