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You are here: Home / News / Basics of Piezoelectric Ceramics / Piezoelectric ceramic mechanical quality factor Qm and its temperature stability

Piezoelectric ceramic mechanical quality factor Qm and its temperature stability

Views:1     Author:Site Editor     Publish Time: 2019-10-10      Origin:Site

Piezoelectric ceramics have occupied a considerable proportion in the field of electronic materials and have been widely used. For different applications of piezoelectric ceramics, the requirements for piezoelectric parameters are also different. For example, in power transducers - liter On the piezoelectric transformer, the boost ratio of the device is proportional to the mechanical quality factor Qm of the PZT material. The piezoelectric material with high Qm value has a high boost ratio and improved working efficiency, but in the low temperature region, the Qm value is easily deteriorated. As a result, the boost ratio is reduced, the working efficiency of the transformer is reduced, and the performance stability is affected. The piezoelectric ceramic material is having a large Qm value and good temperature stability can stabilize the device performance in the application of the power transducer. To improve work efficiency and widen the scope of work. On the other hand, if you want to increase the bandwidth, you need to lower the Qm value. Therefore, to understand the physical nature of Qm, further explore the factors affecting the stability and size of Qm temperature. In practice, the Qm value of the piezoelectric material can be adjusted, and the temperature stability can be improved, thereby meeting the different requirements of the piezo round disc transducer and expanding the application range .

The nature and characterization of Qm

The mechanical quality factor Qm value characterizes the energy consumed by the piezoelectric body to overcome internal friction during resonance. It is defined as: Qm = 2π .The mechanical energy stored in the vibrator during resonance resonates the energy of the mechanical loss of the vibrator per week. The factor Qm value reflects the mechanical loss of the piezoelectric material. The smaller the mechanical loss, the larger the Qm value. When is calculating the Qm value of the material, the following approximate formula is used for the equivalent circuit diagram of the piezoelectric vibrator:
Qm = 1/ 4π( C0 + C1) R1Δf ,

Where C0 is the static capacitance of the piezoceramic crystal quartz rod, R1 is the equivalent resistance of the vibrator resonance, C1 is the dynamic capacitance of the vibrator, and Δf is the difference between the resonant frequency fr of the vibrator and the antiresonant frequency fa. Generally, the transmission line method is used. Δf, R1, etc. are obtained, and then Qm is calculated. From the thermodynamic free energy function, the physical source of Qm value is discussed, and the formula is derived: and the Q-1m value is experimentally verified to be proportional to the dielectric loss. In addition, in the experiment on the basis of this, the Qm value is quantitatively expressed as a function of the space charge amount and the volume resistivity, and the empirical formula is obtained: Qm = (800 lgρ - 7 500) { ( Ps - Pi) / Ps - 0. 2} + 250. Where ρ is the bulk resistivity of the material, Ps is the saturation polarization value, and Pi is the polarization value determined on the hysteresis loop obtained immediately after the alternating electric field is applied, ( Ps - Pi) / Ps is the equivalent and the amount of space charge. When ( Ps - Pi) / Ps ≥0. 2 , ρ ≥109Ω·cm, it is in the good agreement with the experimental results. Both theoretically and experimentally, the essence and characterization of Qm have been carried out. In-depth discussion. This helps us to further study the size of Qm and its temperature stability.

Measurement to improve Qm value and temperature stability

Adjust material ratio
Since the 1960s, based on the PZT piezoelectric ceramic material , the ternary and quaternary piezoelectric ceramic materials have been developed and studied. It is found that the multi-component materials can not only obtain superior pressure. Electrical properties and temperature stability is better. PZT-based ceramic materials at the quasi-homophase boundary, due to the transition zone of ferroelectric tetragonal phase to ferroelectric tripartite phase transition, lattice structure relaxation, spontaneous polarization is easy to turn piezoelectric activity at the same time, the mechanical loss increases, the Qm value is small and the stability is not good. Therefore, different material ratios can be selected according to the requirements of various piezoelectric devices. For example, materials requiring high Qm are selected to leave. For the material formulation at the boundary, if the Qm temperature stability is required, it is necessary to select the material formula in the phase region near the quasi-homogeneous phase boundary.

Doping modification
In addition to changing the ratio of binary, ternary, and quaternary systems, the Qm value of PZT material piezo ceramic disc can be improved to some extent, and doping in the main component of the material can further improve the material properties, including the magnitude and temperature stability of the Qm value. In the study of the piezoelectric properties of hard PZT materials by manganese doping, it was found that Mn can adjust the Qm value due to the change of valence in Mn. In addition, in the quaternary system Pb ( Mg1/ 3Nb2/ 3) (Mn1/ 3Nb2/ 3) TiZrO3 piezoelectric material is doped with a certain amount of CeO2, and the maximum relative deviation of Qm can be obtained in the range of -20-55 °C (relative to the Qm value at 25 °C) | δ( Qm) m | decreases from 42 % to 33 %; the maximum relative offset of a certain formulation is almost unchanged when Sr is doped. Doping in Pb (Mn1/ 3Sb2/ 3) O3 materials Sn improves the low temperature stability of Qm. There are two arguments for doping that explain the temperature stability of Qm. It is said that the deterioration of the electrical properties of piezoelectric materials is often due to microcracks inside the material. Caused by growth. After the doping to enter the crystal lattice, internal compressive stress is generated, which inhibits the growth of microcracks to some extent. In order to avoid the increase of the resonance resistance of the material and ensure the temperature stability of Qm. Another way of saying that the structure of the doping change material includes grain size, grain boundary condition, lattice constant, density, etc., resulting in macroscopic physical properties. thereby improving the temperature variation of the Qm value. Usually adding hard additives such as Eu, Yb, Al2O3, MgO, etc. to increase the Qm value; while adding soft additives such as Nb2O5, La2O3, Ta2O5, etc., lower the Qm value, And Qm value temperature stability is better than hard doping.

Process Optimization
The preparation process of piezo ceramic materials, especially the preparation, calcination, sintering and artificial polarization of powders, directly affects the density, grain size and piezoelectric properties of the samples. At present, the temperature stability of Qm is improved from the preparation process. There are certain difficulties, but the size of the Qm is adjusted from the preparation process. Many researchers have been involved. For example, Cr3 + ion doped Pb (Mn1/ 3Nb2 / 3) TiZrO3 ceramics are very sensitive to sintering temperature, When the sintering temperature is increased, the piezoelectric properties are hardened. Therefore, the Qm value can be flexibly controlled by changing the sintering temperature. Kawasaki compares the doping with the conventional powder preparation by thermal injection doping. It is discussed that some impurity ions such as Fe3 + will increase the Qm value by the thermal injection method, while some ions such as Cr3 + reduce the Qm value. The process is optimized to prepare the ceramic material with excellent performance, which is to adjust the Qm value.

Theoretically, the material ratio and doping modification are studied. In practice, the improvement of the process is to adjust the Qm value of the piezoelectric ceramic material and improve the temperature stability, so that the piezoelectric ceramic material can be more widely obtained. An effective method of application.

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