Study Of Single-Sample Characterization Method For Full Matrix Parameters Of Piezoelectric Materials

As an electromechanical conversion functional material,piezoelectric materials have been widely used in many fields such as information and communication,industrial au-tomation,and medical diagnosis.In recent years,with the expanding application of piezo-electric materials,the comprehensive characterization of piezoelectric material properties has become particularly important to provide a complete understanding of the electrome-chanical properties of the material on the one hand and to make accurate predictions of the material applications and device performance on the other.Full matrix parameters are a set of parameters that can completely describe the electromechanical properties,including elastic constants,dielectric constants,piezoelectric constants,and electrome-chanical coupling coefficients.However,due to the strong anisotropy of piezoelectric materials,samples with low symmetry possess a large number of independent parame-ters.At the same time,the properties of ferroelectric materials,the most widely used piezoelectric materials,are extremely dependent on their polarization state,geometry,etc.Therefore,traditional multi-sample testing methods often encounter the problem of significant differences in results between different samples when testing the same param-eters.Single-sample testing is an effective solution to this problem.Still,all existing single-sample testing methods suffer from the issues of convergence of the inversion results to local solutions and time-consuming and challenging inversion processes due to large deviations in the initial parameter settings.Based on the above problems,this paper proposes a classification method to enhance the sensitivity of parameters based on the ultrasonic impedance spectroscopy inversion method,designs a sample size through theoretical analysis,and proposes a measurement method that can provide high precision initial values as follows.First,this paper characterizes the full matrix parameters of tetragonal lead niobium-magnesite-lead titanate single crystal（PMN-0.37PT）polarized along the direction of[001]_Cusing ultrasonic impedance spectroscopy.It demonstrates that the test results of ultrasonic impedance spectroscopy can more accurately describe the impedance charac-teristics of the material.A parameter classification method based on the relationship between vibration modes and parameters is proposed for parameters that are insensitive to impedance spectra in the characterization process of ultrasonic impedance spectroscopy.And based on this classification method,the inverse values of parameters with poor sensitivity to impedance spectrum are obtained by combining the inversions of[001]_Cand[100]_Cdirections.Compared with the directly measured low-frequency dielectric constant,the calculated parameters of the full-parameter inversion values show a higher agreement and a better match in the simulated impedance spectrum and the test spec-trum.Finally,the full matrix parameters of lead-free potassium tantalum niobate（KTN）single crystals were successfully obtained using this method.The variable temperature measurement of the full matrix parameters was realized.Secondly,to address the high initial parameter accuracy requirements in the ultra-sonic impedance spectroscopy inversion method,this chapter proposes a single-sample full-matrix parameter characterization methods based on the full-matrix parameter rela-tionship.The method is designed to optimize the sample size through theoretical analysis to meet the measurement requirements of resonance method,quasi-static method,echo sound velocity and parallel plate capacitance at the same time,thus obtaining sufficient initial parameter values from a single sample.In addition,the method uses the functional relationship between the full matrix parameters to derive the expressions of the parame-ters from being measured with respect to the measured parameters.It obtains the optimal solutions for the unknown parameters using mathematical optimization methods,which provide high-precision initial parameter values for the impedance spectrum inversion process.The simulated impedance spectrum of the parameters obtained by this method exhibits a high degree of agreement with the test spectrum,thus solving the problems of mode mismatch and convergence to a local solution caused by excessive deviation of the initial parameters.Finally,in this paper,the full-matrix parameters of new small-size Li,Ta,Sb,and Mn elements co-doped potassium sodium niobate（KNNLST:Mn）single crystals were characterized using the above method.The experimental results show that the method can achieve the full-matrix parameter measurement of new small-size piezoelectric materials.It has more advantages for measuring the properties of small-size materials with poor component homogeneity.Meanwhile,the full-matrix parameter test results show that the KNNLST:Mn single crystal has both a high piezoelectric strain constant d₃₃and a large piezoelectric voltage constant g₃₃,and thus has a high potential in the field of energy harvesting.Finally,the excellent energy harvesting performance is demonstrated by experimental tests,which have high potential applications in application scenarios where elemental lead is strictly restricted in the human body,such as pacemakers.