CN103613379A - High performance leadless piezoelectric ceramics and preparation technology - Google Patents

Abstract

A high-performance lead-free piezoelectric ceramic and its preparation process, the raw materials titanium dioxide, barium carbonate, and tin dioxide are mixed according to the stoichiometric ratio of 0.89:1:0.11, ball milled, pre-fired, secondary ball milled, granulated, and formed , and finally cover it with a crucible and put it into the sintering furnace. First, heat up to 500°C at 2°C/min, keep it warm for 2 hours for debinding, then raise the temperature to 1400°C at 4°C/min and hold it for 4 hours, and then heat it up with the furnace After being cooled to room temperature, the required lead-free piezoelectric ceramic can be obtained; the lead-free piezoelectric ceramic material of the present invention has found very high dielectric and piezoelectric properties at the quasi-quaternary point, and the relative permittivity of the material reaches ~ 75000, which is 6-7 times the dielectric constant of pure barium titanate at its Curie temperature; at the same time, the piezoelectric coefficient d ₃₃ has reached 697pC/N, which is equivalent to 5 times the piezoelectric coefficient of pure barium titanate at room temperature. It is also the highest value among lead-free piezoelectric ceramic materials.

Description

A high-performance lead-free piezoelectric ceramic and its preparation process

technical field

The invention relates to the technical field of piezoelectric ceramics, in particular to a high-performance lead-free piezoelectric ceramic and a preparation process thereof.

Background technique

Piezoelectric materials and piezoelectric properties were discovered by the Curie brothers in 1880. Piezoelectricity means that a material will form an accumulated charge on the surface under an external force field to form an electric field, or the material will deform when an external electric field is applied. As a bridge between mechanical energy and electrical energy, piezoelectric materials are widely used in detectors, transducers and actuators, such as inkjet printers and mobile phone microphones used in daily life, and probes for atomic force microscopes in high-end research Console and ultrasonic detection technology. More recently, piezoelectric materials have been used for energy harvesting and storage.

The most widely used piezoelectric materials in industry are leaded piezoelectric materials, such as lead zirconate titanate and so on. Because these lead-containing piezoelectric materials not only have good performance at their quasi-isotropic phase boundaries, but also have good temperature stability. However, lead has toxic and side effects on human body and environment, so many developed countries have banned the production of lead-containing electronic products. Therefore, it is imminent to develop a lead-free piezoelectric material that can replace the lead-containing system.

Contents of the invention

In order to solve the defects of the prior art, the object of the present invention is to provide a high-performance lead-free piezoelectric ceramic and its preparation process. A barium titanate system doped with barium stannate is prepared by a solid-state reaction method under specific conditions. Among them, very high dielectric and piezoelectric properties are found at the quasi-quaternary point of 0.89BaTiO ₃ -0.11BaSnO ₃ , and the relative dielectric constant of the material reaches ~75000, which is the dielectric constant of pure barium titanate at its Curie temperature. At the same time, the piezoelectric coefficient d ₃₃ has reached 697pC/N, which is equivalent to 5 times the piezoelectric coefficient of pure barium titanate at room temperature, which is also the highest value among lead-free piezoelectric ceramic materials.

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

A high-performance lead-free piezoelectric ceramic, barium titanate (0.89BaTiO ₃ -0.11BaSnO ₃ ) doped with barium stannate, its raw material components are stoichiometric ratio, that is, molar ratio:

Titanium dioxide: barium carbonate: tin dioxide=0.89:1:0.11

A preparation process of high-performance lead-free piezoelectric ceramics, comprising the following steps:

(1) Ingredients

The raw materials titanium dioxide, barium carbonate, and tin dioxide are compounded according to the stoichiometric ratio, that is, the molar ratio is 0.89:1:0.11, and the purity of the drug is more than 98%;

(2) Ball milling

Put the raw materials weighed in step (1) into a ball milling tank. The ball milling medium is distilled water and zirconia balls. The mass ratio of raw materials, distilled water, and zirconia balls is 1:2:2. Ball mill for 4 hours, and then ball mill The mixture is placed in an oven at 80°C for drying;

(3) Pre-burning

Put the dried powder in step (2) into the crucible, cover it, raise the temperature to 1150°C at a rate of 4°C/min, keep it warm for 4 hours, and then cool to room temperature with the furnace;

(4) Secondary ball milling

The powder pre-fired in step (3) is ball milled again. The ball milling medium is distilled water and zirconia balls. The mass ratio of raw materials, distilled water, and zirconia balls is 1:2:2. At this time, the ball milling time is 6 hours, and carry out drying;

(5) Granulation

Grind and sieve the powder dried in step (4), add PVA glue accounting for 5% of its weight, and then fully grind until uniform, pass through 60-mesh and 100-mesh sieves, and take the middle of 60-mesh and 100-mesh sieves Powder;

(6) Forming

Put the powder sieved in step (5) into a stainless steel mold, hold 0.5g of each piece under a pressure of 100MPa for 1 minute, and press it into a sheet-shaped embryo body; in addition, use 2-3g of powder under a pressure of 100MPa Prepare columnar samples;

(7) Sintering

Spread a little powder prepared in step (5) on the zirconium plate, then put the green body of step (6) on the powder, cover it with a crucible, and put it into the sintering furnace, first raise the temperature at 2°C/min Heat at 500°C for 2 hours for debinding, then raise the temperature at 4°C/min to 1400°C and hold for 4 hours, then cool down to room temperature with the furnace to obtain the required lead-free piezoelectric ceramics.

Advantages of the present invention:

The lead-free piezoelectric ceramic material of the present invention has found very high dielectric and piezoelectric properties at the quasi-quaternary point, and the relative dielectric constant of the material reaches ~75000, which is the dielectric constant of pure barium titanate at its Curie temperature. At the same time, the piezoelectric coefficient d ₃₃ has reached 697pC/N, which is equivalent to 5 times the piezoelectric coefficient of pure barium titanate at room temperature, which is also the highest value among lead-free piezoelectric ceramic materials. The data show that the performance of the material is closely related to its phase coexistence state. The more phases coexist, the greater the performance improvement. This provides a new idea for the development of high-performance and stable lead-free piezoelectric materials.

Description of drawings

Figure 1 is the phase diagram of barium stannate-doped barium titanate (BT-xBS) system, where QP refers to the quasi-quaternary point of 0.89BaTiO ₃ -0.11BaSnO ₃ components.

Figure 2(a) is the distribution diagram of the piezoelectric constant d ₃₃ of the BT-xBS system, and Figure 2(b) is the dielectric temperature spectrum of the BT-xBS system, where QP refers to the quasi-quaternary point.

Figure 3 is a comparative experiment of two systems. Figure 3(a1) is the phase diagram of the barium stannate-doped barium titanate (BT-xBS) system; Figure 3(a2) is the phase diagram of the calcium titanate-doped barium titanate (BT-xCT) system; Figure 3(b ) is a comparison of the dielectric properties of the Curie temperature points of the two systems, where QP represents the quasi-quaternary point.

Detailed ways

The present invention is described in detail below in conjunction with accompanying drawing,

The present invention is a high-performance lead-free piezoelectric ceramic, barium titanate (0.89BaTiO ₃ -0.11BaSnO ₃ ) doped with barium stannate, and its raw material components are stoichiometrically:

Titanium dioxide: barium carbonate: tin dioxide=0.89:1:0.11

A preparation process of high-performance lead-free piezoelectric ceramics, comprising the following steps:

(1) Ingredients

The raw materials titanium dioxide, barium carbonate and tin dioxide are mixed according to the stoichiometric ratio (molar ratio) of 0.89:1:0.11;

(2) Ball milling

Put the raw materials weighed in step (1) into a ball milling tank. The ball milling medium is distilled water and zirconia balls. The mass ratio of raw materials, distilled water, and zirconia balls is 1:2:2. Ball mill for 4 hours, and then ball mill The mixture is placed in an oven at 80°C for drying;

(3) Pre-burning

Put the dried powder in step (2) into the crucible, cover it, raise the temperature to 1150°C at a rate of 4°C/min, keep it warm for 4 hours, and then cool to room temperature with the furnace;

(4) Secondary ball milling

The powder pre-fired in step (3) is ball milled again. The ball milling medium is distilled water and zirconia balls. The mass ratio of raw materials, distilled water, and zirconia balls is 1:2:2. At this time, the ball milling time is 6 hours, and carry out drying;

(5) Granulation

Grind and sieve the powder dried in step (4), add PVA glue accounting for 5% of its weight, and then fully grind until uniform, pass through 60-mesh and 100-mesh sieves, and take the middle of 60-mesh and 100-mesh sieves Powder;

(6) Forming

Put the powder sieved in step (5) into a stainless steel mold (diameter 11mm), hold 0.5g of each piece at a pressure of 100MPa for 1 minute, and press it into a sheet-shaped embryo; in addition, use 2-3g of powder , columnar samples (diameter 8mm) can be prepared under a pressure of 100MPa;

(7) Sintering

Spread a little powder prepared in step (5) on the zirconium plate, then put the green body of step (6) on the powder, cover it with a crucible, and put it into the sintering furnace, first raise the temperature at 2°C/min Heat at 500°C for 2 hours for debinding, then raise the temperature at 4°C/min to 1400°C and hold for 4 hours, then cool down to room temperature with the furnace to obtain the required lead-free piezoelectric ceramics.

To conduct an electrical test on the lead-free piezoelectric ceramic obtained in this example, the ceramic sheet prepared in step (7) needs to be polished smooth, and then coated with silver paste to form a surface electrode. Put the silver paste-coated sheet on the zirconium plate, place it in a muffle furnace and raise the temperature to 800°C at 4°C/min, keep it warm for 30 minutes, and cool naturally; take out the sheet and grind off the silver electrodes on the surrounding sides.

When conducting piezoelectric tests, the columnar ceramic samples prepared in step (8) need to be polarized. Put the columnar ceramic sample obtained in step (8) into silicone oil, conduct electric polarization for 30 minutes, and the polarization electric field is 2-3kv/mm or 3 times the coercive field; perform a performance test after standing for 24 hours.

Figure 1 shows the phase diagram of barium stannate-doped barium titanate (BT-xBS) material. The phase transition sequence of pure barium titanate is cubic phase-tetragonal phase-orthorhombic phase-rhombic phase (i.e. CTOR). In particular, these three phase phase transitions finally converge to one point (BT-11BS in the phase diagram , about 40 degrees Celsius). This means that these four phases (CTOR) basically coexist together in 0.89BaTiO ₃ -0.11BaSnO ₃ , thus resulting in the excellent performance of 0.89BaTiO ₃ -0.11BaSnO ₃ .

Figure 2(a) is the equivalent diagram of the piezoelectric coefficient of d ₃₃ in the BT-xBS system. It can be seen that at the quasi-quaternary point of 0.89BaTiO ₃ -0.11BaSnO ₃ , the piezoelectric coefficient of d ₃₃ of the material reaches ~700pC/N, which is The largest piezoelectric constant reported now for lead-free ceramics. Figure 2(b) is the dielectric temperature spectrum of BT-xBS. We can easily find that the material has a very large dielectric constant at the quasi-quaternary point of 0.89BaTiO ₃ -0.11BaSnO ₃ , which is much higher than other components. and temperature. These results indicate that the small-field dynamic properties of the material at the quasi-quadruple point, such as piezoelectricity and permittivity, are greatly improved, higher than those of other phase boundaries and compositions.

In order to prove that the performance improvement on the quasi-quaternary point does come from the structural condition of quasi-quaternary coexistence, we conducted a comparative experiment. As shown in Figure 3, we selected the same barium titanate matrix, different dopants barium stannate and calcium titanate, the former forms a quasi-quaternary point at 0.89BaTiO ₃ -0.11BaSnO ₃ while the latter does not, the phase diagram is as follows Figure 3 (a) (b) shown. It was found that the same barium titanate base was doped from barium titanate, and the BT-xBS system had a very high dielectric peak led by the quasi-quadruple point at 0.89BaTiO ₃ -0.11BaSnO ₃ , while The performance of the BT-xCT system is very mediocre because there is no multi-phase coexistence point, with only small fluctuations. This experiment proves that the quasi-quadruple point _{of 0.89BaTiO3-0.11BaSnO3} is the direct cause of the high performance at the QP.

In summary, very high dielectric and piezoelectric properties are found at the quasi-quadruple point of 0.89BaTiO ₃ -0.11BaSnO ₃ , and the relative permittivity of the material reaches ~75000, which is pure barium titanate at its Curie 6-7 times the dielectric constant at high temperature; at the same time, the piezoelectric coefficient d ₃₃ has reached 697pC/N, which is equivalent to 5 times the piezoelectric coefficient of pure barium titanate at room temperature, which is also the highest among lead-free piezoelectric ceramic materials value. The data show that the performance of the material is closely related to its phase coexistence state. The more phases coexist, the greater the performance improvement. This provides a new idea for the development of high-performance and stable lead-free piezoelectric materials.

Claims (2)

1. A high-performance lead-free piezoelectric ceramic, characterized in that its raw material components are in stoichiometric ratio, i.e. the molar ratio is: Titanium dioxide: barium carbonate: tin dioxide=0.89:1:0.11. the 2. A preparation process for high-performance lead-free piezoelectric ceramics, comprising the following steps: (1) Ingredients The raw materials titanium dioxide, barium carbonate, and tin dioxide are batched according to the stoichiometric ratio, that is, the molar ratio is 0.89:1:0.11; (2) Ball milling Put the raw materials weighed in step (1) into a ball milling tank. The ball milling medium is distilled water and zirconia balls. The mass ratio of raw materials, distilled water, and zirconia balls is 1:2:2. Ball mill for 4 hours, and then ball mill The mixture is placed in an oven at 80°C for drying; (3) Pre-burning Put the dried powder in step (2) into the crucible, cover it, raise the temperature to 1150°C at a rate of 4°C/min, keep it warm for 4 hours, and then cool to room temperature with the furnace; (4) Secondary ball milling The powder pre-fired in step (3) is ball milled again. The ball milling medium is distilled water and zirconia balls. The mass ratio of raw materials, distilled water, and zirconia balls is 1:2:2. At this time, the ball milling time is 6 hours, and carry out drying; (5) Granulation Grind and sieve the powder dried in step (4), add PVA glue accounting for 5% of its weight, and then fully grind until uniform, pass through 60-mesh and 100-mesh sieves, and take the middle of 60-mesh and 100-mesh sieves Powder; (6) Forming Put the powder sieved in step (5) into a stainless steel mold, hold 0.5g of each piece under a pressure of 100MPa for 1 minute, and press it into a sheet-shaped embryo body; in addition, use 2-3g of powder under a pressure of 100MPa Columnar samples can be prepared; (7) Sintering Spread a little powder prepared in step (5) on the zirconium plate, then put the green body of step (6) on the powder, cover it with a crucible, and put it into the sintering furnace, first raise the temperature at 2°C/min Heat at 500°C for 2 hours for debinding, then raise the temperature at 4°C/min to 1400°C and hold for 4 hours, then cool down to room temperature with the furnace to obtain the required lead-free piezoelectric ceramics. the

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