CN107827452B

CN107827452B - Method for reducing loss of calcium copper titanate ceramic by air quenching

Info

Publication number: CN107827452B
Application number: CN201711259380.0A
Authority: CN
Inventors: 张建花; 郑杰诚; 李晔城; 刘玉倩; 宋建成; 吝伶艳; 李媛媛
Original assignee: Taiyuan University of Technology
Current assignee: Taiyuan University of Technology
Priority date: 2017-12-04
Filing date: 2017-12-04
Publication date: 2020-12-11
Anticipated expiration: 2037-12-04
Also published as: CN107827452A

Abstract

The invention discloses a method for preparing low dielectric loss copper calcium titanate ceramics by air quenching based on a sol-gel method. The method comprises the following steps: copper nitrate, calcium nitrate and butyl titanate are taken as raw materials, absolute ethyl alcohol is taken as a solvent, and the chemical expression CaCu of copper calcium titanate is firstly adopted₃Ti₄O₁₂Weighing and batching the stoichiometric ratio of each chemical element in (CCTO); then placing the prepared sol in a water bath kettle at the temperature of 80 ℃, and continuously stirring until dry gel is formed; then removing organic matters in the xerogel by using an electric furnace and a muffle furnace in sequence to form CCTO ceramic precursor powder; then adding glue, grinding, granulating and tabletting to prepare a ceramic blank, and then putting the blank into a muffle furnace for sintering and heat preservation; and finally, taking out the CCTO ceramic sample when the temperature in the furnace is reduced to below 1000 ℃ after sintering, and quenching and cooling the CCTO ceramic sample to room temperature in air. The invention has simple operation process, lower sintering temperature, good compactness of the prepared ceramic sample, low dielectric loss and good frequency stability.

Description

Method for reducing loss of calcium copper titanate ceramic by air quenching

Technical Field

The invention belongs to the field of dielectric materials, and particularly relates to low-loss calcium copper titanate (CaCu)₃Ti₄O₁₂CCTO for short) ceramic.

Background

Following science and technologyThe development of the dielectric material is progressing, and the dielectric material has higher standards for miniaturization and high performance in various fields including the microelectronics industry and the new energy industry. Therefore, giant dielectric materials are the focus of research today. By giant dielectric material is meant_r＞10³The dielectric material is one of important conditions for miniaturization and high integration of electronic devices, and has wide application prospect in the fields of high-density energy storage and microelectronic devices.

CCTO ceramic materials are one of the giant dielectric constant materials that have received much attention in the last decade. The CCTO ceramic has high dielectric constant (10) and good temperature stability⁴~10⁵The dielectric constant of 100-600K is hardly changed and no phase change occurs. In addition, CCTO ceramics have excellent pressure sensitive characteristics, which make them expected to be widely used in the fields of high-density information storage, thin-film devices, application-type integrated circuits, high-dielectric capacitors, and nonlinear devices.

However, the CCTO ceramic exhibits an extremely high dielectric constant and is accompanied by a high dielectric loss (> 0.1), which may cause excessive heat generation during the use of the device, increase the element temperature, deteriorate the device performance, and accelerate the device aging. Therefore, how to reduce the dielectric loss of CCTO while ensuring its high dielectric constant is a hot research topic today.

At present, the measures for inhibiting the CCTO ceramic high loss mainly comprise the following two major measures: firstly, new elements are added into the CCTO ceramic by doping or substitution to change the performance of the CCTO ceramic, so that the dielectric loss of the CCTO ceramic is reduced; and secondly, the sintering conditions such as sintering temperature, time and atmosphere are changed to reduce the loss of the alloy. Related methods by changing the cooling conditions after the sintering of the sample have been reported. The invention provides a brand new preparation method for reducing the CCTO ceramic loss.

Open literature "Song river, CaCu₃Ti₄O₁₂The study on the quenching microstructure and the dielectric property of the ceramic, and the CC is prepared in a ceramic arrester, 2017 Ser. number 275 (128-131)' by utilizing a solid phase method and an air quenching cooling modeTO ceramics, however, result in a substantial increase in loss, which is contrary TO the present invention and not in accordance with the requirements for low-loss CCTO ceramics.

Disclosure of Invention

Aiming at the problems, the invention provides a preparation method of CCTO ceramics with low loss. The preparation method can obviously reduce the dielectric loss of the CCTO ceramics and improve the frequency stability and the compactness.

In order to achieve the above purpose, the invention adopts the following technical scheme to realize:

(1) weighing copper nitrate, calcium nitrate, butyl titanate and citric acid with corresponding mass according to the molar ratio of 1:3:4: 9.6;

(2) pouring copper nitrate, calcium nitrate and citric acid into a proper amount of absolute ethyl alcohol, and continuously stirring to fully dissolve the copper nitrate, the calcium nitrate and the citric acid to form solution A;

(3) pouring butyl titanate into a proper amount of absolute ethyl alcohol, and stirring to uniformly dissolve the butyl titanate to form a solution B;

(4) keeping the solution A constantly stirred, and slowly pouring the solution B into the solution A to form sol;

(5) adding a proper amount of polyethylene glycol into the sol, and stirring until the polyethylene glycol is completely dissolved; putting the solution into a water bath kettle with the constant temperature of 80 ℃ and continuously stirring to form gel;

(6) putting the gel into an evaporating dish, removing organic matters by using an electric furnace, and presintering at high temperature by using a muffle furnace to form CCTO ceramic precursor powder;

(7) pouring the precursor powder into an agate mortar, adding a proper amount of PVA (polyvinyl alcohol) colloid, fully grinding, sieving and granulating, and then putting into a drying oven for drying;

(8) weighing a proper amount of the powder prepared in the step (7), putting the powder into a grinding tool, and tabletting to obtain a CCTO ceramic blank;

(9) placing the ceramic blank into a muffle furnace, and sintering for 10-18 h at 1000-1080 ℃;

(10) after sintering, when the temperature in the furnace is reduced to below 1000 ℃, taking out the uncooled CCTO ceramic sample, and putting the sample in air for rapid quenching and cooling.

Detecting the microstructure of the CCTO ceramic by an X-ray diffractometer (figure 1); the dielectric properties (fig. 2) and loss properties (fig. 3) of the samples were measured with a broadband dielectric spectrometer (NOVOCONTROL Concept 80).

The properties of the cooled samples were compared with those of the air-quenched samples.

The invention has the advantages that: compared with the traditional sol-gel method, the CCTO ceramic prepared by the preparation method shortens the preparation period, further reduces the loss (about 0.03) on the original basis, and improves the frequency stability of the dielectric constant.

Drawings

Fig. 1 is an XRD pattern of CCTO ceramic prepared by air quenching.

FIG. 2 is a dielectric spectrum of a CCTO ceramic made by air quenching and furnace cooling.

FIG. 3 is a graph of the loss spectrum of CCTO ceramics made by air quenching and furnace cooling.

Detailed Description

The present invention will be further described with reference to the following embodiments. The following description is merely exemplary in nature and is not intended to limit the scope of the present disclosure.

Example 1

(1) Firstly, 9.5414 g of calcium nitrate tetrahydrate (99%), 29.2851 g of copper nitrate trihydrate (99%) and 75.5270 g of citric acid (99%) are weighed and poured into a beaker filled with 100ml of absolute ethyl alcohol, and the mixture is stirred continuously to be fully dissolved to form solution A;

(2) 55.0015 g of butyl titanate (99.5%) is weighed and poured into 100ml of absolute ethyl alcohol, and the mixture is stirred to be dissolved uniformly to form a solution B;

(3) while continuously stirring the solution A, slowly adding the solution B along the glass rod to form sol; after the mixture is uniformly mixed, 18 ml of polyethylene glycol is added; then putting the sol added with the polyethylene glycol into a water bath kettle at the temperature of 80 ℃, and stirring by keeping a stirring rod at 180 rpm to form gel;

(4) pouring the gel into an evaporating dish, and then placing the evaporating dish on an electric furnace to keep the temperature at 400 ℃ to remove organic matters in the gel; then putting the ceramic powder into a muffle furnace to presintere for 2 h at the high temperature of 600 ℃ to form CCTO ceramic precursor powder;

(5) putting the powder into an agate mortar, adding a sufficient amount of PVA (polyvinyl alcohol) adhesive, manually grinding for 3 h, sieving with a 80-mesh sieve, and finally drying in a drying oven at 120 ℃ for 10 min;

(6) weighing 3.2 g of powder, putting into a die, and pressing into tablets under the pressure of 300 MPa;

(7) putting the zirconia plate and the sample into a muffle furnace, raising the temperature to 100 ℃ at the heating rate of 2 ℃/min, preserving heat for 10 min, dehumidifying and drying, raising the temperature to 600 ℃ at the heating rate of 5 ℃/min, preserving heat for 1 h, removing glue, raising the temperature to 1060 ℃ at the heating rate of 10 ℃/min, preserving heat for 12 h, and sintering;

(8) after sintering, when the temperature in the furnace is reduced to below 1000 ℃, taking out a part of samples, quenching and cooling the samples in air, and cooling the rest samples in the furnace for comparison;

(9) and coating silver paste on the surface of the sintered sample, then preserving heat in a muffle furnace at 500 ℃ for 0.5 h to finish silver plating, and finally measuring the dielectric property.

The air-quenched CCTO ceramic was examined with an X-ray diffractometer and found to be a pure CCTO phase (see fig. 1). The dielectric property and the loss property of a sample are measured by a broadband dielectric spectrometer, and the dielectric frequency stability of the sample subjected to air quenching is obviously superior to that of the sample cooled along with the furnace, and the frequency range of high dielectric constant is also improved (as shown in figure 2); the dielectric loss of the air quenched sample at room temperature at 10 kHz drops to 0.03, which is more than 50% lower than the sample loss (0.07) with furnace cooling, and also increases the frequency range of the low loss section (see fig. 3).

Claims

1. A method for reducing the loss of calcium copper titanate ceramics by air quenching is characterized in that the calcium copper titanate ceramics with low dielectric loss is prepared by air quenching based on a sol-gel method, and the specific preparation method is as follows:

(1) respectively weighing calcium nitrate, copper nitrate, butyl titanate and citric acid with corresponding mass according to the molar ratio of 1:3:4: 9.6;

(5) adding a proper amount of polyethylene glycol into the sol, and stirring until the polyethylene glycol is completely dissolved; putting the sol dissolved with the polyethylene glycol into a water bath kettle with the constant temperature of 80 ℃ and continuously stirring to form gel;

(8) weighing a proper amount of the powder prepared in the step (7), putting the powder into a die, and tabletting to obtain a CCTO ceramic blank;

(9) putting the ceramic blank into a muffle furnace, raising the temperature to 100 ℃ at the heating rate of 2 ℃/min, preserving heat for 10 min, dehumidifying and drying, raising the temperature to 600 ℃ at the heating rate of 5 ℃/min, preserving heat for 1 h, removing glue, raising the temperature to 1060 ℃ at the heating rate of 10 ℃/min, preserving heat for 12 h, and sintering;