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Phase transformations of (001)-cut (Na1/2Bi1/2)TiO3 (NBT) and 1 at. % Mn-doped NBT (Mn-NBT) crystals have been investigated by means of dielectric permittivity, conventional x-ray diffraction (XRD), and high-resolution synchrotron XRD and reciprocal space mapping. An R-R+T-T-C transition sequence was observed in NBT and Mn-NBT upon zero-field heating. R, T, and C are rhombohedral, tetragonal, and cubic phases, respectively. R+T represents that the ferroelastic T phase coexists with the ferroelectric R phase. The Mn dopant can enhance dielectric response and reduce the dielectric loss in the high-temperature region due to the increased degree of ordering. [ABSTRACT FROM AUTHOR]

This work investigates dielectric and photovoltaic behaviors in Pb(Mg1/3Nb2/3)0.64Ti0.36O3 single crystal doped with 0.5 mol % WO3. Dielectric permittivities measured as functions of temperature and frequency reveal two first-order-type phase transitions upon heating and cooling. The photovoltaic response strongly depends on illumination wavelength, sample thickness, and prior electric-field poling. The relation of photovoltage and light intensity under near-ultraviolet (λ=406 nm) illumination for the poled samples can be expressed by an exponential equation. Optical transmission reveals that the cutoff wavelength is near 400 nm and indicates a minimum electronic energy gap of ∼3.0 eV. [ABSTRACT FROM AUTHOR]

A sequence of field-induced phase transformations was observed by means of a polarizing microscope on a (111)-cut single crystal Pb(Mg[sub 1/3]Nb[sub 2/3])[sub 0.67]Ti[sub 0.33]O[sub 3] at room temperature with an electric field applied along the [111] direction. As electric field increases, polarizations of the rhombohedral R domains whose polar directions are not along [111] rotate first toward a tetragonal T phase associated with 90° domain walls. Then the crystal gradually reaches total optical extinction for all polarizer angles at 12 kV/cm, indicating a single [111] rhombohedral R[sub 111] domain with polarization aligned with the electric field. These field-induced phase transformations are irreversible and proceed most likely through M[sub A]-type monoclinic distortions, i.e., R→M[sub A]→T→M[sub A]→R[sub 111]. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]