M. M. El-Desoky 1 Department of Physics, Faculty of Education, Suez Canal University, Al-Arish, Egypt

Transcription

1 Giant electrical conductivity enhancement in BaO-V 2 O 5 Bi 2 O 3 glass by nanocrystalization M. M. El-Desoky 1 Department of Physics, Faculty of Education, Suez Canal University, Al-Arish, Egypt The effects of the annealing of 20BaO-30V 2 O 5 50Bi 2 O 3 glass on the structural and electrical properties were studied by Scanning electron micrographs (SEM), X- ray diffraction (XRD), differential scanning calorimeter (DSC) density (d) and dc conductivity ( ).The XRD and SEM observations have shown that the sample under study undergoes structural changes: from amorphous at the beginning, to partly crystalline after nanocrystalization at crystallization temperature (T c ) for 1h and to colossal crystallization after the annealing at the same temperature for 24h. The average size of these grains after nanocrystalization at T c for 1h was estimated to about 25-35nm. However, the glass heat treated at T c =580 o C for 24 h the microstructure changes considerably. The nanomaterials obtained by nanocrystalization at T c for 1h exhibit giant improvement of electrical conductivity up to four order of magnitude and better thermal stability than the as- received glass. The major role in the conductivity enhancement of this nanomaterial is played by the developed interfacial regions "conduction tissue" between crystalline and amorphous phases, in which the concentration of V 4+ V 5+ pairs responsible for electron hopping, is higher than inside the glassy matrix. The annealing at T c for 24h leads to decrease of the electronic conductivity. This phenomena lead to disappearance of abovementioned "conduction tissue" for electrons and substantial reduction of electronic conductivity. The high temperature (above θ/2) dependence of conductivity could be qualitatively explained by the small polaron hopping (SPH) model. The physical parameters obtained from the best fits of this model are found reasonable and consistent with the glass compositions.

2 Structural and transport properties of Li-intercalated vanadium pentoxide nanocrystalline films M. S. Al-Assiri 1,#, M. M. El-Desoky 1,2, A. Alyamani 3, A. Al-Hajry 1, A. Al-Mogeeth 1, and A. A. Bahgat 1 1 Department of Physics, College of Science, King Khalid University, PO Box 9003, Abha SA. 2 Department of Physics, Faculty of Education, Suez Canal University, Al-Arish, Egypt 3 National Center for Mathematics and Physics, P.O. Box 6086, Riyadh 11442, KS A. X-ray diffraction (XRD), density, electrical and thermoelectric power properties of nanocrystalline Li xv 2O 5, nh 2O films (0 < x < 22 mol %) were investigated in the present work. These films have been produced by the sol-gel technique (colloidal route) which was used for preparation of high purity and uniform films at room temperature. The films were studied by x-ray diffraction showed that, Li xv 2O 5, nh 2O films are highly orientated nanocrystals. The particle size was found to be about 6.0 nm. The relative intensity of the diffraction line (002) increases with increasing Li-content. Electrical conductivity and thermoelectric power were measured in the temperature range K for the as prepared films parallel to the substrate surface; i.e. normal to the c-axis. The electrical conductivity on the other hand, shows that all samples are semiconductor and increases with increasing Li content. The hopping carrier mobility were also evaluated and found to vary from to cm -2 V -1 s -1 at T = 380 K. The carrier density is evaluated to be x x cm -3. The conductivity of the present system was primarily determined by hopping carrier mobility. The conduction was confirmed to obey the non-adiabatic small polaron hopping. The thermoelectric power, Seebeck effect, increases with increasing the Li content. The obtained results showed an n-type semiconducting behavior within the whole temperature range.

3 Effect of nanocrystallization on the electrical conductivity enhancement and Mössbauer hyperfine parameters of iron based glasses M. M. El-Desoky 1, F. A. Ibrahim 1, A.G. Mostafa 2, and M. Y. Hassaan 2 1 Department of Physics, Faculty of Education, Suez Canal University, Al-Arish, Egypt 2 Department of Physics, Faculty of Science, Al-Azhar University, Nasr City, 11884, Cairo, Egypt Selected glasses of Fe 2O 3- PbO 2 Bi 2O 3 system have been transformed into nanomaterials by annealing at temperature close to crystallization temperature (T c) for one hour. The effects of the annealing of the present samples on its structural and electrical properties were studied by Mössbauer spectroscopy, transmission electron micrograph (TEM), differential scanning calorimeter (DSC) and dc conductivity ( ). Mössbauer spectroscopy was used in order to determine the states of iron and its hyperfine structure. The effect of nanocrystalization on the Mössbauer hyperfine parameters did not exhibit significant modifications in present glasses. However, in case of glass-ceramic nanocrystals show a distinct decrease in the quadrupole splitting (Δ) is observed, reflecting an evident decrease in the distortion of structural units like FeO 4 units. In general, the Mössbauer parameters of the nanocrystalline phase exhibit tendency to increase with PbO 2 content.tem of as quenched glasses confirm the homogeneous and essentially featureless morphology. TEM of the corresponding glass-ceramic nanocrystals indicates nanocrystals embedded in the glassy matrix with average particle size of about 32nm. The crystallization temperature (T c) was observed to decrease with PbO 2 content. The glass-ceramic nanocrystals obtained by annealing at T c exhibit improvement of electrical conductivity up to four orders of magnitude than the starting glasses. This considerable improvement of electrical conductivity after nanocrystallization is attributed to formation of defective, well-conducting phases "easy conduction paths along the glass crystallites interfaces.

4 Ferroelectricity of the glassy material Bi-Pb-Cu-O doped with K ions A.A. Bahgat 1, B.A.A. Makram 1, E.E. Shaisha 1 and M.M. El-Desoky 2 1)Department of Physics, Faculty of Science, Al-Azhar University, Nasr City 11884, Cairo, Egypt. 2) Department of Physics, Faculty of Education, Suze Canal University, El-Arish, Egypt. Glass sample of the composition 31.4 Bi 2 O Pb 3 O CuO 1.74 K 2 O in mol% was prepared by the conventional quenching melt technique. The as quenched single phase glass shows interesting ferroelectric properties which is not familiar in the field of glass science. If the as quenched glass is heat treated at or above the glass transition temperature all signs of ferroelectricity disappears completely. X- ray diffraction and transmission electron microscopy as well as differential thermal analysis were used to recognize the glassy nature of the as quenched sample. Ac dielectric measurements were performed at different applied frequencies as a function of temperature. On the other hand the dc electrical conductivity of the present glass can be fitted with Mott's model of nearest neighbor hopping at high temperature, while at intermediate temperature the Greaves VRH (variable-range hopping) model was found to be appropriate. The conduction was confirmed to obey the adiabatic small polaron hopping (SPH) and was mainly due to electronic transport between Cu ions. The dominant factor determining conductivity was the hopping carrier mobility in this glass. From the best fits, reasonable values of various SPH and VRH parameters are obtained.

5 Spectroscopic study of nanocrystalline V 2 O 5 _nh 2 O films doped with Li ions M.S. Al-Assiri a, M.M. El-Desoky a,b, A. Alyamani c, A. Al-Hajry a, A. Al-Mogeeth a, A.A. Bahgat a,d, a Department of Physics, College of Science, King Khalid University, P.O. Box 9003, Abha, Saudi Arabia b Department of Physics, Faculty of Education, Suez Canal University, El-Arish, Egypt c National Center for Mathematics and Physics, P.O. Box 6086, Riyadh 11442, Saudi Arabia d Department of Physics, Faculty of Science, Al-Azhar University, Nasr City 11884, Cairo, Egypt Optical properties of nanocrystalline, LixV 2O 5 _ nh 2O films (0-22 mol%), are explored in the present work. These films have been produced by the sol gel technique (colloidal route), which was used for the preparation of high purity and homogeneity films. Optical measurements were carried out using a doublebeam spectrophotometer. The optical constants such as refractive index n, the extinction coefficient k, absorption coefficient a, and optical band gap of the films material have been evaluated. The optical absorption coefficient was calculated from the measured normal reflectance, R, and transmittance, T, spectra. The optical spectra of all samples exhibited two distinct regions: at high energy, which suggests a direct forbidden transition with optical gap ranging from 1.75 to 2.0 ev and increases with increase in Licontent. On the other hand a second low-energy band suggests a direct allowed transition with optical gap ranging from 0.40 to 0.42 ev. The width of the localized states (band tail) Ee was also estimated for all samples. Additional calculations applying the real part of the optical dielectric function led to the evaluation of the charge carrier concentration and their effective mass.