Advances in the development of low-temperature sintered PZT piezoelectric ceramics are mainly low-melting glass, compounds or compounds which can be solid-solved with PZT piezoelectric ceramics.
4.1 Cooling by adding a low melting point substance
The sintering temperature of the PZT piezo ceramic sensor is lowered by doping the low-melting material PbO·WO3 by the solid phase method. It was found that when the PbO·WO3 doping amount is 0.5 mol%, the pure perovskite phase can be obtained by holding at 900 °C . The best performance of the composition can be obtained by holding at 1100 °C. dielectric constant is 1593, dielectric loss tan δ = 0. 019, piezoelectric coefficient d33 = 363. 5 × 10 pCPN , electromechanical coupling coefficient Kp = 0. 596 , mechanical quality factor Qm = 88. 4. It is found that the low melting point PbO·WO3 completely forms a liquid phase during the sintering process and enters the crystal lattice, which acts as a liquid phase sintering, the sintering temperature and avoids the formation of two phases. the effects of different sintering temperatures on the microstructure and piezoelectric properties of PMS-PZT piezoelectric ceramics. The experimental results show that PMS - PZT ceramics can still form a dense structure at medium and low temperature sintering from 1100 to 1150 °C, and the piezoelectric and dielectric properties are close to those obtained at the optimum sintering temperature (1240°C). This is mainly because PbO and Sb2O5 can form a transition liquid phase at a lower sintering temperature (1100 to 1150 °C), thereby promoting densification of the material and enriching as a secondary phase at the grain boundary. As the sintering temperature increases, they can re-enter the crystal lattice to form a single perovskite structure. The low-temperature sintering of PMN-PZT multi-layer laminated piezoelectric ceramic transformer was studied. By adding Li2CO3 and Bi2O3 as sintering aids in PMN-PZT ceramics, LiBiO2 liquid phase was formed during sintering to reduce PMN-PZT porcelain. The purpose of sintering temperature and Bi3 + (0. 96 ! ) and Li + (0. 74 ! ) replaced Pb2 + ( 1. 18 ! ) and Ti4 + (0. 68 ! ), respectively, and formed Pb vacancies. And the O vacancy has played a dual modification role. The piezo ceramic material can be sintered at a low temperature of 940 ° C, and the density reaches 96% of the theoretical density, and has excellent dielectric and piezoelectric performance parameters. It is added Bi4 Ti3O12 composite oxide as sintering aid to reduce the sintering temperature of PZT (52P48) ceramics. It was confirmed that Bi4 Ti3O12 can form a large amount of liquid phase to promote sintering densification during sintering. others tried to add Li2O to PMN-PZT to form a transition liquid phase to promote sintering, and a sufficiently sintered compact at 950 °C. In addition, liquid phase sintering of PZT can also be achieved by adding MnO2, PbF2, NaF, V2O5, and the like. However, the addition of a low-melting glass or oxide may introduce a second phase, and the presence of too much second phase inevitably leads to a significant decrease in the dielectric constant of the piezo ceramic, and an increase in the dielectric loss tan δ, which must be noted.
3. 2 cooling by forming a solid solution
It is prepared a conventional solid phase synthesis method using Pb0. 94 Sr0. 06 (Ni1P2 W1P2 ) 0. 02 (Mn1P3 Nb 2P3) 0. 07 ( Zr0. Ti0. 49 ) 0. 91 ( 0. 02PNW - 0. 07PMnN - 0. 91PZT) piezoelectric disc crystal. By adding low-melting BiFeO3 to introduce soft doping ions such as Fe3 + and Bi3 + , since the ion size, lattice type and electricity price are not much different from those of PZT piezo crystal phase A, they can be mutually dissolved to form a solid solution. A liquid phase is formed during sintering to promote sintering. At the same time, the introduction of soft ions can also improve the properties of piezoelectric ceramics. When the doping amount of BiFeO3 is 10% (mol), the PNW-PMnN-PZT ceramic sintered at 950 °C has the best piezoelectric properties. It is obtained a ternary compound of PZT-PCN by adding Pb (Cu0. 33Nb0. 67) O3 to PZT by a conventional solid phase method. When the relative content of PCN is 0.08, at 1050 The density of sintering for 2 h can reach 7.8 to 7. 9 gPcm3, which is 98% of the theoretical density. Sintering at 950 °C for 2 h gave better electrical properties: d33 = 473 pCPN, εr = 1636, Kp = 0.64. The authors believe that PCN and PZT form a solid solution, in which the initial melting of CuO contributes to the doping modification of Nb5 + , and the liquid phase formed simultaneously reduces the sintering temperature. Waited for the case where MnO2 is doped with PZT-PZN. When the doping amount of MnO2 is 0.4 wt%, the PZT-PZN ceramic can be completely densified after sintering at 930 °C for 4 h. The best electrical properties available are Qm = 1000, Kp = 0.62, d33 = 330 pCPN. The mechanism is as follows PZT forms a solid solution with PZN, which reduces the sintering temperature and improves the electrical properties of the piezo ceramic. By adding MnO2, it plays the role of thickening and sintering, making the material denser and easier to sinter, and improving the Qm value of the material. Further, a solid solution capable of forming a solid solution with PZT ceramics is BaCu0. 5W0. 5 O3 (BCW) , NaNbO3 [20 ], Sr (Cu1P2 W1P2 ) O3 , BiFeO3 (BF), and the like.These additives not only reduce the sintering temperature, but also maintain and improve their performance, which is of great significance for energy saving and environmental pollution reduction.
In general, improperly lowering the sintering temperature of the piezoceramic tube transducer material results in a decrease of performance. Therefore, while the temperature is greatly reduced, the density and good performance of the ceramic body can be ensured to achieve the low temperature sintering of the piezoelectric ceramic material. Of course, low-temperature sintering is not only achieved by a single route, but requires a combination of various methods, coordination, and long-term complement to achieve the best results. Due to the simple process of liquid phase sintering, low cost, and good performance of piezo ceramics at lower temperatures, it has become a hot research topic at home and abroad, and has broad application prospects in industrial production. At present, in order to reduce the cost of preparing multilayer piezo ceramic chip devices and realize the purpose of using co-fired internal electrodes of silver and copper as chip devices, it is particularly important to study the low-temperature sintering technology of PZT piezoelectric ceramics..