No abstract

Converse and direct piezoelectric coefficients ͑d 33 C and d 33 D ͒ of ͑001͒-cut Pb͑Mg 1/3 Nb 2/3 ͒ 0.70 Ti 0.30 O 3 ͑PMN-30%PT͒ single crystals have been investigated as a function of poling electric ͑E͒ field. E-field-dependent domain structures were observed by using a polarizing microscope. Both d 33 C and d 33 D 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 M A 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.

This work is a study of the thermal stability of ͑001͒-cut Pb͑Mg 1/3 Nb 2/3 ͒ 1−x Ti x O 3 ͑x = 0.30͒ single crystals before and after an electric ͑E͒-field poling by means of dielectric permittivity, hysteresis loop, domain structure, polarization current, and x-ray diffraction. An R͑R NT ͒-R͑R NT ͒ / T͑T NT ͒-T͑T NT ͒-C transition sequence was observed upon heating in the unpoled sample. R, R NT , T, T NT , and C are the rhombohedral, rhombohedral nanotwin, tetragonal, tetragonal nanotwin, and cubic phases, respectively. R / T indicates coexistence of the R and T phases. R͑R NT ͒ and T͑T NT ͒ indicate that the R NT and T NT structures mimic monoclinic phases in the R and T matrices, respectively. After a prior E-field poling, an R͑R NT ͒-T͑T NT ͒-C phase sequence takes place upon heating. The dielectric permittivity 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 T B = 510 K. This study suggests that nanotwins ͑R NT and T NT ͒ can play an important role in high-strain piezoelectric crystals while phase transition takes place. Under E =38 kV/ cm, ͓001͔ T domains randomly appeared in the matrix, suggesting that the matrix consists of a glassy matrix and ferroelectric nanoclusters.

Two polyaniline (PANI)/polymer nano-composites exhibiting huge negative dielectric permittivity have been synthesized for the first time. These novel chemical processes open a new approach for fabrication of the negative index materials (NIMs), since most of the NIMs prepared today are obtained by a structural approach – by putting together two structured materials that exhibit separately a negative permittivity and a negative permeability. We found the negative permittivity of these nano-composites is a function of the content of the dopant (i.e., PANI) as well as of the frequency. The generation of huge negative permittivity can be rationalized by the well-dispersed PANI-DBSA nano-particles which form a pseudo-continuous conductive pathway in these nano-composites.

By means of combined dielectric permittivity and thermal current density measurements and in situ high-resolution synchrotron x-ray diffraction study, it is shown that the unpoled and poled 0.93Pb(Zn1/3Nb2/3)O3–0.07PbTiO3 (PZN–7%PT) single crystals undergo a R−(R+RNT+T+TNT)−(T+TNT)−C transformation sequence upon zero-field heating, where R, T and C are rhombohedral, tetragonal and cubic phases, respectively. Rhombohedral (RNT) and tetragonal (TNT) nanotwin domains were detected in the vicinity of the R–T transformation temperature (TR−T) in both the unpoled and poled states. These nanotwins are likely bridging phases which help to alleviate the internal stresses accompanying the phase transformations.