RU2021207C1 - Magnesium-, zinc- and nickel-substituted bismuth niobates - Google Patents

Abstract

FIELD: metallurgy. SUBSTANCE: enumerated magnesium-, zinc- and nickel-substituted bismuth niobates having general formula of (Bi_2/3[]_1/3)₂(Me $\genfrac{}{}{0ex}{}{\text{2+}}{\text{1/}}$ ₃Nb_2/3)₂O₆[]₁, where [] denotes vacancies and Me²⁺ represents magnesium, zinc or nickel can be employed as high-frequency capacitor materials having marked dielectric permeability, dielectric permeability temperature coefficient and low value of dielectric loss angle tangent. EFFECT: higher quality. 4 tbl

Description

The invention relates to chemical compounds niobium oxide, bismuth and divalent metal - magnesium, zinc and nickel general formula (Bi _2/3 [] _{1/3) 2} (Me _1/3 ²⁺ Nb _{2/3) 2} O ₆ [] ₁ where [] are vacancies, Me ²⁺ - Mg ²⁺ , Zn ²⁺ or Ni ²⁺ , and can be used for the production of high-frequency ceramic capacitors.

Currently, in the manufacture of these capacitors are widely used compounds of titanates and niobates of alkaline earth elements, as well as magnesium and bismuth, as well as SrTiO ₃ , CaTiO ₃ , MgTiO ₃ , Bi ₂ Ti ₂ O ₇ , Pb ₂ Nb ₂ O ₇ and others, properties which are given in table. 1 and are described in the literature.

As can be seen from the data given in table. 1, in the manufacture of ceramic capacitors, compounds of various crystal structures are used. Compounds with the perovskite structure SrTiO ₃ , CaTiO _{3 are} characterized by a relatively high dielectric constant ε = 250,150 and a large negative temperature coefficient of dielectric constant TKE = -2500.10 ^-6 deg ^-1 or -1500.10 ^-6 deg ^-1 , respectively.

The compound Pb ₂ Nb ₂ O ₇ with the pyrochlore structure used in the manufacture of capacitors, having ε ≈ 140, is also characterized by a large negative temperature coefficient TKE, while the compound of lanthanum dithitanate (La ₂ Ti ₂ O ₇ ) or neodymium (Nd ₂ TiO ₇ ) has a small ε ≈ 40–50 for small positive TKE values (see table 1).

Moreover, all compounds have a sintering temperature T _cn. (1200-1400) ^о С, which makes it impossible to obtain low-temperature ceramic materials for capacitors on their basis and to use low-temperature compositions, in particular, Ag-Pd alloys, as electrodes of monolithic capacitors.

 The purpose of the invention is to increase the dielectric constant of ceramic materials while maintaining the temperature coefficient of the dielectric constant of the TKE and lower their sintering temperature for the manufacture of high-frequency capacitors of thermally compensating TKE groups.

Для структурного типа пирохлора общая формула имеет вид А₂В₂О₇, где А и В - металлы, образующие собственные подрешетки. В предлагаемом соединении в качестве элемента А выступает Вi³⁺, а элемента В - Nb⁵⁺ и двухвалентные металлы Ме²⁺ - -Мg²⁺, Zn²⁺ или Ni²⁺.This goal is achieved by the fact that as a basis for high-frequency capacitor ceramic materials it is proposed to use a new compound with the structure of defective pyrochlore - magnesium, zinc, nickel-substituted bismuth niobates (Bi _2/3 [] _1/3 ) ₂ (Me _1/3 ²⁺ Nb _{2 / 3} ) ₂ O ₆ [] ₁ , where [] are vacancies, Me ²⁺ - Mg ²⁺ , Zn ²⁺ or Ni ²⁺ structural formula

For the structural type of pyrochlore, the general formula has the form A ₂ B ₂ O ₇ , where A and B are metals forming their own sublattices. In the proposed compound, Bi ³⁺ acts as element A, and Nb ⁵⁺ and divalent metals Me ²⁺ - Mg ²⁺ , Zn ²⁺ or Ni ²⁺ act as element A.

The proposed compound is obtained by solid-phase synthesis from oxides of niobium, bismuth and a divalent metal Mg ²⁺ , Zn ²⁺ or Ni ²⁺ . The chemical composition of the compounds of the general formula (Bi _2/3 [] _1/3 ) ₂ (Me _1/3 ²⁺ Nb _2/3 ) ₂ O ₆ [] 1 or (Bi _0.67 [] _0.33 ) ₂ (Me ^{2 +} _0.33 Nb _0.67 ) ₂ O ₆ [] ₁ , where Me ²⁺ - Mg ²⁺ , Zn ²⁺ or Ni ²⁺ , are given in table. 2.

 The following are examples of the synthesis of a new compound.

PRI me R 1. Oxides of bismuth, niobium and magnesium, taken in a molar ratio of 1: 1: 1, which corresponds to the mass ratio given in table. 2 for Example 1 were mixed and milled in a vibrating mill, whereupon the synthesis of the compounds at a temperature T _c = 850-900 ^{° C} in a chamber furnace for 2 hours. Then the synthesized product was milled in a vibrating mill or, if necessary, wet grinding in a mill in within 1-3 or 10-12 hours to the specific surface S _beats = (0.6-1.5) m ² / g When applying wet grinding, the resulting product is dried, then press powder is prepared, samples are pressed in the form of disks at a specific pressure of P ≈ 1000 kg / cm ² . samples were sintered in the range of 1120-1180 ^{° C} for 2 hours. The sintered disc specimens coated with a silver paste, which vzhigayut at a temperature of (840 ± 20) ^{° C,} after which the measured electrical characteristics.

PRI me R 2. Oxides of bismuth, niobium and zinc, taken in a molar ratio of 1: 1: 1, which corresponds to the mass ratio of example 2, subjected to grinding and mixing in a vibration mill, produce synthesis at T _c = 850-900 ^about in a chamber furnace for 1.5-2.0 hours. Then the synthesized product is ground in a vibrating mill for 1-3 hours or a wet grinding mill for 10-15 hours to a specific surface area S _beats. = (0.6-1.5) m ² / g. After drying and preparation of the press powder, samples are prepared by pressing at P _beats. = 1000 kg / cm ^2, which are sintered in the range of 1020-1120 ^{° C,} coated with the electrode paste, which when vzhigayut (840 ± 20) ^{° C} measured electrical characteristics.

PRI me R 3. Oxides of bismuth, niobium and Nickel in quantities corresponding to the mass ratios specified in example 3 of the table. 2, mixed and synthesized under conditions similar to examples 1 and 2. Sintering of the samples is carried out in the range of 1080-1160 ^about C for 2 hours

 The proposed chemical compounds have a fundamentally new atomic structure, which leads to an increase in the dielectric constant and a decrease in sintering temperature, which makes it possible to use it as the dielectric of high-frequency capacitors of thermally compensating TKE groups.

 X-ray diffraction phase analysis of the samples was carried out on domestic DRON-2 and DRON-3 diffractometers with a GP-4 goniometric attachment for studying polycrystalline samples.

- излучение, Ni - фильтр. Режим работы трубки: напряжение 40 кВ, ток 18 mА. Регистрацию интенсивностей производили в режиме непрерывной записи со скоростью движения детектора 0,5 град/мин. Для повышения чувствительности и точности измерения рефлексов использовали различные масштабы записи (шкалы регистрации интенсивности). Интегральную интенсивность оценивали по площади пиков. Расчет теоретических значений интенсивностей и уточнение параметров проводили на ЭВМ по программе Гамильтона с использованием блок-диагонального метода МНК. Фактор сходимости экспериментальных и расчетных значений IK = 11,05%.To determine the atomic structure of the proposed compounds, we performed an analysis of the intensity of 28 reflections of single-phase powder samples of ceramic compositions corresponding to molar ratios: 1Bi ₂ O ₃ 1Nb ₂ O ₅ 1Me ²⁺ O, where Me ²⁺ is -Mg ²⁺ , Zn ²⁺ or Ni ^{2 +} . The intensity was collected on a DRON-2 X-ray diffractometer. Used Cu, K

- radiation, Ni - filter. Tube operating mode: voltage 40 kV, current 18 mA. The intensities were recorded in continuous recording mode with a detector speed of 0.5 deg / min. To increase the sensitivity and accuracy of the measurement of reflexes, various recording scales (intensity registration scales) were used. The integrated intensity was estimated by the peak area. The calculation of the theoretical intensities and the refinement of the parameters were carried out on a computer using the Hamilton program using the block-diagonal OLS method. The convergence factor of the experimental and calculated values of IK = 11.05%.

 In accordance with the proposed crystal chemical formula, the x-ray density of the obtained compounds was calculated and compared with the experimental one. The experimental density was determined by hydrostatic weighing.

(для Ме²⁺ = Ni²⁺), а = 10,557

(для Ме²⁺= Мg²⁺) и а = 10,560

(для Ме²⁺ = Zn²⁺).The ideal composition of the compound corresponds to the molar ratio of bismuth oxides, divalent metal Me ²⁺ - Mg ²⁺ , Zn ²⁺ or Ni ²⁺ and niobium 1: 1: 1 - 1 Bi ₂ O ₃ xx 1Me ²⁺ O ˙ 1Nb ₂ O ₅ . This composition can be written as Bi ₂ Me ²⁺ Nb ₂ O ₉ or Bi _2/3 Me _1/3 ²⁺ Nb _2/3 O ₃ . Atoms Me ²⁺ and Nb occupy atomic positions in the B sublattice in the structure of type A ₂ B ₂ O ₇ statistically. This is confirmed by the absence of a superstructure in the compound samples. All fixed reflexes (see table 3), depending on the composition of Me ^2+, are described by the lattice parameters: а = 10.542

(for Me ²⁺ = Ni ²⁺ ), a = 10.557

(for Me ²⁺ = Mg ²⁺ ) and a = 10.560

(for Me ²⁺ = Zn ²⁺ ).

In accordance with the space group of pyrochlore Fd3m (N 227), the atoms in the structure occupy the following crystallographic positions:
B1 16s 1/8 1/8 1/8
Me ²⁺ , Nb 16d 5/8 5/8 5/8
01 48f x 0 0 X = 0.3065
02 8a 0 0 0
In the table. Figure 3 shows the experimental (dexp) and calculated (d habit.) Interplanar spacings for unit compounds for unit cell parameters “a”:
(Bi _2/3 [] _1/3 ) ₂ (Ni _1/3 Nb _2/3 ) ₂ O ₆ [] 1,
(Bi _2/3 [] _1/3 ) ₂ (Mg _1/3 Nb _2/3 ) ₂ O ₆ [] ₁ .

(Bi _2/3 [] _1/3 ) ₂ (Zn _1/3 Nb _2/3 ) ₂ O ₆ [] ₁ .

X-ray density for the specified composition, for example, for Me ²⁺ = Mg ²⁺ is 6.28 g / cm ³ , the experimental density is 6.19 g / cm ³ .

 The observed convergence of experimental and calculated data confirms the reliability of the proposed crystallographic model of the structure of “defective” pyrochlore, in which vacancies are statistically distributed in the A sublattice and in the positions of oxygen atoms.

When bringing the composition of the proposed compounds to the formula of the structural type of pyrochlore, the following crystal chemical formulas are obtained:
(Bi _2/3 [] _1/3 ) ₂ (Me _1/3 ²⁺ Nb _2/3 ) ₂ O ₆ [] ₁ or
(Bi _0.67 [] _0.33 ) ₂ (Me _0.33 + Nb _0.67 ) ₂ O ₆ [] ₁ , where [] are vacancies,
Me ²⁺ - Mg ²⁺ , Zn ²⁺ or Ni ²⁺ .

 For an ideal composition, as can be seen from the formula, 1/3 of vacancies are formed in the positions of atoms A and 1/7 of vacancies in the positions of oxygen atoms.

 The electrical properties and lattice parameters for the three compounds of bismuth niobates with the structure of pyrochlore are given in table. 4.

As can be seen from the data presented, bismuth niobate compounds have a high dielectric constant ε = 145-148 at TKE satisfying the temperature stability groups M330 (TKE = - (330 ± 60) .10 ^-6 deg ^-1 ) and M470 (TKE = = - (470 ± 60) .10 ^-6 deg ^-1 ), low dielectric losses tg δ = (2-3) .10 ^-4 and high specific volume resistance (ρv at a temperature of 155 ^о С ˙ 10 ¹² ... 10 ¹³ Ohm, cm), which meets the requirements for ceramics for high-frequency capacitors of thermocompensating groups according to TKE.

Claims (1)

MAGNESIUM-, ZINC-, NICKEL-SUBSTITUTED BISMUTH NIOBATES of the crystal chemical formula
(Bi _2/3 [] _1/3 ) ₂ (Me $\genfrac{}{}{0ex}{}{\text{2+}}{\text{1/}}$ ₃ Nb _2/3 ) ₂ O ₆ [] ₁ ,
where [] - vacancies;
Me ²⁺ - magnesium, zinc or nickel,
having a structural formula

as high-frequency capacitor materials.

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