This paper concerns the homogenization problems for porous piezocomposites with infinitely thin metalized pore surfaces.To determine the effective properties,we used the effective moduli method and the finite element ...This paper concerns the homogenization problems for porous piezocomposites with infinitely thin metalized pore surfaces.To determine the effective properties,we used the effective moduli method and the finite element approaches,realized in the ANSYS package.As a simple model of the representative volume,we applied a unit cell of porous piezoceramic material in the form of a cube with one spherical pore.We modeled metallization by introducing an additional layer of material with very large permittivity coefficients along the pore boundary.Then we simulated the nonuniform polarization field around the pore.For taking this effect into account,we previously solved the electrostatic problem for a porous dielectric material with the same geometric structure.From this problem,we obtained the polarization field in the porous piezomaterial;after that,we modified the material properties of the finite elements from dielectric to piezoelectric with element coordinate systems whose corresponding axes rotated along the polarization vectors.As a result,we obtained the porous unit cell of an inhomogeneously polarized piezoceramic matrix.From the solutions of these homogenization problems,we observed that the examined porous piezoceramics composite with metalized pore boundaries has more extensive effective transverse and shear piezomoduli,and effective dielectric constants compared to the conventional porous piezoceramics.The analysis also showed that the effect of the polarization field inhomogeneity is insignificant on the ordinary porous piezoceramics;however,it is more significant on the porous piezoceramics with metalized pore surfaces.展开更多
Mn-doped 0.92(K_(0.5)Na_(0.5))NbO_(3)-0.08LiNbO_(3)(0.92KNN-0.08LN)lead-free piezoelectric cer-amics have been prepared by a developed sol-gel routes using Nb_(2)O_(5)as Nb source.Due to thehigh quality of gel precurs...Mn-doped 0.92(K_(0.5)Na_(0.5))NbO_(3)-0.08LiNbO_(3)(0.92KNN-0.08LN)lead-free piezoelectric cer-amics have been prepared by a developed sol-gel routes using Nb_(2)O_(5)as Nb source.Due to thehigh quality of gel precursor,Mn-doped 0.92KNN-0.08LN nanopowders with the mean particlesize about 20 nm were obtained at 500℃.The addition of Mn can promote the densification ofnanopowders effectively at 950℃,and also influences in a pronounced way both the crystal structure and microstructure of the materials.With the increase of the amount of Mn addition,0.92KNN-0.08LN ceramics are transformed from dominant orthorhombic to coexistence of the orthorhombic and tetragonal phases,and the grain sizes are enhanced simultaneously.Optimizedparameters,such as d_(33)=212 pC/N and k_(p)=0.46,were achieved in 0.2 Mn-doped0.92KNN-0.08LN systems,which are good candidate material for lead-free piezoelectric devices.展开更多
基金the framework of the RFBR project 16-58-48009 IND omi and DST.
文摘This paper concerns the homogenization problems for porous piezocomposites with infinitely thin metalized pore surfaces.To determine the effective properties,we used the effective moduli method and the finite element approaches,realized in the ANSYS package.As a simple model of the representative volume,we applied a unit cell of porous piezoceramic material in the form of a cube with one spherical pore.We modeled metallization by introducing an additional layer of material with very large permittivity coefficients along the pore boundary.Then we simulated the nonuniform polarization field around the pore.For taking this effect into account,we previously solved the electrostatic problem for a porous dielectric material with the same geometric structure.From this problem,we obtained the polarization field in the porous piezomaterial;after that,we modified the material properties of the finite elements from dielectric to piezoelectric with element coordinate systems whose corresponding axes rotated along the polarization vectors.As a result,we obtained the porous unit cell of an inhomogeneously polarized piezoceramic matrix.From the solutions of these homogenization problems,we observed that the examined porous piezoceramics composite with metalized pore boundaries has more extensive effective transverse and shear piezomoduli,and effective dielectric constants compared to the conventional porous piezoceramics.The analysis also showed that the effect of the polarization field inhomogeneity is insignificant on the ordinary porous piezoceramics;however,it is more significant on the porous piezoceramics with metalized pore surfaces.
基金supported by the National Natural Science Foundation of China(Grant No.51072008,No.51172006)the Natural Science Foundation of Beijing(Grant No.2102006)the Funding Project for Academic Human Resources Development in Institutions of Higher Learning Under the Jurisdiction of Beijing Municipality,IHLB(Grant No.PHR201008012,No.PHR201007101).
文摘Mn-doped 0.92(K_(0.5)Na_(0.5))NbO_(3)-0.08LiNbO_(3)(0.92KNN-0.08LN)lead-free piezoelectric cer-amics have been prepared by a developed sol-gel routes using Nb_(2)O_(5)as Nb source.Due to thehigh quality of gel precursor,Mn-doped 0.92KNN-0.08LN nanopowders with the mean particlesize about 20 nm were obtained at 500℃.The addition of Mn can promote the densification ofnanopowders effectively at 950℃,and also influences in a pronounced way both the crystal structure and microstructure of the materials.With the increase of the amount of Mn addition,0.92KNN-0.08LN ceramics are transformed from dominant orthorhombic to coexistence of the orthorhombic and tetragonal phases,and the grain sizes are enhanced simultaneously.Optimizedparameters,such as d_(33)=212 pC/N and k_(p)=0.46,were achieved in 0.2 Mn-doped0.92KNN-0.08LN systems,which are good candidate material for lead-free piezoelectric devices.
