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Sr, Zn, and Sn co-doping in CCTO ceramics alters their intrinsic and extrinsic properties and makes them useful for industrial dielectric applications such as Z9R-capacitors (Δε′ < ±15%, D < 0.05 between 30–200 °C).

Fine powders synthesized via sol-gel route were employed to fabricate Sr(2-x)(Na0.5Bi0.5)(x)Bi4Ti5O18 (SNBT, where x = 0, 0.1, 0.25, 0.3, 0.4, and 0.5) ceramics. The composition (x)-dependent structural changes associated with SNBT ceramics were analyzed using X-ray powder diffraction, transmission electron microscopy, and Raman spectroscopic techniques. Average grain size analyses carried out on the SNBT ceramics by scanning electron microscopy revealed an important role played by the dopants in inhibiting the grain growth. Dielectric constants and the Curie temperature of the ceramics were found to decrease and increase, respectively, with increase in x. The increase in Curie temperature with increase in x was attributed to the decrease in the tolerance factor. The specific composition (x = 0.3) of the SNBT ceramics exhibited improved piezo- and ferroelectric properties associated with a higher Curie temperature (569 K). The piezoelectric coefficient (d(33)) and the planar electromechanical coupling coefficient (k(p)) of SNBT(x = 0.3) were enhanced by 25% and 42%, respectively, as compared to the undoped ceramics.

Transparent glasses of the 1.2CaO–0.2MoO3–B2O3 system were fabricated using the conventional melt-quenching technique. The glasses were heat-treated above the glass transition temperature (Tg) to yielded nanocrystalline composites of CaMoO4 (CMO) and CaB2O4 (CBO). The structural characterization of as-quenched and heat-treated glasses corroborated the crystallites of CaMoO4 and CaB2O4 using powder X-ray diffraction (XRD) and Raman spectroscopy. The various morphologies of the samples were studied using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Optical transmittance spectrum for as-quenched glass shows, approximately, 77% transparency (uncorrected for the reflection losses) from 2600 ​nm to 325 ​nm with a lower cut-off wavelength at 324 ​nm. The optical band gap (Eg) and refractive index (η) of the as-quenched transparent glass were found to be 3.43 ​eV and 1.615, respectively. Room-temperature photoluminescence properties of the as-quenched and glass nanocrystal composites (GNC) exhibit broad blue emission with UV excitation wavelengths (using laser and Xe lamp). Such distribution of CMO crystallites of nano-dimensions embedded in borate glass matrix could be used for various PL applications.

Fine powders comprising nano-crystallites of Sr2Bi4Ti5O18 (SBT) were synthesized via citrate-assisted sol–gel route. Different ceramics of SBT with different grain sizes (93 nm–1.42 μm) were fabricated by varying sintering temperatures and durations. The usage of nano-crystalline powders for fabricating ceramics facilitated lower sintering temperatures. The grain growth in these powder compacts was found to be controlled by the grain boundary curvature mechanism, associated with the activation energy of 181.9 kJ/mol. Interestingly, with a decrease in grain size there was an increase in structural distortion which resulted in a shift of Curie temperature (phase transition) toward higher temperatures than that of conventional bulk ceramics. Extended Landau phenomenological theory for the spherical ferroelectric particles was invoked to explain experimentally observed size-dependent phase transition temperature, and the critical size for SBT is predicted to be 11.3 nm. Grain size-dependent dielectric, ferroelectric and piezoelectric properties of the SBT ceramics were studied and the samples comprising average grain size of 645 nm exhibited superior physical properties that include remnant polarization (2P r) = 16.4 μC cm−2, coercive field (E c) = 38 kV cm−1, piezoelectric coefficient (d 33) = 22 pC N−1 and planar electromechanical coupling coefficient (k p) = 14.8 %.

Nanocrystalline powders of Ba1-xMgxZr0.1Ti0.9O3 (x = 0.025-0.1) were synthesized via citrate assisted sol-gel method. Interestingly, the one with x = 0.05 in the system Ba1-xMgxZr0.1Ti0.9O3 exhibited fairly good piezoelectric response aside from the other physical properties. The phase and structural confirmation of synthesized powder was established by X-ray powder diffraction (XRD) and Raman Spectroscopic techniques. Two distinct Raman bands i.e., 303 and 723 cm(-1) characteristic of tetragonal phase were observed. Thermogravimetric analysis (TGA) was performed to evaluate the phase decomposition of the as-synthesized Ba0.95Mg0.05Zr0.1Ti0.9O3 sample as a function of temperature. The average crystallite size associated with Ba0.95Mg0.05Zr0.1Ti0.9O3 was calculated using Scherrer formula based on the XRD data and was found to be 25 nm. However, Scanning and Transmission Electron Microscopy studies revealed the average crystallite size to be in the range of 30-40 nm, respectively. Kubelka-Munk function was employed to determine the optical band gap of these nanocrystallites. A piezoelectric response of 26 pm/V was observed for Ba0.95Mg0.05Zr0.1Ti0.9O3 nanocrystal by Piezoresponse Force Microscopy (PFM) technique. Photoluminescence (PL) study carried out on these nanocrystals exhibited a blue emission (470 nm) at room temperature.

Semitransparent (45% transparency at 1 mu m) composites comprising poly (vinylidene fluoride) PVDF] and 2-methyl-4-nitroaniline MNA] were fabricated by home-built hot-pressing technique. The composite nature of thus fabricated samples was confirmed via x-ray powder diffraction (XRD) studies. Formation of beta-phase (2 theta similar to 20.7 (200)) was observed in the hot-pressed PVDF-MNA composites through XRD data. Scanning Electron Microscopy (SEM) carried out on these samples revealed the presence of platy and rod shaped features of individual crystallite of MNA (nearly 5-20 mu m) embedded in the PVDF matrix. Optical transmission for 10 wt% MNA in PVDF was found to be around 40% (uncorrected for the reflection/scattering losses) at 446 nm and has higher towards longer wavelengths. The second harmonic generation (SHG) studies confirmed an increase in intensity with an increase in weight percentage of MNA in PVDF. Room temperature dielectric constant and dielectric loss measurements were conducted on the hot-pressed PVDF and composites of PVDF and MNA as a function of frequency (100 Hz-100 MHz). The polarization versus electric field (Hysteresis loop) behaviour of hot-pressed PVDF and composites of MNA and PVDF was also investigated. The remnant polarization (2P(r) = 0.246 mu C/cm(2)) was observed the semitransparent hot-pressed composite (10 wt% MNA in PVDF).

Ceramics of Bi1-xPrxFeO3 (x = 0-0.1) were fabricated using the nanocrystalline powders obtained via sol-gel route. X-ray powder diffraction studies confirmed that these belonged to rhombohedral perovskite structure associated with R3c space group. The dielectric properties of the ceramic samples as a function of frequency (100 Hz-10 MHz) and temperature (30 degrees C-250 degrees C) were studied. The dielectric constant increased while the loss decreased with the increase of Pr content. Dielectric dispersion in these samples was found to be poly dispersive Debye type relaxation as confirmed by invoking Cole-Cole relation. Impedance spectroscopy was employed to determine the electrical parameters associated with the grain and grain boundaries. Grain and grain boundary resistances were found to decrease with the increase of temperature for all the samples under study. The activation energies for the dielectric relaxation were evaluated by electric modulus spectra and these increase with the increase of Pr dopant level. The frequency dependent conductivity at various temperatures demonstrated the involvement of correlated barrier hopping conduction mechanism. The electrical conduction in these ceramics was ascribed to long and short range migration of oxygen ion vacancies as demonstrated by temperature dependent ac conductivity studies.

The present work deals with the structural and efficient down-shifting (DS) and up-conversion (UC) luminescence properties of erbium ion (Er3+) doped nanocrystalline barium sodium niobate (Ba2Na1-3xErxNb5O15, where x = 0, 0.02, 0.04 and 0.06) powders synthesized via novel citrate-based sol-gel route. The monophasic nature of the title compound was confirmed via x-ray powder diffraction followed by FT-IR studies. High-resolution transmission electron microscopy (HRTEM) facilitated the establishment of the nanocrystalline phase and the morphology of the crystallites. The Kubelka-Munk function, based on diffused reflectance studies and carried out on nano-sized crystallites, was employed to obtain the optical band-gap. The synthesized nanophosphor showed efficient DS/PL-photoluminescence and UC luminescence properties, which have not yet been reported so far in this material. The material emits intense DS green emission on excitation with 378 nm radiation. Interestingly, the material gives intense UC emission in the visible region dominated by green emission and relatively weak red emission on 976 nm excitation (NIR laser excitation). Such a dual-mode emitting nanophosphor could be very useful in display devices and for many other applications.