The hexagonal w-type ferrite has a general formula in which A can be Ba, Pb or Sr and Me, a bivalent cation such as Ni, Fe or Co. This kind of ferrite with uniaxial anisotropy not only has the big crystal anisotropy but it has high saturation magnetization and magnetic inhibition. For this reason, today, it has been attracted many attentions in various industries. In the thesis, we have tried to synthesize the w-type hexaferrite nanostructures with a combination of PbCo2 Fe16O27 using the sol-gel auto-combustion method and studied the effects of time and temperature on the morphology, structural, magnetic, optic and dielectric properties of PbCo2Fe16O27 nanostructures. After using the thermal weighing (TG/DTA) All these properties were measured by X-ray Diffraction Pattern (XRD), Field Diffraction Scanning Electron Microscopy (FESEM), UV-vis spee, Fourier Transform Infrared Spectrum (FT-IR), Vibrational Sample Magnetometer (VSM) and LCR-meter. The results show that the most appropriate calcination temperature and time to prepare the nanostructure PbCo2Fe16O27 are respectively 6000c and 4 hours. In this calcination time and temperature, the special saturation magnetism and the special magnetic hysteresis have the highest value. The results from the measurements of the samples' dielectric proprieties show that in different calcination times and temperatures, the relative dielectric constant and dielectric loss of all samples are decreased with the increase in frequency, and their ac electric conductivity have an increasing trend in high frequency.

Spinel ferrites have the general formula MFe2O4 in which M can be divalent cation such as Mn, Zn and Sr. Ferrites of spinel are widely used in medical and industrial. Magnetic and optical properties of spinel ferrites depend on particles size, morphology, impurities and distribution of cations in tetrahedral and octahedral sites. In this thesis, strontium spinel ferrite (SrFe2O4) nanoparticles was synthesized by using the sol-gel method and then the effect of sintering temperature and time on structural , microstructural, magnetic, dielectric and optical properties have been investigated. The structural, microstructure, and morphology properties of samples were investigated by Thermo-Gravimetric analysis and Differential thermal analysis (TGA/DTA), X-ray diffraction pattern (XRD), Field emission scanning electron microscope (FESEM) and Fourier transform infrared spectroscopy (FT-IR). Also, the magnetic, dielectric and optical properties of the prepared samples, by Vibrating sample magnetometer (VSM), LCR meter, Ultraviolet-visible (UV-vis) spectrometer and Photoluminescence spectrum (PL) were characterized, respectively. Hysteresis loops of the samples showed that by increasing sintering temperature and time, the magnetic coercivity have been increased. Also, optical studies of the samples show that the energy gap of strontium spinel ferrite decreases by increasing sintering temperature. The results of the photoluminescence spectrum (PL) of SrFe2O4 nanoparticles show that a peak is related to the exiton transition. Also, by increasing the sintering temperature up to 900 0C not has shown a significant change in maximum wavelength of emission spectrum. For investigation Curie temperature of SrFe2O4 nanoparticles was used from a Faraday equilibrium technique. The results of the measurements show that the best sintering temperature and time for the preparation of SrFe2O4 nanoparticles is 700°C and 4h. The results of the dielectric measurement of the samples show that the dielectric constant and the dielectric loss were decreased by increasing the frequency, while ac electrical conductivity increases by increasing frequency and these changes were studied by the Maxwell – Wagner model.

M-type hexaferrites with general formula MFe12O19 where M= Ba, Sr, Pb are permanent magnet materiales. Hexaferrites have very important applications in industry due to high electrical resistivity, large saturation magnetization and high uniaxial anisotropy. Lead hexaferrite with the crystallization temperature lower than hexaferrit of strontium and barium is uery not eworthy. The thermal behavior of the precursor gel was evaluated by TG/DTA analysis. The structure, magnetic and dielectric properties were investigated by Fourier transform infrared spectroscopy, X-ray diffraction pattern, Scanning electron microscopy, vibrating sample magnetometer and LCR meter. In this thesis, the PbFe12-xCoxO19 nanoparticles with x= 0.5, 1, 1.5, 2 by sol gel method were synthesized and then the effect of doping cobalt, annealing temperature, annealing time on the structural, morphology, magnetic and dielectric properties were investigated. The results of magnetic measurements show that by increasing doping of Co in the PbFe12-xCoxO19 composition, the saturation magnetization and remanence magnetization increase, while coercivity decreases. Also, the results of LCR meter show that in all samples Co-doped lead hexaferrites the dielectric constant and dielectric loss decrse while ac electrical conductivity increases.The measurments show that the best sample is PbFe11Co1O19 with annealing temperature 850℃ and 1 h. also, the PbFe12-xMnxO19 nanoparticles with x= 0.5, 1, 1.5, 2 by sol gel method were synthesized and then the effect of doping manganese on the structural, morphology, magnetic and dielectric properties were investigated.

 Y- type hexaferrite is a ferimagnetic material with general formula of Ba2Me2Fe12O22 which Ba and Me can substituded by bivalent cations Sr2+ or pb2+, and divalent cation such as Co2+ or Cu2+, respectively. The most of the Y-type hexaferrites has a magnetization perpendicular to the c axis at room temperature. In this thesis first Y- type hexaferrites nanostructures with Sr2Co2Fe12O22 composition was synthesized by sol- gel auto-combustion method and than the effect of the annealing temperature, time, the molar ratio of citric acid to metal nitrates with the molar ratios of 0.5, 1, 1.5 and 2 have been studied. Then the effect of doping Cu2+ ion instead of Co2+ with x=0-1.2 were investigated. The structure and microstructure properties and also magnetic and dielectric properties of Sr2Co2Fe12O22 and Sr2Co2Cu2-xFe12O22 studied by thermogravimetric analysis (DTA/TGA), X- ray diffraction pattern (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM). Also magnetic and dielectric properties by VSM and LCR meter at room temperature have been characterized. The results of investigations show that the best sample with annealing temperature and time of 1000 ℃ and 3h, respectively. The molar ratio of citric acid 1:1.5 and also doping content of x= 0.15 was obtained. The XRD analysis showed that there are no impurities in the doped samples uo to x=1.2 while for the Cu doped sampeles with x≥1.2 SrCu2O2 phase appeared in the samples. This result shows the solubility limit for the sample is 1.2. The results of microstructure and magnetic properties of the Cu doped samples show that the sample with Cu content of 0.15 has the minimum thickness of plate and maximum magnetic properties in composition other samples. The results LCR meter show that the dielectric constant and dielectric loss decreased with frequency while the ac conductivity the samples show a reduction behavior. This variation of conductivity with frequency are evaluated on the has of Maxwell- Wagner and Koop’s theory.

Spinel ferrites have a chemical formula MFe2O4 where M is divalent metal ions such as Ni, Co or Pb. These materials have interesting properties which due to very high electrical resistance, low conduction losses and high magnetic permeability. In this thesis, the spinel ferrite nanoparticles with PbFe2O4 composition was prepared by the sol-gel method and then the effect of annealing temperature, annealing time, Mn doped for Pb and the effect of surfactants on the structural, micro structural, morphology, magnetic and dielectric properties were investigated. Synthesizing condition, structure and morphology of the samples using thermogravimetric analysis (DTA/TGA), X-ray diffraction pattern (XRD), Fourier transform infrared spectroscopy (FT-IR) and field emission scanning electron microscope (FESEM) images and also magnetic and dielectric properties were characterized by vibrating sample magnetometer (VSM) and LCR meter at room temperature. The results show that the best annealing temperature and time for synthesizing PbFe2O4 nanoparticles are 700°C and 2h, respectively. The results of dielectric measurement of all samples show that with increasing frequency, the dielectric constant, dielectric loss decrease while electrical ac conductivity of samples are increased. This behavior of properties can be described on the basis of Maxwell-Wagner model and Koops theory.

Hexaferrites have very important applications in industry due to high electrical resistivity, high uniaxial anisotropy and large saturation magnetization. Lead hexaferrite due to lower crystallization temperature compared to the same samples (strontium hexaferrite and barium hexaferrite) is considered. In this thesis, the PbFe12-xNixO19 nanoparticles with x=0-1 by sol gel method were prepared. The results of magnetic measurements show that by increasing doping of Ni in the PbFe12-xNixO19 composition, the saturation magnetization, remanence magnetization and coercivity decrease. The measurments show that the best sample is PbFe11.8Ni0.2O19 with annealing temperature 800℃. The studies reveal that the best annealing temperature and annealing time for prepare PbFe11.8Ni0.2O19 nanoparticles are 800℃ and 3h. The thermal behavior of the precursor gel was evaluated by TG/DTA analysis. The structure, magnetic and dielectric properties were investigated by Fourier transform infrared spectroscopy, X-ray diffraction pattern, Scanning electron microscopy, vibrating sample magnetometer and LCR meter. Also, the results of LCR meter show that in all samples Ni-doped lead hexaferrites into the pure sample (PbFe12O19), decrease the dielectric constant, dielectric loss and ac electrical conductivity. There for, they are suitable for use in microwave devices.

W-type hexaferrites with general formulaAMe2Fe16O27where A= (Ba, Sr, Pb) and Meis divalent metal ionssuch as Ni, Co or Fe. This ferrite has interesting properties due to thehigh saturationmagnetization, highcoercivity and high magneticuniaxialanisotropy. In this thesis, W-type hexaferritenanostructure with SrNi2Fe16O27composition was prepared by the sol-gel auto- combustion method and the effect of annealing temperature, annealing time,andmolar ratio of acid citricto metal nitrates on thestructural, morphology,magnetic and dielectric properties were investigated.In order toinvestigate the molar ratio of the acid citric to metal nitrateson theproperties of theSrNi2Fe16O27nanostructure, the samples molar ratios of the acid citric to metal nitrates1, 1.5 and 2were prepared. Structure and morphology of the samples using thermogravimetric analysis (DTA/TGA), X-ray diffraction pattern (XRD), Fourier transform infrared spectroscopy (FT-IR) and (SEM) images and also magnetic and dielectric properties were studied by VSM and LCR meter at room temperature. The results show that the best annealing temperature and time for prepare SrNi2Fe16O27nanostructure are 1100oC and 4h, respectively. The results of dielectric measurement of all samples show that with increasing frequency, the dielectrie constant, dielectric loss and electrical ac conactivity are decreased. This behavior of properties can be describe on the basis of Maxwell-Wagner and Koopʼs theory.

The so-gel technique has been used in the preparation of Cd doped Bi1.64Pb0.36Sr2Ca2-xCdxCu3O10 ceramic supeerconductors. In this study, the value of doping Cd has been varied from x=0-0.2 at different annealing times (32, 48, 56 and 64h) for preparing samples. To find the temperature of annealing, the TGA analysis has been done from dried gel. According to TGA diagram, a mass reduction has been occured smoothly in around 750 to 850℃ tempratures, in which the superconducting phase has been formed. Hence annealing temperature of samples has been selected 845℃.
Analysises of XDR and SEM has been done to study the morphology and microstructur of samples. The results of XRD indicated that the maximum values of the Bi-2223 phase percent was obtained for sample doped with x=0.02 Cd. Also a study of SEM images show that this sample has a plate like structure which is caused increase in the critical current density.
The critical current density and the critical temperature of samples have been measured by four-probe method. The results show that the sample which was doped with x=0.02 has maximum value of critical current density and critical temperature.
The resistance at room temperature has been measured for samples with doping values of x=0, 0.02, 0.04, 0.06 and annealing time of 48h and also for x=0.02 with various annealing times. The results show that the sample with x=0.02 and annealing time of 48h has the minimum value of resistance.
 

In this study, the effect of Ba substitution for Sr in the Bi-Pb-Sr-Ca-Cu-O (BPSCCO) system was investigated. The Bi1.6Pb0.4Sr2-xBaxCa2Cu3Oy superconductor with x= 0.0, 0.05, 0.1, 0.15, 0.2 and 0.25 at annealing times of 32, 48, 64 h was made by sol-gel method. In order to determine annealing temperature and study of microstructure of sample, TG/DTA analyze of the dry gel with Ba content x= 0.0 and SEM images and X-ray diffraction (XRD) was performed. The crystal lattice parameters of this compound by using of the diffraction angles and miller indices, were measured. The critical current density and critical temperature of the samples were measured by the four probe method. The results indicated that, Improved superconducting properties with Ba doping and the maximum values of the Bi-2223 phase fraction, critical temperature and current density are obtained for sample at annealing time of 32h with Ba content x= 0.2. Also, the studies show that, the critical current density decreases by increasing annealing time. The volume of the unit cell were increased by increasing Ba doped, which is shown Sr substituted by Ba. This is because, the ionic radius of the Sr is larger than the Ba.

M-type hexaferrites with general formula MFe12O19 where M= (Ba, Sr, Pb) are permanent magnet materiales. This ferrite has interesting properties due to high saturation magnetization, high coercivity and high magnetic uniaxial anisotropy. Lead hexaferrite due to lower crystallization temperature compared to the same samples is considered. In this thesis, lead hexaferrite (PbFe12O19) nanoparticles was prepared by sol-gel method and the effect of annealing temperature, annealing time, pH and molar ratio of iron to lead on the structural, morphology and magnetic properties were investigated. In order to investigate the effect pH and molar ratio of iron to lead on the properties PbFe12O19 nanoparticles, the samples with pH=3, 5, 6, 7, 8 and molar ratios of iron to lead Fe/Pb= 8, 10, 11, 12, 14 were prepared. Structure and morphology of the samples using thermogravimetric analysis (DTA/TGA), X-ray diffraction pattern (XRD), Fourier transform infrared spectroscopy (FT-IR) and (SEM) images and also magnetic properties were studied by VSM and LCR meter at room temperature. The results show that the best annealing temperature and time for prepare PbFe12O19 nanoparticles are 800oC and 3h, respectively