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PZT piezoelectric ceramic material and its development trend

In the introduction doped PZT piezoelectric ceramic material prepared on the basis of summed up the best firing conditions to produce doped PZT materials, pointed out that the sample has been developed to meet or exceed the the piezoelectric ignition material level, but the selected system still potential to be tapped, as long as the appropriate technology, performance completely again raise the prospect of the development trend of lead-free piezoelectric ceramic materials.
Keywords: PZT; piezoelectric ceramic material; firing conditions; lead-free piezoelectric ceramics
CLC: TB321 Document code: A
The piezoelectric ceramic is important electromechanical energy conversion material. Currently widely used in daily life, industrial, military and medical. Piezoelectric ceramic fastest development in Japan, accounting for 2/3 of the world's production.
The piezoelectric ceramic material based on lead zirconate titanate (PZT)-based ternary ceramic material, mainly: Pb (Me1/2Nbl/2) O3-PbTiO3-PbZrO3 (Me = Mg, Co, Mn, Zn) and Pb (Mel / 2, Nb1 / 2) O3-PbTiO3-PbZrO3 (Me = In, Y, Sb) series.
Production of piezoelectric ceramic (PZT) general: Ingredients → mixed → calcined → broken → adhesives mixed → granulation sintering molding → → → processing → → Test electrode → polarization. Piezoelectric ceramic performance is good or bad, a very close relationship with the manufacturing process, the same formula, the change of process conditions can cause very different material properties.
In order to improve the performance of the lead zirconate titanate-based piezoelectric ceramic, the use of the same element to override the original constituent elements, or the incorporation of trace impurities hot press sintering method was modified. By the incorporation of trace impurities can greatly change the electromechanical coupling coefficient K, the dielectric constant ε, the mechanical quality factor Qm to obtain all kinds of material to meet different purposes, such as a ceramic filter, and the piezoelectric ignition material. Thermocompression sintered high-density ceramics such as Pb0.8Nd0.2 (Ti0.94Mn0.02In0.04) O3 delay temperature coefficient close to zero. PbZrO3-PbTiO3-Pb (Sbl/2Nb1/2) O3 stability close to the quartz crystal. MnO2, Al2O3 composite added Pb (Znl/3Nb2/3) O3-PbZrO3-PbTiO3 ternary system can obtain high quality factor, high-stability piezoelectric ceramics.
Of this study is PbZrO3-PbTiO3-Pb (Lil/4Nb3/4) O3 ternary, discuss the following questions: First, PZ (PbZrO 3 or), PT (PbTiO3), Pb (Lil/4Nb3/4) O3 synthesis conditions; second is the sintering temperature of PZT solid solution structure; Third PbO on the PZT composition and performance control; Fourth Li2O, Nb2O5, Cr2O3 doping modification; affect PZT ternary piezoelectric ignition material properties the instability factors; six lead-free piezoelectric ceramic materials trends. The focus is to summarize the most reasonable formulation of ternary and optimum conditions.
1 Materials Preparation process
Selected Pb (Lil/4Nb3/4) O3-PbTiO3-PbZrO3 as ceramic base side, and then add the Li2O, Nb2O5, Cr2O3.
Determination of the proportion of triples:
(1) Fixed PbZrO3/PbTiO3 mass proportion, i.e. m (ZrO2) / m (TiO2) = 53/47, changing the content of the third element, the sintering performance changes little, relative dielectric constant to increase a lot, the selected third The optimum ratio of the group element is 2.
(2) to ensure that the third group was 2% (molar ratio), observed m (Zr) / M (Ti) of the impact, found m (ZrO2) / m (TiO2) = 53/47, the best performance .
Determine the composition of the chemical formula: [(PbZrO3) 0.53, (PbTiO3) 0.47] 0.98 [Pb (Lil/4Nb3/4) O3] 0.02.
Incorporation molar ratio were 0.375% Li2O, 1.125% Nb2O5, 0.5% Cr2O3, used to improve the performance of the material.
This paper were synthesized by the groups, and then mixed into a secondary firing blanks sintered. Sintering apparatus is shown schematically in Figure 1. The process is:
Ingredients (I) → grinding → drying → synthesis → X-ray analysis → body → grinding → Ingredients (II) → grinding → → drying pressing sintering processing → cleaning → coated Ag electrode → polarization.
Each element composition ingredients: PbO and ZrO2, PbO and TiO2 equimolar weighing, r (PbO): r (LiCO3): r (Nb2O5) = 8:1:3; particle diameter less than 3 μm ; oven temperature less than 110 ℃, drying and then crush. 3 synthesis, synthesis conditions: temperature of 700 ℃ to 900 ° C, 1 h for 2 h; of Pb (Lil/4Nb3/4) O3 synthetic choose from 500 ℃ to 700 ° C, time 1 h ~ 2 h phase analysis to check the firing situation 60 mesh size requirements; Formula ingredients added in proportion to the additives.
The preparation of the binder: binder is an aqueous solution of the mass fraction of 5% (C2H4O) x (polyvinyl alcohol); evenly mixed; proportion of 8% of the added binder, molding pressure of 500 kg/cm2; pressure good The wafer sample was placed in the apparatus of Figure 1, sintered, the sintering temperature is 1 100 ° C to 1 300 ° C, time 1 h to 2 h, the bulk density was measured to determine the optimum sintering temperature and the PbO content. Mill made of standard size; placed in deionized water and boiled, and then rinsed with deionized water and dried; AgNO3, decomposition or Ag powder sintering method; DC electric field of the sump.
Results and discussion
2.1 PbZrO3 and PbTiO3 and Pb (Lil/4N3/4) O3 synthesis conditions choice
Group element synthesis:
ZrO2 + PbO = PbZrO3
TiO2 + PbO = PbTiO3
Li2CO3 +8 PbO +3 Nb2O5 = 8Pb (Lil/4Nb3/4) O3 + CO2 ↑
The reaction is a solid-phase sintering reaction, raising the temperature, the reaction will be carried out more completely, but the higher the temperature, the denser the structure of the synthetic product, the greater the intensity, is not easy to crush, impact experiments Next, so to choose an the proper temperature. Product of synthesis temperature sintering in Table 1.
(1) on the 750 ℃ ​​PbZrO3 sintering discussion: phase analysis by X-ray was known in 750 ℃ ​​PbZrO3 has most of the formation.
(2) 800 ℃ PbZrO3 sintering discussion: phase analysis by X-ray was known at 800 ℃ without PbO and ZrO2, or minimal content.
Sintering properties of the reference product, 750 ℃ ​​~ 800 ℃ the PbZrO3 ideal sintering temperature, holding time 1 h.
(3) the PbTiO3 sintering discussion: From Table 1 it can be seen, of PbTiO3 a sintered PbZrO3 similar, and therefore determine its synthesis conditions: 700 ° C to 750 ° C for 1.5 h incubation.
(4) Discussion: 600 ℃ Pb (Lil/4Nb3/4) O3 sintered phase analysis by X-ray was known product contains more Nb2O5 is Pb (Lil/4Nb3/4) O3 or even does not occur. That the product content is very low, the sintering is far from complete. Instructions the O3 reaction of the of 600 ℃ synthetic Pb (Lil/4Nb3/4) is not complete, you need to raise the temperature sintering refer to Table 1, to 700 ℃ to 750 ℃, can still study the appropriate conditions for the synthesis of 700 ℃ to 750 ℃ The incubation time was extended to 2 h.
2.2 synthetic Pb (ZrTi) of O3 selection
According to the density of the relationship between the firing temperature (see Figure 2), select the density reaches a great temperature 1 270 ° C as the best.
As can be seen from Figure 2:
(1) The bulk density is not reached before the optimum temperature is increased with increasing temperature, the starting heating of the porcelain blanks, porosity, or open, when the binding between the particles is not therefore very low density. Heated, so that forming a bond between the particles, the stomatal slowly closed, when the density is somewhat increased, this is the rising portion of the curve.
(2) the bulk density extremum. As the temperature rises, the overwrapped gas diffusion along the grain boundaries, so that the density is further increased, and can reach more than 95% of the theoretical density. If excessively heated, the volatile content of the heavier elements of Pb increases while forming a honeycomb-shaped porous structure, and the result that the density decreases. The maximum value of the density is formed between the density rising trend to a decreasing trend.
(3) addition to the firing temperature and bulk density, and additives. LiCO3 can significantly reduce the firing temperature of the composition.
2.3 Sintering parameters and performance testing
Tables 2 and 3 respectively for the sintering parameters and performance testing results.
(1) changes in bulk density. The literature values ​​of the bulk density of the material is still not big enough. PbO content and the distribution of the density has a significant effect, A. I. Kingon the form of lead acetate, adding 2% excess of PbO, and found that the density is increased by a few percent. This experiment was to add 3% to 5% excess of PbO, but decreased density, possible reasons: First, lead acetate uniformity better than the distribution of PbO; PbO excess caused by changes in the composition of the material, resulting in a reduction of the sintering temperature, These will eventually lead to a decrease in density.
(2) the relative permittivity changes. Compared with literature values, the relative permittivity is slightly different, εr = Ct/ε0A, the key to improve the capacitance C, the composition of the material itself to determine the size of εr, so concerned with the process of factors of the material preparation. Density low porosity, the dielectric constant of air is very small, causing a decline in the value of the dielectric constant of the entire medium, if the electrode and the contact of the material does not close, the presence of tiny pores in the middle, the bubble will cause the value of capacitor C decreases, the dielectric constant of the last calculated also decreases.
(3) the change in dielectric loss. Dielectric loss by the polarization loss, leakage current loss and medium uneven wear and tear composition. Under the high temperatures and the strong electric field, leakage loss is large, B and A2, due to the low dielectric constant, the larger the electric field in the polarization voltage, so there is leakage. The relatively poor uniformity of the material in the medium of its dielectric loss is also large, the worse the performance of its material.
The polarization electric field can cause dielectric breakdown, is likely to be due to the pores, cracks and other physical defects. Breakdown field strength ceramic thickness, shape and electrode have relations. Raising the temperature of the ceramic internal electrical domain ease of rotation, the desired polarization electric field strength can be reduced. As can be seen from the above, a breakdown, leakage sample density is smaller.
In summary, the density is an important indicator of the performance of the material, the density values ​​close to the literature value of the D series of performance is better, and the density as determined by the composition and the firing process, and therefore to improve the process conditions, the difference of the density can be further reduced. Add binder press molding, firing the previous increase of one step: Low 110 ℃ volatile binder, reducing the preform organic composition, the porosity can be further reduced in the sample, and to increase the final density, reducing C conductive possibilities.
Of 2.4 pairs piezoelectric performance discussion
As ignition element of a piezoelectric ceramic, requirements: first, in a small external force, resulting in high discharge voltage and discharge energy; Second, good mechanical strength, and multiple impacts not broken; third, good stability, and more times after impact, stable output voltage, long life.
Wtot = ■ εr · g332, require larger εr · g332, g33 = d33 / (εr · ε0), εr is too large, it will lead g33 decline, so usually requires the εr not small at a certain value, try to increase d33.
Piezoelectric ceramic performance data from Table 4 shows that:
(1) In addition to the leakage of B, A2, piezoelectric strain constant d33 at 240 or more piezoelectric voltage constant at 30 or more, compared with similar products at home and abroad, quite superior performance. In this paper, the material of D2 has reached the requirements of the piezoelectric ceramic material, the other can also be seen from the preferred value, the system under study, to further improve the process conditions, the piezoelectric properties of the materials are expected to be further improved.
(2) on the impact properties of the test has not been carried out, but is now generally believed that the incorporation of Cr3 can improve the aging resistance of the piezoelectric ceramic material to enhance the mechanical quality factor Qm, temperature, time stability and impact resistance. So, in order to improve performance, mainly to increase εr and (d33) in the process improvement measures are proposed:
First, required to further improve the purity of raw materials, require finer particles, the fine particles is used to ensure the uniformity of the microscopic structure. Second, mixed, not only for the synthesis is, higher requirements for sintering. To achieve the above two requirements, the process can be used coprecipitation manufacturing fine powder to obtain a purer, finer, more uniform raw material. Third, additional binder low temperature volatile process. Fourth, to determine the appropriate heating rate, especially in the final sintering stage. Fifth, precise control of the PbO atmosphere during the sintering of the sample. Such as the use of certain PbO-containing material covering above the sintered samples in order to reduce the amount of volatilization of PbO. Sixth, instead of excess PbO excess lead acetate was added to the raw materials, is expected to further increase the density of the material.
2.5 Summary
Each group of $ Synthesis conditions:
PbZrO3: 750 ℃ ​​~ 800 ℃ incubated for 1 h;
PbTiO3: 700 ℃ ~ 750 ℃ ​​incubated for 1 h;
Pb (Lil/4Nb3/4) O3: 700 ℃ ~ 750 ℃ ​​for 2 h.
Synthesis of lead zirconate titanate conditions: 1 270 ℃ insulation 1 h.
PbZrO3-PbTiO3-Pb (Lil/4Nb3/4) O3-doped sample firing conditions: 1 260 ℃ was incubated for 1 h.
Firing samples around the need to maintain a PbO atmosphere, and strictly control the ingredients.
In this paper, the system samples has reached or exceeded the level of the piezoelectric ignition material, but the selected system still has the potential to be tapped. As long as the process is suitable, and completely can be further improved.
3 lead-free piezoelectric ceramics outlook
Piezoelectric ceramic material widely used in daily life, industrial, military and medical, and a large class of information has become an irreplaceable functional materials. However, large-scale use of piezoelectric ceramic materials is lead-based piezoelectric ceramic material, the PbO (Pb3O4) accounted for about 60% of the total mass of the raw materials to 70%. These lead-free piezoelectric ceramic materials in the production, use and waste treatment process will bring serious harm to humans and the ecological environment. Prevent environmental pollution in order to protect the Earth and humanity's ecological space, research and development lead-free piezoelectric ceramic material is a subject of great social and economic significance.
Lead-free piezoelectric ceramic materials are mainly the following system: BaTiO3 based lead-free piezoelectric ceramics; (Na0.5Bi0.5) TiO3 in-(K0.5Bi0.5) TiO3, (Bi4Ti3O12) system lead-free piezoelectric ceramic materials; niobium salt-type lead-free piezoelectric ceramics and bismuth layered structure of lead-free high-temperature materials. By doping BaTiO3 piezoelectric properties is only moderate, it is difficult to significantly improve the performance, and the Curie temperature is not high, so its application is greatly limited. The niobate system piezoelectric ceramic frequency devices candidate materials, the layered structure of the bismuth-based lead-free piezoelectric ceramics, mainly used in high temperature piezoelectric sensor.
piezoelectric ceramic of Department of xNa0.5Bi0.5TiO3-(1-x) K0.5Bi0.5TiO3, tripartite ~ Quartet morphotropic phase boundary at x = 0.81, where ceramic radial coupling coefficient and elastic compliance coefficient maxima . Having a higher thickness of the electromechanical coupling coefficient K (0.46 ~~ 0.48) in the sodium-rich region near the phase boundary, the high-frequency constant Nt and a smaller dielectric constant, is a class excellent anisotropic high frequency ultrasonic transducers material. Less research in the area of ​​K-rich material in the stability of the tetragonal and K0.5Bi0.5TiO3 high depolarization temperature (270 ℃), materials structure and properties of potassium-rich area has practical value and theoretical significance. In addition to the Bi4Ti3O12 system the doping modification may also be high-voltage ceramic.
Lead-free piezoelectric ceramics future should focus on the conduct the communication frequency devices and high-power technology development of the material. According to reports, the University of Tokyo, Japan, Professor Komiyama Teng, doped bismuth titanate system V, W can be manufactured at unbeatable performance PZT piezoelectric ceramics.


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