Composition of piezoelectric ceramic material

Different application ranges have different performance requirements for piezoelectric ceramic materials. 1 Perovskite piezoelectric ceramic material, the chemical formula is ABO3, A is a positive ion with a large radius, which can be +1, +2, +3; B is a positive ion with a small radius, which can be +3 , +4, +5, +6. The ionic radius of the three ions A, B and O can satisfy the following relationship to form the ABO3 structure: RA+RO=t√2 (RB+RO, t is a tolerance factor, generally can form calcium between 0.86 and 1.03. Titanium ore structure Typical formulation: (1) 0.99 [PbTiO3 + 0.04 La2 / 3TiO3] + 0.01 MnO2, calcination temperature is 850 ° C, heat preservation for 2 hours, firing temperature is 1240 ° C, heat preservation for 1 hour. ε = 240, Kp=0.096, Qm=1050, Nt=2120 (2) High frequency (30M-100MC) filter porcelain PbTiO3+1wt%MnO2+1wt%Pb3O4ε=150, Kp=0.40, Qm=800~1000, temperature and time Good stability. 3PbTiO3+3.0wt%CeO2++0.3MnO2+2.53wt%Nb2O5,ε=230,Qm=1000.

(1) With the change of Zr:Ti, the Curie point changes almost linearly from 235 °C to 490 °C, and the Tc line is a cubic paraelectric phase with no piezoelectric effect.

(2) Zr: There is a quasi-homogeneous phase boundary near Ti=53:47, the titanium-rich side is the tetragonal ferroelectric phase FT; the zirconium-rich side is the high-temperature trigonal ferroelectric phase FR, the temperature of piezoelectric ceramics transducers rise, and this phase boundary is zirconium-rich The side is inclined and intersects the Tc line at 360 ° C (indicating that the Curie temperature Tc is high near the phase boundary), and the unit cell parameters are abruptly changed near the phase boundary. There is a strong piezoelectric effect near the phase boundary between the tetragonal ferroelectric phase FT and the trigonal ferroelectric phase FR. Kp, ε has a maximum value and Qm has a very small value. The piezoelectric properties of PZT porcelain near the phase boundary are much higher than those of BaTiO3 porcelain. Since the Tc of the PZT porcelain at the boundary is high (360 ° C), KP and ε are both stable within 200 ° C, which is an ideal piezoelectric material. Doping Modification of PZT Porcelain of electronic piezo ceramics transducer. In order to meet different purposes, we need PZT piezoelectric ceramics with various properties. For this reason, we can add different ions to replace the Pb2+ ion at the A site or the Zr4+, Ti4+ ion at the B site. Thereby improving the performance of the material.

Other substitution modified hard substitution modified soft substitution modified heterovalent substitution equivalent substitution doped modified PZT (1) equivalent substitution equivalent substitution means that the radius of Ca2+, Sr2+, Mg2+ is smaller than that of Pb2+ ion The ion substitution of Pb2+ ions results in an increase in the dielectric constant ε of the PZT piezo ceramic disk , an increase in the electromechanical coupling coefficient KP, and an increase in the piezoelectric constant d, thereby improving the piezoelectric properties of the PZT ceramic. The term "soft substitution modification" means that the addition of these additives can reduce the coercive field strength EC by ↓, and the polarization is easy, so that the material properties become "soft" under the action of electric field or stress.

(a) La3+, Bi3+, Sb3+, etc. replace the A-site Pb+2 ion (donor doping); Nb5+, Ta5+, Sb5+, W6+, etc. Substituting B-position Zr4+, Ti4+ ions (donor doping). The properties of PZT porcelain modified by soft substitution have the following changes: the coercive field strength EC decreases ↓, the mechanical quality factor Qm decreases ↓; the dielectric constant ε increases ↑, the dielectric loss tan δ increases ↑, the electromechanical coupling coefficient KP When ↑ is increased, the aging resistance is increased and the insulation resistivity ρ is increased ↑. The reason for this is that their addition leads to the formation of a Pb2+ deficiency. For example, if every two La3+s replace 3 Pb2+, in order to maintain the balance of the electricity price, the number of cations at the A position in the perovskite structure is reduced, and an A vacancy is generated. Due to the absence of Pb2+, the domain motion is made easy, and even small electric field strength or mechanical stress can cause the domain walls to move. 

As a result, an increase in the dielectric constant and the elastic compliance coefficient of Pzt piezoceramic ceramic transducers occurs, and at the same time, dielectric loss and mechanical loss increase, and Qm decreases. Moreover, since the steering of the domains is easy, the number of domains oriented in the direction of the electric field is increased, thereby increasing the polarization, so that the piezoelectric effect is greatly increased, which is represented by an increase in the Kp value. Since the steering resistance of the domain becomes small, the coercive field for reversing the polarization to overcome the resistance is small, and the return line is nearly rectangular. Moreover, due to the absence of Pb2+, the internal stress caused by the 90-domain steering is buffered, so that the residual strain becomes small. In other words, since the domain walls are easily moved, the internal stress of the domains is easily released, so the aging performance is good. "Soft" additives are commonly used modifying additives.

(b) For example, the accepting type underwater acoustic transducer material is often doped with La2O3 and Nb2O5 in order to increase the Kp value and the dielectric constant. Pb0.95Sr0.05(Zr0.52Ti0.48)O3+0.9%La2O3+0.9%Nb2O5, Kp=0.60, ε=2100, Qm=80, good stability, volume resistivity 1012 ohm “soft” additive The amount generally does not exceed 5%. b Hard substitution modification, the so-called "hard substitution modification" means that the addition of these additives can increase the coercive field strength EC, and the polarization becomes difficult, so the material properties become "hard" under the action of electric field or stress.

(a) K+, Na+, etc. substituting A-site Pb2+ ions (acceptor doping);

(b) Zr4+ and Ti4+ ions (acceptor doped) substituted for B at Fe2+, Co2+, Mn2+ (or Fe3+, Co3+, Mn3+), Ni2+, Mg2+, Al3+, Cr3+, and the like.

The properties of PZT porcelain modified by hard substitution have the following changes: Coercive field strength EC increases ↑, mechanical quality factor Qm increases ↑; dielectric constant ε decreases , dielectric loss tan δ decreases ↓, electromechanical coupling coefficient KP decreases Small ↓, the aging resistance is reduced, and the insulation resistivity ρ is reduced.

Ternary perovskite piezoelectric ceramic

By changing the Zr/Ti ratio and incorporating a small amount of additives, although some properties can be improved, due to the wider and wider range of piezoelectric materials, the requirements for materials are getting higher and higher, and only binary systems cannot meet the requirements for use. So there is a ternary system.The so-called ternary perovskite piezoelectric ceramic material refers to a solid solution formed of a composite perovskite compound and lead zirconate titanate.