CN1275902C - Columbate microeave dielectric ceramic and method for preparing same - Google Patents

Abstract

The invention discloses a class of high dielectric constant ceramics used for microwave components and ceramic capacitors or temperature compensation capacitors. The ceramics are (Ba _{1-y Sry} ) _3-x (La _s Nd _t Bi _u ) _1+x Ti _x Nb _3-x O ₁₂ is the main phase, where 0.00≤x≤2, 0.00≤y≤1, s+t+u=1, prepared by the corresponding method, the ceramic is well sintered, and the high-frequency dielectric constant reaches 30-90, low loss, small temperature coefficient of resonant frequency, has great application value in industry.

Description

Niobate microwave dielectric ceramic and preparation method thereof

technical field

The invention relates to a dielectric ceramic material, in particular to a dielectric resonator, a filter and other microwave components used at microwave frequencies, as well as the dielectric ceramic material of a ceramic capacitor or a temperature compensation capacitor and a preparation method thereof.

Background technique

Microwave dielectric ceramics refer to ceramics that are used as dielectric materials in microwave frequency band (mainly UHF, SHF frequency band) circuits and perform one or more functions. They are widely used as resonators, filters, and dielectric substrates in modern communications. Chips, dielectric waveguide circuits and other components are the key basic materials of modern communication technology. They have been used in portable mobile phones, car phones, cordless phones, TV satellite receivers, military radars, etc. It is playing an increasingly important role in the process of miniaturization and integration.

Since the size of the microwave dielectric resonator is inversely proportional to the square root of the dielectric constant ε _r of the material used, the larger the ε _r, the more conducive to the miniaturization of the device. While pursuing a high dielectric constant ε _r , it is also necessary to ensure a high material quality factor Q value or a small dielectric loss tan δ and high thermal stability (the temperature coefficient τ _f of the resonance frequency is as close to zero as possible). Internationally, since the late 1930s, there have been attempts to apply dielectric materials to microwave technology.

According to the relative permittivity ε _r and the frequency band used, the microwave dielectric ceramics that have been developed and are being developed can usually be divided into three categories.

(1) Microwave dielectric ceramics with low ε _r and high Q value, mainly BaO-MgO-Ta ₂ O ₅ , BaO-ZnO-Ta ₂ O ₅ or BaO-MgO-Nb ₂ O ₅ , BaO-ZnO-Nb ₂ O ₅ system or composite system MWDC materials between them. Its ε _r =25～30, Q=(1～3)×10 ⁴ (at f≥10GHz), τ _f ≈0. It is mainly used as a dielectric resonator device in microwave communication devices such as f≥8GHz satellite broadcasting.

(2) Microwave dielectric ceramics with medium ε _r and Q value, mainly MWDC materials based on BaTi ₄ O ₉ , Ba ₂ Ti ₉ O ₂₀ and (Zr, Sn)TiO ₄ , whose ε _r ≈ 40, Q=(6~9)×10 ³ (at f=3~4GHz), τ _f ≤5ppm/°C. It is mainly used as a dielectric resonant device in microwave military radar and communication systems in the frequency range of 4-8GHz.

(3) Microwave dielectric ceramics with high ε _r and low Q value are mainly used in civil mobile communication systems in the frequency range of 0.8-4GHz, which is also the focus of research on microwave dielectric ceramics. Since the 1980s, Kolar, Kato and others have successively discovered and studied perovskite-like tungsten bronze BaO-Ln ₂ O ₃ -TiO ₂ series (Ln=La, Sm, Nd, Pr, etc., referred to as BLT series), composite calcium Titanite structure CaO-Li ₂ O-Ln ₂ O ₃ -TiO ₂ series, lead-based series materials, Ca _1-x Ln _2x/3 TiO ₃ series and other high ε _r microwave dielectric ceramics, among which BaO-Nd of BLT system The dielectric constant of the ₂ O ₃ -TiO ₂ material reaches 90, and the dielectric constant of the lead-based series (Pb, Ca)ZrO ₃ reaches 105. )

With the accelerated development of information technology, mobile communication systems are developing in the direction of high frequency, miniaturization, integration, and high reliability. The dielectric constant of the medium dielectric constant material system is low, and it is very easy to maintain the Q value without reducing it. Difficult to meet the needs of further miniaturization. The high dielectric constant is mainly due to poor comprehensive performance and small Q f value, which makes it difficult to meet the development needs of high frequency and high reliability.

Contents of the invention

The object of the present invention is to provide a kind of dielectric ceramic material with low loss and good thermal stability, and high-frequency dielectric constant up to 30-90 and its preparation method.

The dielectric ceramic material of the present invention is composed of Ba, Sr, La, Nd, Bi, Ti and Nb in the form of oxides, and has the following chemical composition as the main phase,

(Ba _1-y Sr _y ) _3-x (La _s Nd _t Bi _u ) _1+x Ti _x Nb _3-x O ₁₂

In the formula, 0.00≤x≤2, 0.00≤y≤1

s+t+u=1

The dielectric ceramic material is prepared as follows.

First, raw powders of BaCO ₃ , SrCO ₃ , La ₂ O ₃ , Nd ₂ O ₃ , Bi ₂ O ₃ , TiO ₂ and Nb ₂ O ₅ with a purity of more than 99.9% are mixed according to the above chemical composition range, wet Ball milling for 12-24 hours, the solvent is distilled water, after drying, pre-fire in the atmosphere at 1280-1450 °C for 4-8 hours, then add binder to the pre-fired powder and granulate, then press to form, and finally in Sintering in air atmosphere at 1300~1500℃ for 1~8 hours.

The preparation method of this dielectric ceramic material has a main phase and a secondary phase. The main phase is first made into a pre-fired main phase powder according to the above method, and at the same time, the original oxide powder with a purity of more than 99.9% of the elements contained in the secondary phase composition is used. Set the proportion of ingredients, mix by wet ball mill for 12-24 hours, the solvent is distilled water, after drying, pre-fire in the atmosphere of 1280-1450 ℃ for 3 hours to synthesize the secondary phase powder, and then mix the main phase component powder and secondary phase component powder Wet ball milling according to the set weight percentage for 12-24 hours. The solvent is distilled water. After drying, add a binder and granulate, then press and shape, and finally sinter in the atmosphere at 1300-1500 ° C for 1-8 hours.

The binder is polyvinyl alcohol aqueous solution with a concentration of 5wt%, and the dosage generally accounts for 1% to 15% of the total mass of the powder.

Description of drawings

Figure 1 is the X-ray diffraction pattern of Ba ₂ La ₂ TiNb ₃ O ₁₂

Detailed ways

Further illustrate the composition and performance of the dielectric ceramic material of the present invention by the following examples

Table 1 shows several specific examples of the content of each component constituting the present invention and their microwave dielectric properties. Its preparation method is as described above, performance test is to use powder X-ray diffraction method to carry out phase analysis to the ceramic sample after sintering, Fig. 1 is the X-ray diffraction collection of illustrative plates of embodiment 2, and carry out microwave dielectric resonator method with cylindrical dielectric resonator Evaluation of electrical properties.

It can be known from Table 1 that the high dielectric constant dielectric material provided by the present invention has a dielectric constant of 30-90, and has low loss and a small temperature coefficient of resonance frequency. The dielectric material with higher dielectric constant provided by the invention can further miniaturize microwave devices, and can also be applied to high-frequency ceramic capacitors or temperature compensation capacitors. Therefore, the present invention has great industrial value.

Elements with similar structure and chemical properties to Nd, Sm, La, Bi, such as Y, Ce, Pr, Eu, Gd, Tb, Dy, Ho, Tm, Yb, Lu, etc., elements with similar structure and chemical properties to Ba, such as Ca, Pb, etc., elements similar in structure and chemical properties to Nb, such as Ta, etc., and elements similar in structure and chemical properties to Ti, such as Sn, Zr, and dielectric ceramics similar in crystal structure and properties to the present invention can also be made.

[Table 1] Example x the y the s t u molecular formula εr Qf(GHz) τ _f (ppm/℃) 1 0 0 1 0 0 Ba ₃ LaNb ₃ O ₁₂ 45 27000 15 2 1 0 1 0 0 _{Ba2La2TiNb2O12 _ _ _} 90 28000 4 3 1 0 0 0.9 0.1 Ba ₂ Nd _1.8 Bi _0.2 TiNb ₂ O ₁₂ 68 24000 -8 4 1 1 0.8 0 0.2 Sr ₂ La _1.6 Bi _0.4 TiNb ₂ O ₁₂ 30 20000 5 5 1.4 0 0.5 0.5 0 Ba ₁₆ La _1.2 Nd _1.2 Ti _1.4 Nb _1.6 O ₁₂ 53 15000 -30 6 2 0.5 0 0.9 0.1 Ba _0.5 Sr _0.5 Nd _2.7 Bi _0.3 Ti ₂ NbO ₁₂ 58 21000 18 7 2 0 1 0 0 BaLa ₃ Ti ₂ NbO ₁₂ 53 15000 -30

Claims (2)

1. A class of high dielectric constant ceramics, characterized by being composed of Ba, La, Nd, Sr, Bi, Ti, Nb in the form of oxides, and having the following chemical composition as the main phase (Ba _1-y Sr _y ) _3-x (La _s Nd _t Bi _u ) _1+x Ti _x Nb _3-x O ₁₂ In the formula, 0.00≤x≤2, 0.00≤y≤1 s+t+u=1 2. The method for preparing high dielectric constant ceramics according to claim 1, characterized in that: firstly, BaCO ₃ , SrCO ₃ , La ₂ O ₃ , Nd ₂ O ₃ , Bi ₂ O ₃ with a purity of 99.9% or more , TiO ₂ and Nb ₂ O ₅ raw powder ingredients according to the chemical composition range described in claim 1, wet ball milling and mixing for 12 to 24 hours, the solvent is distilled water, pre-fired in the atmosphere at 1280 to 1450 ° C after drying for 4 ~8 hours, then add binder to the calcined powder and granulate, then press molding, and finally sinter at 1300~1500°C in the air atmosphere for 1~8 hours, the concentration of the binder is 5wt%. Polyvinyl alcohol aqueous solution, the dose accounts for 1% to 15% of the total mass of the powder.