A co-doped strontium titanate ceramic material with giant dielectric constant and low loss and a preparation method thereof

Abstract

This invention discloses a co-doped strontium titanate ceramic material with giant dielectric and low loss, and its preparation method, belonging to the field of electronic ceramic materials technology. The chemical formula of the ceramic material is SrTi. 1‑x (ZrNb 4 / 5 ) x / 2 O3, where x ranges from 0.003 to 0.020. This invention introduces Zr through the B-position. 4+ and Nb 5+ Ions, using Zr 4+ The resulting localized lattice distortion promotes the formation of polar nanoregions, providing a source of giant dielectric response, while Nb 5+ Donor doping regulates carrier concentration and suppresses leakage loss; the synergistic effect of both methods, combined with conventional air atmosphere sintering, yields uniform polarization centers and extremely low losses. This ceramic exhibits a dielectric constant ≥18000 and dielectric loss ≤0.007 over a wide frequency range at room temperature. The dielectric constant variation rate is <±15% within the temperature range of -60 to 150°C. 2 ~10 6 The dielectric loss remains below 0.01 Hz throughout the frequency range. This invention requires no reducing atmosphere, uses air sintering throughout the entire process, has low equipment requirements, low cost, and good batch stability, making it suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of electronic ceramic materials technology, specifically relating to a co-doped strontium titanate ceramic material with giant dielectric and low loss for capacitors and its preparation method. Background Technology

[0002] With the rapid development of microelectronics technology towards miniaturization, integration, and high frequency, higher performance requirements are being placed on energy storage components and capacitor dielectric materials, especially those with high dielectric constants (ε > 10). 4 Giant dielectric materials with low dielectric loss (tanδ <0.01) have become key basic materials urgently needed in the fields of high-density integrated circuits, power electronic devices and microwave communications.

[0003] Strontium titanate (SrTiO3), as a typical perovskite structure material, has broad application prospects in ceramic capacitors, phase shifters, microwave tuning devices, and other fields due to its excellent dielectric properties, good thermal stability, and high voltage resistance. However, the dielectric constant of pure strontium titanate at room temperature is low (about 300), far from reaching the giant dielectric level, which cannot meet the high energy density requirements of modern electronic devices. Existing strontium titanate doping modification technology mainly has the following problems: (1) Single donor (such as Nb 5+ ) or recipient (e.g., Fe) 3+ (1) Doping has a limited effect on improving the dielectric constant (usually ε < 3000), and is often accompanied by a sharp increase in dielectric loss (tanδ > 0.1), which cannot simultaneously meet the requirements of large dielectric constant and low loss. (2) Sintering in a reducing atmosphere (N2 / H2, etc.) to introduce oxygen vacancies and Ti 3+ To obtain a high dielectric constant, but this route requires special sealed equipment, has a narrow process window, and poses a great safety hazard. Moreover, the dielectric loss is generally high (tanδ > 0.05), and the cost and performance are not ideal. (3) Co-doping lacks precise ratio design and synergistic mechanism, and the functional division of doping elements is unclear. It is still impossible to break through the technical bottleneck of "high dielectric constant and low dielectric loss are difficult to achieve at the same time".

[0004] Therefore, how can we achieve a giant dielectric constant (>10) in strontium titanate ceramics under normal air atmosphere through a reasonable co-doping system design? 4 The extremely low dielectric loss (<0.01) has become a key technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the technical problem that existing strontium titanate doping techniques cannot simultaneously achieve a large dielectric constant and extremely low dielectric loss, this invention provides a co-doped strontium titanate ceramic material with large dielectric constant and low loss, and its preparation method.

[0006] The chemical formula of the co-doped strontium titanate ceramic material with giant dielectric and low loss provided by this invention is SrTi. 1-x (ZrNb 4 / 5 ) x / 2 O3, where x takes values ​​from 0.003 to 0.020.

[0007] This invention introduces Zr through the B site. 4+ and Nb 5+ Zr ions, of which Zr 4+ The large ionic radius causes local lattice distortion, promoting the formation of polar nanoregions and providing a polarization source for the giant dielectric response; Nb 5+ As high-cost donor dopants, they effectively regulate carrier concentration and suppress leakage losses. When doped in a specific ratio, they spontaneously form uniformly distributed polarization centers during air sintering, while keeping dielectric losses at extremely low levels.

[0008] Furthermore, the preferred value of x is 0.003 to 0.005.

[0009] Furthermore, the preferred value for x is 0.015.

[0010] The preparation method of the above-mentioned co-doped strontium titanate ceramic material with giant dielectric and low loss includes the following steps:

[0011] Step 1: According to SrTi 1-x (ZrNb 4 / 5 ) x / 2 To obtain the stoichiometric ratio of O3, weigh out 99.9% pure strontium carbonate (SrCO3), titanium dioxide (TiO2), niobium oxide (Nb2O5), and zirconium oxide (ZrO2), mix them thoroughly, ball mill for 8–12 hours, and dry them to obtain the raw material mixture;

[0012] Step 2: Pre-calcine the raw material mixture in air at 950-1050℃ for 2-3 hours to obtain pre-calcineed powder;

[0013] Step 3: After the pre-calcined powder is ball-milled twice, granulated, pressed into sheets, and debinded, it is sintered in air at 1440-1600℃ for 2-3 hours to obtain co-doped strontium titanate ceramic material with large dielectric and low loss.

[0014] Furthermore, in step 2 above, it is preferable to pre-calcine the raw material mixture in air at 1050°C for 2 hours.

[0015] Furthermore, in step 3 above, it is preferable to sinter at 1540–1600°C for 2 hours in an air atmosphere.

[0016] Furthermore, in step 3 above, the preferred temperature for glue removal is 600°C, and the glue removal time is 2 hours.

[0017] Furthermore, in step 3 above, the preferred heating rate for calcination is 3-5°C / minute.

[0018] This invention utilizes Zr 4+ and Nb 5+ Ion co-doping creates a stable defect dipole electron pinning effect (or internal barrier layer capacitance effect, IBLC effect) in the crystal lattice. During high-temperature air sintering, this unique co-doped structure effectively suppresses the long-range migration of oxygen vacancies, thereby maintaining micro-region polarization within the grain and ensuring a large dielectric constant while significantly reducing dielectric loss caused by leakage current, thus guaranteeing low loss. This microscopic mechanism is independent of reducing atmosphere sintering, thus achieving a perfect combination of fabrication process and material properties.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. This invention achieves for the first time the coexistence of a high dielectric constant and extremely low dielectric loss in strontium titanate ceramics sintered in an air atmosphere. Through the synergistic design of Zr and Nb co-doping in a specific ratio, the ceramics prepared by this invention exhibit a dielectric constant of over 12,000 and a dielectric loss as low as below 0.01 at room temperature and over a wide frequency range. The overall dielectric performance far exceeds that of existing single-doped or co-doped systems sintered in an air atmosphere, and is also superior to process routes that require complex reducing atmospheres.

[0021] 2. This invention does not rely on a reducing atmosphere and the entire process is completed in a normal air atmosphere. It only requires a conventional muffle furnace, which greatly reduces equipment investment and operational risks. The process is simple, low-cost, and has good batch stability, which is conducive to large-scale industrial production.

[0022] 3. The dielectric constant of the ceramic of this invention changes by less than ±15% over a wide temperature range of -60 to 150°C, and at 10... 2 ~10 6 The dielectric loss remains below 0.01 Hz within the frequency range, meeting the stringent requirements of high-end capacitors for the stability of dielectric materials. Attached Figure Description

[0023] Figure 1 These are dielectric constant diagrams of the ceramic materials prepared in Examples 1-4 and Comparative Example 1 at different test frequencies.

[0024] Figure 2 These are dielectric loss diagrams of the ceramic materials prepared in Examples 1-4 and Comparative Example 1 at different test frequencies.

[0025] Figure 3 These are the dielectric constant temperature spectra of the ceramic materials prepared in Example 1 and Comparative Example 1.

[0026] Figure 4These are the dielectric loss temperature spectra of the ceramic materials prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The specific embodiments described herein are merely illustrative and are not intended to limit the invention.

[0028] Example 1

[0029] Step 1: According to SrTi 0.997 (ZrNb 4 / 5 ) 0.0015 To determine the stoichiometric ratio of O3, weigh 6.507g of SrCO3 (99.9% purity), 3.478g of TiO2 (99.9% purity), 0.007g of Nb2O5 (99.9% purity), and 0.008g of ZrO2 (99.9% purity). Using anhydrous ethanol as the medium, mill the mixture for 10 hours using a zirconium oxide grinding ball. After mixing thoroughly, dry the mixture in an oven at 80℃ to obtain the raw material mixture.

[0030] Step 2: Pre-calcine the raw material mixture in air at 1050°C for 2 hours to obtain pre-calcined powder.

[0031] Step 3: Add 5% (w / w) of polyvinyl alcohol aqueous solution to the pre-calcined powder for granulation. The amount of polyvinyl alcohol aqueous solution added is 50% of the mass of the secondary ball milled powder. Then, press it into a circular green sheet with a diameter of 10 mm and a thickness of 1 mm under a pressure of 150 MPa. Place the green sheet in a muffle furnace, remove the binder at 600°C for 2 hours in an air atmosphere, then heat it to 1540°C at a heating rate of 3°C / min, sinter it at a constant temperature for 2 hours, and cool it with the furnace to obtain a co-doped strontium titanate ceramic material with giant dielectric and low loss.

[0032] Example 2

[0033] Step 1: According to SrTi 0.995 (ZrNb 4 / 5 ) 0.0025 To determine the stoichiometric ratio of O3, weigh 6.505g of SrCO3 (99.9% purity), 3.470g of TiO2 (99.9% purity), 0.012g of Nb2O5 (99.9% purity), and 0.014g of ZrO2 (99.9% purity). Use anhydrous ethanol as the medium and ball mill with zirconium oxide grinding balls for 10 hours. After mixing evenly, dry the mixture in an oven at 80℃ to obtain the raw material mixture.

[0034] Step 2: Pre-calcine the raw material mixture in air at 1050°C for 2 hours to obtain pre-calcined powder.

[0035] Step 3: Add 5% (w / w) of polyvinyl alcohol aqueous solution to the pre-calcined powder for granulation. The amount of polyvinyl alcohol aqueous solution added is 50% of the mass of the secondary ball milled powder. Then, press it into a circular green sheet with a diameter of 10 mm and a thickness of 1 mm under a pressure of 150 MPa. Place the green sheet in a muffle furnace, remove the binder at 600°C for 2 hours in an air atmosphere, then heat it to 1600°C at a heating rate of 3°C / min, sinter it at a constant temperature for 2 hours, and cool it with the furnace to obtain a co-doped strontium titanate ceramic material with giant dielectric and low loss.

[0036] Example 3

[0037] In step 1 of this embodiment, according to SrTi 0.985 (ZrNb 4 / 5 ) 0.0075 To obtain the stoichiometric ratio of O3, 6.495 g of SrCO3 (99.9% purity), 3.429 g of TiO2 (99.9% purity), 0.035 g of Nb2O5 (99.9% purity), and 0.041 g of ZrO2 (99.9% purity) were weighed out and ball-milled for 10 hours using a zirconium oxide grinding ball in anhydrous ethanol. After mixing thoroughly, the mixture was dried in an oven at 80°C to obtain the raw material mixture. Other steps were the same as in Example 2, resulting in a co-doped strontium titanate ceramic material with giant dielectric and low loss.

[0038] Example 4

[0039] In step 1 of this embodiment, according to SrTi 0.98 (ZrNb 4 / 5 ) 0.01 To obtain the stoichiometric ratio of O3, 6.489 g of SrCO3 (99.9% purity), 3.401 g of TiO2 (99.9% purity), 0.046 g of Nb2O5 (99.9% purity), and 0.054 g of ZrO2 (99.9% purity) were weighed out and ball-milled for 10 hours using a zirconium oxide grinding ball in anhydrous ethanol. After mixing thoroughly, the mixture was dried in an oven at 80°C to obtain the raw material mixture. Other steps were the same as in Example 2, resulting in a co-doped strontium titanate ceramic material with giant dielectric and low loss.

[0040] Comparative Example 1

[0041] The difference from Example 1 is that Nb2O5 and ZrO2 are not added, but the other steps are the same as in Example 1.

[0042] The surfaces of the ceramic materials prepared in Examples 1-5 and Comparative Example 1 were successively polished to a thickness of 0.05-0.1 mm using 1500-mesh and 2000-mesh diamond abrasive. Silver paste was then coated onto the upper and lower surfaces of the ceramics, and the mixture was sintered at 800°C for 15 minutes to serve as electrodes for dielectric property testing. The dielectric constant and dielectric loss of the samples were measured using a broadband dielectric spectrometer (4294A) in the frequency range of 40 Hz to 1 MHz at room temperature. The test results are as follows: Figures 1-4 As shown.

[0043] Depend on Figure 1 As can be seen, within the test frequency range of 40 Hz to 1 MHz, the ceramic materials prepared in Examples 1 to 3 of this invention exhibit extremely high dielectric constants. The dielectric constant of the ceramic material in Example 1 remains stable between 16000 and 17000, and its decreasing trend with increasing frequency is extremely gradual throughout the entire bandwidth, demonstrating excellent frequency stability. In contrast, the dielectric constant of the ceramic material in Comparative Example 1 is only 900 to 1200 within the same frequency range. Compared to the comparative example, the dielectric constant of the ceramic material of this invention is increased by more than an order of magnitude, successfully realizing the giant dielectric effect.

[0044] Depend on Figure 2 As can be seen, the ceramic materials prepared in Examples 1-3 of this invention significantly improve the dielectric constant while effectively suppressing the deterioration of dielectric loss. Specifically, the dielectric loss of the ceramic material in Example 1 remains at an extremely low level (values ​​between 0.006 and 0.04) throughout the entire frequency range of 40 Hz to 1 MHz, and the overall curve is stable without obvious polarization relaxation peaks, exhibiting excellent broadband stability. In contrast, the dielectric loss of the ceramic material in Comparative Example 1 fluctuates drastically with frequency, exhibiting a typical "U"-shaped characteristic—especially below 10 Hz. 3 The low-frequency range of Hz and above 10 5 In the high-frequency region of Hz, the loss increases sharply, even exceeding 0.2 at the high-frequency end, which can easily lead to severe Joule heating in high-frequency applications. The ceramic material of this invention effectively overcomes the defect of the sharp increase in loss in the high-frequency range, maintaining a lower and more stable dielectric loss over a wide frequency range.

[0045] To further verify the working stability of the ceramic material of the present invention under complex temperature environments, a comparative test was conducted on the dielectric properties of the ceramic materials prepared in Example 1 and Comparative Example 1 as a function of temperature. The test temperature range was -100 to 250℃, and the test results are as follows: Figure 3 and Figure 4 As shown.

[0046] Depend on Figure 3 As can be seen from the dielectric constant temperature spectrum, the ceramic material of Example 1 of this invention exhibits a significantly enhanced dielectric response across the entire wide temperature range. The dielectric constant remains consistently at 1.2 × 10⁻⁶.4 The highest peak value can reach approximately 2.3 × 10⁴. 4 It exhibits typical giant dielectric characteristics. In contrast, the dielectric constant of the ceramic material in Comparative Example 1 is only 2.2 × 10⁻⁶ within the same temperature range. 3 ~3.4×10 3 Compared to Comparative Example 1, the dielectric constant of the ceramic material of this invention is increased by nearly an order of magnitude, and it maintains a consistently stable giant dielectric response across the entire wide temperature range, exhibiting excellent dielectric stability over a wide temperature range.

[0047] Depend on Figure 4 The dielectric loss temperature spectrum shows that the ceramic material of Example 1 of this invention, while improving the dielectric constant, also endows the material with excellent temperature stability. The dielectric loss of the ceramic material of Example 1 remains extremely low over an ultra-wide temperature range of -100 to 250°C, with a smooth and nearly flat curve, indicating a highly stable internal structure and no significant temperature-induced polarization relaxation. In contrast, the dielectric loss of the ceramic material of Comparative Example 1 fluctuates significantly with temperature changes, especially showing a distinct loss peak in the 100–150°C range, and exhibiting an upward trend in the high-temperature region, indicating that it is prone to high leakage current and Joule heating at high temperatures. The ceramic material of this invention successfully overcomes the defects of traditional dielectric materials, such as drastic loss fluctuations and deterioration at high temperatures or over a wide temperature range, exhibiting excellent low-loss characteristics over a wide temperature range.

[0048] In summary, this invention successfully breaks through the performance bottleneck of traditional dielectric materials, where "high dielectric constant is often accompanied by high dielectric loss." The resulting ceramic material not only possesses excellent combined performance of a large dielectric constant and low dielectric loss, but also exhibits excellent broadband response stability. Furthermore, this invention overcomes the technical challenge of maintaining temperature stability in large dielectric materials; the prepared material maintains extremely low and stable dielectric loss over an ultra-wide and demanding temperature range of -100℃ to 250℃. Therefore, the ceramic material of this invention has significant industrial application value and broad prospects in fields such as microelectronic devices, high-frequency energy storage capacitors, and miniaturized integrated circuits.

Claims

1. A co-doped strontium titanate ceramic material with giant dielectric constant and low loss, characterized in that: The chemical formula of the ceramic material is SrTi 1-x (ZrNb 4 / 5 ) x / 2 O3, wherein x has a value of 0.003 to 0.

02.

2. The co-doped strontium titanate ceramic material with giant dielectric and low loss according to claim 1, characterized in that: The value of x ranges from 0.003 to 0.

005.

3. The co-doped strontium titanate ceramic material with giant dielectric and low loss according to claim 1, characterized in that: The value of x is 0.

015.

4. A method for preparing the giant dielectric low-loss co-doped strontium titanate ceramic material according to claim 1, characterized in that: Includes the following steps: Step 1 : According to SrTi 1-x (ZrNb 4 / 5 ) x / 2 O3 stoichiometric ratio, the purity of 99.9% strontium carbonate, titanium dioxide, niobium oxide and zirconium oxide, ball milling for 8-12 hours, dried to obtain the raw material mixture; Step 2: Pre-calcine the raw material mixture in air at 950-1050℃ for 2-3 hours to obtain pre-calcineed powder; Step 3: After the pre-calcined powder is ball-milled twice, granulated, pressed into sheets, and debinded, it is sintered in air at 1440-1600℃ for 2-3 hours to obtain co-doped strontium titanate ceramic material with large dielectric and low loss.

5. The method for preparing the giant dielectric low-loss co-doped strontium titanate ceramic material according to claim 4, characterized in that: In step 2, the raw material mixture is pre-fired at 1050°C for 2 hours in an air atmosphere.

6. The method for preparing the giant dielectric low-loss co-doped strontium titanate ceramic material according to claim 4, characterized in that: In step 3, sintering is carried out at 1540–1600°C for 2 hours in an air atmosphere.

7. The method for preparing the giant dielectric low-loss co-doped strontium titanate ceramic material according to claim 4, characterized in that: In step 3, the temperature for discharging the adhesive is 600℃, and the discharging time is 2 hours.

8. The method for preparing the giant dielectric low-loss co-doped strontium titanate ceramic material according to claim 4 or 6, characterized in that: In step 3, the heating rate of the roasting is 3-5°C / minute.

Images