Browsing by Author "Hsieh, C.-M."

Now showing 1 - 3 of 3

Nanotwin and phase transformation in tetragonal Pb(Fe1/2Nb1/2)1-xTixO3 single crystal
(2008) Tu, Chi-Shun; Tseng, C.-T.; Chien, R.R.; Schmidt, V. Hugo; Hsieh, C.-M.
This work is a study of phase transformation in (001)-cut Pb(Fe1/2Nb1/2)1−xTixO3Pb(Fe1/2Nb1/2)1−xTixO3 (x=48%)(x=48%) single crystals by means of dielectric permittivity, domain structure, and in situ x-ray diffraction. A first-order T(TNT)-C(TNT)T(TNT)-C(TNT) phase transition was observed at the Curie temperature TC≅518KTC≅518 K upon zero-field heating. T, TNTTNT, and C are tetragonal, tetragonal nanotwin, and cubic phases, respectively. T(TNT)T(TNT) and C(TNT)C(TNT) indicate that minor TNTTNT domains reside in the T and C matrices. Nanotwins, which can cause broad diffraction peak, remain above TC≅518KTC≅518 K and give an average microscopic cubic symmetry in the polarizing microscopy. Colossal dielectric permittivity (>104)(>104) was observed above room temperature with strong frequency dispersion. This study suggests that nanotwins can play an important role in relaxor ferroelectric crystals while phase transition takes place. The Fe ion is a potential candidate as a BB-site dopant for enhancing dielectric permittivity.
Nanotwins and phases in high-strain Pb(Mg1/3Nb2/3)1-xTixO3 crystal
(2008) Tu, Chi-Shun; Hsieh, C.-M.; Chien, R.R.; Schmidt, V. Hugo; Wang, F.-T.; Chang, W.S.
This work is a study of the thermal stability of (001)-cut Pb(Mg1/3Nb2/3)1−xTixO3 (x=0.30) single crystals before and after an electric (E)-field poling by means of dielectricpermittivity, hysteresis loop, domain structure,polarization current, and x-ray diffraction. An R(RNT)-R(RNT)/T(TNT)-T(TNT)-C transition sequence was observed upon heating in the unpoled sample. R, RNT, T, TNT, and C are the rhombohedral, rhombohedral nanotwin, tetragonal, tetragonal nanotwin, and cubic phases, respectively. R/T indicates coexistence of the R and T phases. R(RNT) and T(TNT) indicate that the RNT and TNTstructures mimic monoclinic phases in the R and T matrices, respectively. After a prior E-field poling, an R(RNT)-T(TNT)-C phase sequence takes place upon heating. The dielectricpermittivity and current density evidenced an additional polarization at 355 K, which is associated with the vanishing of the dielectric dispersion, which reappears near 410 K and remains up to the Burns temperature TB=510 K. This study suggests that nanotwins (RNT and TNT) can play an important role in high-strain piezoelectric crystals while phase transition takes place. Under E=38 kV/cm, [001] T domains randomly appeared in the matrix, suggesting that the matrix consists of a glassy matrix and ferroelectric nanoclusters.
Piezoelectric response and origin in (001) Pb(Mg1/3Nb2/3)0.70Ti0.30O3 crystal
(2008) Tu, Chi-Shun; Hsieh, C.-M.; Schmidt, V. Hugo; Chien, R.R.; Luo, H.
Converse and direct piezoelectric coefficients (dC33 and dD33) of (001)-cut Pb(Mg1/3Nb2/3)0.70Ti0.30O3 (PMN-30%PT) single crystals have been investigated as a function of poling electric (E) field. E-field-dependent domain structures were observed by using a polarizing microscope. Both dC33 and dD33 exhibit a rapid increase at E=1–2 kV/cm and reach maxima at E=2.5–4 kV/cm. This study suggests that polarization rotation from rhombohedral to monoclinic MA phases plays an important role while the high piezoelectric response builds up. Overpoling phenomenon evidenced by a sudden reduction in piezoelectric coefficient with increasing field is very sensitive to Ti content.