Udayan De

Structural and Optical Investigations of Radiation Damage in Transparent PET Polymer Films

Effects of gamma irradiation at different doses up to 135 kGy on polyethylene terephthalate (PET) polymer films have been investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and ultraviolet-visible (UV-VIS) spectroscopy. From XRD analysis, it was found that even at a high dose of gamma irradiation of 135 kGy, crystallinity of the PET samples remain unchanged. However, the FTIR peak at 871 cm−1 (depicting C–H bending mode of out-of-plane vibration) and another at 1303 cm−1 (representing C–H bending mode of in-plane vibration) disappear for gamma-irradiated PET. In this study, it has also been found that γ-irradiation in air enhances the optical absorption in the wavelength region 320–370 nm. This has been attributed to free radicals being produced in the polymer by the γ-radiation. Further, the free radicals react with oxygen of air to form carbonyl group and hydroxyls. With increasing γ-dose, there is a red shift of the UV—near visible cutoff for PET. XRD and FTIR observations on γ-damage have been correlated.

Structural Characterization of Orthorhombic and Rhombohedral Lead Meta-Niobate Samples

The meta-stable orthorhombic phase of lead meta-niobate (PbNb2O6), as obtained by quenching, is piezoelectric, but difficult to prepare in pure state as a few competing phases like the non-piezoelectric rhombohedral PbNb2O6 tend to form during the preparation. However, it can have an attractively high Curie temperature above 570°C. High Curie temperature piezoelectric sensors are desirable for imaging and other applications in certain industrial and research sectors. Presently, both phases have been synthesized as single phase samples as shown here from structural Rietveld analysis of their XRD. Characterization of both compounds by FTIR and XRD have been carried out and presented.

Ferroelectric Materials for High Temperature Piezoelectric Applications

Electronic control and operation in almost all advanced devices or machines involve use of various sensors and actuators, many of which are based on piezoelectric (PE) effect. Ferroelectric (FE) materials forming a sub-group of piezoelectric materials have additional applications. Subject to success in materials and related developments, PE and FE devices perform competitively with alternative devices but at lower cost in most cases. There is increasing commercial and technical interest for PE actuators (ranging from electronic muscles, fuel injectors and inkjet printers to various vibrators), PE sensors (pressure and other sensors and motion detection to energy recovery), and ultrasonic imaging devices. PE to non-PE transition temperature (Curie temperature for FE PE materials) and piezoelectric coefficients together decide the choice of the right material for any particular application. Since most of these applications, including medical ultrasonic imaging, are done at or near room temperature, low Curie temperature (but otherwise attractive) piezoelectric materials, based on barium titanate (BT), lead zirconate titanate (PZT) and relaxor ferroelectric ceramics, have served us well. However, a few important applications, in automobile and rocket exhausts, in some engines and gadgets, and inside high pressure molten metal in nuclear Fast Breeder Reactors (FBRs) involve high temperatures (HTs), higher than or nearing the Curie temperature of even PZT. These applications including FBRs, generating nuclear fuel and power, demand development of high temperature piezoelectric materials. FBRs can close the nuclear fuel cycle by partially using the nuclear waste (containing U-238) and thus minimize waste disposal problem. That makes nuclear energy a better green energy. Working on Th-232 from monazite sand, FBRs can breed Th-233, a nuclear fuel, with simultaneous generation of electricity. Ranging and imaging of nuclear fuel rods and control rods through the liquid metal coolant in FBRs, especially during insertion and withdrawal, help correct positioning of the rods to avoid any misalignment and possible nuclear accident. This “viewing” through the optically opaque liquid metal or alloy coolant, is possible by ultrasonic imaging of the rods using HT PE ultrasonic-generators and-detectors, an active area of research. Lithium niobate with T(Curie) > 1000°C and orthorhombic PbNb2O6 with T(Curie) > 570°C are two of many HT PE materials under development or in trial runs. In the present work, world-wide R & D on HT piezoelectric materials has been reviewed after an outline of the basics.

Positron annihilation and ion-conductivity studies of PEO-NH4ClO4 complexes

Abstract We present positron annihilation lifetime spectroscopy (PALS) results on the polymer electrolyte [PEO](1− x )–[NH 4 ClO 4 ]( x ), for different x , denoting weight fraction and their correlation to other properties. Variation of composition through change in x causes the ion conductivity and crystallinity to vary. We find that the changes are well reflected in variation of the positron annihilation lifetime components and their intensities. Although three distinct positron lifetime components have been identified, most of the earlier work considered only the longest component arising out of the noncrystalline regions in their explanation of ion-conductivity variation with temperature. Our room temperature study shows a new correlation. The average and bulk lifetimes, calculated from the two shorter lifetime components, is less at compositions with higher ion conductivity, suggesting some contribution of the crystalline regions to conductivity.

Dielectric Properties of PbNb2O6 up to 700°C from Impedance Spectroscopy

Piezoelectric materials have wide band gap and no inversion symmetry. Only the orthorhombic phase of lead metaniobate (PbNb2O6) can be ferroelectric and piezoelectric below Curie temperature, but not the rhombohedral phase. High temperature piezoelectric applications in current decades have revived international interest in orthorhombic PbNb2O6, synthesis of which in pure form is difficult and not well documented. Second problem is that its impedance spectroscopy (IS) data analysis is still incomplete. Present work attempts to fill up these two gaps. Presently found synthesis parameters yield purely orthorhombic PbNb2O6, as checked by X-ray Rietveld analysis and TEM. Present 20 Hz to 5.5 MHz IS from room temperature to 700°C shows its ferroelectric Curie temperature to be one of the highest reported, >574°C for 0.5 kHz and >580°C for 5.5 MHz. Dielectric characteristics and electrical properties (like capacitance, resistance and relaxation time of the equivalent CR circuit, AC and DC conductivities, and related activation energies), as derived here from a complete analysis of the IS data, are more extensive than what has yet been reported in the literature. All the properties show sharp changes across the Curie temperature. The temperature dependence of activation energies corresponding to AC and DC conductivities has been reexamined.

Dielectric Properties of Rhombohedral

Dielectric materials are needed in many electrical and electronic applications. So, basic characterizations need to be done for all dielectrics. (PN) is ferroelectric and piezoelectric only in its orthorhombic phase, with potential high temperature applications. So, its rhombohedral phase, frequently formed as an undesirable impurity in the preparation of orthorhombic PN, has been ignored with respect to possible dielectric characterizations. Here, essentially single phase rhombohedral PN has been prepared, checking structure from XRD Rietveld Analysis, and the real and imaginary parts of permittivity measured in an Impedance Spectrometer (IS) up to ~ and over 20 Hz to 5.5 MHz range, for heating and some cooling runs. Variations, with temperature, of relaxation time constant (), AC and DC conductivity, bulk resistance, activation energy and capacitance have been explored from our IS data.

Dielectric and Thermal Investigations on PbNb2O6 in Pure Piezoelectric Phase and Pure Non-Piezoelectric Phase

A high piezoelectric transition temperature is indicated for present orthorhombic samples of lead meta-niobate (PbNb2O6) by the high value of the temperature (Tm) at which the real part (ϵ′) of electrical permittivity peaks. It is 573 to 580°C. The imaginary component (ϵ″) increases sharply at these temperatures. Cooling run after heating to 700°C gives changed values of ϵ′ and ϵ″ and Tm. Present work reports impedance spectroscopy (up to 700°C over 20 Hz to 5.5 MHz) and Differential Scanning Calorimetry or DSC on the pure orthorhombic phase, and, for the first time, on the pure rhombohedral phase. DSC shows an endothermic dip across Tm during heating and an exothermic peak during cooling for the orthorhombic sample only.