الفهرس 
Theoretical backgroundOnly 14 pages are availabe for public view
 |  | from | 199 |  |  |
| | | from | 199 | | |
Abstract
In the present work synthesis and characterization of undoped and Mn-doped ZnO nanoparticles are reported. Mn doped ZnO nanoparticles having composition (Zn1-xMnxO), where x = 0.00, 0.01, 0.03, 0.05, 0.07, 0.09, and 0.10 were synthesized by co-precipitation method, and sintered at 900oC for 4 hours in Argon gas atmosphere.
The physical properties of the samples were examined by X-Ray diffraction (XRD), Fourier transform infra-red spectroscopy (FTIR), and imaging the samples by the Transmission Electron Microscope (TEM).
The ac conductivity and the dielectric constant of Mn-doped ZnO were investigated at temperatures from 320 to 515K in the frequency range from 102 to 106 Hz using LCR meter.
The magnetization curve was measured for the samples at room temperature using a vibrating sample magnetometer (VSM).
We can summarize the main results as follows:
• The solubility limit of Mn in the host lattice (ZnO) is up to 5%, beyond this concentration a secondary phase (MnO) appears in the XRD patterns as well as in the FTIR spectra.
• The XRD patterns suggest that all the Mn-doped ZnO nanoparticles are constituted in a hexagonal wurzite crystal structure.
• With the increase in Mn concentration the crystal lattice parameters and the average crystallite size increases up to 5% and then decreases, while the strain has showed the opposite behavior.
• Both the dielectric constant and the dielectric loss were found to decrease with the increase in frequency and increase with the increase in temperature but the dielectric constant increases with Mn content, however the dielectric loss decreases with Mn content.
• The ac conductivity increases with the increase in temperature and the frequency of the applied field and decreases with the increase in Mn concentration.
• The non overlapping small polaron Tunneling (NSPT) mechanism is the predominant conduction mechanism in the first temperature range, while the correlated barrier hopping (CBH) mechanism is the predominant one in the second temperature range for these samples.
• The crossover temperature from tunneling to hopping over the barrier mechanism increases with the Mn content which enables the non overlapping small polaron tunneling conduction mechanism (NSPT) at room temperature and above for bare and Mn doped ZnO.
• By making a fitting of the experimental data in each temperature region with the above two models, the polaron hopping energy (WH), the spatial decay parameter (α-1) and the tunneling distance (Rω) for NSPT model and the maximum barrier height (WM ), the concentration of the pair states (N), and the hopping distance (Rω ) for CBH model could be calculated.
• The Mn doped samples show a ferromagnetic behavior, while a typical diamagnetic behavior was observed for pure ZnO.
• The magnetization values were increased from 26.9*10-3 emu/g to 75.5*10-3 emu/g for the 3% and the 5% Mn-doped ZnO nanoparticles, respectively.
Finally, based on results, Mn doping and preparing the samples in oxygen deficient atmosphere (Ar atmosphere) lead to the ferromagnetic behavior of the Mn doped ZnO samples. as well as lead to increase in the crossover temperature from tunneling to hopping over the barrier mechanism which enables the non overlapping small polaron tunneling conduction mechanism (NSPT) at room temperature and above and this may be helpful for improving the spintronics devices.