Shivani Suri

Mechanical Behaviour and Fracture Mechanics of Praseodymium Modified Lead Titanate Ceramics Prepared by Solid-State Reaction Route

The praseodymium modified lead titanate ceramics with composition where = 0.04, 0.06, 0.08, and 0.10 prepared by solid-state reaction technique were subjected to indentation induced hardness testing method. The indentations were induced in the applied load ranging from 0.245 N to 4.90 N. The microhardness varies nonlinearly with load and was best explained by the concept of Newtonian resistance pressure as proposed by Hays and Kendall’s law. Crack propagation, fracture toughness (), brittleness index (), and yield strength () were studied to understand the effect of Pr content on various mechanical parameters. The load independent values were found to increase with the increase in praseodymium content.

Dielectric and Conductivity Studies on Pure and Cadmium Doped Barium Phosphate Crystals

Single crystal barium phosphate and cadmium doped barium phosphate has been grown by a room temperature solution technique. Single crystal x-ray diffraction (XRD) establishes that the grown crystal belongs to the orthorhombic system. The dielectric and a.c conductivity properties were investigated thoroughly with regard to change in temperature and frequency. The variation of the dielectric constant (ϵ/), dielectric loss (tanδ) and a.c conductivity ln(σac) was measured in the frequency range of 5 kHz to 1 MHz and in the temperature range of 40 to 420°C. The increase in the value of ϵ/ is almost linear at low temperature whereas, at high temperature its value increases sharply. However, in barium phosphate crystals, there is a shift in the value of ϵ/ at higher temperature indicating relaxor type behaviour of the material. The dielectric measurements indicate the transition in the material to be a diffuse phase transition, whose nature can be explained by the relation 1/ϵ/ − 1/ϵ/ max = A (T – Tc)γ. The tanδ and ln (σac) shows the temperature as well as frequency dependence. The activation energy at various fixed frequencies is calculated from the slope of the graph between ln (σac) versus 1/T (x 103 K−1).

Effect of neodymium doping on structural, microscopic and electrical properties of barium phosphate system

Neodymium-doped barium phosphate (NdBP) was prepared as single crystal by room temperature solution technique known as gel encapsulation technique. Single crystal X-ray diffraction shows that the crystal belongs to orthorhombic system. The flower type morphology was observed by scanning electron microscope (SEM) and the stoichiometric composition of the prepared crystal was observed by energy dispersive X-ray analysis (EDAX). The presence of functional group and other groups was studied by Fourier transform infrared spectroscopy (FTIR). The electrical properties of these materials like dielectric constant (e′), dielectric loss (tanδ) and ac conductivity [ln(σac)] was studied at different temperatures ranging from 40°C to 420°C in the frequency range of 5 kHz to 1 MHz. The activation energy values decreases with increase in frequency suggesting that the conduction mechanism is because of hopping of charge carriers.

Synthesis, Characterization, and Thermal Kinetics of Mixed Gadolinium: Calcium Heptamolybdate System.

Synthesis of mixed gadolinium calcium heptamolybdate (GdCaHM) system in silica gel medium using single gel single tube technique has been successfully achieved. The grown crystal exhibits various morphologies, which includes spherulites, multifaceted, and square platelets. The nature of the grown material was established by X-ray diffraction (XRD) studies. Fourier transform infrared spectroscopy (FTIR) study signifies the presence of heptamolybdate (Mo7O24) and water symmetry structure, whereas energy dispersive X-ray analysis (EDAX) establishes the stoichiometric of the grown crystal as GdCaMo7O24·8H2O. The thermal behaviour was studied using the thermoanalytical techniques, which include thermogravimetry (TG), differential thermal analysis (DTA), and differential scanning calorimetry (DSC). Results obtained on the application of TG based models, namely, Horowitz-Metzger, Coats-Redfern, and Piloyan-Novikova, suggest the contracting cylindrical model as the relevant model for the thermal decomposition of the material. The kinetic parameters, namely, the order of reaction (n), activation energy (E a), frequency factor (Z), and entropy (ΔS∗), were also calculated using these three models.

Preparation of Samarium Doped Calcium Hydrogen Phosphate and Study of Its Density and Thermal and Dielectric Characteristics

Samarium doped calcium hydrogen phosphate was synthesized as single crystal by room temperature solution growth technique, namely, silica gel technique. The kinetics of the growth parameters was studied with regard to variation of pH, dopant concentration, gel ageing, and upper reactant concentration. The optimum conditions for the growth of good quality single crystal were worked out. Single crystal X-ray diffraction analysis establishes that the crystal belongs to monoclinic system. The density observed by the flotation method is greater than the density of the reported pure calcium hydrogen phosphate thereby suggesting the incorporation of the dopant (Sm) ion into the lattice of host (CHP). Thermal analysis gave two sharp endothermic peaks which are due to partial dehydration and phase transition, respectively. Dielectric studies establish a shift in the Curie temperature from 355 to 370°C only at higher frequencies thereby suggesting the relaxational behavior of the material.

Microstructural, Thermal and Dielectric Characteristics of Yttrium Modified Lead Titanate Ceramics

Yttrium modified lead titanate were prepared by solid-state reaction technique with molecular formula Pb1-xYxTi1–2yMoyFeyO3 with varying ‘x’ (where x = 0.05, 0.10, 0.15, 0.20) and keeping ‘y’ as constant (i.e., y = 0.02). Cold pressed pallets were firstly calcinated at temperature 800°C and then sintered at 1100°C for 2hrs. The grown material belongs to tetragonal crystal with lattice parameter a = b = 3.899 Å, and c = 4.103 Å. Microstructural analysis and energy dispersive x-ray analysis (EDAX) were carried out to find the grain size as well as the chemical composition of the grown material respectively. Thermal analysis suggests that calcinated yttrium modified lead titanate (PT) ceramics are not single phase. Dielectric characteristics suggest frequency and temperature dependence of yttrium modified lead titanate.