R. Nath

Study of ferroelectric properties in sodium nitrite:poly(vinyl alcohol) nanocomposite films

The ferroelectric properties of sodium nitrite (NaNO2):poly(vinyl alcohol) nanocomposite films prepared by the solvent cast method have been studied. The optimization of the ferroelectric properties of the composite films as a function of the composition gave 50wt% to be the optimum value. The enhanced remanent polarization was observed in the composite in the frequency range of 10Hz–1kHz. The stability of the ferroelectric polarization shows improvement over the pure NaNO2 films. The x-ray diffraction study revealed that the strain is reduced in the composite films. The images of field emission scanning electron microscope showed the nanosize and uniform distribution of particles in 50wt% composite. The improved values of the polarization and stability have been attributed to the reduced strain in the composite. The ferroelectric phase transition peak was observed in the differential scanning calorimetry (DSC) scan. The ferroelectric phase transition temperature of the composite film obtained from the ca...

Ferroelectric phase stability studies in potassium nitrate: Polyvinylidene fluoride composite films

The structural and thermal properties of potassium nitrate (KNO3): polyvinylidene fluoride composite films have been studied. Differential scanning calorimetry has been employed to characterize the phase transitions in the composite and x-ray diffraction has been used to quantify the crystalline phases. The ferroelectric phase (III) of KNO3 is stabilized relative to the paraelectric phase (II) at room temperature at concentration ⩽50wt%, with the largest proportion at 50wt%. The enthalpies and transition temperature width are also affected in the composite. The polarization hysteresis loops also show that the remanent polarization is largest at 50wt% of KNO3. The capacitance–voltage characteristics exhibit strong hysteresis with pronounced peaks and some asymmetry. The switching current behavior of the composite film was also investigated and supports the presence of ferroelectric phase in the composite film at room temperature.

Ferroelectric polarization switching in KNO3 : PVDF films

The ferroelectric behaviour of KNO3 : PVDF composite films was studied. The ferroelectric polarization versus voltage (P–V) and polarization current density versus voltage (J–V) characteristics were simultaneously investigated in 20% KNO3 composite film. The remanent polarization and coercive voltage have been obtained. The frequency dependence of coercive voltage (Vc) shows Vc∝f1/n, where n≈6.6. The polarization fatigue effect investigations on the composite films gave Pr to be approximately constant up to 4×105 cycles. The switching response was studied using square wave signal and Ishibashi and Takagi theory was applied to the switching current transient. The needle like domain growth is believed to be involved in the switching process of the composite films. The effective of voltage and doping per cent of KNO3 (by weight) on switching transients has been also investigated. The effective dimensionality has been found to decrease with doping percentage of KNO3. The switched charges do not show monotonic increase with voltage for the composite films below 50% KNO3 doping level.

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.

The piezoelectric effect and stored polarization in corona charged ABS films

The piezoelectric coefficient of poly-(acrylonitrile-co-butadiene-co-styrene) (ABS) terpolymer films has been measured as a function of various poling and stretching conditions. has been measured in ABS films for a poling field of about , poling temperature C and stretching ratio 4. The stored polarization in piezo ABS films has been estimated using thermally stimulated depolarization current (TSC) experiments. The contributions of the dimensional effect and the polarization to the piezoelectricity in the ABS films have been determined. Cooperative dipolar behaviour is believed to be involved in the stored polarization.

Thermal and ferroelectric properties of potassium nitrate: polyvinyl fluoride composite films

The thermal and ferroelectric properties of potassium nitrate (KNO/sub 3/): polyvinyl fluoride (PVF) composite films have been studied. The dielectric constant has been measured as a function of temperature and shows a sharp change during heating and cooling cycles. Differential scanning calorimetry (DSC) has been employed to characterize the phase transitions and corresponding enthalpies in the composite. A good correlation has been found between the transition peak temperatures of the DSC and the transition temperatures of the dielectric measurements in the composite films. The DSC experiments suggest that phase III is retained at room temperature in the composite films. The switching current investigations support the presence of ferroelectric phase in the composite film. The capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics of the composite films exhibit essential butterfly features of a ferroelectric material.

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.