Ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material as well as preparation method and application thereof

Abstract

The invention discloses a ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material as well as a preparation method and application thereof, the stoichiometric formula of the material is (1-x) (0.67 BiFeO3-0.33 BaTiO3)-xSmNbO4, x represents molar percentage and is 0.03-0.07, x represents molar percentage, x represents molar percentage, and x represents molar percentage. The preparation method comprises the following steps: carrying out ball milling on raw materials, drying, sieving, calcining in air at 800-850 DEG C for 3-4 hours, adding 0.1 wt% of manganese dioxide, carrying out secondary ball milling, drying, sieving, pouring into a mold, carrying out compression molding, demolding, and carrying out cold isostatic pressing to obtain a blank body; embedding the green body into powder with the same components, putting the powder into a muffle furnace, and keeping the temperature for 2-4 hours at 1020-1040 DEG C in an air atmosphere to obtain the ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material. According to the invention, rhombohedral phase / pseudo-cubic phase (R / PC) regulation and control are combined with a perovskite-pyrochlore composite structure, so that a high dielectric constant, excellent breakdown strength and excellent frequency-temperature stability are obtained, and polarization intensity and energy storage density are improved at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials and relates to composite ceramic materials, in particular to a ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material and a preparation method and application thereof. Background Art

[0002] In the context of renewable energy integration, pulse power systems (such as electromagnetic weapons, fast charging devices, smart grids, etc.) require ultra-high power density (>10 8 w / kg) and extreme environmental stability. Dielectric ceramic capacitors have become a core technology for high-power applications due to their ultra-fast charge and discharge capabilities, zero leakage characteristics, and wide temperature adaptability. However, traditional lead-based ceramic materials (such as Pb(Zr,Ti)O3(PZT), Pb(Zn 1 / 3 Nb 2 / 3 )O3-PbTiO3(PZN-PT) etc.) are subject to environmental restrictions. At the same time, lead-free ferroelectrics (such as Na 0.5 Bi 0.5 Energy storage density of TiO3(NBT), BaTiO3(BT), NaNbO3(NN), BiFeO3-BaTiO3(BFO-BTO), etc.) Affected by polarization difference (ΔP=P max -P r ) and breakdown strength (E b ) influence. Therefore, the design has a high maximum polarization intensity (P max ), low remnant polarization intensity (P r ) and high breakdown strength (E b ) is the key to achieving high performance. Specifically, the inherent physical mechanism of the material leads to P max and E b Strong antagonism between. High P max Usually a high dielectric constant (P and dielectric constant ε r ) is positively correlated), but according to the Stark-Garton relationship (E b ∝ε r -α ), (α=0.5-0.65) the increase of dielectric constant will significantly reduce the breakdown strength. This antagonistic coupling gives the simultaneous optimization of P max and E b This poses significant challenges and limits the development of advanced energy storage systems. Summary of the Invention

[0003] In view of the deficiencies of the prior art, the purpose of the present application is to provide a ternary lead-free BiFeO3-based perovskite-cryptomelane composite ceramic material with excellent energy storage performance, a preparation method and application thereof, wherein the Bi2Ti2O7 cryptomelane phase with ultra-low loss, low dielectric constant and excellent breakdown strength is precipitated by introducing SmNbO4, so as to simultaneously improve the polarization strength and energy storage density of the composite ceramic material.

[0004] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0005] A ternary lead-free BiFeO3-based perovskite-cryptomelane composite ceramic material, the stoichiometric formula of which is (1-x)(0.67BiFeO3-0.33BaTiO3)-xSmNbO4, wherein x represents the mole percentage, x=0.03-0.07.

[0006] The present application also protects a preparation method of the ternary lead-free BiFeO3-based perovskite-cryptomelane composite ceramic material as described above, comprising the following steps:

[0007] Step one, after the analytical pure BaCO3, Sm2O3, Nb2O5, Bi2O3, Fe2O3 and TiO2 are prepared according to the stoichiometric ratio and uniformly mixed by ball milling, the powder is dried, sieved and obtained, the powder is calcined in air at 800-850 DEG C for 3-4h, and the mixed powder is obtained;

[0008] Step two, after 0.1wt% of manganese dioxide is added to the powder calcined in step one, secondary ball milling, drying and sieving are carried out, then the powder is poured into a mold, pressed and formed, demolded and the green body is obtained by cold isostatic pressing;

[0009] Step three, the green body obtained in step two is embedded in the powder with the same composition and placed in a muffle furnace, heated to 1020-1040 DEG C at a rate of 3-5 DEG C / min in an air atmosphere, kept for 2-4h, then reduced to 500 DEG C at a rate of 5 DEG C / min, and then sintered into a ceramic by cooling to room temperature with the furnace, to obtain the ternary lead-free BiFeO3-based perovskite-cryptomelane composite ceramic material.

[0010] Preferably, the ball milling in step one is mixed ball milling of the raw materials, zirconia balls and deionized water at a mass ratio of 1:5:1 for 10-12h.

[0011] Preferably, the sieving in step one and step two is sieving through a 120-200 mesh sieve.

[0012] Preferably, the drying in step one and step two is drying in an oven at 80 DEG C for 12-24h.

[0013] Preferably, the secondary ball milling in step 2 is performed by mixing the raw materials, zirconia balls and deionized water in a mass ratio of 1:5:1 and milling for 8 hours.

[0014] Preferably, the cold isostatic pressing process in step 2 is cold isostatic pressing for 3 minutes at a pressure of 200 MPa.

[0015] The present invention also protects a ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material prepared by the above-mentioned method and its application in dielectric ceramic capacitors.

[0016] Compared with the prior art, the present invention has the following technical effects:

[0017] The present invention combines rhombohedral / pseudo-cubic phase (R / PC) regulation with a perovskite-pyrochlore composite structure. A 0.67BiFeO3-0.33BaTiO3 system with high polarization near the morphotropic phase boundary is used as the matrix. SmNbO4 (SNO4) with a scheelite structure is introduced. The introduction of SmNbO4 precipitates a Bi2Ti2O7 pyrochlore phase with ultra-low loss, low dielectric constant, and excellent breakdown strength. This constructs a perovskite-pyrochlore composite ceramic, ultimately achieving simultaneous improvements in polarization strength and energy storage density. Specifically:

[0018] Sm 3+ Occupies the A site, Nb 5+ Replaces the B site, resulting in enhanced composition disorder; in addition, due to the high temperature sintering process, Bi 3+ Volatility, and Ti 4+ By the higher price Nb 5+ The substitution generates cation vacancies to maintain charge neutrality, weakening the bond between the A-site ions and the oxygen octahedron. The structural instability caused by the proximity of the B-site ions to the center of the oxygen octahedron ultimately leads to the formation of the pyrochlore phase and the precipitation of the highly insulating Bi2Ti2O7 pyrochlore phase (Fd-3m). The ionic radius mismatch destroys the long-range ferroelectric order, promotes the transformation of R3c to PC, forms polar nanodomains, and enhances the polarization difference (ΔP = 44.76 μC / cm 2 ); At the same time, the dispersed Bi2Ti2O7 pyrochlore phase forms a perovskite-pyrochlore composite structure, which inhibits the accumulation of space charge and promotes uniform electric field distribution, making E b The SN-0.03 composite ceramic achieved a 6.12 J / cm 3 W rec, while achieving high dielectric constant and excellent breakdown strength, and having excellent frequency-temperature stability, which provides a practical way to develop lead-free dielectric capacitors with high energy storage capacity, and is conducive to the miniaturization and integration of dielectric capacitors in practical applications;

[0019] The present invention uses a more advanced cold isostatic pressing technology in the preparation process, which reduces the debinding process, thereby improving the density of the ceramic and saving the production cost. It has a simple process, low material cost, and is green and environmentally friendly. It is expected to become an important candidate material that is both technically and economically superior to replace lead-based ceramic materials for high-end industrial application materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 XRD patterns of the SN-x perovskite-pyrochlore composite ceramics prepared in Examples 1-3 and Comparative Example 1 at room temperature;

[0021] Figure 2 (ae) are SEM images and statistical particle size distribution (measured by nanomeasurement software) of the composite ceramic materials prepared in Examples 1-3 and Comparative Examples 1 and 2. Figure 2 (f, g) are the changes of grain size and relative density with x;

[0022] Figure 3 Dielectric-temperature profiles of the SN-x perovskite-pyrochlore composite ceramics prepared in Examples 1-3 and Comparative Examples 1 and 2: (a) Temperature dependence of the dielectric constant, with the inset showing the relationship between the dielectric loss and temperature for different x contents; (b, c) εm and Tm for different x contents; (d) Uncorrected Curie-Vans fitting curve; (e) Relationship between γ and SNO4;

[0023] Figure 4 Energy storage characteristics of composite ceramic materials prepared in Examples 1-3 and Comparative Examples 1 and 2: (a) Unipolar PE loop, (b-c) Variation of Pmax, Pr, ΔP, Wrec, Wtal, and η with x; (d) Comparison of key performance parameters (Eb, η, and Wrec) of SN-0.00 and SN-0.03 composite ceramics; (e) Comparison of energy storage performance between this study and other studies;

[0024] Figure 5Temperature-frequency stability and pulse discharge performance test of the SN-0.03 perovskite-melanocerite composite ceramic prepared in Example 1: (a) frequency-dependent P-E loop at 100 kV / cm; (b) Wrec and η calculated based on the P-E loop of (a); (c) temperature-dependent P-E loop at 100 kV / cm; (d) Wrec and η calculated based on the P-E loop of (c); (e) under-damped discharge current curves at different fields and Imax, CD, PD (inset); (f) over-damped discharge current curves (R = 200 Ω) at different fields and Imax (inset); (g) Wdis calculated from the over-damped curve as a function of time. DETAILED DESCRIPTION

[0025] The specific content of the application is further explained in detail in the following combined with examples.

[0026] Example 1

[0027] The present embodiment gives a preparation method of a ternary lead-free BiFeO3-based perovskite-melanocerite composite ceramic material, comprising the following steps:

[0028] Step one, according to the stoichiometric ratio 0.97 (0.67BiFeO3-0.33BaTiO3)-0.03SmNbO4, analytical pure BaCO3, Sm2O3, Nb2O5, Bi2O3, Fe2O3 and TiO2 are prepared, then mixed ball milled for 12 h to be mixed uniformly according to the mass ratio of raw materials, zirconia ball, deionized water 1:5:1, then dried in an oven at 80℃ for 24 h, sieved through a 120 mesh sieve to obtain a uniform size powder, and the powder is calcined at 800℃ in air for 4 h to obtain a mixed powder;

[0029] Step two, after adding 0.1wt% manganese dioxide to the calcined powder of step one, the mixed powder is ball milled for 8 h according to the mass ratio of raw materials, zirconia ball, deionized water 1:5:1, then dried in an oven at 80℃ for 12 h, sieved through a 200 mesh sieve, and the obtained powder is poured into a mold for compression molding, demolded, and cold isostatic pressed under a pressure of 200 Mpa for 3 min to obtain a green body;

[0030] Step three, the green body obtained in step two is embedded in a powder of the same composition and placed in a muffle furnace, heated to 1020℃ at a rate of 5℃ / min in air atmosphere, kept for 3 h, then reduced to 500℃ at a rate of 5℃ / min, and then cooled to room temperature with the furnace to sinter the ceramic, thereby obtaining a ternary lead-free BiFeO3-based perovskite-melanocerite composite ceramic material.

[0031] The prepared ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material was first polished to a sample thickness of 0.3 mm with 240-grit sandpaper, and then polished to a thickness of 0.1 mm on both sides with 2000-grit sandpaper. It was ultrasonically cleaned in distilled water for 10 minutes, and silver electrode slurry was coated on both sides. The samples were sintered at 580°C for 10 minutes and tested.

[0032] Example 2

[0033] This embodiment provides a method for preparing a ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material, comprising the following steps:

[0034] Step 1: After preparing analytically pure BaCO3, Sm2O3, Nb2O5, Bi2O3, Fe2O3 and TiO2 according to the stoichiometric ratio of 0.95 (0.67BiFeO3-0.33BaTiO3)-0.05SmNbO4, the raw materials, zirconia balls and deionized water are mixed in a mass ratio of 1:5:1 and ball milled for 12 hours until the mixture is uniform. The mixture is then placed in an oven and dried at 80°C for 24 hours, passed through a 120-mesh sieve to obtain a powder of uniform size, and the powder is calcined in air at 800°C for 4 hours to obtain a mixed powder;

[0035] Step 2: Add 0.1 wt% of manganese dioxide to the powder calcined in step 1, and then mix and ball-mill for 8 hours according to the mass ratio of raw materials, zirconia balls, and deionized water of 1:5:1. Then, place it in an oven and dry it at 80°C for 12 hours. After passing through a 200-mesh sieve, the resulting powder is poured into a mold, pressed into shape, and demolded. After that, it is cold isostatically pressed at a pressure of 200 MPa for 3 minutes to obtain an embryo body;

[0036] Step 3: The green body obtained in step 2 is embedded in powder of the same composition and placed in a muffle furnace. The temperature is raised to 1020°C at a rate of 5°C / min in an air atmosphere. After keeping the temperature for 3 hours, the temperature is lowered to 500°C at a rate of 5°C / min. The green body is then cooled to room temperature and sintered into porcelain to obtain a ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material.

[0037] The prepared ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material was first polished to a sample thickness of 0.3 mm with 240-grit sandpaper, and then polished to a thickness of 0.1 mm on both sides with 2000-grit sandpaper. It was ultrasonically cleaned in distilled water for 10 minutes, and silver electrode slurry was coated on both sides. The samples were sintered at 580°C for 10 minutes and tested.

[0038] Example 3

[0039] This embodiment provides a method for preparing a ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material, comprising the following steps:

[0040] Step 1: According to the stoichiometric ratio of 0.93 (0.67BiFeO3-0.33BaTiO3)-0.07SmNbO4, analytically pure BaCO3, Sm2O3, Nb2O5, Bi2O3, Fe2O3 and TiO2 are prepared, and the raw materials, zirconia balls and deionized water are mixed in a mass ratio of 1:5:1 and ball milled for 12 hours until the mixture is uniform. The mixture is then placed in an oven and dried at 80°C for 24 hours, and passed through a 120-mesh sieve to obtain a powder of uniform size. The powder is calcined in air at 800°C for 4 hours to obtain a mixed powder;

[0041] Step 2: Add 0.1 wt% of manganese dioxide to the powder calcined in step 1, and then mix and ball-mill for 8 hours according to the mass ratio of raw materials, zirconia balls, and deionized water of 1:5:1. Then, place it in an oven and dry it at 80°C for 12 hours. After passing through a 200-mesh sieve, the resulting powder is poured into a mold, pressed into shape, and demolded. After that, it is cold isostatically pressed at a pressure of 200 MPa for 3 minutes to obtain an embryo body;

[0042] Step 3: The green body obtained in step 2 is embedded in powder of the same composition and placed in a muffle furnace. The temperature is raised to 1020°C at a rate of 5°C / min in an air atmosphere. After keeping the temperature for 3 hours, the temperature is lowered to 500°C at a rate of 5°C / min. The green body is then cooled to room temperature and sintered into porcelain to obtain a ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material.

[0043] The prepared ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material was first polished to a sample thickness of 0.3 mm with 240-grit sandpaper, and then polished to a thickness of 0.1 mm on both sides with 2000-grit sandpaper. It was ultrasonically cleaned in distilled water for 10 minutes, and silver electrode slurry was coated on both sides. The samples were sintered at 580°C for 10 minutes and tested.

[0044] Example 4

[0045] This embodiment provides a method for preparing a ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material, comprising the following steps:

[0046] Step 1: According to the stoichiometric ratio of 0.96 (0.67BiFeO3-0.33BaTiO3)-0.04SmNbO4, analytically pure BaCO3, Sm2O3, Nb2O5, Bi2O3, Fe2O3 and TiO2 are prepared, and the raw materials, zirconia balls and deionized water are mixed in a mass ratio of 1:5:1 and ball milled for 10 hours until the mixture is uniform. The mixture is then placed in an oven and dried at 80°C for 12 hours, passed through a 200-mesh sieve to obtain a powder of uniform size, and the powder is calcined in air at 850°C for 3 hours to obtain a mixed powder;

[0047] Step 2: Add 0.1 wt% of manganese dioxide to the powder calcined in step 1, then mix and ball-mill for 8 hours according to the mass ratio of raw materials, zirconia balls, and deionized water of 1:5:1, and then perform secondary ball milling. Then, place it in an oven and dry it at 80°C for 24 hours, pass it through a 200-mesh sieve, pour the obtained powder into a mold, press it into shape, demold it, and cold isostatically press it at a pressure of 200 MPa for 3 minutes to obtain an embryo body;

[0048] Step 3: The green body obtained in step 2 is embedded in powder of the same composition and placed in a muffle furnace. The temperature is raised to 1040°C at a rate of 3°C / min in an air atmosphere. After keeping the temperature for 2 hours, the temperature is lowered to 500°C at a rate of 5°C / min. The green body is then cooled to room temperature and sintered into porcelain to obtain a ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material.

[0049] The prepared ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material was first polished to a sample thickness of 0.3 mm with 240-grit sandpaper, and then polished to a thickness of 0.1 mm on both sides with 2000-grit sandpaper. It was ultrasonically cleaned in distilled water for 10 minutes, and silver electrode slurry was coated on both sides. The samples were sintered at 580°C for 10 minutes and tested.

[0050] Example 5

[0051] This embodiment provides a method for preparing a ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material, comprising the following steps:

[0052] Step 1: According to the stoichiometric ratio of 0.94 (0.67BiFeO3-0.33BaTiO3)-0.06SmNbO4, analytically pure BaCO3, Sm2O3, Nb2O5, Bi2O3, Fe2O3 and TiO2 are prepared, and the raw materials, zirconia balls and deionized water are mixed in a mass ratio of 1:5:1 and ball milled for 11 hours until the mixture is uniform. The mixture is then placed in an oven and dried at 80°C for 18 hours, and passed through a 150-mesh sieve to obtain a powder of uniform size. The powder is calcined in air at 820°C for 3.5 hours to obtain a mixed powder;

[0053] Step two, after adding 0.1wt% manganese dioxide to the powder calcined in step one, the raw material, zirconia ball stone, deionized water are mixed in a mass ratio of 1:5:1 for secondary ball milling for 8h, then dried in an oven at 80℃ for 18h, sieved through a 150 mesh sieve, the obtained powder is poured into a mold for compression molding, demolded, and cold isostatic pressing under a pressure of 200Mpa for 3min to obtain a blank;

[0054] Step three, the blank obtained in step two is embedded in powder of the same composition and placed in a muffle furnace, heated to 1030℃ at a rate of 4℃ / min in an air atmosphere, held for 5h, then reduced to 500℃ at a rate of 5℃ / min, and then cooled to room temperature with the furnace to sinter the porcelain, obtaining a ternary lead-free BiFeO3-based perovskite-melanocerite composite ceramic material.

[0055] The prepared ternary lead-free BiFeO3-based perovskite-melanocerite composite ceramic material is first polished to a thickness of 0.3mm with 240 grit sandpaper, then polished to a thickness of 0.1mm with 2000 grit sandpaper on both sides, placed in distilled water for ultrasonic cleaning for 10min, and silver electrode paste is coated on the front and back surfaces, sintered at a temperature of 580℃ for 10min, and tested.

[0056] Comparative Example 1

[0057] The present example gives a preparation method of a ternary lead-free BiFeO3-based perovskite-melanocerite composite ceramic material, comprising the following steps:

[0058] Step one, according to the stoichiometric ratio of 0.99(0.67BiFeO3-0.33BaTiO3)-0.01SmNbO4, analytical pure BaCO3, Sm2O3, Nb2O5, Bi2O3, Fe2O3 and TiO2 are prepared, then mixed ball milled for 12h according to the mass ratio of raw material, zirconia ball stone, deionized water 1:5:1 until mixed uniformly, then dried in an oven at 80℃ for 24h, sieved through a 120 mesh sieve to obtain a powder with uniform size, and the powder is calcined in air at 800℃ for 4h to obtain a mixed powder;

[0059] Step two, after adding 0.1wt% manganese dioxide to the powder calcined in step one, the raw material, zirconia ball stone, deionized water are mixed in a mass ratio of 1:5:1 for secondary ball milling for 8h, then dried in an oven at 80℃ for 12h, sieved through a 200 mesh sieve, the obtained powder is poured into a mold for compression molding, demolded, and cold isostatic pressing under a pressure of 200Mpa for 3min to obtain a blank;

[0060] Step 3: The green body obtained in step 2 is embedded in powder of the same composition and placed in a muffle furnace. The temperature is raised to 1020°C at a rate of 5°C / min in an air atmosphere. After keeping the temperature for 3 hours, the temperature is lowered to 500°C at a rate of 5°C / min. The green body is then cooled to room temperature and sintered into porcelain to obtain a ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material.

[0061] The prepared ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material was first polished to a sample thickness of 0.3 mm with 240-grit sandpaper, and then polished to a thickness of 0.1 mm on both sides with 2000-grit sandpaper. It was ultrasonically cleaned in distilled water for 10 minutes, and silver electrode slurry was coated on both sides. The samples were sintered at 580°C for 10 minutes and tested.

[0062] Comparative Example 2

[0063] This embodiment provides a method for preparing a ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material, comprising the following steps:

[0064] Step 1: After preparing analytically pure BaCO3, Sm2O3, Nb2O5, Bi2O3, Fe2O3 and TiO2 according to the stoichiometric ratio (0.67BiFeO3-0.33BaTiO3)-0SmNbO4, the raw materials, zirconia balls and deionized water were mixed in a mass ratio of 1:5:1 and ball-milled for 12 hours until the mixture was uniform. The mixture was then dried in an oven at 80°C for 24 hours and passed through a 120-mesh sieve to obtain a powder of uniform size. The powder was calcined in air at 800°C for 4 hours to obtain a mixed powder.

[0065] Step 2: Add 0.1 wt% of manganese dioxide to the powder calcined in step 1, and then mix and ball-mill for 8 hours according to the mass ratio of raw materials, zirconia balls, and deionized water of 1:5:1. Then, place it in an oven and dry it at 80°C for 12 hours. After passing through a 200-mesh sieve, the resulting powder is poured into a mold, pressed into shape, and demolded. After that, it is cold isostatically pressed at a pressure of 200 MPa for 3 minutes to obtain an embryo body;

[0066] Step 3: The green body obtained in step 2 is embedded in powder of the same composition and placed in a muffle furnace. The temperature is raised to 1020°C at a rate of 5°C / min in an air atmosphere. After keeping the temperature for 3 hours, the temperature is lowered to 500°C at a rate of 5°C / min. The green body is then cooled to room temperature and sintered into porcelain to obtain a ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material.

[0067] The prepared ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material was first polished to a sample thickness of 0.3 mm with 240-grit sandpaper, and then polished to a thickness of 0.1 mm on both sides with 2000-grit sandpaper. It was ultrasonically cleaned in distilled water for 10 minutes, and silver electrode slurry was coated on both sides. The samples were sintered at 580°C for 10 minutes and tested.

[0068] Figure 1 The XRD patterns of the composite ceramic materials prepared in Examples 1-3 and Comparative Example 1 are as follows; Figure 1 It can be seen that a single perovskite phase structure is presented at low doping levels (x<0.03), confirming that SNO4 is successfully dissolved in the 0.67BFO-0.33BTO lattice; when x≥0.03, a secondary phase peak appears, which is determined to be Bi2Ti2O7 pyrochlore phase by PDF card matching (00-032-0118); this phenomenon is due to the Bi2Ti2O7 pyrochlore phase during high temperature sintering. 3+ Volatility, and Ti 4+ By the higher price Nb 5+ In order to maintain charge neutrality, substitution generates cation vacancies, which weaken the bonding between the a-site ions and the oxygen octahedron. The structural instability caused by the B-site ions being close to the center of the oxygen octahedron ultimately leads to the formation of the pyrochlore phase.

[0069] Figure 2 The SEM images and statistical particle size distribution (measured by nanomeasurement software) of the composite ceramic materials prepared in Examples 1-3 and Comparative Examples 1 and 2 are shown. Figure 2 (f, g) are the changes of grain size and relative density with x; Figure 2 It can be seen that all ceramics exhibit a uniform and dense microstructure without observable pores (relative density > 90%); it is worth noting that when x ≥ 0.03, polyhedral grains appear at the grain boundaries, which is mainly attributed to the inherent structural characteristics of the Bi2Ti2O7 pyrochlore phase, whose low surface energy along specific low-refractive-index crystal planes is conducive to the formation of polyhedral morphology; with the increase of SNO4 content, the average grain size gradually decreases (from 2.99 μm to 0.85 μm); this reduces the increase in strain energy barrier when the ionic radius of the doped ion is smaller than the substituted ion radius; this enhanced strain resistance hinders lattice migration and inhibits grain growth; in addition, the relatively small secondary phase grain size (G) contributes to the reduction of G value in SN-x ceramics to a certain extent; the grain size (G) is inversely proportional to the breakdown strength, indicating that grain refinement improves the breakdown performance; in addition, the ultra-low dielectric loss, low dielectric constant and fast polarization response (low P r ) and high P of 0.67BFO-0.33BTO matrix maxThis enables the perovskite-pyrochlore composite ceramic material to simultaneously obtain a high dielectric constant and excellent breakdown strength, as well as excellent frequency-temperature stability, providing a practical approach for the development of lead-free dielectric capacitors with high energy storage capacity, which is beneficial to the miniaturization and integration of dielectric capacitors in practical applications.

[0070] Figure 3 The dielectric-temperature spectrum of the composite ceramic materials prepared in Examples 1-3 and Comparative Examples 1 and 2: (a) The temperature dependence of the dielectric constant, the insert shows the relationship between the dielectric loss and temperature at different x contents; (b, c) ε m and Tm; (d) Curie-Vans fitting curve without correction; (e) Relationship between γ and SNO4; Figure 3 (b) and Figure 3 (c) shows the ε m and T m With the change of doping content. After SNO4 doping, T m The peak shifts to lower temperature, and ε m It gradually decreases, indicating that the diffusion phase transition is enhanced and the relaxation behavior is promoted. XRD analysis shows that the incorporation of SNO4 increases the disorder of the structure, resulting in a weakening of ferroelectricity. It is worth noting that the dielectric loss (tanδ) of SN-x ceramics shows a significant surge above 300℃ ( Figure 3 (a) illustration), which may be related to the thermal activation of local defects. With the introduction of SNO4, the dielectric loss gradually decreases, which is more conducive to practical applications. In order to quantify the relaxation characteristics, the diffusion coefficient ( Figure 3 (d) and 5(e)). While conventional ferroelectrics obey the Curie-Weiss law, the SN-x composite ceramic deviates significantly due to its diffuse phase transition. The diffusion coefficient gradually increases with the incorporation of SNO4, confirming the enhanced relaxation behavior that facilitates the formation of elongated PE loops.

[0071] Figure 4 Energy storage properties of the composite ceramic materials prepared in Examples 1-3 and Comparative Examples 1 and 2: (a) Unipolar PE loop; (bc) Variation of Pmax, Pr, ΔP, Wrec, Wtal, and η with x; (d) Comparison of the main performance parameters (Eb, η, and Wrec) of SN-0.00 and SN-0.03 composite ceramics; (ij) Comparison of energy storage performance between this study and other studies. The unipolar PE loop was measured at a 10 Hz breakdown critical electric field, as shown in Figure 2. Figure 4 (a) is shown. Calculate the corresponding parameter W rec 、W rec 、W tal and η as a function of SNO4, such as Figure 4(b) shown. For SN-0.00 ceramic, the large size ferroelectric domains show a clear hysteresis effect under the applied electric field, resulting in high P r (16μC / cm 2 ) and low energy storage efficiency (η ~ 48%). With the addition of SNO4, the disorder in the composite ceramic increases, destroying the long-range order of ferroelectricity and generating small size domains with fast polarization response. This leads to lower P r and finer P-E loops. The SN-0.03 composite ceramic achieves a balance enhancement of E b (355kV / cm) and ΔP (P max -P r = 44.76μC / cm 2 ), providing excellent energy storage performance (W rec ~ 6.12J / cm 3 ). Figure 4 A direct comparison of SN-0.00 and SN-0.03 can be found in (c-d), where the E b of the 0.67BFO-0.33BTO system modified by SNO4 is improved by ~ 2.37 times, and the W rec is improved by 3.62 times, indicating that the feasibility of optimizing the energy storage performance by inducing the construction of composite ceramics through SNO4 is very high. Figure 4 The analysis in (e) shows that SN-0.03 is superior to other reported systems in terms of recoverable energy storage density (W rec ), normalized energy storage density (W rec / E b ) and polarization difference (ΔP), highlighting the potential of constructing composite ceramics in advanced energy storage applications.

[0072] Figure 5 Temperature-frequency stability and pulse discharge performance tests of the SN-0.03 perovskite-melanotekite composite ceramic prepared in Example 1: (a) frequency-dependent P-E loops at 100kV / cm; (b) Wrec and η calculated based on the P-E loops of (a); (c) temperature-dependent P-E loops at 100kV / cm; (d) Wrec and η calculated based on the P-E loops of (c); (e) underdamped discharge current curves and Imax, CD, PD (inset) at different fields; (f) overdamped discharge current curves (R = 200Ω) and Imax (inset) at different fields; (g) Wdis calculated from the overdamped curves as a function of time. In order to ensure the reliable operation of electronic devices in harsh environments, dielectric materials must exhibit excellent performance in terms of frequency and temperature stability. Figure 5 (a, c) are the P-E loops of the SN-0.03 perovskite-melanotekite composite ceramic sample at 100kV / cm electric field under different frequencies and different temperatures, respectively. Figure 5(b, d) are the curves of wrc, Wtal and η calculated based on PE loop with frequency and temperature. rec The changes in η and η with temperature and frequency are within ±10%, indicating that the SN-0.03 composite ceramic has excellent stability in the frequency range of 1 to 100 Hz and the temperature range of 25 to 125°C. In addition to temperature and frequency stability, the pulse discharge performance of the ceramic is also an important criterion for evaluating its practical application potential at room temperature. Figure 5 (e) and Figure 5 (f) shows the charge and discharge performance of SN-0.03 composite ceramics under different electric fields, showing underdamped and overdamped current distributions, respectively. The illustration shows the peak current (I max ), P D and C D The electric field dependence of max 、P D and C D It gradually increases and reaches the maximum value of 23.67A and 355.03A / cm at 120kV / cm 2 and 20.11MW / cm 3 . Figure 5 (f) shows the overdamped discharge curve of SN-0.03 under a 200Ω load resistance. Figure 5 (g) shows the discharge energy density (W) under different electric fields dis ) over time. dis As the electric field increases from 0.04J / cm 3 Increased to 0.14 J / cm 3 The SN-0.03 composite ceramic achieved a nanosecond discharge rate (58ns), demonstrating excellent pulse discharge capability and fast charge-discharge kinetics. These indicators collectively validate the material's potential for high-power applications requiring instantaneous energy release.

Claims

1. A ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material, characterized in that: The stoichiometric formula is: (1-x)(0.67BiFeO3-0.33BaTiO3)-xSmNbO4, wherein x represents molar percentage, x=0.03~0.

07.

2. A method for preparing the ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material according to claim 1, characterized in that: The following steps are involved: Step 1: Prepare analytically pure BaCO3, Sm2O3, Nb2O5, Bi2O3, Fe2O3 and TiO2 according to the stoichiometric ratio, mix them evenly by ball milling, then dry and sieve to obtain a powder of uniform size, and calcine the powder in air at 800-850°C for 3-4 hours to obtain a mixed powder; Step 2: Add 0.1 wt% of manganese dioxide to the powder calcined in step 1, perform secondary ball milling, dry, and sieve, then pour into a mold, press into shape, demould, and cold isostatically press to obtain an embryonic body; Step 3: The green body obtained in step 2 is embedded in a powder of the same composition and placed in a muffle furnace. The temperature is raised to 1020-1040°C at a rate of 3-5°C / min in an air atmosphere. After keeping the temperature for 2-4 hours, the temperature is lowered to 500°C at a rate of 5°C / min. The green body is then cooled to room temperature and sintered into porcelain to obtain a ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material.

3. The method for preparing the ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material according to claim 2, characterized in that: The ball milling in step 1 is performed by mixing the raw materials, zirconia balls and deionized water in a mass ratio of 1:5:1 and milling for 10 to 12 hours.

4. The method for preparing the ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material according to claim 2, characterized in that: The sieving in step 1 and step 2 is through a 120-200 mesh sieve.

5. The method for preparing the ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material according to claim 2, characterized in that: The drying in step 1 and step 2 is performed by placing the product in an oven at 80° C. for 12 to 24 hours.

6. The method for preparing the ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material according to claim 2, characterized in that: The secondary ball milling in step 2 is performed by mixing the raw materials, zirconia balls and deionized water in a mass ratio of 1:5:1 and milling for 8 hours.

7. The method for preparing the ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material according to claim 2, characterized in that: The cold isostatic pressing process described in step 2 is cold isostatic pressing for 3 minutes under a pressure of 200 MPa.

8. A ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material prepared by the method according to any one of claims 2 to 7.

9. Use of the ternary lead-free BiFeO3-based perovskite-pyrochlore composite ceramic material as claimed in claim 8 in dielectric ceramic capacitors.

Images