Coupling Raman, Brillouin and Nd3+ Photo Luminescence Spectroscopy to Distinguish the Effect of Uniaxial Stress from Cooling Rate on Soda-Lime Silicate Glass.

Evolution of spectroscopic properties of a soda-lime silicate glass with different thermal history and under applied uniaxial stress was investigated using Raman and Brillouin spectroscopies as well as Nd3+ photoluminescence techniques. Samples of soda-lime silicate with a cooling rate from 6 × 10-4 to 650 K/min were prepared either by controlled cooling from the melt using a differential scanning calorimeter or by a conventional annealing procedure. Uniaxial stress effects in a range from 0 to -1.3 GPa were investigated in situ by compression of the glass cylinders. The spectroscopic observations of rearrangements in the network structure were related to the set cooling rates or the applied uniaxial stress to calculate an interrelated set of calibrations. Comparing the results from Raman and Brillouin spectroscopy with Nd3+ photoluminescence analysis, we find a linear dependence that can be used to identify uniaxial stress and cooling rate in any given combination concurrently. The interrelated calibrations and linear dependence models are established and evaluated, and equations relating the change of glass network due to effects of cooling rate or uniaxial stress are given.

Lead-Free Multilayer Piezoceramic Composites: Effect of Cosintering on Electromechanical Properties.

The macroscopic electromechanical behavior of lead-free multilayer composites was characterized from room temperature to 150 °C. The polar seed component consisted of a nonergodic relaxor (Bi1/2Na1/2)TiO3-7BaTiO3, with an electric-field-induced long-range ferroelectric order, whereas the nonpolar matrix was an ergodic relaxor Bi0.5(Na0.75K0.25)0.5 TiO3-6BiAlO3 that undergoes a reversible electric-field-induced macroscopic nonpolar-to-polar transition. Microstructural evidence of the effects of cosintering are demonstrated through examination of grain size, interdiffusion, and pore structure. By manipulating the sintering interactions between the two constituents, namely, diffusion paths and residual stresses, both internal mechanical and electrical fields, as well as compositional gradients can be used to enhance the unipolar strain over that expected by a rule of mixtures approximation, thereby improving the properties needed for application of such materials to actuator systems.

Inverted electro-mechanical behaviour induced by the irreversible domain configuration transformation in (K,Na)NbO3-based ceramics.

Miniaturization of domains to the nanometer scale has been previously reported in many piezoelectrics with two-phase coexistence. Despite the observation of nanoscale domain configuration near the polymorphic phase transition (PPT) regionin virgin (K0.5Na0.5)NbO3 (KNN) based ceramics, it remains unclear how this domain state responds to external loads and influences the macroscopic electro-mechanical properties. To this end, the electric-field-induced and stress-induced strain curves of KNN-based ceramics over a wide compositional range across PPT were characterized. It was found that the coercive field of the virgin samples was highest in PPT region, which was related to the inhibited domain wall motion due to the presence of nanodomains. However, the coercive field was found to be the lowest in the PPT region after electrical poling. This was related to the irreversible transformation of the nanodomains into micron-sized domains during the poling process. With the similar micron-sized domain configuration for all poled ceramics, the domains in the PPT region move more easily due to the additional polarization vectors. The results demonstrate that the poling process can give rise to the irreversible domain configuration transformation and then account for the inverted macroscopic piezoelectricity in the PPT region of KNN-based ceramics.

Enhancing electromechanical properties of lead-free ferroelectrics with bilayer ceramic/ceramic composites.

The macroscopic electromechanical behavior of lead-free bilayer composites was characterized at room temperature. One layer consisted of a nonergodic relaxor, (Bi1/2Na1/2)TiO3-7BaTiO3, with an electric-field-induced longrange ferroelectric order, whereas the other is understood to be an ergodic relaxor [(Bi1/2Na1/2)TiO3-25SrTiO3] that undergoes a reversible electric-field-induced macroscopic nonpolar-to-polar transition. Microstructural evidence of a bilayer with low diffusion between the two components is also demonstrated. By taking advantage of the different macroscopic strain- and polarization-electric-field responses of the two constituents, internal mechanical and electrical fields can be developed that enhance the unipolar strain over that expected by a rule of mixtures approximation, thereby improving the properties needed for application of such materials to actuator systems. It is possible through further tailoring of the volume fractions and macroscopic properties of the constituents to optimize the electromechanical properties of multilayer lead-free ferroelectrics.

Electric-field-induced phase transitions in co-doped Pb(Zr1-xTix)O3 at the morphotropic phase boundary.

The strain- and polarization-electric field behavior was characterized at room temperature for Pb0.98Ba0.01(Zr1-x Ti x )0.98Nb0.02O3, 0.40 ⩽ x ⩽ 0.60. The investigated compositions were located in the vicinity of the morphotropic phase boundary, giving insight into the influence of crystal structure on the hysteretic ferroelectric behavior. The remanent strain of particular compositions is shown to be larger than theoretically allowed by ferroelectric switching alone, indicating the presence of additional remanent strain mechanisms. A phenomenological free energy analysis was used to simulate the effect of an applied electric field on the initial equilibrium phase. It is shown that electric-field-induced phase transitions in polycrystalline ferroelectrics can account for the experimental observations. The experimental and simulation results are contrasted to neutron diffraction measurements performed on representative compositions in the virgin and remanent states.