Chander Shekhar

Mn-doped calcium fluoride (CaF₂) Nanophosphors with varying dopant concentrations (1–4 mol%) were successfully synthesized via a facile and cost-effective combustion method. The X-ray diffraction (XRD) studies confirm the cubic fluorite lattice structure of CaF₂ with prominent reflections indexed to the (111), (220), (311), (400), (331), and (422) planes. No secondary phases were observed, indicating successful doping of Mn2+ ions into the CaF₂ lattice with average crystallite size of ~56 nm for undoped CaF₂ calculated using the Scherrer equation. Surface morphology examined by scanning electron microscopy (SEM) revealed uniformly & densely packed nanograins with nearly spherical to irregular morphology distribution, while Mn-doped samples showed variations in particle size with increasing dopant concentration in SEM images. The elemental composition was confirmed by Energy-dispersive X-ray spectroscopy (EDS) analysis. Thermoluminescence (TL) characteristics of the prepared phosphors were evaluated after irradiation with a 6 MV photon beam and computerized glow peak de-convolution (CGCD) method was used to find the number of component glow peaks. The effect of Mn2⁺ concentration on TL response was systematically investigated and the maximum TL intensity and sensitivity was observed at 1 mol% of Mn dopant. Also, the prepared CaF₂: Mn nanophosphor exhibited a linear TL dose response in the clinical dose range of 1.5 to 100 Gy, demonstrating their potential application as TL phosphors for clinical radiation dosimetry.

The Pb(Ni_1/3Nb_2/3)O₃ (PNN) ceramics was synthesized by two different methods, viz. (i) single step and (ii) double step. Phase formation of powders prepared by both the methods at various temperatures and lead excess were analyzed by X-ray diffraction (XRD) and Raman scattering experiments. The studies revealed that for single step method the unreacted phases diminished with increase of firing temperature and only impure nickel niobate phase remained at 1200°C. Addition of 4 wt% excess lead oxide reduced the impure nickel niobate phase concentration from 8.9% to 4.2% for the single step method. Addition of 2 wt% excess lead oxide was found sufficient to remove pyrochlore nickel niobate phase for double step method. Temperature dependent XRD showed pure phase throughout the temperature range of 35 to 350 K indicating the stability of the phase formed. The Raman study also confirmed the formation of pure perovskite phase. GRAPHICAL ABSTRACT

Lead nickel tantalate (PNT) ceramic was prepared by solid-state reaction method using 2-step columbite precursor route. Phase analysis of samples sintered at 1473 K shows PNT pyrochlore phase with minute peaks of NiO rich phase. 2-phase Rietveld refinement of x-ray diffraction patterns reveal ∼92.4 (0.33) % pyrochlore phase (cubic structure; space group: Fd-3m; a = 10.5867(4) Å). From temperature dependent dielectric constant and dissipation factor study, strong frequency dependent dielectric anomaly within 140–240 K, related to relaxation rather than structural changes in PNT ceramic is obtained. Observed Arrhenius behavior of dielectric relaxation is believed to be associated with single-ionized oxygen defect hopping.

Dielectric properties of single phase PbNi_1/3Nb_2/3O₃ (PNN) ceramic prepared by two step coulmbite method has been investigates thoroughly. The value of degree of relaxational constant ΔT_m ∼24, and diffuseness parameter calculated from the modified Curie-Weiss fitting δ_A ∼111, suggests higher dielectric relaxation strength for PNN in comparison to well-known PbMg_1/3Nb_2/3O₃ PMN. Frequency dependence of temperature of dielectric maximum (ε^’_m) is fitted with Arrhenius, Dipolar glass, stretched exponential and cluster glass model. The attempt frequency of physically acceptable process has been obtained from cluster glass model, which indicates critical slowing down of PNR dynamics.