Polycrystalline samples of the modified Pb(Zr1−x Tix)O3 (PZT) composition, with representative formula Pb0.92(LazBi1−z)0.08(Zr0.65Ti0.35)0.98O3 (PLBZT), a family of relaxor ferroelectrics, were prepared via the chemical route with z = 0.3, 0.6 and 0.9. Crystalline phases of powders calcined at different temperatures and the microstructure of the sintered pellets were investigated by x-ray diffraction (XRD) analysis and scanning electron microscopy, respectively. XRD confirms the result obtained by differential scanning calorimetry. The XRD profile shows that the samples having z = 0.9 and 0.6 do not exhibit a pyrochlore phase, whereas the samples with z = 0.3, have 3% of the pyrochlore phase. Microstructural analysis suggests that the shape of grains and intergranular residual pores are modified upon La doping. The dielectric constant and dielectric losses were measured as a function of frequency at room temperature for different frequencies starting from 0.1 kHz to 1 MHz. The dielectric constant was found to be strongly influenced by frequency whereas the Curie temperature remained almost the same. Finally, we conclude that the dielectric constant, loss and activation energy of PLBZT strongly suggest that these compounds are suitable for the preparation of high value capacitors and may be good candidates for device applications.
The optical properties of nano-ceria (nano-CeO 2 ) dispersed ferroelectric liquid crystals (FLCs) have been investigated by excitation wavelength dependent photoluminescence (PL) spectroscopy. The PL spectra of nano-ceria exhibited a strong excitation wavelength dependence in the 255-370 nm range. The red shift in the violet emission band of ceria i.e. from 368 nm to 396 nm with increasing excitation wavelength, has been attributed to the recombination of electrons trapped in the defect band and the deeply trapped holes in oxygen vacancies. This excitation wavelength dependence of ceria has noticeably been manifested in the PL response of FLC-CeO 2 nanocomposites as well. PL emission recorded at an excitation wavelength where host and guest materials show intense emission, i.e. 340 nm, exhibits a quenching effect connected to the overlapping of emission and absorption bands of the host FLC and guest ceria NPs respectively. No blue/red shift in the spectral energy band was observed at 310 and 340 nm excitations. On the other hand, emission spectra at a lower excitation wavelength followed a reverse trend: an increase in the emission intensity, with a large blue shift in spectral energy band. The mechanisms involved in the changes of the PL spectrum of FLC-ceria nanocomposites with varying ceria concentration and excitation wavelengths are discussed in detail.
Here, we report the polymeric (copolymer of benzene and pentacene) nanoparticles (PNPs) induced vertical alignment in ferroelectric liquid crystals (FLCs). The nanoparticles used in this study have been synthesized via chemical route method. The PNPs have been doped in FLC mixture. It has been observed that pentacene molecules (presented in PNPs used) prefer an upright orientation on the indium-tin-oxide-coated surfaces, which in turn provide assistance to align FLC molecules vertically (or homeotropically). It has also been observed that the addition of PNPs into the FLC materials improves the electro-optical response. However, the transition temperatures of the PNPs-doped FLC materials have been lowered. These findings will provide a fascinating tool to align FLC materials devoid of any surface treatment. Moreover, these studies would be helpful in the realization of low threshold and faster liquid crystal display devices.
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