CN103922739B - A B-site substituted BNT microwave dielectric ceramic material and preparation method thereof - Google Patents

Abstract

A B-site substituted BNT microwave dielectric ceramic material and a preparation method thereof belong to the technical field of functional materials. The general chemical formula of the microwave dielectric ceramic material is Ba _3.75 Nd _9.5 Ti _18-y (M,N) _y O ₅₄ , where 0.6≤y≤2.5; composed of BaO, Nd ₂ O ₃ , TiO ₂ , metal elements M, The oxides of N are prepared by batching, ball milling, pre-sintering and sintering according to the molar ratio of the general chemical formula; the oxides of the element M are Nb ₂ O ₅ , and the oxides of the element N are Al ₂ O ₃ , MgO, ZnO, One or more of Co ₂ O ₃ and NiO. In the present invention, the B sites in Ba _6-3x Nd _8+2x Ti ₁₈ O ₅₄ are simultaneously replaced by high and low price elements, and the microwave dielectric ceramic material obtained through a single synthesis process has a higher dielectric constant, lower loss characteristics and The low temperature coefficient of frequency can meet the needs of the microwave communication industry, especially suitable for making radio frequency electronic tags.

Description

A B-site substituted BNT microwave dielectric ceramic material and preparation method thereof

technical field

The invention belongs to the technical field of functional materials, and relates to a microwave dielectric ceramic material and a preparation method thereof, in particular to a microwave dielectric ceramic material suitable for making radio frequency electronic tags and a preparation method thereof.

Background technique

In recent years, with the development of mobile communication technology and Internet of Things technology and the combination of the two, the development of radio frequency identification technology (radio frequency identification, RFID) has been promoted. Radio frequency identification technology is one of the core technologies of the perception layer of the Internet of Things; radio frequency identification technology is also a wireless communication technology, which consists of readers, antennas and electronic tags. Electronic tags, antennas and readers need to be used Microwave dielectric ceramics. Microwave dielectric ceramics are the core basic materials for the preparation of radio frequency electronic tags, and are generally made of microwave dielectric ceramic materials with a dielectric constant exceeding 60. With the development and application of microwave communication technology and the Internet of Things, high frequency, high stability, simple preparation process and low cost have become important requirements for the manufacture and production of radio frequency electronic tags. With the development of the Internet of Things, the requirements for microwave dielectric ceramic materials are also increasing: higher dielectric constant, lower frequency temperature coefficient, and lower microwave loss. These three performance indicators are all important parameters of microwave dielectric materials: under the same conditions, microwave devices use materials with higher Q value to make devices with lower loss, which effectively solves the problem of heat generation in device integration. It can be considered that the Q value of microwave dielectric materials The value is an important parameter to measure the performance of microwave materials; the use of microwave dielectric materials with a large dielectric constant is helpful for the miniaturization of microwave devices; at the same time, the temperature coefficient of frequency tending to zero is an important parameter for the stability of device performance. Therefore, the development of microwave dielectric ceramic materials with high dielectric constant, low loss and frequency temperature coefficient tending to zero at microwave frequency has great application value.

Among the current microwave dielectric ceramics, the material systems that have been studied more in various countries include microwave ceramics and lead-containing ceramics with composite perovskite structures. Among them, the composite perovskite has a high Q×f value and a small frequency temperature coefficient, but its dielectric constant is generally low (usually less than 60), which is not suitable for use in radio frequency identification. Lead-containing ceramics are volatile and toxic at high temperatures, and are now less used. In practical applications, more BaO-Nd ₂ O ₃ -TiO ₂ system ceramics with tungsten-copper structure are used. The cost is relatively low, and the firing temperature is wide. It has become one of the most widely used microwave dielectric ceramic materials. , can be used to make dielectric filters, multilayer ceramic capacitors and dielectric resonators, etc.

Although the Ba _6-3x Nd _8+2x Ti ₁₈ O ₅₄ system ceramics have a high dielectric constant and excellent Q×f value, the frequency temperature coefficient is too large (60-140ppm/℃), which hinders its mass production. in the application. This prompts people to adopt various means to adjust the value of the frequency temperature coefficient. The current research solves the problem by mixing two kinds of ceramics with opposite temperature frequency coefficients on the one hand, and on the other hand uses various doping modifications or A-site substitution to improve performance. The two-phase composite often reduces the dielectric constant of the system. For example, Yu Shengquan used BaNd ₂ Ti ₄ O ₁₂ and BaZn ₂ Ti ₄ O ₁₁ composite in Ceramic International (SCI), and the obtained ceramic Q×f value up to 60000 GHz, the temperature frequency coefficient is also close to zero, but the dielectric constant is about 34; Zhu Jianhua in the Journal of the European Ceramic Society (SCI) Ba _4.2 Nd _9.2 Ti ₁₈ O ₅₄ system doped such as LnAlO ₃ , successfully reduced the temperature frequency coefficient, but the mechanism is not clear; Belous used Ca to replace the Ba site to prepare (Ba _1-y Ca _y ) ₆ - _x Nd _8+2x Ti ₁₈ O ₅₄ ceramics, successfully reduced the frequency The temperature coefficient is adjusted to zero. Researchers from various countries have done a lot of research work on the use of A-site substitution in the BaO-Nd ₂ O ₃ -TiO ₂ system, and have obtained various ceramic materials with excellent performance, and a relatively high dielectric constant of about 90.

There are few studies on the B-site substitution of Ba _6-3x Nd _8+2x Ti ₁₈ O ₅₄ system ceramics at home and abroad. The reason is generally due to the difficulty of substitution or poor modification effect. In 1996, M. Mizuta et al. published a document in the Japanese Journal of Applied Physics "Tungsten-like copper ore (Ba ₆ - _3x Sm _8+2x ) Ti _18-y Al _y O ₅₄ (α= 1+y/36) Solid Solution Synthesis and Microwave Dielectric Properties" (Formation of tungsten bronze-type(Ba _6-3x Sm _8+2x ) _ɑ Ti _18-y Al _y O ₅₄ (α=1+y/36) solid solutions and microwave dielectric properties) reported that Al ³⁺ was used to replace Ti ⁴⁺ . With the increase of Al ₂ O ₃ content, the dielectric constant decreased, the Q×f value increased, and the temperature frequency coefficient was more negative; in 2002, Chen et al. in the "Journal of the American Ceramic Society" (Journal of the American Ceramic Society) "Ba _6-3x Sm _8+2x Ti ₁₈ O ₅₄ in A, B co-substituted ceramic performance research" (A-and B Site CosubstitutedBa _6-3x Sm _8+2x Ti ₁₈ O ₅₄ Microwave Dielectric Ceramics) reported the data of B site substitution; in 1997, R.UBIC et al. reported Ba _{6- 3x} Nd _8+2x Ti ₁₈ O ₅₄ , when x=0.75, the dielectric constant of the system is about 89, Q×f>10000GHz, and the frequency temperature coefficient is around 60ppm/℃. In 2007, L. Zhang et al. published the article "Ba _6-3x Nd _8+2x Ti ₁₈ O ₅₄ to form a new tungsten copper ore solid solution in the upper limit of x" in the "Journal of the European ceramic society""(Upper limit of x in Ba _6-3x Nd _8+2x Ti ₁₈ O ₅₄ new tungstenbronze solid solution) reported that the higher x value (near 0.75) is still a single tungsten copper crystal phase, and its frequency temperature coefficient Also relatively low (57 ~ 70ppm / ℃). Although so far, the research on B-site substitution has not been satisfactory for practical microwave dielectric ceramics, but these studies have confirmed the feasibility of B-site substitution in Ba _6-3x Nd _8+2x Ti ₁₈ O ₅₄ .

The present invention innovatively adopts the research on simultaneous substitution of B-site high and low-priced elements in Ba _6-3x Nd _8+2x Ti ₁₈ O ₅₄ , and develops a kind of simple process, low raw material cost and high dielectric constant through this method. Microwave dielectric ceramic materials with low loss characteristics and low frequency temperature coefficient to meet the application requirements of the microwave communication industry.

Contents of the invention

The invention innovatively adopts the method of B-site substitution, and provides a BNT microwave dielectric ceramic material and a preparation method thereof with higher dielectric constant, lower loss, frequency temperature coefficient close to zero, simple production process and low cost.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A B-site substituted BNT microwave dielectric ceramic material has a tungsten-copper crystal phase structure and its general chemical formula is Ba ₃ . ₇₅ Nd _9.5 Ti _18-y (M,N) _y O ₅₄ , where 0.6≤y≤2.5, M is the metal element Nb, and N is one or more of the metal elements Al, Mg, Zn, Co, Ni; _The B _- site substituted BNT microwave dielectric ceramic material is prepared by _compounding , It is made by ball milling, pre-calcination at 1050-1150°C and sintering at 1250-1350°C; its Q×f value reaches 6000-13000GHz, the relative dielectric constant is adjustable between 65-85, and the temperature coefficient of resonance frequency is ±10ppm Within /°C; wherein the oxide of the metal element M is Nb ₂ O ₅ , and the oxide of the metal element N is one or more of Al ₂ O ₃ , MgO, ZnO, Co ₂ O ₃ , and NiO .

The preparation method of the B-site substituted BNT microwave dielectric ceramic material comprises the following steps:

Step 1: Ingredients; use BaO, Nd ₂ O ₃ , TiO ₂ , oxides of metal element M and oxides of metal element N according to the general chemical formula Ba _3.75 Nd _9.5 Ti _18-y (M,N) _y O The molar ratio of each element in ₅₄ is compounded; where 0.6≤y≤2.5, the oxide of the metal element M is Nb ₂ O ₅ , and the oxide of the metal element N is Al ₂ O ₃ , MgO, ZnO, One or more of Co ₂ O ₃ and NiO.

Step 2: ball milling; the mixture in step 1 is ball milled to obtain a ball mill;

Step 3: drying and sieving; drying the ball mill material obtained in step 2 and passing through a 60-mesh sieve to obtain a dry powder;

Step 4: pre-calcining; pre-calcining the dry powder obtained in step 3 at a temperature of 1050-1150°C for 3-5 hours to obtain a pre-calcining powder;

Step 5: Granulation and compression molding; the calcined powder obtained in step 4 is mixed with polyvinyl alcohol aqueous solution and then granulated. The granulation size is controlled at 80-160 mesh, and the granules are put into a molding mold and dry-pressed to obtain raw Blank;

Step 6: sintering; sintering the green body obtained in step 5 at a temperature of 1250-1350° C. for 1.5-3 hours to obtain the final B-site substituted BNT microwave dielectric ceramic material.

The specific ball milling process in step 2 is: use zirconia balls as the ball milling medium, and grind for 6 to 8 hours according to the mass ratio of mixture: balls: deionized water is 1: (3 ~ 5): (1 ~ 1.5) A uniformly mixed ball abrasive is obtained.

The main functions of the raw materials used in the present invention are as follows: BaO, Nd ₂ O ₃ and TiO ₂ are mainly used to form the main crystal phase, and the substitution of Ti ⁴⁺ by high-priced or low-priced elements alone will cause valence mismatch and cause charge non-conservation problem, thereby simultaneously using one of low-priced aluminum oxide (Al ₂ O ₃ ), magnesium oxide (MgO), zinc oxide (ZnO), nickel oxide (NiO), and dicobalt oxide (Co ₂ O ₃ ) Or several and high-priced niobium pentoxide (Nb ₂ O ₅ ) to replace the Ti ⁴⁺ site, so as to reduce the frequency temperature coefficient of the system and improve the Q value of the ceramic.

The microwave dielectric ceramic material provided by the invention has lower loss, namely higher Q value, higher dielectric constant and nearly zero temperature coefficient of resonant frequency after testing.

Compared with the prior art, the present invention has the following characteristics:

1. The present invention adopts the implementation of B-site high and low-valent elements in Ba _6-3x Nd _8+2x Ti ₁₈ O ₅₄ to replace the Ti site at the same time, which is different from the traditional A-site substitution and achieves the purpose of reducing the frequency temperature coefficient of the system, and Both the dielectric constant and the temperature coefficient of frequency are adjustable while maintaining a high Q×f value.

2. The formula of the present invention does not contain volatile or heavy metals such as Pb and Cd, and is an environmentally friendly microwave dielectric ceramic.

3. The sintering temperature of most formulations is reduced to about 1300°C on the basis of 1350°C of pure BaO-Nd ₂ O ₃ -TiO ₂ , which has certain energy-saving advantages.

4. Using a single synthesis process, it is easy to achieve stable production of materials.

5. The performance has been greatly improved: the Q×f value of the existing technical formula is generally around 5000-10000, and its resonant frequency temperature coefficient is +50-140ppm/℃, which cannot meet the application requirements of microwave devices for radio frequency identification , the Q×f value of the microwave dielectric ceramic material provided by the present invention is between 6000 and 13000 GHz, the relative permittivity ε _r is between 65 and 85, and the temperature coefficient of the resonant frequency is within ±10ppm/°C, and the performance is stable. It can meet the application requirements of modern microwave devices.

6. The domestic supply of raw materials is sufficient and the price is low, which makes it possible to reduce the cost of high-performance microwave ceramics.

Description of drawings

Fig. 1 is the XRD analysis result of the B-site substituted BNT microwave dielectric ceramic material provided by the present invention.

Fig. 2 is a scanning electron microscope SEM image of the microwave ceramic dielectric material prepared in the present invention.

Detailed ways

specific embodiment

first step:

Accurately weigh various raw materials according to the mass percentage in Table 1, ball mill in deionized water for 6-8 hours, then dry and sieve, and pre-calcine at 1050-1150°C for 5-8 hours.

Step two:

Weigh the pre-calcined Ba _3.75 Nd _9.5 Ti _18-y (M,N) _y O ₅₄ powder, add polyvinyl alcohol aqueous solution for granulation, and dry press molding under a pressure of 22Mpa to obtain a diameter of 14.5mm and a thickness of The 7.8mm cylindrical green body was sintered at 1250-1350°C for 1.5-3 hours to obtain a sintered block. The process and performance test results are shown in Table 2.

The material composition of table 1 embodiment

Technology and microwave dielectric properties adopted by the embodiment of table 2

Claims (3)

1. B position replaces a BNT microwave dielectric ceramic materials, and have tungsten bronze(s) ore deposit crystal phase structure, its chemical general formula is Ba _3.75nd _9.5ti _18-y(M, N) _yo ₅₄, wherein 0.6≤y≤2.5, M to be metallic element Nb, N be in metal element A l, Mg, Zn, Co, Ni one or more; Described B position replaces BNT microwave dielectric ceramic materials by BaO, Nd ₂o ₃, TiO ₂, the oxide compound of metallic element M and the oxide compound of metallic element N according to the mol ratio of element each in described chemical general formula through batching, ball milling mixing, sinter at pre-burning and 1250 ~ 1350 DEG C at 1050 ~ 1150 DEG C and make; Its Q × f value reaches 6000 ~ 13000GHz, and relative permittivity is adjustable between 65 ~ 85, and temperature coefficient of resonance frequency is within ± 10ppm/ DEG C; The oxide compound of wherein said metallic element M is Nb ₂o ₅, the oxide compound of described metallic element N is Al ₂o ₃, MgO, ZnO, Co ₂o ₃, one or more in NiO.

2. B position replaces a preparation method for BNT microwave dielectric ceramic materials, comprises the following steps:

Step 1: batching; Adopt BaO, Nd ₂o ₃, TiO ₂, the oxide compound of metallic element M and metallic element N oxide compound according to chemical general formula Ba _3.75nd _9.5ti _18-y(M, N) _yo ₅₄in the mol ratio of each element prepare burden; Wherein 0.6≤y≤2.5, the oxide compound of described metallic element M is Nb ₂o ₅, the oxide compound of described metallic element N is Al ₂o ₃, MgO, ZnO, Co ₂o ₃, one or more in NiO;

Step 2: ball milling; By step 1 compound carry out ball milling, obtain ball milling material;

Step 3: dry, sieve; Step 2 gained ball milling material is dried and crossed 60 mesh sieves and obtains dry powder;

Step 4: pre-burning; Under dry for step 3 gained powder is placed in 1050 ~ 1150 DEG C of temperature condition, pre-burning obtains pre-burning powder in 3 ~ 5 hours;

Step 5: granulation, compression molding; Granulation after step 4 gained pre-burning powder is mixed with polyvinyl alcohol water solution, pellet, at 80 ~ 160 orders, is put into that forming mould is dry-pressing formed obtains green compact by granulation size control;

Step 6: sintering; Step 5 gained green compact are placed in 1250 ~ 1350 DEG C of temperature condition sintering 1.5 ~ 3 hours, obtain final B position and replace BNT microwave dielectric ceramic materials.

3. B position according to claim 2 replaces the preparation method of BNT microwave dielectric ceramic materials, it is characterized in that, in step 2, concrete mechanical milling process is: be ball-milling medium with zirconia balls, according to compound: abrading-ball: the mass ratio of deionized water is 1:(3 ~ 5): (1 ~ 1.5) carries out the ball milling material that grinding obtains mixing for 6 ~ 8 hours.