Nidhi Sinha

p-type K-doped ZnO nanorods for optoelectronic applications

Single crystalline p-type K-doped ZnO nanorods (NR) have been synthesized by convenient and low-cost solution technique. X-ray diffraction analysis confirmed the hexagonal system of K-doped ZnO nanorods and a preferred a axis orientation. The diameter and length were found to be 30–50 nm and 150–200 nm, respectively, in electron microscopic studies. The p-type nature and high hole density of 2.36×1019 per cm3 was demonstrated by Hall studies. A sharp lower cutoff and reduction in the bandgap was observed in UV-Vis study which is linked to its smaller size and p-type conduction in NR. In Photoluminescence studies, a near band emission in the UV range and a yellow emission with a blueshift were detected in the visible region in K-doped ZnO NR. The variation in intensity of peaks is correlated with the dimensions of NR. The redshift observed in Raman peaks is explained in terms of the stress developed in ZnO nanostructure due to lattice mismatch by K doping. These results provide better insight of K-doped Zn...

Structural, electrical, ferroelectric and mechanical properties with Hirshfeld surface analysis of novel NLO semiorganic sodium p-nitrophenolate dihydrate piezoelectric single crystal

Novel non-linear sodium para-nitrophenolate dihydrate (SPNPD) single crystals were grown by the controlled evaporation method. Various functional groups and chemical bonding were identified by FTIR and Raman analysis. Hirshfeld surface and fingerprint plots were drawn and analyzed to investigate the intermolecular interactions present in the crystal structure. UV-visible studies indicate the high transmittance of the crystals in the visible region with a wide band gap 2.80 eV. In the photoluminescence spectrum, a sharp broad emission peak centered at 525 nm indicates green emission. In the dielectric study a broad peak with low dielectric constant value was observed at 34 °C which may be due to a ferroelectric to paraelectric transition. Piezoelectricity was confirmed by determining the piezoelectric charge coefficient (d33 = 2.24 pC N−1). The hysteresis loop shows values of remnant polarization and coercive field of 2.67 μC cm−2 and 7.43 kV cm−1, respectively. Piezo-/ferroelectricity were reported for the first time in p-nitrophenolate based compounds. SHG efficiency of this material was found to be 4.15 times of that of KDP. The mechanical strength was confirmed from a Vicker’s microhardness study and void volume. Thus the promising piezoelectric, ferroelectric behavior of the material along with high SHG efficiency and low dielectric constant, established SPNPD as a potential material for transducer, optoelectronics and nonvolatile memory devices applications.

Growth and characterization of piezoelectric benzil single crystals and its application in microstrip patch antenna

Organic non-linear optical single crystals of benzil have been grown by Czochralski (Cz) and slow-evaporation techniques. The crystal morphology was characterized by computing the growth rates of the planes, which were found to be affected by solvent modification. Intermolecular interactions of the benzil crystal were explored by Hirshfeld surface and 2D fingerplot in a novel visual manner. A linear optical study was carried out by UV-vis transmission spectroscopy, in which the Cz grown crystal was found to be more transparent with a cut-off wavelength at 406 nm. Photoluminescence emission was observed in the green region with higher intensity in Cz grown crystal. The piezoelectric charge coefficients were found to be 4, 1, 6 and 3 pC N−1 along (100), (010), (001) and (10) planes of the solution grown crystal. The study of Vickers microhardness and volume of voids in the grown crystals confirmed that the Cz grown crystal has better mechanical strength. Patch antenna based on the substrate of Cz grown benzil crystal was simulated for resonant frequency at 12.6 GHz and fabricated, and is suitable for piezoelectric, sensor and telecommunication applications.

Performance of crystal violet doped triglycine sulfate single crystals for optical and communication applications

Single crystals of 0.01 and 0.02 mol% crystal violet dye doped triglycine sulfate (NH2CH2COOH)3·H2SO4 (TGS) have been grown by a slow evaporation technique. Enhanced dielectric, optical, thermal and mechanical properties have been achieved by dye doping. Monoclinic structures showing particular coloring patterns and morphology change with dye concentration were obtained. Various functional groups and dye incorporation in the grown crystals were confirmed qualitatively by FTIR and Raman analysis. A significant increase in Curie temperature from 50 to 55 °C with a decrease in maximum permittivity has been observed. The UV-vis spectra showed an increased transmittance window and an increased optical band gap from 5.61 to 6.11 eV as a result of doping. An increase in the sharpness and intensity of the photoluminescence peak with a blue shift has been observed in doped crystals. The thermal stability and the decomposition temperature were found to increase by about 10 °C in 0.01 mol% dye doped TGS. The mechanical strength of the grown crystals was estimated by the Vickers microhardness test and was found to be high for dye doped TGS. A high piezoelectric charge coefficient d33 of 16 pC N−1 was observed for pure TGS which decreased as a result of the dye effect. The fabrication of a patch antenna was carried out after simulating its resonant frequency, making it suitable for telecommunication applications.

Combined structural, electrical, magnetic and optical characterization of bismuth ferrite nanoparticles synthesized by auto-combustion route

Abstract Phase-pure multiferroic bismuth ferrite (BFO) nanoparticles were synthesized by energy efficient, simple and low temperature sol–gel followed by auto-combustion route. Highly crystalline and well-shaped BFO nanoparticles of size about 50 nm were observed in TEM. Thermal analysis was used to optimize the calcination temperature as 500 °C. An endothermic peak at 834 °C has been detected in the DTA curve, representing the Curie temperature. The dielectric anomaly around Neel temperature (TN) was observed signifying the magnetoelectric coupling. The BFO nanoparticles were found to be highly resistive (ρ ∼ 3 × 109 Ω-cm) and had very low leakage current of the order of μA/cm2, which resulted from phase purity. A significantly enhanced weak ferromagnetism was observed due to smaller particles size and remnant magnetization and coercive field were 0.067 emu/g and 185 Oe, respectively. P–E loop confirmed the ferroelectric behavior of BFO nanoparticles. The direct band gap energy was calculated to be 2.2 eV from UV–vis studies.

Dielectric studies and band gap tuning of ferroelectric Cr-doped ZnO nanorods

Effect of Cr-doping on the optical behavior of ZnO nanorods (NRs) (size: diameter ∼ 40 nm and length ∼ 400 nm) is reported. Significant red shift of 18 nm was observed in UV-Vis studies, i.e., a band gap tuning is achieved by Cr doping. In photoluminescence studies, a very remarkable blue shift of 16 nm in green emission was observed. Significant shifts in various modes of Raman spectra of Cr-doped ZnO nanorods are observed in low and high wavenumber region, along with appearance and disappearance of other peaks. The results suggest that Cr-doping can affect the defects and oxygen vacancies in ZnO nanomaterials giving the possibility of fine band gap tuning for tailor made applications of nano-optoelectronics devices. A very high dielectric constant (950) at low frequency side and ferroelectric phase transition (69 °C) were found for Cr-doped ZnO NR, which make it suitable for charge storage and nanoscale memory devices.

Flux growth of lead free (Na0.5Bi0.5)TiO3–(K0.5Bi0.5)TiO3 ferroelectric single crystals and their characterization

We have grown single crystals of lead-free (Na0.5Bi0.5)TiO3–(K0.5Bi0.5)TiO3 (abbreviated as BNKT) as promising materials for ferroelectric applications. The single crystals were grown by a high temperature self-flux solution method in which A-site compounds were used as complex flux. The crystal structure was analyzed by means of an X-ray diffraction technique showing a perovskite phase with tetragonal symmetry at room temperature. The surface morphology of the BNKT crystals was examined by scanning electron microscopy (SEM) and was found depicting a layered like hopper structure. The temperature and frequency dependence of the dielectric constant and loss for the as-grown single crystals was investigated, showing a decrease in Tmax from 316 °C at 50 kHz to 310 °C at 1 MHz. To study the degree of dielectric relaxation, modified power law fitting and Lorentz type quadratic fitting were performed. The relative composition of the studied sample and its phase transition behavior were confirmed by Raman spectroscopy. The piezoelectric coefficient d33 with optimized poling field was found to be 216 pC N−1. The ferroelectric response of the BNKT crystals with temperature at an applied field of 37 kV cm−1 was studied. The results suggest a promising approach for growing high quality alkali based single crystals with a relatively large size for piezoelectric and ferroelectric applications.

Synthesis of 0.64Pb(Mg1/3Nb2/3)O3–0.36PbTiO3 ceramic near morphotropic phase boundary for high performance piezoelectric, ferroelectric and pyroelectric applications

Abstract A near MPB composition of 0.64PMN–0.36PT ceramic has been synthesized by solid-state reaction technique using columbite precursor. Sintering at 1030 °C resulted in a single perovskite phase with tetragonal structure having uniform and dense microstructure as revealed by powder XRD, Raman spectroscopy and FESEM analyses. An excellent dielectric response was obtained with room temperature dielectric permittivity value of 142 and high-phase transition temperature (Tm) of 210 °C at 1 kHz. A huge value of piezoelectric charge coefficient (490 pC/N) was obtained, which shows potential of PMN–PT for piezoelectric device applications. Well-shaped and fatigue-free P–E hysteresis loops over a wide temperature range of 30–230 °C were traced. A very large value of pyroelectric coefficient (p ∼ 2739.2 μC m−2 °C−1) was obtained.

Flux growth of 0.94[Na0.5K0.5NbO3]–0.06LiNbO3 piezo-/ferroelectric crystals for long duration and high temperature applications

High quality lead free ferroelectric single crystals of 0.94[Na0.5K0.5NbO3]–0.06LiNbO3 (NKLN) were grown by the self-flux method. The crystals were characterized for structural and dielectric properties, piezo/ferro response (both on the macro and microlevel) and electrical behavior. The characterization confirmed a perfectly homogeneous stoichiometry having negligible defects in the sample. Further, the crystals were found to exhibit high Curie phase transition (~420 °C) with a high value of d33 coefficient (=115 pC N−1) and remnant polarization (=4.01 μC cm−2 at 30 °C). Its pyroelectric coefficient was found to be ~309.8 μC m−2 °C−1. In addition, the crystals did not show any fatigue. Further, ferroelectric domains were analyzed using piezoresponse force microscopy and the effective d33 coefficient on the microlevel was calculated to be ~80 pm V−1 after a 20 min relaxation of 75 V induced bias. The results suggest NKLN crystals to be a very promising material in the family of available lead free materials for various ferroelectric applications.

Growth, crystal structure, Hirshfeld surface, optical, piezoelectric, dielectric and mechanical properties of bis­(l-asparaginium hydrogensquarate) single crystal

Molecular organic single crystals of bis(L-asparaginium hydrogensquarate) monohydrate [BASQ; (C8H10N2O7)2·H2O] have been grown by solution technique. Crystallographic information was investigated by single-crystal X-ray diffraction (SCXRD) analysis. Hirshfeld surface and fingerprint plot studies were performed to understand the intermolecular interactions of the BASQ crystal in graphical representation. Functional group identification was studied with FT-IR (Fourier transform-IR) spectroscopy. The positions of proton and carbon atoms in the BASQ compound were analyzed using NMR spectroscopy. High transparency and a wide band gap of 3.49 eV were observed in the linear optical study by UV-vis-NIR spectroscopy. Intense and broad photoluminescence emissions at room temperature were observed in blue and blue-green regions. The frontier molecular orbitals of the BASQ molecule were obtained by the DFT/B3LYP method employing 6-311G** as the basis set. The dielectric study was carried out with temperature at various frequency ranges. The piezoelectric charge coefficient (d33) value of BASQ crystal was found to be 2 pC/N, which leads to its application in energy harvesting, mechanical sensors and actuators applications. In the non-linear optical study, the BASQ crystal showed promising SHG conversion efficiency. Mechanical properties of the BASQ crystal were studied experimentally by Vickers microhardness technique, which revealed that the grown crystal belonged to the softer category. BASQ crystal void estimation reveals the mechanical strength and porosity of the material.