Jae-Gwan Park

Piezoelectric properties in PMN–PT relaxor ferroelectrics with MnO2 addition

Abstract The temperature dependence of piezoelectric properties in the PMN–PT relaxor ferroelectric system with MnO 2 addition was studied in the temperature range from −40 to 30°C. Samples were poled at −40°C and the piezoelectric properties were measured by resonance–antiresonance method. Q m increased by increasing the doping contents of Mn. When 0.5 wt.% MnO 2 was doped, Q m increased from 95 to 480. From the experimental results, it is predicted that Mn behaves as an acceptor and a domain pinning element. The effects of MnO 2 observed in PZT-based normal ferroelectrics were also confirmed in PMN-based relaxor ferroelectrics.

Local cationic ordering behavior in Ba(Mg1/3Nb2/3)O3 ceramics

Abstract We have studied the effect of sintering temperature and time on cationic ordering in BaMg 1/3 Nb 2/3 O 3 (BMN) microwave dielectric ceramics using transmission electron microscopy. Energy-dispersive spectroscopy was used to analyze the local chemical compositions. It is revealed that according to the sintering conditions the BMN ceramics show diverse local cationic ordering behavior, such as the development of domain twinning and ‘core-shell’-structured grains and the formation of local disordered domains, although generally having 1:2 cation ordering structure. The disordered structure is formed in Mg-excess regions. Such local chemical variation seems to be caused by the formation of BaNb 2 O 6 second phase in the neighboring grain boundary. Microwave dielectric properties of the ceramics will also be discussed in relation to the structural variation.

Effect of microstructure on the microwave properties in dielectric ceramics

Abstract Electromagnetic simulation of the quality factor measurement was compared to the measurement with a network analyzer. Scattering matrix S 21 obtained from the network analyzer was compared to the S 21 obtained from the simulation. From electric field distribution, the dominant resonant TE 01δ mode could be easily determined. The effects of the pore and the conductive inclusion inside the dielectric were investigated. The quality factor decreased with the pore and the second phase in the dielectrics. The decrease of quality factor is more significant when dielectric have conductive inclusions inside the dielectric. Due to the limitations in computer resources and analysis time, the size of the inclusions inside the dielectrics in simulation are not actual size.

Analysis of defect formation in Nb-doped SrTiO 3 by impedance spectroscopy

The thermal activation energies for conduction of Nb-doped SrTiO 3 grains and grain boundaries have been investigated by impedance spectroscopy. First, to observe the effect of electrode/SrTiO 3 bulk interface, the varied impedances of SrTiO 3 single crystal were measured with temperatures. The activation energy of an electrode/bulk interface was determined to be 1.3 eV, whereas that of bulk was 0.8 eV. When the impedances of Nb-doped SrTiO 3 ceramics were measured, it was suggested that the more precise impedance values of a single grain and a single grain to grain junction be obtained using a microelectrode method. The activation energies for a grain, a grain boundary, and an electrode/bulk interface were determined to be about 0.8, 1.3, and 1.5 eV, respectively. From these measured results, it was suggested that the activation energy, 0.8 eV, measured in grain was originated from oxygen vacancies and the activation energy, 1.3 eV, in grain boundary was from strontium vacancies.

Effect of MnO addition on the electrical properties of Nb-doped SrTiO3 varistor

Abstract The effect of MnO addition on the microstructure and electrical properties of Nb-doped SrTiO 3 varistors was investigated by using scanning electron microscopy, I–V and C–V measurement, complex-capacitance plane analysis, and impedance spectroscopy. It was observed that the grain size and dielectric constant of the ceramics decreased with increasing MnO content. The non-linearity coefficient defining varistor characteristics increased significantly from 5 to 43 as the MnO content increased from 0 to 0.03 mol%. The addition of MnO brought on changes in the grain boundary electronic states: as the MnO content increased, the potential barrier height and the breakdown voltage increased but the charge carrier concentration decreased. This behavior was explained through the effect of Mn ions substituting for Ti sites. The substitutional defect Mn Ti ′′ (or Mn Ti ′), formed in both grain boundary region and grain interior, acts as an electron-trap.

Effect of MnO2 addition on the piezoelectric properties in Pb(Mg1/3Nb2/3)O3 relaxor ferroelectrics

Abstract The effects of MnO 2 addition on the piezoelectric properties in Pb(Mg 1/3 Nb 2/3 )O 3 relaxor ferroelectrics were studied in the ferroelectricity-dominated temperature range from −40 to 30°C. Dielectric, piezoelectric, and electrostrictive properties were examined to clarify the effect of MnO 2 addition. As an added amount of MnO 2 increases, the dielectric constant decreases and the mechanical quality factor increases in Pb(Mg 1/3 Nb 2/3 )O 3 . From the experimental results, it has been found that Mn behaves as a ferroelectric domain pinning element.

Influence of Defect Segregation on the Electrical Properties of Nb-doped SrTiO3 Grain Boundary Layer

The influences of defect segregation on electrical properties were investigated for a single grain boundary layer in Nb-doped SrTiO3. The electrical properties were compared with those of a grain embedded with a platinum wire. On the basis of the current–voltage (I–V) characteristics, it was found that the grain boundary of Nb-doped SrTiO3 could be presented as a back-to-back double Schottky model. The segregation of defects, strontium vacancies, in grain boundary was suggested from the results of currnet–time (I–t) measurement, impedance spectroscopy, and capacitance–voltage (C–V) measurement. It was also postulated that the space charge originating from this defect segregation forms the potential barrier. The activation energy for conduction through a grain boundary changed with applied voltage from 1.60 eV to 0.97 eV.

Computer Simulation on the Relations between the Porosity and the Microwave Properties in Dielectric Ceramics

Effects of porosity on the microwave properties in dielectric ceramics were studied by the electromagnetic simulation. Scattering matrix S21 obtained from the network analyzer was compared to the S21 obtained from the simulation. From electric field distribution, the dominant resonant TE01 mode could be easily determined. The effects of the porosity inside the dielectrics on the microwave properties were investigated. Quality factor decreased with the porosity and the pore size.