Jae Shi Choi

Electrical conductivity of pure and doped α-ferric oxides

Abstract Electrical conductivities of αFe 2 O 3 containing 1 2, 2 3 and 3 8 mol% CdO were measured in the temperature range of 300 to 1300°C at Po 2 s of 10 −9 to 10 −1 atm Plots of log σ vs 1 T at constant Po 2 s were found to be linear with an inflection at temperatures around 500°C and higher Po 2 s than 1 × 10 −4 atm. The activation energies obtained by the least-squares method were 1 34 eV for the intrinsic region and 0 51 eV for the extrinsic region on αFe 2 O 3 doped with 38 mol% CdO The extrinsic conductivities disappeared at lower Po 2 s than 1 × 10 -4 atm , and the intrinsic conduction appeared on the specimens investigated The electrical conductivities decreased with increasing amount of CdO doping The predominant defects in this system are believed to be interstitial Fe 2 for the intrinsic region and oxygen vacancies for the extrinsic region.

Electrical conductivity and defect structure of Ni-doped and “CO-reduced” Ni-doped SrTiO3 single crystals

Abstract The electrical conductivities of Ni-doped and “CO-reduced” Ni-doped SrTiO3 single crystals were measured at temperatures 700–1200°C and Po2s of 10−7–10−1 atm. Plots of log σ vs 1 T at constant Po2s were found to be linear, and the activation energies appeared to be 0.92 eV for Ni-doped SrTiO3 and 0.50 eV for “CO-reduced” Ni-doped SrTiO3 single crystals, respectively. Plots of log σ vs log Po2 at constant temperature were found to be linear with an average slope of − 1 4 for SrTiO3:Ni and of − 1 6 for “CO-reduced” SrTiO3:Ni single crystals, respectively. The electrical conductivity dependencies on Po2 indicate that a triply ionized titanium interstitial and an oxygen vacancy model are applicable to Nidoped and “CO-reduced” Ni-doped SrTiO3 single crystals, respectively. The small polaron conduction was suggested on “CO-reduced” Ni-doped SrTiO3 single crystal from the temperature dependence of conductivity.

The chemical and physical properties of electrochemically prepared polyaniline tetrafluoroborates (PATFB)

Abstract Polyaniline tetrafluoroborate (PATFB) was obtained by the electrochemical technique from 0.2 M aniline in 1:99 water/acetonitrile solution containing 0.1 M tetraethylammonium tetrafluoroborate (TEABF 4 ) as the supporting electrolyte. Following polarographic and cyclic voltammetry measurements, the values of the half-wave potential ( E 1 2 ), transfer coefficient (α) and number of electrons ( n ) were measured to be 643 mV, 0.414 and 2, respectively. The results of TGA and DSC showed that the weight loss was most rapid in the temperature range from 523 to 623 K, and the maximum value of the reaction rate was 0.366mg min −1 at 596.6 K. The electrical conductivity of PATFB was measured at temperatures from 103 to 298 K. From the plot of resistivity vs 1/ T , the obtained activation energy ( E a ) was 0.082 eV. It is suggested from the temperature dependence of the conductivity and ESR measurements that the conduction mechanism for PATFB is possibly a small polaron hopping conduction.

Electrical conductivity of the system ThO2Er2O3

Abstract ThO2Er2O3 systems containing 3, 6, 9 and 12 mol% Er2O3 were found to be solid solutions by XRD techniques. The lattice parameters (a) were obtained by various diffraction-angle analysis methods, and these values increased with increasing dopant level. The residual factors (R) obtained from the intensity analysis were 0.018–0.162 for the oxygen vacancy model. The results of DTA, TGA and DTG showed that no phase transition occurred in the measured temperature range. The electrical conductivities were measured as a function of temperature from 520 to 1100°C and of oxygen partial pressure from 1 × 10−4 to 2 × 10−1 atm. The electrical conductivities increase with increasing temperature, and show a maximum with increasing dopant level. The calculated activation energies (Ea) decrease with increasing dopant level, but an abrupt increase in Ea appears in the 12 mol% sample. The phenomenon of the maximum in the conductivity occurring simultaneously with the minimum in the Ea can be explained by the ordering of free dopant ions and charged associates. The exponential dependence of the conductivity on the oxygen pressure (σ ∞ P 1 n O2) is 1 n = 1 4 , and the main defect is an oxygen vacancy for oxygen pressures above 10−3 atm. Below 10−3 atm, the conductivity no longer has linearity. The conduction mechanism for this system is mixed ionic and electronic conduction due to oxygen ions and holes.

Electrical conductivity of the solid solution ThxGd2−2xO3−x

Abstract Gd 2 O 3 ThO 2 solid solutions containing 1, 3 and 5 mol % ThO 2 were synthesized with spectroscopically pure Gd 2 O 3 and ThO 2 polycrystalline powders. X-ray spectroscopy reveals that all synthesized specimens have the modified fluorite structure, and the lattice parameter of Gd 2 O 3 is nearly unchanged with increased ThO 2 mol %. The morphology of the solid solution was examined by metallurgical microscopy. Both a.c. and d.c. electrical conductivities were measured in the temperature range 600–1000°C under oxygen partial pressures from 10 −1 to 10 −6 atm. The d.c. conductivities are nearly independent of oxygen pressure, and agree with the values determined from a.c. experiments. This implies that the solid solutions are ionic conductors. The conductivity increases with increasing ThO 2 mol fraction, with an average activation energy of 1.15eV. Oxygen interstitial defects as well as an ion hopping conduction are suggested.

Characterization of BiSrCaCuO superconducting materials by Raman spectroscopy

Abstract A series of high T c superconducting materials, BiSrCaCu x O y , x = 1, 2 and 3, with a variable amount of copper were prepared and their Raman spectra recorded and analysed. Characteristic Raman frequencies were obtained using a Raman microprobe. With single microcrystals, selective extinction of the Raman bands was recorded. Four distinct spectra were obtained which correspond to four scattering configurations of the crystals. These results indicate some deviation from a tetragonal structure.

Infrared spectra and electrical conductivity of the α-Fe2O3-B2O3 system

Abstract Changes in network structures of H3BO3 and materials in the X B2O3-(1 − X)-α-Fe2O3 system (X = 0.6, 0.7, 0.8) occurring as the temperature is varied were investigated by means of infrared spectroscopy, X-ray analysis, density, and electrical conductivity measurements. Analyses of the network structures were carried out based on a division into three classes: (1) networks of H3BO3 treated at various temperatures; (2) Fe2O3-modified networks; and (3) networks unmodified by Fe2O3. Borate networks are classified into modified and unmodified networks, where the modified networks are formed by the three-dimensional arrangement of simple modified BO3 and BO4 groups while the unmodified networks are made by three-dimensional arrays of clusters with unmodified BO3 groups, BO4 groups, BO bonds and non-bridging oxygens. The kind of clusters in unmodified networks depends on the stability of the network built up under given conditions. In the B2O3-Fe2O3 system, the modified specimens, which were prepared at high temperature, have glassy structures and small volumes. The unmodified samples, which were made at low temperature, contain Fe2O3 particles and have large volumes. The electrical-conduction mechanism depends on the state of the Fe2O3.

Electrical conductivity of the solid solutions XGd2O3 + (1 −X)ThO2; 0.01⩽X⩽0.12

Abstract Gd 2 O 3 -doped ThO 2 systems (GDT) containing 1, 5, 8 and 12 mol% Gd 2 O 3 were found to be solid solutions by diffraction angle (θ) analysis. The lattice parameters ( a ) were obtained by the Nelson-Riley method and the values decreased with increasing dopant content. Thermal analysis showed that no phase transition occurred in the temperature range covered in this experiment. The electrical conductivity was measured as a function of temperature from 500 to 1000°C at oxygen partial pressures from 1× 10 −5 to 2× 10 −1 atm. The conductivity and the Ea vs dopant mol% curves show maximum and minimum values, respectively. The exponential dependence of the conductivity on the oxygen pressure ( σ ∝ P 1/ n O 2 ) is 1 n = 1 4 and the main defect is an oxygen vacancy in the experimental range of oxygen pressures above 10 −5 atm.

Electrical conductivity of the system ZrO2−Er2O3

ZrO2-Er2O3, solid solutions containing 10, 15, and 20 mol% Er2O3 were prepared with spectroscopically pure ZrO2; and Er2O3 polycrystalline powder. All systems were found to have the cubic fluorite structure by X-ray diffraction techniques. Electrical conductivities were measured as a function of temperature from 400 to 1000°C and of oxygen partial pressure from 10−6 to 2 × 10−1 atm. The defect structure, type of semiconductor behavior and the electrical conduction mechanism were deduced from these results. The temperature dependence of the electrical conductivities shows different behavior in the low- and high-temperature regions. The activation energies increase with decreasing oxygen pressure and increasing dopant level. The dependence of the conductivity on the oxygen partial pressure (σ∞ PO2−1n) are 1n = 0 and n = 40−4 in the low- and high-temperature regions, respectively. The n values in the high-temperature region decrease with increasing temperature. From the variation of the n values with temperature, mixed ionic and electronic conduction is suggested. Oxygen ion conduction is also suggested in the low-temperature region from the oxygen ion mobility.

Electrical conductivity of the solid solutions XTm2O3 + (1 − X)ThO2; 0.01 ⩽ X ⩽ 0.15

Abstract Tm2O3-doped ThO2 systems containing 1, 3, 5, 8, 10 and 15 mol.% Tm2O3 were found to be solid solutions by XRD techniques. The lattice parameter (a) was obtained by the Nelson-Riley method, and the value decreased with increasing dopant content. The residual factor (R) obtained from X-ray intensity analysis ranged from 0.0389 to 0.1293 based on the oxygen vacancy model. Thermal analysis showed that no phase transition occurred in the temperature range covered in this experiment. The electrical conductivity was measured as a function of temperature from 550 to 1100°C and at oxygen partial pressures from 1 × 10-5 to 2 times; 10-1 atm. The electrical conductivity increases with increasing temperature, and the activation energy decreases with increasing dopant content. The exponential dependence of the conductivity on the oxygen pressure (σ ∞ PO2 1 n ) is 1 n = 1 4 , and the main defects are the oxygen vacancies for oxygen pressures above 10−4 atm. Below 10−4 atm, the ionic conductivities increase with increasing dopant mol.%. The suggested conduction mechanisms for the TDT system are mixed ionic and electronic conductions due to oxygen ions and holes.