A method for improving the dielectric properties of MgTiO3-based microwave dielectric ceramics

Abstract

The application discloses a method for improving dielectric properties of MgTiO3-based microwave dielectric ceramic, and supercritical fluid is used to perform supercritical oxidation treatment on the MgTiO3-based microwave dielectric ceramic; CO2 is used as a solvent in the supercritical fluid, and H2O2 is used as a solute in the supercritical fluid; H2O2 molecules are infiltrated into the MgTiO3-based dielectric ceramic through the supercritical fluid technology, -OH groups in the H2O2 molecules react with Ti atom dangling bonds at oxygen vacancy defect positions to form Ti-OH coordination covalent bonds, then two -OH groups in the oxygen vacancy form H2O molecules and leave oxygen atoms to fill the oxygen vacancies, and the dielectric properties are greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of microwave dielectric ceramic preparation technology, specifically relating to a method for improving the dielectric properties of MgTiO3-based microwave dielectric ceramics. Background Technology

[0002] Microwave dielectric ceramics are a new type of functional dielectric ceramic developed in recent decades. They are dielectric materials used in microwave frequency circuits as transmission media to perform one or more functions. In 5G and millimeter-wave communications, they are used as resonators, filters, dielectric substrates, and dielectric antennas. MgTiO3-based microwave dielectric ceramics (including MgTiO3, MgTiO3-CaTiO3, MgTiO3-SrTiO3, etc. ceramic systems) have moderate dielectric constants and high quality factors (Q), and are widely used as filters in 5G communication base station systems. It is generally believed that the quality factor (Q) of MgTiO3-based microwave dielectric ceramics is mainly affected by external factors, including porosity, grain boundaries, impurities, secondary phases, and lattice defects. In particular, lattice defects such as oxygen vacancies play a crucial role in the dielectric loss of microwave ceramics. However, the preparation process of MgTiO3-based microwave dielectric ceramics often requires a long high-temperature sintering process. During the high-temperature sintering process, lattice oxygen of MgTiO3-based microwave dielectric ceramics will be precipitated and a large number of oxygen vacancies will be generated, which will increase the dielectric loss (Q value decrease) and make it impossible to guarantee sufficient performance and working stability.

[0003] Therefore, it is expected that reducing the oxygen vacancy content of MgTiO3-based microwave dielectric ceramics can improve their microwave dielectric properties. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for improving the dielectric properties of MgTiO3-based microwave dielectric ceramics. The method of this invention can significantly improve the dielectric properties of MgTiO3-based microwave dielectric ceramics.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention discloses a method for improving the dielectric properties of MgTiO3-based microwave dielectric ceramics, which involves supercritically oxidizing the MgTiO3-based microwave dielectric ceramics with a supercritical fluid, wherein the solute in the supercritical fluid is H2O2.

[0007] Supercritical fluid is the state of a substance or fluid when subjected to temperatures and pressures exceeding its critical point. Substances in the supercritical fluid state possess both the solubility of a liquid and the permeability of a gas. Based on this property, supercritical fluid can be used as a solvent, with other substances dissolved in it as solutes. The high solubility and permeability of supercritical fluid can be used to introduce these substances into devices or materials, where they undergo physicochemical reactions. This process can be used for defect repair, doping, passivation, and other functions, enabling targeted control of material properties. The inventors discovered that by using H₂O₂ solution as a solute dissolved in CO₂ supercritical fluid, MgTiO₃ ceramics can be oxidized, thereby reducing their oxygen vacancy content and improving their dielectric properties.

[0008] In a preferred embodiment, the solvent in the supercritical fluid is CO2, and the solute is an H2O2 solution.

[0009] In this invention, MgTiO3-based microwave dielectric ceramics include ceramic systems such as MgTiO3, MgTiO3-CaTiO3, and MgTiO3-SrTiO3.

[0010] In a preferred embodiment, the MgTiO3-based microwave dielectric ceramic is selected from at least one of MgTiO3, MgTiO3-CaTiO3, and MgTiO3-SrTiO3.

[0011] In a preferred embodiment, MgTiO3-based microwave dielectric ceramic and a container containing H2O2 are placed in a reaction vessel, CO2 is introduced, and the mixture is heated and pressurized to allow the CO2 to enter a supercritical fluid state and dissolve the H2O2 solution, forming a supercritical fluid mixture of CO2 and H2O2. Then, the MgTiO3-based microwave dielectric ceramic is subjected to supercritical oxidation treatment.

[0012] In this invention, MgTiO3-based microwave dielectric ceramics and a container containing H2O2 are placed in a reaction vessel, and CO2 gas is introduced. Under high temperature and high pressure, CO2 enters the supercritical fluid and dissolves the H2O2 solution, forming a supercritical fluid of CO2 and H2O2. Then, the high permeability of the supercritical fluid is used to perform supercritical oxidation treatment on the MgTiO3-based microwave dielectric ceramics.

[0013] In a preferred embodiment, the supercritical oxidation treatment is performed at a temperature >31.1°C and a pressure >1100 psi.

[0014] In this invention, CO2 is used as the solvent and H2O2 as the solute in the supercritical fluid. The critical temperature of CO2 gas is 31.1℃ and the critical pressure is 1100psi. In actual operation, MgTiO3-based microwave dielectric ceramic is placed in a reactor, and the reactor is heated and pressurized to above the critical temperature and pressure. CO2 is converted to a supercritical state, possessing the solubility of a liquid and the permeability of a gas. Some H2O2 molecules dissolve in the supercritical carbon dioxide fluid and are carried into the interior of the MgTiO3 ceramic, where they undergo an oxidation reaction. The -OH groups in the H2O2 molecules react with the dangling bonds of Ti atoms at the oxygen vacancy defect sites to form Ti-OH coordinated covalent bonds. Subsequently, the two -OH groups in the oxygen vacancy form H2O molecules, which are precipitated, leaving oxygen atoms to fill the oxygen vacancy, thus significantly improving the dielectric properties.

[0015] Further preferably, the supercritical oxidation treatment is performed at a temperature ≥80°C, a pressure ≥1500 psi, and a time ≥30 min. Further increases in pressure and temperature help improve the solubility and permeability of the supercritical carbon dioxide fluid, thus promoting the oxidation reaction process.

[0016] In a further preferred embodiment, the supercritical oxidation treatment is performed at a temperature of 80–200°C, a pressure of 1500–4000 psi, and a time of 30–300 min.

[0017] Principles and advantages

[0018] This invention employs supercritical fluid to oxidize MgTiO3-based microwave dielectric ceramics. CO2 is used as the solvent and H2O2 as the solute in the supercritical fluid. Through supercritical fluid technology, H2O2 molecules are infiltrated into the MgTiO3 dielectric ceramic. The -OH groups in the H2O2 molecules react with the dangling bonds of Ti atoms at the oxygen vacancy defect sites to form Ti-OH bonds. Subsequently, the two -OH groups in the oxygen vacancy form H2O molecules, which are precipitated and leave oxygen atoms to fill the oxygen vacancy, thus significantly improving the dielectric properties. Attached Figure Description

[0019] Figure 1 Diagram of a supercritical reactor.

[0020] Figure 2 Flowchart of supercritical oxidation reaction.

[0021] Figure 3 Figure showing the change in oxygen vacancy concentration before and after supercritical treatment of MgTiO3 microwave dielectric ceramics sintered at different temperatures for 4 hours.

[0022] Figure 4 Changes in Q×f value of MgTiO3 microwave dielectric ceramics before and after supercritical treatment at different temperatures for 4 hours. Detailed Implementation

[0023] Example 1

[0024] 1. Preparation of MgTiO3-CaTiO3 ceramics:

[0025] High-purity CaCO3, TiO2, and MgO powders were weighed according to the stoichiometric ratio of 0.95MgTiO3-0.05CaTiO3 ceramics, with a weighing error not exceeding ±0.001g. The precisely weighed raw materials were placed in a nylon ball mill jar, using 5mm and 10mm diameter zirconia balls as the milling medium and alcohol as the solvent. The mass ratio of alcohol, zirconia balls, and raw materials was 2:1:1:1. Wet mixing and ball milling were performed in a planetary ball mill at a speed of 300 r / min, running for 1 hour and stopping for 10 minutes, for a total running time of 24 hours. The wet-mixed powder slurry was separated from the zirconia grinding balls and placed in a beaker for drying in a forced-air drying oven. Since the solvent was alcohol, the oven temperature was set to 75℃ to prevent alcohol from boiling over. The dried powder was placed in a corundum crucible and pre-fired in an energy-saving rapid-heating resistance furnace at 1150℃ to synthesize 0.95MgTiO3-0.05CaTiO3 ceramic powder. The pre-calcined powder was mixed with 5 wt% paraffin wax and 3 wt% stearic acid, then wet-milled and granulated. The granulated powder was then pressed into shape at a pressure of 1500 kg / cm³. 3 The pressure was maintained for 3 minutes to obtain a ceramic green body with a composition of 0.95MgTiO3-0.05CaTiO3.

[0026] 2. Sintering process of MgTiO3-CaTiO3 ceramics: A hot debinding process is adopted, with the temperature increased to 400℃ at a rate of 1℃ / min and held for 1 hour, followed by increasing the temperature to 600℃ at a rate of 1℃ / min and holding for 1 hour to complete the binder removal process. (Ba(Co,Zn)) 1 / 3 Nb 2 / 3 After removing the binder from the O3 ceramic sample, the temperature was increased to 1350℃-1450℃ at 5℃ / min and sintered for 4 hours. Then, the temperature was decreased to 1000℃ at 1℃ / min and cooled in the furnace.

[0027] 3. Supercritical oxidation treatment: CO2 was selected as the supercritical solvent, and H2O2 solution was selected as the supercritical solute. The reactor temperature was 120℃, the pressure was 3000psi, and the reaction time was 60 minutes.

[0028] 4. Oxygen vacancy detection and performance testing of MgTiO3-CaTiO3 ceramics:

[0029] The changes in oxygen vacancy concentration in ceramic samples before and after treatment were measured using XPS, such as... Figure 3As shown, with increasing temperature, the oxygen vacancy concentration in the ceramic sample increased from 19.6% to 26.7%. After supercritical treatment, the oxygen vacancy concentration inside the ceramic decreased significantly; the oxygen vacancy concentration in the sample sintered at 1450℃ for 4 hours decreased from 26.7% to 18.5%, a reduction of 30%. Figure 4 As shown, dielectric property tests revealed that the Q×f value of the ceramic increased by 11.3% to 19.0% after supercritical treatment. The Q×f value of the sample sintered at 1450℃ for 4 hours increased from 65,200 GHz to 77,600 GHz after supercritical treatment.

Claims

1. A method for improving the dielectric properties of MgTiO3-based microwave dielectric ceramics, characterized in that: The MgTiO3-based microwave dielectric ceramic and a container filled with H2O2 were placed in a reaction vessel, and CO2 was introduced. The mixture was heated and pressurized to allow the CO2 to enter a supercritical fluid state and dissolve the H2O2 solution, forming a supercritical fluid mixture of CO2 and H2O2. Then, the MgTiO3-based microwave dielectric ceramic was subjected to supercritical oxidation treatment. The supercritical oxidation treatment is performed at a temperature of 80-200℃, a pressure of 1500-4000 psi, and a time of 30-300 min.

2. The method for improving the dielectric properties of MgTiO3-based microwave dielectric ceramics according to claim 1, characterized in that: The MgTiO3-based microwave dielectric ceramic is selected from at least one of MgTiO3, MgTiO3-CaTiO3, and MgTiO3-SrTiO3.

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