109 research outputs found
Stability of the monoclinic phase in the ferroelectric perovskite PbZr(1-x)TixO3
Recent structural studies of ferroelectric PbZr(1-x)TixO3 (PZT) with x= 0.48,
have revealed a new monoclinic phase in the vicinity of the morphotropic phase
boundary (MPB), previously regarded as the the boundary separating the
rhombohedral and tetragonal regions of the PZT phase diagram. In the present
paper, the stability region of all three phases has been established from high
resolution synchrotron x-ray powder diffraction measurements on a series of
highly homogeneous samples with 0.42 <=x<= 0.52. At 20K the monoclinic phase is
stable in the range 0.46 <=x<= 0.51, and this range narrows as the temperature
is increased. A first-order phase transition from tetragonal to rhombohedral
symmetry is observed only for x= 0.45. The MPB, therefore, corresponds not to
the tetragonal-rhombohedral phase boundary, but instead to the boundary between
the tetragonal and monoclinic phases for 0.46 <=x<= 0.51. This result provides
important insight into the close relationship between the monoclinic phase and
the striking piezoelectric properties of PZT; in particular, investigations of
poled samples have shown that the monoclinic distortion is the origin of the
unusually high piezoelectric response of PZT.Comment: REVTeX file, 7 figures embedde
Unfolding grain size effects in barium titanate ferroelectric ceramics
Grain size effects on the physical properties of polycrystalline ferroelectrics have been extensively studied for decades; however there are still major controversies regarding the dependence of the piezoelectric and ferroelectric properties on the grain size. Dense BaTiO3 ceramics with different grain sizes were fabricated by either conventional sintering or spark plasma sintering using micro- and nano-sized powders. The results show that the grain size effect on the dielectric permittivity is nearly independent of the sintering method and starting powder used. A peak in the permittivity is observed in all the ceramics with a grain size near 1μm and can be attributed to a maximum domain wall density and mobility. The piezoelectric coefficient d33 and remnant polarization Pr show diverse grain size effects depending on the particle size of the starting powder and sintering temperature. This suggests that besides domain wall density, other factors such as back fields and point defects, which influence the domain wall mobility, could be responsible for the different grain size dependence observed in the dielectric and piezoelectric/ferroelectric properties. In cases where point defects are not the dominant contributor, the piezoelectric constant d33 and the remnant polarization Pr increase with increasing grain size
Domain effects in polycrystalline barium titanate
Upon depoling ceramic barium titanate, up to 9% of the domains reorient by 90° , indicating that during poling at least this percentage of the domains was permanently reoriented by 90° . Ceramic barium titanate shows a strong anelastic effect in the ferroelectric state, presumably due to domain reorientations under stress. Application of tensile and compressive stresses causes up to 13% of the domains to change their orientation by 90° , but, unlike the electric case, no permenent domain reorientation is found. These domain switches are detected by X-ray intensity and strain measurements. The agreement between the percent domain switches computed from the X-ray data and that computed from the strain data is good in the case of mechanical compression, but not in the case of electrical and mechanical tension. In the latter case more domains appear to switch in the bulk than in the surface of the material. A space-charge effect at the surface of ferroelectric barium titanate is suggested as a reason for this anomaly. Experimental evidence of the effect of grinding, etching, and irradiation on the domain orientation in the surface layer of ceramic barium titanate is cited
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