Arvind Nautiyal

Structural and ferroelectric properties of spray deposited sodium nitrite:poly(vinyl alcohol) composite films

The composite films of sodium nitrite (NaNO2) and poly(vinyl alcohol) (PVA) have been deposited by spray technique at different substrate temperatures. The x-ray diffraction study revealed structural distortion (b/a ratio) in the composite films. The field-emission scanning electron microscopy images suggest that PVA polymer facilitate the homogeneous distribution of spherical grains of NaNO2 with less porosity. The grain size is found to increase with the deposition temperature. The study of hysteresis loop characteristics gave optimum Pr at deposition temperature of 200 °C, which may be due to large structural distortion and less porosity. The back switching calculations and the switching characteristics indicate that 180° domains contribute more in the composite than the pure NaNO2 film. The 1/ϵ0(dP/dE)-E curves exhibit two coercive fields correspond to 180° and 90° domains. The composite film also showed improved fatigue characteristics.

Analysis of ferroelectric polarization switching in (NH4)0.39K0.61NO3 films using nucleation limited switching model

The polarization switching transients of spray deposited ferroelectric (NH4)0.39K0.61NO3 (NKN) films has been analyzed with nucleation limited switching (NLS) model by considering domain growth limited process. The experimentally measured microscopic polarization switching curves fitted well with NLS model and the characteristic switching times obeyed the Lorentzian distribution function. The local field variation was found to be minimum at pulse amplitude 15 V, which makes the polarization reversal more probable. The value of spontaneous polarization, Ps and coercive field, Ec was found to be 6.58 μC/cm2 and 4.10 kV/cm, respectively. The value of Ps from the switching and P-E loop is in good agreement with each other. The field emission scanning electron microscopy and atomic force microscopy images of the NKN film reveal the formation of nanoparticles of NKN.The polarization switching transients of spray deposited ferroelectric (NH4)0.39K0.61NO3 (NKN) films has been analyzed with nucleation limited switching (NLS) model by considering domain growth limited process. The experimentally measured microscopic polarization switching curves fitted well with NLS model and the characteristic switching times obeyed the Lorentzian distribution function. The local field variation was found to be minimum at pulse amplitude 15 V, which makes the polarization reversal more probable. The value of spontaneous polarization, Ps and coercive field, Ec was found to be 6.58 μC/cm2 and 4.10 kV/cm, respectively. The value of Ps from the switching and P-E loop is in good agreement with each other. The field emission scanning electron microscopy and atomic force microscopy images of the NKN film reveal the formation of nanoparticles of NKN.

Preparation and Characterization of the Ferroelectric Potassium Nitrate: Poly(vinyl alcohol) Composite Films

The composite films of ferroelectric potassium nitrate (KNO3):poly(vinyl alcohol) (PVA) with different weight percentages of KNO3 have been prepared at 200degC using the spray-deposition technique. The remanent polarization (Pr) and peak current density for all composite films was estimated by tracing the polarization-electric field (P-E) hysteresis loop and current density-electric field (J-E) loop, respectively, using a modified Sawyer-Tower circuit. Pure KNO3 is known not to exhibit any ferroelectricity under ambient conditions, but the X-ray diffraction (XRD) studies of PVA:KNO3 composite films reveal the presence of a ferroelectric phase III of KNO3 in the composite films at room temperature. The composite film containing KNO3:PVA in equal proportions shows maximum Pr and peak intensity ratio of approximately 20.10 muC/ cm2 and 2.67, respectively, at room temperature. The J-E and capacitance voltage (C-V) characteristics exhibit butterfly features that supports the presence of a ferroelectric phase in the composite films. The field emission scanning electron microscopy (FE-SEM) image of the composite film containing equal proportions of KNO3 and PVA shows the homogenous distribution of spherical grains of KNO3 of size ~225 nm.

Ferroelectric and Magnetic Properties of Hot-Pressed BiFeO3-PVDF Composite Films

The ferroelectric and magnetic properties of hot-pressed BiFeO3- (BFO) polyvinylidene fluoride (PVDF) composite films have been studied. The BiFeO3 (BFO) ceramics have been synthesized by a rapid liquid phase sintering technique. The X-ray diffraction (XRD) studies revealed that the impure phase observed in pure BFO ceramics was significantly reduced in the composite films. The presence of both ferroelectric and magnetic hysteresis loops confirms the multiferroic nature of the composite films at room temperature. A well-saturated ferroelectric hysteresis loop with a remanent polarization (𝑃𝑟)∼4.8 μC-cm−2 and coercive field (𝐸𝑐)∼1.55 kV/cm has been observed in composite thin films at room temperature. The magnetic hysteresis loops were traced at room temperature with SQUID. The remanent magnetization (𝑀𝑟)∼3.0×10−3 emu/gm and coercive field (𝐻𝑐)∼0.99 kOe was observed in the composite film. The magnetic polarization of the composite films has found to be enhanced as compared to pure BFO and correlated to reduction in BFO impure peak intensity.

Polarization Switching in Ferroelectric Sodium Nitrite Thick Film

The effect of pulse amplitude on the domain switching properties of sodium nitrite film at room temperature has been studied. The atomic force microscopy (AFM) has been employed to estimate the grain size and morphology of the film. The polarization current and the switching time exhibit the exponential dependence on the pulse amplitude. The activation field, domain wall velocity and nucleation rate are determined by employing finite grain theory to the experimental switching current transients. The exponential dependence of wall velocity suggests the nucleation mechanism for the domain wall motion.

Ferroelectric and Switching Properties of Spray Deposited NaNO2: PVA Composite Films on Porous Silicon

The ferroelectric and switching properties of spray deposited sodium nitrite (NaNO2) - poly vinyl alcohol (PVA) composite films on porous silicon template have been analyzed. The image of field emission scanning electron microscope (FE-SEM) shows that the average pore size varies from 800 to 1250 nm with the anodization time of silicon. The remanent polarization of the composite films is dependent on the pore size of the silicon. The optimum value of remanent polarization (Pr) = 41μC/cm2 is observed in NaNO2: PVA composite film for pore size 1250 nm. The switching kinetics of the composite films has been analyzed by different theoretical model. The switching current data are fitted well with infinite-grain model (IGM) in the lower time region and deviate in later time region. The nucleation limited switching (NLS) model gives excellent agreement with the experimental polarization reversal transients throughout the whole time range.

Investigation on structural and ferroelectric properties of spray deposited Cs 1-x K x NO 3 : PVA : composite films

The ferroelectric and fatigue properties of spray deposited K - substituted cesium nitrate: poly (vinyl alcohol) composite films have been studied. The XRD pattern confirms the presence of ferroelectric phase of CsNO3 in the composite films upto doping concentration of 7.5%. The elemental analysis has been studied using EDX measurements. It is observed the remanent polarization (Pr) increases linearly that with doping concentration and optimum value of Pr = 9.2 μC/cm2 was found. The fatigue measurements also show improvement in K - substituted composite films. The switching time has been found to reduce four times in the K - substituted films. The C - V characteristics of the composite films show the butterfly feature and also confirm presence of ferroelectricity in the composite films.

Switching Kinetics in Cesium Nitrate: Poly (Vinyl Alcohol) Composite Film

The effect of pulse amplitude on the switching properties of cesium nitrate: poly (vinyl alcohol) composite film at room temperature has been studied. The switching response of the composite film was studied using the bipolar square pulses. The switching current transients were analyzed using finite grain model (FGM) and infinite grain media (IGM). The Matlab programming based upon the assumptions of FGM and IGM theories is used to fit the experimental data with the theoretical. The microscopic parameters such as effective dimensionality, switching time, nucleation rate, and domain wall velocity have been estimated. The polarization current and domain wall velocity exhibited exponential dependence on the pulse amplitude.

Structural and Ferroelectric Properties of NaNO2: PVF Composite Film

The structural and ferroelectric properties of NaNO2: PVF composite film prepared by hot press method have been studied and analyzed. The x-ray diffraction study revealed that the strain is reduced in the composite film. The image of field emission scanning electron microscope shows uniform distribution of NaNO2 grains of 150 nm size in the composite film. The differential scanning calorimetric curve supports the presence of ferroelectric phase. The polarization reversal characteristics were studied with the bipolar square pulse. The application of Ishibashi and Shur’s theory to the experimental switching transients supports needle like domain growth (1D) during switching process. The remanent polarization obtained from the polarization reversal is in agreement with the hysteresis loop value. The composite film shows faster switching time compared to pure NaNO2 film and may be attributed to the reduced strain.

Suspended microstrip line on multilayer ferroelectric - polymer composite film for ku-band tuneable applications

Suspended microstrip line on multilayer ferroelectric-polymer composite film is investigated to determine its dispersion and propagation characteristics. Full wave FEM simulator HFSS is used to determine propagating modes and their field configurations in this complex structure. Initial dielectric constant of the ferroelectric film (BaTiO3) is selected as 10 and it is varied up to 300. For low value of epsivr film (~10), this structure supports propagating mode similar to quasi TEM mode. But as we increase the value of dielectric constant of film, higher order modes starts propagating and the energy transmission takes place mainly through surface wave like modes and field lines of desired mode in the structure is concentrated in the high dielectric constant film layer and wave propagation is taking place through the dielectric.