Hydrostatic piezoelectric response characteristics of porous PZT ceramic and composite

Abstract

As piezoelectric ceramic is used in various ultrasonic devices and sensors, simulation-based structure design and performance prediction technology for accurate driving frequency and displacement control are in the spotlight. In particular, in the field of sound navigation ranging, excellent hydrostatic piezoelectric characteristics (Hydrostatic Figure of Merit : HFOM) for underwater sound detection are required. In addition, since it is a field that requires very precise design, accurate measurement of material properties is essential. So far, many efforts have been made to improve hydrostatic properties, and a representative example of the method is a PZT-polymer composite. The principle of the piezoelectric composite is to increase the hydrostatic characteristics by reducing the volume fraction of the piezoelectric body. Since the volume fraction of the piezoelectric material has been reduced on a macroscopic scale, there is a limit to improving the hydrostatic properties of the composite, and material properties including piezoelectric, dielectric, mechanical properties and other properties of the piezoelectric composite are very important in the design of this PZT-polymer composite. However, since variables according to the volume and arrangement of the polymer must be considered, it becomes difficult to accurately measure these material properties when the volume fraction is reduced. In this study, in order to improve the hydrostatic piezoelectric properties, a method for improving the hydrostatic pressure piezoelectric properties through porous synthesis of PZT ceramic of the existing 1-3type PZT-polymer composite was presented by reducing the volume fraction on a micro scale. In addition, a simulation technique was proposed to accurately measure and evaluate material properties for the design of the 1-3 type porous PZT-polymer composite manufactured in this study. Material properties for designing piezoelectric devices include piezoelectric charge constant (eij, dij), permittivity, and elastic modulus. In order to calculate the piezoelectric charge constant (eij), Density functional perturbation theory(DFPT) calculation, which is a kind of first-principles-based Density functional theory(DFT) calculation, was performed. A method of deriving the piezoelectric charge constant (eij) through only crystal structure calculation through crystal structure optimization instead of complicated and time-consuming DFPT calculation was presented by deriving the correlation between the piezoelectric properties obtained through calculation and the piezoelectric ceramic crystal structure. Through this, a cost effective piezoelectric material design method was devised. In addition, the elastic modulus, permittivity, and piezoelectric charge constant (dij) of porous PZT were calculated using finite element analysis-based simulation, and porous ceramic was manufactured using the polymer as a medium for pore formation. The material properties of the porous piezoelectric ceramics were optimized by calculating the displacement according to the electrical input of the material including pores, and the mechanical properties including the elastic compliance were optimized by applying the variable estimation method based on the experimentally obtained impedance spectrum. By utilizing the piezoelectric properties acquired, the hydrostatic piezoelectric properties and electromechanical conversion coefficient of the type 1-3 porous PZT-polymer composite were calculated, and an optimized shape was designed by FEM simulation. The designed piezoelectric composite was fabricated through ceramic injection molding(CIM) method. As a result, a porous 1-3type PZT-polymer composite with HFOM characteristics of 4050(10-15Pa) higher than that of the existing type 1-3 piezoelectric composite was prepared. In addition, this method of optimizing material properties and manufacturing process of porous ceramics can be extended to other types of piezoelectric materials that are challenging to measure piezoelectric properties and shape fabrication