Mehmet Ari

Thermal and electrical conductivities of Cd-Zn alloys

The composition and temperature dependences of the thermal and electrical conductivities of three different Cd-Zn alloys have been investigated in the temperature range of 300-650 K. Thermal conductivities of the Cd-Zn alloys have been determined by using the radial heat flow method. It has been found that the thermal conductivity decreases slightly with increasing temperature and the data of thermal conductivity are shifting together to the higher values with increasing Cd composition. In addition, the electrical measurements were determined by using a standard DC four-point probe technique. The resistivity increases linearly and the electrical conductivity decreases exponentially with increasing temperature. The resistivity and electrical conductivity are independent of composition of Cd and Zn. Also, the temperature coefficient of Cd-Zn alloys has been determined, which is independent of composition of Cd and Zn. Finally, Lorenz number has been calculated using the thermal and electrical conductivity values at 373 and 533 K. The results satisfy the Wiedemann-Franz (WF) relation at T 373 K), the WF relation could not hold and the phonon component contribution of thermal conductivity dominates the thermal conduction.

The effect of annealing temperature on the structural, optical, and electrical properties of CdS films

Cadmium sulfide (CdS) photocatalyst films were grown on glass by chemical bath deposition (pH 9.4, 70 °C) and then annealed in nitrogen from 423 K to 823 K in steps of 100 K. The XRD crystallite size increases in a sigmoidal manner from 60 nm to 100 nm while the optical band gap energy decreases from 2.42 eV to 2.28 eV. This trend is paralleled by the decreasing Urbach energy, but only up to 623 K, where it increases again. This is the temperature where the Cd effectively surpasses the phase transformation from cubic to hexagonal, and the activation energy for electronic transport drops by a factor of nearly two.

Phase stability, thermal, electrical and structural properties of (Bi2O3)1−x−y(Sm2O3)x(CeO2)y electrolytes for solid oxide fuel cells

ABSTRACT In this study, (Bi2O3)1−x−y(Sm2O3)x(CeO2)y ternary system was synthesized by using solid-state reaction method. Structural, morphological, thermal and electrical properties of the samples were evaluated by means of X-ray diffraction (XRD), scanning electron microscopy, thermo gravimetry/differential thermal analyzer and four-probe method. The XRD measurement results indicated that the samples (x = 10–15, y = 5–10–15–20) had cubic δ-phase crystallographic structure. The phase stability of the samples was checked by the differential thermal analyzer measurements, which indicates most of the samples have stable δ-Bi2O3 phase. The electrical conductivity measurement results showed that the electrical conductivity increased with mol% CeO2 molar ratio at a fixed molar ratio of Sm2O3. The highest electrical conductivity obtained for the (Bi2O3)0.65(Sm2O3)0.15(CeO2)0.20 system was 1.55 × 10−2 (Ω.cm)−1 at 600 °C. The activation energies were also calculated at low temperature range (350–650 °C) which vary from 1.1325 to 1.4460 eV and at high temperature (above 650 °C) which vary from 0.4813 to 1.1071 eV.

Oxide ionic conductivity and crystallographic properties of tetragonal type Bi2O3-based solid electrolyte doped with Ho2O3

Abstract In the present work, the authors have investigated the binary system of (Bi2O3)1–x(Ho2O3)x. For the stabilisation of the tetragonal type solid solution, small amounts of Ho2O3 were doped into the monoclinic Bi2O3 via solid state reactions in the stoichiometric range 0·01≤x≤0·1. The crystal formula of the formed solid solution was determined as Bi(III)4–4xHo(II)4xO6–2xVo(2+2x) (where Vo is the oxide ion vacancy) according to the XRD and SEM microprobe results. In the crystal formula, stoichiometric values of x were 0·04≤x≤0·08, 0·03≤x≤0·09, 0·02≤x≤0·09 and 0·04≤x≤0·09 for annealing temperatures at 750, 800, 805 (quench) and 760°C (quench) respectively. The four probe electrical conductivity measurements showed that the studied system had an oxide ionic type electrical conductivity behaviour, which is increased with increasing dopant concentration and temperature. The obtained solid electrolyte system has an oxygen non-stoichiometry characteristic, and it contains O2– vacancies, which have disordered arrangements in its tetragonal crystal structure. The increase in the amount of Ho2O3 doping and temperature causes an increasing degree of the disordering of oxygen vacancies and a decrease in the activation energy Ea.

Temperature and Thickness Effects on Electrical Properties of InP Films Deposited by Spray Pyrolysis

InP film samples are prepared by spray pyrolysis technique using aqueous solutions of InCl3 and Na2HPO4, which are atomized with compressed air as carrier gas onto glass substrates at 500° C with different thicknesses of the films. The structural properties of the samples are determined by x-ray diffraction (XRD). It is found that the crystal structure of the InP films is polycrystalline hexagonal. The orientations of all the obtained films are along the c-axis perpendicular to the substrate. The electrical measurements of the samples are obtained by dc four-probe technique on rectangular-shape samples. The effects of temperature on the electrical properties of the InP films are studied in detail.

Correlation of high temperature x-ray photoemission valence band spectra and conductivity in strained LaSrFeNi oxide on SrTiO3(110)

Reversible and irreversible discontinuities at around 573 K and 823 K in the electric conductivity of a strained 175 nm thin film of (La0.8Sr0.2)0.95Ni0.2Fe0.8O3-{\delta} grown by pulsed laser deposition on SrTiO3 (110) are reflected by valence band changes as monitored in photoemission and oxygen K-edge x-ray absorption spectra. The irreversible jump at 823 K is attributed to depletion of doped electron holes and reduction of Fe4+ to Fe3+, as evidenced by oxygen and iron core level soft x-ray spectroscopy, and possibly of a chemical origin, whereas the reversible jump at 573 K possibly originates from structural changes.Reversible and irreversible discontinuities at around 573 and 823 K in the electric conductivity of a strained 175 nm thin film of (La0.8Sr0.2)0.95Ni0.2Fe0.8O3−δ grown by pulsed laser deposition on SrTiO3 (110) are reflected by valence band changes as monitored in photoemission and oxygen K-edge x-ray absorption spectra (XAS). The irreversible jump at 823 K is attributed to depletion of doped electron holes concomitant with reduction of Fe3+ toward Fe2+, as evidenced by oxygen and iron core level soft XAS, and possibly of a chemical origin, whereas the reversible jump at 573 K possibly originates from structural changes.

Synthesis and electrical properties of CuBr2 complexes with 1,10-phenanthroline monohydrate

Using 1,10-phenanthroline monohydrate and CuBr2 in molar ratios of 1:1 and 2:1, in CH3OH/H2O (ϕr = 1:1), the complexes [(phen)CuBr2]2, (I), and {[(phen)2CuBr]Br·H2O}, (II), have been prepared. The hydrogen bondings and aqua bridges between coordinated and noncoordinated bromides of II have been observed by XRD. Complex II has a triclinic crystal structure with distorted trigonal bipyramidal coordination geometry. Possibilities of ligand exchange with hydroxide or ammonia have been examined in both complexes. While the mononuclear complex II is stable in a refluxed ammonia solution and the complex {[phen)2CuBr]Br·3H2O}, (IV), trihydrate of II, is obtained; the binuclear complex I reacts with the ammonia solution to replace one of its bromides in the subunits with hydroxide to give {[(phen)2Cu2Br2(OH)2]·4H2O}, (III). Structural and electrical properties of the complexes have been investigated by elemental analysis, vibrational and electronic spectroscopy, mass spectrometry, TGA, XRD and the four-point probe method. The temperature coefficients of resistivity and the activation energies of the complexes have also been obtained. All complexes behave as intrinsic semiconductor in the temperature range of 310–440 K.

Synthesis of (Bi2O3)0.9-x(Tb4O7)0.1(Sm2O3)x electrolyte for IT-SOFCs

ABSTRACT In this study (Bi2O3)0.9-x(Tb4O7)0.1(Sm2O3)x ternary solid solutions were synthesized by solid-state synthesis techniques. The products were characterized by means of X-ray powder diffraction, differential thermal analysis/thermal gravimetry, and the four-point probe technique (4PPT). Total electrical conductivity (σT) depending on the temperature and doping concentration has been measured by 4PPT. Activation energy of the four samples are calculated by Arrhenius relation. Activation energies of the samples increases with the concentration of dopant Sm2O3. Bi2O3-based ceramic system doped with Sm2O3 and Tb4O7 showed an oxide ionic-type electrical conductivity which is increased with the increasing amount of Sm2O3. The highest conductivity value is found as 3.48 × 10−1 S cm−1 for the (Bi2O3)0.85(Tb4O7)0.1(Sm2O3)0.05 ternary system at 850°C.

STRUCTURAL, SURFACE AND TRANSPORT PROPERTIES OF Sn–Ag ALLOYS

The structural, surface and transport properties of Sn–Ag alloys were investigated by X-ray diffraction (XRD), radial heat flow, energy-dispersive X-ray (EDX) analysis, scanning electron microscopy (SEM) and four-point probe techniques. We observed that the samples had tetragonal crystal symmetry except for the pure Ag sample which had cubic crystal symmetry, and with the addition of Ag the cell parameters increased slightly. Smooth surfaces with a clear grain boundary for the samples were shown on the SEM micrographs. The grain sizes of pure Ag, β-Sn and the formed Ag3Sn intermetallic compound phase for Sn–x wt.% Ag [x=1.5, 3.5] binary alloys were determined to be 316nm, between 92nm and 80nm and between 36nm and 34nm, respectively. The values of electrical resistivity for pure Sn, pure Ag and Sn–x wt.% Ag [x=1.5, 3.5] were obtained to be 22.60×10−8, 62.36×10−8, 23.54×10−8, 24.62×10−8Ω⋅m at the temperature range of 300–450K, respectively. Thermal conductivity values of pure Sn and Sn–x wt.% Ag [x=1.5, 3.5] binary alloys were found to be 60.60±3.75, 69.00±4.27 and 84.60±5.24W/Km. These values slightly decreased with increasing temperature and increase with increasing of the Ag composition. Additionally, the temperature coefficients of thermal conductivity and electrical resistivity and the Lorenz numbers were calculated.

Electrical properties of triple-doped bismuth oxide electrolyte for solid oxide fuel cells

ABSTRACT In this study, the quaternary solid solutions of (Bi2O3)(0.8−x)(Tb4O7)0.1(Ho2O3)0.1(Dy2O3)x (x = 0.05, 0.10, 0.15, 0.20) as an electrolyte were synthesized for solid oxide fuel cells by the technique of solid-state synthesis. The products were characterized by X-ray powder diffraction, differential thermal analysis/thermal gravimetry and the four-point probe technique (4PPT). The total electrical conductivity is measured on the temperature and the doped concentration by 4PPT. All samples have been obtained as the δ-phase. According to the measurements of the 4PPT, the electrical conductivities of the samples increase with the temperature but decrease with the amount of doping rate. The value of the highest conductivity (σ) is found as 1.02 × 10−1 S cm−1 for the system of (Bi2O3)0.75(Tb4O7)0.1(Ho2O3)0.1(Dy2O3)0.05 at 850 °C. The thermal gravimetry (TG) curve shows that there is no mass loss of sample during the measurement. The analyses of differential thermal reveal that there are neither endothermic peaks nor exothermic peaks during the heating and cooling cycles (ranging from 30 to 1000 °C).