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Open Access
Development of unified model for the size and shape dependent properties of nanomaterials
(G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand), 2019-11) Chhabra, Hina; Munish Kumar
In the present thesis, we made an attempt to develop a unified model based on the Bond energy model to study the thermodynamic properties of nanomaterials under varying conditions of size, shape, pressure, and temperature. We extended the model to compute the size and shape dependence of magnetic properties viz. Curie temperature TC(D), magnetization MS(D) and Neel temperature TN(D), where D denotes the size of nanoparticles. It is found that TC(D) and MS(D) decrease with decrease in size. TN(D) is found to increase or decrease with dropping D, depending on the interaction strength at the film/substrate interface. It is observed that the shape effect is much more prominent for the smaller size and decreases for greater size. The model was extended to other nanomaterials in different sizes and shapes. The results obtained for corresponding bulk material are also included for comparison purposes. Surface to volume atomic ratio is also computed using the present model and used to explain the results. We used Murnaghan EOS to study the compression behavior of nanomaterials and it shows a slight variation at high pressures for bulk materials. Further, a unified model has also been used to study the effect of size, shape, pressure, and temperature on different properties of nanomaterials as well as bulk materials. A fair agreement between theory and experiment demonstrates the suitability of the theory used in the present thesis. Some results are reported in the absence of experimental data that may be useful for future studies. To discuss different phenomena using a single model is the dream of researchers, which is much difficult task. Moreover, the present thesis provides the theory for this purpose and therefore, the work may be useful for researchers.
Open Access
Comparative study of Bell's states
(G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand), 2019-08) Airy, Balwant Singh; Johri, U.C.
I have studied the effect of one and two sided amplitude damping, phase damping and depolarization channels on the Bell’s states. I found that in the case of two sided amplitude damping second state protects more entanglement compared to the first state and in the case of one sided amplitude damping both states protect the same amount of entanglement. In the case of one or two sided phase damping both the Bell’s states protect same amount of entanglement. In the case of two sided depolarization channels both the Bell’s states protect the same amount of entanglement while in the case of one sided depolarization channels, second state protects more amount of entanglement compared to the first. Ihave used weak measurement and quantum measurement reversal to protect entanglement against amplitude damping. I found that by using one or two qubit weak measurement and quantum measurement reversal entanglement can be protected effectively. Either in the case of two qubit weak measurement and quantum measurement reversal or one qubit weak measurementand quantum measurement reversal, second state is more protected as compared to the first state. I also studied the effect of correlated amplitude damping on Bell’s states and found that the memory parameter plays an important role. It helps in the protection of entanglement. I found that in the case of correlated amplitude damping, second state protects more entanglement as compared to the first state. As in the case of amplitude damping, weak measurement and quantum measurement reversal can be effectively used to protect entanglement.I found that in the case of two qubit as well as one qubit weak measurement and quantum measurement reversal, second state protects more amount of entanglement as compared to the first state.
Open Access
Thermal and electrical behaviour of nanomaterials under the influence of size, shape and pressure
(G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand), 2019-08) Pachauri, Uma; Joshi, Depika P.
In the present work, the effect of size, shape and pressure have been studied on thermal and electrical properties of nanomaterials. Collective effect of size and pressure has been analyzed on thermal properties like Grüneisen parameter, melting temperature and Debye temperature for metallic nanoparticles. It was observed that Grüneisen parameter decreases with the decrement in the size of nanoparticle. The obtained results from the combined study of size and pressure on Grüneisen parameter revealed that Grüneisen parameter decreases linearly with increment of pressure. Most of the metal nanoparticles show approximately 5-10 % decrement. While the Debye temperature and melting temperature show an opposite behavior (i.e. increment) under the effect of pressure for nanoparticles. Present thesis work not only focused on metal nanoparticles but also provides the size and shape dependent behaviour of electrical resistivity for metal nanowires. On moving towards the nano range, the scattering effects play important role therefore in this study the effect of electron scattering (surface scattering and grain-boundary scattering) is incorporated with size and different cross-sectional shapes of nanowires. It has been obtained that electrical resistivity have higher value than the bulk value due to size reduction and scattering effects. The results also revealed that the shape effect is also an important factor at nano range. The electrical resistivity is higher for nanowires having large shape factor and is lowest for circular nanowires. An enhancement in the value of electrical resistivity has observed with the increment in reflection coefficient. The present work also includes the dielectric study of semiconductor nanomaterials. The size and dimension effect on electrical susceptibility and dielectric constant has been observed. It was found that electrical susceptibility and dielectric constant both decreases with decreasing size of nanomaterials. It was also observed that the electrical susceptibility and dielectric constant depends on the dimension of nanomaterials, the largest decrement was found in nanoparticles and the least for nanofilms. Shape effect has also been incorporated for semiconductor nanowires and the results showed that non-cylindrical nanowires have less value of dielectric constant in comparison to cylindrical nanowires. The obtained results have been compared with the available simulated and experimental data. Consistency in results of proposed model and available experimental data supports the validity of present work.
Open Access
Neutronics study for materials of interest in fusion technology
(G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand), 2019-02) Pandey, Jyoti; Agrawal, H.M.
Open Access
Dynamics of quantum correlation in presence of environment
(G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand), 2019-01) Awasthi, Natasha; Johri, U.C.
We establish uncertainty relations between information loss in general open quantum systems and the amount of nonergodicity of the corresponding dynamics. The relations hold for arbitrary quantum systems interacting with an arbitrary quantum environment. The elements of the uncertainty relations are quantified via distance measures on the space of quantum density matrices. The relations hold for arbitrary distance measures satisfying a set of intuitively satisfactory axioms. The relations show that as the nonergodicity of the dynamics increases, the lower bound on information loss decreases, which validates the belief that nonergodicity plays an important role in preserving information of quantum states undergoing lossy evolution. Considering a model of a central qubit interacting with a fermionic thermal bath its reduced dynamics is investigated for the information loss and nonergodicity. Recently, it was argued that the binegativity might be a good quantifier of entanglement for two-qubit states. Like the concurrence and the negativity, the binegativity is also analytically computable quantifier for all two qubits. Based on numerical evidence, it was conjectured that it is a PPT (positive partial transposition) monotone and thus fulfills the criterion to be a good measure of entanglement. This investigation shows its behaviour under noisy channels which indicate that the binegativity is decreasing monotonically with respect to increasing noise. Binegativity is closely connected to the negativity and has closed analytical form for arbitrary two qubits. Our study supports the conjecture that the binegativity is a monotone. The effect of correlated Markovian noise channels on the quantum speed limit of an open system is examined. This is done for correlated dephasing and amplitude damping channels for a two qubit atomic model. Our model serves as a platform for a detailed study of speed of quantum evolution in correlated open systems.
Open Access
Study for the thermodynamic properties of nanomaterials under varying conditions of size, shape, pressure and temperature
(G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand), 2017-07) Bhatt, Sandhya; Munish Kumar
Present thesis is an attempt to develop a unified theoretical model based on thermodynamic theory of solids to study the thermodynamic properties of nanomaterials under varying conditions of state parameters like pressure and temperature as well as on size and shape. We extended the bond energy model to study the effects of size and shape on melting and superheating for free-standing and embedded nanomaterials. Melting temperature of free standing nanomaterials decreases with the reduction of particle size whereas a reverse trend was found for embedded nanomaterials. A single model was found sufficient to explain both the phenomena. Then, the model was used to explain the specific heat and thermal conductivity of different nanomaterials for spherical as well as polyhedral shapes. Debye temperature and Raman frequency have been predicted successfully for different nanomaterials with spherical, wire and film shapes. Debye temperature, Raman frequency and thermal conductivity decrease with decreasing size whereas specific heat increases. Different models proposed for compression of solids have been modified. The effects of size, shape and temperature have been studied for density of nanoscale materials. Density decreases with the effect of size and shape. However, these effects were found obvious in low size range. A Model has also been developed to study the thermodynamic and elastic properties of nanominerals with the incorporation of size and shape which is also applicable for their bulk counterparts. The results obtained were found in fair agreement with the available experimental and simulation data thereby supporting the validity and applicability of formulations developed. To explain different cases using single model is the dream of researchers and in this thesis we made an attempt to make this dream true. The model predictions may be useful for future studies on nanomaterials.
Open Access
Studies on graphite based magnetic nano-composites
(G.B. Pant University of Agriculture and Technology, Pantnagar (Uttarakhand), 2016-12) Versha Rani; Srivastava, R.C.
Synthesis of composite systems with superparamagnetic and graphitic nanostructures is highly demanding due to their extensive applications in various fields. In the present work graphite (G) and graphene-oxide (GO) were used as fillers and magnetite (Fe3O4) NPs were used as matrix to form the graphite based magnetic nano-composites. All the samples were synthesized via the chemical coprecipitation method. Samples were characterized by XRD, FTIR, SEM, TGA/DTG, UV-Vis and VSM. The DC electrical conductivities, as a function of temperature were measured by using four probe method for various voltage compliances (1 V, 10 V and 100 V). Dielectric measurements were performed for the frequency range 500Hz-1MHz. The co-existence of both phases of G/GO and ferrite NPs were confirmed by XRD diffraction and FTIR. The addition of G and GO induced a surprising reduction in the crystallite size of ferrite NPs ranging 17.50 to 12 nm with retained cubic structure. The surface morphology of the samples were investigated by SEM. Fe3O4 NPs were found spherical in shape with a narrow particle size distribution. The grains could not be appeared clearly for the composites. TGA/DTG analysis indicated that all the samples showed the one step thermal decomposition behavior except G and GO. The thermal stability of the composite samples was found to increase with the addition of ferrite NPs into it. All the samples exhibited superparamagnetism at the room temperature. By the addition of G/GO into the ferrite NPs, the saturation magnetization was found to be reduced. The dielectric constant (ε’), loss tangent (tanδ) and loss factor (ε’’) rapidly decreased for the lower frequency range and reached a constant value for the high frequency range. The dielectric constant for composites get enhanced with the ferrite NPs. DC electrical conductivities for all the samples were found to increase with the increasing temperature. Composite samples showed the semiconducting nature. By adding G/GO, optical band gap of the samples were found to decrease. These results remark that graphitic nanocomposites have great potential for magnetic, capacitive and microwave absorption applications.
Open Access
Study for the effect of size, shape and pressure on thermophysical properties
(G.B. Pant University of Agriculture and Technology, Pantnagar (Uttarakhand), 2016-12) Arora, Neha; Joshi, Deepika P.
Present study is an effort to understand the effect of size, shape and pressure on thermophysical properties of nanomaterials. Thermodynamic properties like melting temperature, cohesive energy, vacancy formation energy and Debye temperature of nano metals for spherical and non spherical nanoparticles with different size have been studied. Effect of cross-sectional shape on melting temperature of metallic nanowires has also been observed. It was found that these thermal properties show decreasing trend with decrement in size of the nanomaterial. The obtained results also revealed that shape of the nanomaterial plays a vital role to affect the thermodynamic properties. We have extended our model for investigating effect of size and pressure on bulk modulus and melting of the nanometals, a general equation for melting has been derived. It is found that as the pressure increases there is the elevation in the melting temperature of nanometals. Under pressure melting temperature of small sized nanoparticles increases with the decrement of size. We have not only provided a pathway to study the thermophysical properties of nanometals but also studied some important properties of semiconductors at nanorange. A quantitative thermodynamic model for thermal conductivity and diffusivity of semiconductors was established considering surface scattering effects and atomic thermal vibrations with different size and dimension. Thermal conductivity and diffusivity of semiconducting nanomaterials with partially smooth and partially rough surfaces of different sizes and dimension have been calculated. Besides this a fresh approach has been proposed to study band gap of nanowires by incorporating shape effect with size. The results obtained are compared with the available simulated and experimental data. It is concluded that computed results are in close agreement with the experimental data, which supports the validity of present work.
Open Access
Study of thermo-elastic properties of nanomaterials under high pressure and high temperature
(G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand), 2008-05) Jeewan Chandra; Gupta, B.R.K.
T he study based on the EOS at high-pressure and high temperature is of fundamental interest because they permit interpolation and extrapolation in to the regions in which the experimental data are not available adequately. The Present work describes the theoretical study of thermo-elastic properties especially compression, thermal expansion, bulk modulus, thermal expansion coefficient of some of the nanomaterials by making use of Equation of State. For different class of solids a lot of numbers of equation of states are available. Among the number of isothermal and isobaric EOS described earlier, we prefer isothermal Usual Tait’s Equation of State (UTE) and isobaric Singh and Gupta Integral form of Equation of State (IFEOS) because of their simple and straightforward applications in high pressure and high temperature physics. We have reported the results obtained for thermo physical properties of nanomaterials i.e. n-SnO2, n-CeO2, n-PbS, n-MgO, nCuO, n-AlN, n-ZnO, n-NiO, n-TiO2, n-Ni, n-Ti, n-(Ni+Fe), n-Mo, individual single wall carbon nanotube (SWCNT), under effect of high temperatures and high pressures. The variation of compression (V/V0), isothermal bulk modulus (KT) and relative isothermal expansion coefficient ǂ(P)/ǂ0) with pressure have plotted and shown in tables, for nanocrystalline n-SnO2 with three particle sizes 3nm, 8nm and 14nm, n-CeO2, nanocrystalline MgO ( 100nm and 200nm), n-CuO, n-PbS ( 2.6nm, 5.4nm and 8.8nm), n-Ni(20nm and 62nm), n-Mo and n-AlN n-TiO2( 35nm and 6nm) and nZnO using Usual Tait’s equation of state. We have also calculated temperature dependence of thermal expansivity (ǂT), relative volume thermal expansion (V/V0) and bulk modulus (KT) of nanomaterials { n-ZnO, n-TiO2 anatase, n-NiO, n-Ni, n(Ni+Fe), n-Ti, and SWCNT(armchair CNT (5, 5), and zig-zag CNT (9, 0); both in axial as well as radial directions)}using IFEOS at different temperature and atmospheric pressure. The Integral form of Equation of State( IFEOS) is entirely free from the use of potentials and need only three input parameters such as Anderson Gruneisen parameter( 0 Tǅ ), volume thermal expansion coefficient(ǂ0) at zero pressure, reference temperature, and the thermo-elastic parameter k which can be calculated from the slope of the graph between log(ǅT) and log(T/T0). The calculated values are plotted with temperature and compared to available experimental data in order to compare the present results. All the results have been presented graphically. It may be noted here that the calculated values are in close agreement to the experimental data. Thus it is emphasized here that the Integral form of Equation of State (IFEOS) and Usual Taits Equation of State(UTE) successfully explains the thermo-elastic properties nanomaterials.

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