V M Jali
Articles written in Bulletin of Materials Science
Volume 25 Issue 3 June 2002 pp 191-196 Thermal Properties
The low thermal expansion ceramic system, Ca1-𝑥Sr𝑥Zr4P6O24, for the compositions with 𝑥 = 0, 0.25, 0.50, 0.75 and 1 was synthesized by solid-state reaction. The sintering characteristics were ascertained by bulk density measurements. The fracture surface microstructure examined by scanning electron microscopy showed the average grain size of 2.47 𝜇m for all the compositions. The thermal expansion data for these ceramic systems over the temperature range 25–800°C is reported. The sinterability of various solid solutions and the hysteresis in dilatometric behaviour are shown to be related to the crystallographic thermal expansion anisotropy. A steady increase in the amount of porosity and critical grain size with increase in 𝑥 is suggested to explain the observed decrease in the hysteresis.
Volume 31 Issue 4 August 2008 pp 631-634 Ceramics and Glasses
This paper describes the synthesis and spectroscopic studies of the glass system, 20Na2O–(20–𝑥) ZnO–𝑥ZnF2–60B2O3 (𝑥 = 0, 5, 10, 15, 20), prepared by melt quenching method. The analyses of DSC and XRD did not show the crystallinity of the glass sample. 11B MAS–NMR shows the presence of sharp peak around –14 ppm. From the IR studies, the broadening of the peak around 1200–1400 and 800–1100 cm-1 shows the presence of mixed linkages like B–O–B, B–O–Zn in the network.
Volume 32 Issue 6 December 2009 pp 597-601 Ceramics and Glasses
Elastic properties of Na2O–ZnO–ZnF2–B2O3 oxyfluoride glasses with different ZnF2 concentrations have been investigated using ultrasonic velocity measurements at room temperature, at a frequency of 10 MHz. Glasses prepared by melt quenching method were suitably polished for the ultrasonic velocity measurements using pulse-echo superposition method. Various elastic moduli have been calculated and their compositional dependence has been examined. The compositional dependence of elastic moduli with the concentration of ZnF2 shows decrease in the moduli initially, with further increase in ZnF2 the moduli sharply increases and then again tend to decrease when ZnF2 concentration is 20 mol%. The values of Poisson’s ratio lie in the range of 0.24–0.30, which is typical to covalent bonded network. The variation of 𝜃D with ZnF2 indicates complex behaviour of the glass network. The results have been analysed in view of the modified borate glass network. Addition of ZnF2 into the pure glass seems to influence the borate network by replacement of B–O–B linkages with B–O–Zn.
Volume 33 Issue 3 June 2010 pp 191-196 Thin Films and Nanomatter
The present paper deals with the study of the effects of electron (8 MeV) irradiation on the dielectric and ferroelectric properties of PbZrO3 thin films grown by sol–gel technique. The films were (0.62 𝜇m thick) subjected to electron irradiation using Microtron accelerator (delivered dose 80, 100, 120 kGy). The films were well crystallized prior to and after electron irradiation. However, local amorphization was observed after irradiation. There is an appreciable change in the dielectric constant after irradiation with different delivered doses. The dielectric loss showed significant frequency dispersion for both unirradiated and electron irradiated films. 𝑇c was found to shift towards higher temperature with increasing delivered dose. The effect of radiation induced increase of 𝜀′(𝑇) is related to an internal bias field, which is caused by radiation induced charges trapped at grain boundaries. The double butterfly loop is retained even after electron irradiation to the different delivered doses. The broader hysteresis loop seems to be related to radiation induced charges causing an enhanced space charge polarization. Radiation-induced oxygen vacancies do not change the general shape of the AFE hysteresis loop but they increase 𝑃s of the hysteresis at the electric field forced AFE to FE phase transition. We attribute the changes in the dielectric properties to the structural defects such as oxygen vacancies and radiation induced charges. The shift in 𝑇c, increase in dielectric constant, broader hysteresis loop, and increase in 𝑃r can be related to radiation induced charges causing space charge polarization. Double butterfly and hysteresis loops were retained indicative of AFE nature of the films.
Volume 34 Issue 5 August 2011 pp 1027-1031
Polycrystalline samples of the mixed nanoferrites, Li0.5+0.5𝑥Ti𝑥Fe2.5−1.5xO4 (0.02 ≤ 𝑥 ≤ 0.1), were prepared by combustion method at lower temperatures compared to the conventional high temperature sintering for the first time at low temperatures, using PEG which acts as a new fuel and oxidant. XRD patterns reveal a singlephase cubic spinel structure. The as synthesized Li–Ti ferrites are in nanocrystalline phase. The crystallite size was found to be in the range 16–27 nm. SEM images reveal rod-like morphology in all the samples with a discontinuous grain growth. The B–H loops have been traced using VSM technique, for all the compositions, at room temperature and the hysteresis parameters are calculated. Saturation magnetization decreases with increase in Ti content due to the fact that the Ti4+ ion, which is a non-magnetic ion, replaces a magnetic Fe3+ ion. The hysteresis loops show clear saturation at an applied field of ±10 kOe and the loops are highly symmetric in nature. The cation distribution is known indirectly by using saturation magnetization values.
Volume 42 | Issue 6
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