ABSTRACT
In this work we describe the synthesis, micro structure (XRD, SEM) and EPR of NiO nanoparticles synthesized by urea-based combustion method using Ni nitrate as the source of Ni. We used fuel-to-oxidizer ratio (psi) as a control parameter to investigate how lattice parameter, particle size and EPR susceptibility vary with psi = 0.25 to 2. Earlier we have studied NiO as a substitutional solute in MgO. The average particle size of NiO was estimated from the full width half maximum (gaussian and lorentzian fits) of the X-ray diffraction peaks of powders using Sherrer's formula and Williamson-Hall plot. The particle size varies from 7 nm to 38 nm as psi is varied systematically. The surface areas were measured using BET method. FT-IR confirms the Ni-O crystalline bond formation. We also calculated porosity and strain in the NiO nanoparticles with varying psi. EPR spectra have yielded the susceptibility of the NiO nanoparticles. Band gap of NiO was determined by UV-visible absorption edge.
ABSTRACT
Electron paramagnetic resonance (EPR) of two intrinsic paramagnetic centers generated by soft mechanochemistry of Ag and I to yield zinc blende gamma-AgI nanoparticles (approximately 38 nm) has been used for the first time to probe the gamma-alpha (body centered cubic) superionic phase transitions in AgI at (423 +/- 1) K. These results are agreeable with the differential scanning calorimetric studies. A transmission electron microscope picture shows the average crystallite size in the range of approximately 30-40 nm. A hole-type Ag-related paramagnetic center (Ag2+) with an average g = 2.21025 value is remarkably sensitive to the first-order phase transition exhibiting sharp drops at the phase transition temperature (T(t)) and complete reversibility. The T(t) is characterized by a sharp, abrupt rise in the inverse paramagnetic susceptibility 1/chi by 1 order (7.4 x 10(10) to 3.17 x 10(11) in kg m(-3)) which reflects changes in the bonding of the material. Furthermore, a sharp signal at g = 2.0019 (deltaH(PP) = 10 G) due to an electron-excess center (Ag0) as a result of Ag metal nanoclusters also formed during the mechanochemical reaction (MCR) yields an abrupt and drastic decrease in the intensity observed at T(t) = 423 K. From high-temperature (323 to 433 K) I-V characteristics, the evolution of nonohmic behavior is observed on the order of 10(-9)-10(-6) A with increasing temperature until below T(t) which becomes ohmic thereafter. The reason could be the creation of an electronic defect such as Ag0 metal nanoclusters formed during the near-equilibrium mechanochemical reaction, with the increased excess free energy favoring the formation of gamma-AgI nanoparticles.
ABSTRACT
Controlled iodization and Sn doping of vacuum-evaporated Ag films has helped understand the initial-stage kinetics of AgI nanoparticle growth under ambient conditions. Use of XRD, optical spectroscopy, and AFM has unravelled systematic correlation between Sn-induced disorder in Ag crystal structure, nanoparticle size, and exciton growth dynamics. Sn doping of Ag leads to three specific effects: removal of UV absorption minimum in Ag, introduction of a plasmon-type absorption in the red region, and a reduction in particle size in thicker (than 10 nm) films (but an increase in particle size in 10 nm films) relative to that in undoped Ag films.
Subject(s)
Iodides/chemistry , Nanostructures/chemistry , Nanostructures/ultrastructure , Photochemistry/methods , Silver Compounds/chemistry , Tin/chemistry , Crystallization/methods , Iodides/analysis , Iodides/radiation effects , Light , Luminescence , Materials Testing , Nanostructures/analysis , Particle Size , Semiconductors , Silver Compounds/analysis , Silver Compounds/radiation effects , Solutions , Tin/analysis , Tin/radiation effectsABSTRACT
EPR and optical absorption spectra of Cr3+ ions doped in KZnClSO4 x 3H2O single crystals have been studied at room temperature. The EPR spectrum exhibits a group of three fine structure transitions characteristic of Cr3+ ions. From the observed EPR spectra, the spin-Hamiltonian parameters have been determined. The optical absorption spectrum exhibits two broad bands characteristic of Cr3+ ions in an octahedral symmetry. From the observed band positions, the crystal field parameters have been evaluated.