Papers by Author: Muangjai Unruan

Abstract: The fabrication of lead-free (1-x)Bi_0.5Na_0.5TiO₃ - xKNbO₃ or (1-x)BNT-xKN ceramics where x = 0.00, 0.05, 0.10, and 0.15 was carried out by the modified two-step mixed oxide method. The effects of KNbO₃ on structure, piezoelectric and ferroelectric properties were systematically investigated. XRD results revealed that the (1-x)BNT-xKN ceramics with low KN content of x less than 0.05 contained ferroelectric phase with a rhombohedral symmetry while the ceramics with x = 0.05 possessed pseudocubic structure. The higher KN content (x ≥ 0.10) ceramics had symmetries rhombohedral structure. At room temperature, the highest P_r and low E_c were obtained when the composition of x = 0.05. Moreover, the results showed the moderate KN addition could enhance the piezoelectric response. The d₃₃ of 0.95BNT-0.05KN reached as high as 125 pC/N.

Abstract: Effects of perpendicular compressive stress on the ferroelectric properties of ceramics in PZT-PZN system were investigated. The (1-x)Pb(Zr1/2Ti1/2)O3-xPb(Zn1/3Nb2/3)O3 or (1-x)PZT- (x)PZN (x = 0.1-0.5) ceramics were prepared by a conventional mixed-oxide method. The ferroelectric properties were measured under compressive stress applied perpendicular to an electric field direction at stress levels up to 90 MPa using a compressometer in conjunction with a modified Sawyer-Tower circuit. It was found that with increasing compressive stress the area of the ferroelectric hysteresis (P-E) loops, the maximum polarization (Pmax), and the remanent polarization (Pr) decreased, while the coercive field (Ec) remained relatively constant. These results were interpreted through the domain switching, clamping of domain walls and de-poling mechanisms.

Abstract: Apart from aging effect, barium titanate ceramics usually subjected to the mechanical loading when it is used in electronic device. Thus, it is very interesting to investigate the influence of various compressive stresses on ferroelectric aging behavior of Ba(Ti0.99-xFe0.01Nbx)O3 , x=0.005-0.015. In this study, the P-E hysteresis loops were observed by using compressometer in conjunction with a modified Sawyer-Tower circuit. The stress level was varied from 0 to 185 MPa. The results showed that the dissipation energy, saturation polarization (Psat), remnant polarization (Pr) and the coercive field (Ec) decreased with increasing of stress. The aging behavior was still observed in acceptor-dominant of hybrid doped ceramics. The aging was also enhanced under application of the external stress. The explanation based on the defect-dipole and domain-reorientation processes was discussed.

Abstract: In this study, a room temperature aging behavior of Ba(Ti0.99Fe0.01)O3 was investigated. It was found that the dielectric constant decreased with time and ferroelectric P-E hysteresis loops became constricted loops after aging. Moreover, the room temperature aging behavior under various stresses was also observed. It was found that the relative changes of dielectric constant with time of Ba(Ti0.99Fe0.01)O3 ceramics under stress were lower than those under the stress-free condition. For P-E hysteresis loop measurement, it can be observed that P-E hysteresis loop of Ba(Ti0.99Fe0.01)O3 ceramics became constricted loops and remanant polarizations (Pr), saturated polarizations (Ps) were decreased after aging under all stress levels. These results suggested that the applied stress may partly clamp the domain wall motion, and altered the aging behavior of the ceramics.

Abstract: Lead-free, bismuth sodium titanate-potassium sodium niobate piezoelectric ceramics (Bi1/2Na1/2)TiO3-(K1/2Na1/2)NbO3 have been prepared by a conventional mixed-oxide method via vibro-milling technique. The (K1/2Na1/2)NbO3 (KNN)-based compositions with a morphotropic phase boundary (MPB) have shown greater advantages over another typical lead-free piezoelectric candidate material system, (Bi1/2Na1/2)TiO3 (BNT)-based MPB materials. More importantly, when used this type of material is often subjected to self-induced or external stress. It is, therefore, of interest to investigate influence of stress on properties of the ceramics. In this study, the influences of compressive stress on the dielectric properties of BNT-KNN ceramics were investigated. The dielectric properties were determined under compressive stress applied parallel to electric field. The results indicate significant changes of both properties with the imposed compressive stress. The results were explained in terms of non-180˚ domain switching and de-aging of the dielectric properties under the influence of the applied stress.

Abstract: In this work, effects of compressive stress on the ferroelectric properties of 0.7PMN–0.3PT ceramics were investigated. The ceramics with the formula (0.7)Pb(Mg1/3Nb2/3)O3-(0.3)PbTiO were prepared by a conventional mixed-oxide method. The ferroelectric properties under compressive stress were observed at stress up to 80 MPa using a compressometer in conjunction with a modified Sawyer-Tower circuit. The results showed that applied stress had a significant influence on the ferroelectric properties of 0.7PMN–0.3PT ceramics. Ferroelectric characteristics, i.e. the area of the ferroelectric hysteresis (P-E) loop, the saturation polarization (Psat), the remanent polarization (Pr) and loop squareness (Rsq), decreased with increasing compressive stress, while the coercive field (Ec) remained relatively constant. Stress-induced domain wall motion suppression and non-180oC ferroelectric domain switching processes are responsible for the changes observed.

Abstract: It is well known that acceptor and donor doping results in opposite ferroelectric aging effects; however, the aging effects in hybrid-doped (acceptor+donor) has remained unclear. Thus, the aging effect of dielectric and ferroelectric properties in Fe3+/Nb5+ hybrid-doped BaTiO3 ceramics was investigated in this research. The concentration of acceptor dopant (Fe3+) was fixed at 1 mol% while that of donor dopant (Nb5+) was varied from 0.5-2.0 mol%. XRD technique was used to study the phase morphology. Before measuring dielectric and ferroelectric aging effect, all samples were deaged at 250 °C for 1 hour. The results showed that the dielectric properties of all deaged samples have decreased exponentially with time. The deaged samples with 0.5 and 1.0 mol% of Nb5+ obviously showed double hysteresis loop while that with higher concentration of Nb5+ (1.5-2.0 mol%) showed the rectangular (normal) hysteresis loop. The explanations based on the effect of defect dipole were discussed.

Abstract: In this study, the influence of Mn addition on phase formation, microstructure and electrical properties of Ba(Ti1-xMnx)O3 where x = 0.01 to 0.2 was investigated. The XRD patterns showed that the crystal structure of Ba(Ti1-xMnx)O3 at room temperature changed from tetragonal to hexagonal as Mn concentration increased, which also caused the room temperature dielectric constant decrease from 1143 to 47. The microstructure of Ba(Ti1-xMnx)O3 ceramics at low concentration revealed a bimodal microstructure. As the x value increased, the well grown grains decreased with the extent of fine-grained increased. Ferroelectric hysteresis (P-E) loop was not clearly observed as Mn concentration increased because of the formation of paraelectric hexagonal phase