الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Glasses with nominal composition 70Bi2O3-30Fe2O3 (BFO), 10BaO-60Bi2O3-30Fe2O3 (BBFO), 10CaO-60Bi2O3-30Fe2O3 (BCFO) and 10SrO-60Bi2O3-30Fe2O3 (BSFO), (mol. %); were prepared by the conventional melt quenching technique. X-ray diffraction (XRD), differential thermal analysis (DTA) and differential scanning calorimeter (DSC) confirm the amorphous nature of the glass samples. The dc conductivity of the glass samples containing alkaline earth elements enhanced. Glass sample containing Sr shows interesting electrical properties. All glass samples showed a transition from negative to positive Seebeck coefficient, this means that the conduction is mixed of electrons and holes charge carriers. The conduction mechanism of all samples obeys non-adiabatic small polaron hopping model of electron between iron ions. The calculated small polaron coupling constant, (γp) was found to be in the range of 10.25–17.28. Also, the calculated hopping mobility (μ) and carrier density (Nc) of glasses were in the range of 4.65× 10− 7 - 4.11× 10−3 (cm2V −1 s −1 ) and 0.029-10 (× 101 7 cm−3 ) at 333 K, respectively. The BSFO glass sample had the maximum electrical conductivity and was heat treated for varied times (2,4 and 8 h) in air at 600 ℃ to obtain glass-ceramic nano-composites. The influence of heat-treating temperature at different times on the nanostructural, ferromagnetic, electrical, dielectric and ferroelectric properties were investigated. XRD patterns display the formation of cubic perovskite structure (SrFeO2.97) with space group Pm-3m for BSFO glass-ceramic nano-composites. The average nanocrystallite sizes (D) were determined to be between 13.48 and 17.26 nm. The HR-TEM images of a BSFO glass sample that was heat treated at 600° C for 4 h show the nanocrystallites dispersed in glass matrix with particle size in the range of 17 nm. The density of the glass-ceramic nano-composite samples is clearly higher than the density of the glass sample. XVIII All glass-ceramic nano-composites showed a negative sign of Seebeck coefficient which indicates that the majority of charge carriers are electrons and then the glass ceramic samples are n-type semiconductors. The calculated values of dc conductivity of glass-ceramic nano-composites decreased with an increment in crystallite size, this is attributed to an increase in grain boundary scattering. The conduction mechanism of all samples obeys non-adiabatic small polaron hopping model of electron between iron ions. Real part of permittivity (ε’) of glass-ceramic nano-composites decreased sharply with the increment in frequency for all samples. The change in ac conductivity σac with the temperature for glass–ceramic nano-composites is the same trend as dc conductivity, with the highest conductivity occurring at HT 2 h. An increase in remnant polarization Pr with the increment in electric field is observed for all glass–ceramic nano-composites, confirming the ferroelectric nature. The efficiency (η) of the glass–ceramic nanocomposites are increased with an increment of heat treatment time. The Wr is found to be maximum for HT 8 h sample and equal to 34.3 mJ/cm3 , which makes HT 8 h a candidate for designing energy storage devices. The HT 8 h sample confirmed the AFM trend with a weak ferromagnetic (FM)nature. The HT 8 h sample had the highest Mm, Mr and Hc values. These values can be advantageous in energy storage devices. The BSFO glass sample showed a relaxor ferroelectric-like behavior. The presence of polar clusters (PCs) imbedded in the glass matrix was confirmed using a HR-TEM, which indicates the presence of relaxor ferroelectric (RFE) behavior in BSFO glass. The low frequency Raman spectra displays a Boson peak at 72 cm-1 , which confirms polar clusters (PCs) formation in BSFO glass. Systematically measured dielectric properties revealed relaxor ferroelectric-like behavior in a broad range of frequency and temperature for BSFO glass. The BSFO glass sample depicts a wide as well as diffuse peak of dielectric permittivity ε’(ω) and XIX tangent loss tan δ, wide as well as diffuse peak shifted to the higher temperatures (from 538 K to 553K), a typical relaxor behavior is indicated by this type of diffuse transition. The measured energy storage density of the BSFO glass was 4 mJ.cm-3 with efficiency of 70 % under an applied electric field of 17 kV.cm-1 at room temperature. Magnetic properties via vibrating-sample magnetometer (VSM) show a typical anti ferromagnetic behavior for BSFO. Finally, these results depict that the BSFO glass and corresponding glass-ceramic nano composites can be regarded a promising candidate for designing energy storage devices.