Articles you may be interested inElectric-field-temperature phase diagram of the ferroelectric relaxor system (1−x)Bi1/2Na1/2TiO3−xBaTiO3 doped with manganese J. Appl. Phys. 115, 194104 (2014); 10.1063/1.4876746Long ranged structural modulation in the pre-morphotropic phase boundary cubic-like state of the lead-free piezoelectric Na1/2Bi1/2TiO3-BaTiO3 J. Appl. Phys. 114, 234102 (2013) On the phase identity and its thermal evolution of lead free (Bi 1/2 Na 1/2 )TiO 3 -6 mol% BaTiO 3 Temperature-dependent dielectric permittivity of 0.94(Bi 1/2 Na 1/2 )TiO 3 -0.06BaTiO 3 (BNT-6BT) lead-free piezoceramics was studied to disentangle the existing unclear issues over the crystallographic aspects and phase stability of the system. Application of existing phenomenological relaxor models enabled the relaxor contribution to the entire dielectric permittivity spectra to be deconvoluted. The deconvoluted data in comparison with the temperature-dependent dielectric permittivity of a classical perovskite relaxor, La-modified lead zirconate titanate, clearly suggest that BNT-6BT belongs to the same relaxor category, which was also confirmed by a comparative study on the temperature-dependent polarization hysteresis loops of both materials. Based on these results, we propose that the low-temperature dielectric anomaly does not involve any phase transition such as ferroelectric-toantiferroelectric. Supported by transmission electron microscopy and X-ray diffraction experiments at ambient temperature, we propose that the commonly observed two dielectric anomalies are attributed to thermal evolution of ferroelectric polar nanoregions of R3c and P4bm symmetry, which coexist nearly throughout the entire temperature range and reversibly transform into each other with temperature.

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Piezoelectric materials convert between electrical and mechanical energies such that an applied stress induces a polarization and an applied electric field induces a strain. This review describes the fundamental mechanisms governing the piezoelectric response in high-performance piezoelectric single crystals, ceramics, and thin films. While there are a number of useful piezoelectric small molecules and polymers, the article focuses on inorganic materials displaying the piezoelectric effect. Piezoelectricity is first defined, and the mechanisms that contribute are discussed in terms of the key crystal structures for materials with large piezoelectric coefficients. Exemplar systems are then discussed and compared for the cases of single crystals, bulk ceramics, and thin films.

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One- and two-photon fluorescence excitation and emission spectra of the S1↔S0 transition of trans,trans-1,3,5,7-octatetraene have been measured for the first time in free jet expansions. The one-photon excitation spectrum is the same, with the exception of significant differences in the intensities of a few lines, as the two-color, resonance-enhanced, two-photon ionization spectrum, previously assigned to the 2 1A′←1 1A′ transition of cis,trans-1,3,5,7-octatetraene. However, comparison of the one- and two-photon fluorescence excitation spectra shows clearly that the carrier of the spectrum has inversion symmetry, as expected for trans,trans-1,3,5,7-octatetraene. The one-photon spectrum is built on bu Herzberg–Teller promoting modes, which are origins of progressions in ag modes, while the two-photon spectrum is due to a single progression in ag modes starting from the 2 1Ag←1 1Ag electronic origin. The appearance of out-of-plane vibrations, possibly including torsions of the polyene framework, suggests large differences in force constants and perhaps in the geometries of the 2 1Ag and 1 1Ag potential surfaces. For 2 1Ag vibronic levels with energies ≤1000 cm−1, the fluorescence lifetimes vary between 170 and 450 ns due to the dependence of radiative and nonradiative decay rates on the vibronic state. An abrupt increase in the nonradiative decay rates at ∼2100 cm−1 excess energy is tentatively ascribed to trans→cis isomerization. This work demonstrates that the one- and two-photon cross sections of the 2 1Ag←1 1Ag transitions of all-trans linear polyenes are sufficiently large to allow the study of 2 1Ag states under isolated, unperturbed conditions.

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The possible domain states of perovskite ferroelectrics under applied fields are reviewed and, as an illustration, a phenomenological study of barium titanate is carried out. Electric field-temperature phase diagrams, the polarization, and the lattice strain of barium titanate single crystals are calculated from the Landau–Ginzburg–Devonshire theory of ferroelectrics for applied fields up to 20 MV m−1 and for temperatures from 1 to 450 K. The calculations are carried out for fields applied along the pseudocubic [001], [101], and [111] axes, revealing the temperature and field dependence of all the ferroelectric phase transitions. Large piezoelectric coefficients can be identified close to field-induced transitions. Good agreement is seen with experimental data for the piezoelectric coefficient parallel to [001] over a wide range of temperature. The series of transitions predicted for increasing field parallel to [111] at room temperature is qualitatively similar to that observed experimentally but with somewhat larger critical fields and lower piezoelectric coefficients. Similarities are noted between the phase diagrams for fields along [001] and [111] and those describing PbBa2+ and ZrTi4+ substitutions.