Keu Hong Kim

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 ThO2ue5f8Er2O3 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 ue5f8ThO 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.

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 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.

Defect structure and electrical conductivity of pure and doped lutetium sesquioxides

Abstract Pure Lu 2 O 3 and Lu 2 O 3 -CaO solid solutions containing 1, 5 and 10 mol % CaO were prepared and found to have the rare earth-type cubic structure by X-ray diffraction technique. Electrical conductivities were measured as a function of temperature from 600 to 1100°C and of P o 2 from 10 −5 to 2 × 10 −1 atm. The defect structures, type of semiconductor and the electrical conduction mechanisms were deduced from the results. The temperature dependence of the electrical conductivities shows different behaviors for pure and doped Lu 2 O 3 , showing different activation energies, 1.92 and 1.58 eV, respectively. The 1 n values in σαP 1 n o 2 are 1 n = 1 6 and 1 n = 1 4 for pure and doped Lu 2 O 3 at P o 2 s higher than 10 −4 and 10 −3 atm, respectively. From the variation of the 1 n values from 1 n ≅ 0 to 1 n = 1 6 or 1 n = 1 4 , ionic and electronic conduction mechanisms are suggested in the low- and high-oxygen partial pressure regions with two possible defect models.

Electrical conductivity of the system X ZrO2 + (1−X) Er2O3; 0.05 ⩽ X ⩽ 0.15

Abstract ZrO 2 -Er 2 O 3 solid solutions containing 5, 10 and 15 mol% ZrO 2 were synthesized from spectroscopically pure Er 2 O 3 and ZrO 2 polycrystalline powders. All systems were found to have the modified 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 and electrical conduction mechanism was suggested from the conductivity data. The activation energies range from 1.23 to 1.42 eV and from 0.47 to 0.62 eV for the high- and low-temperature regions, respectively, across the compositions examined. The dependence of the conductivity on the oxygen partial pressure is of the form σ ∝ Po 2 1/ n where n = 5.3 and n = 6 in the high- and low-temperature regions. The n values increase with decreasing temperature. Combining this data with the activation energies, different electrical conduction mechanisms are suggested for high and low temperatures. In the low-temperature region, interstitial oxygen predominates, while metal vacancy does in the high-temperature region.

The chemical and physical properties of electrochemically prepared polyaniline hexafluorophosphate (PAPF6)

Abstract Polyaniline hexafluorophosphate (PAPF 6 ) was synthesized by electrochemical oxidation from 0.2 M aniline in acetonitrile solution containing 0.1 M TEAPF 6 as a supporting electrolyte. It was confirmed that this electrode reaction was irreversible. The morphology of the PAPF 6 film was certificated by SEM. The maximum values ( R max ) of the reaction rates ( R ) for polyaniline- and polyindole-based systems at temperatures between 25 and 800 °C were calculated from thermal analyses. From the results, it has been shown that each of these polymers had distinguishable thermal characteristics. The electrical conductivity of the PAPF 6 pellet was measured at temperatures between −150 and 25 °C. From a plot of conductivity versus 1/ T , the activation energy ( E a ) was found to be 0.057 eV. The conduction mechanism in the PAPF 6 pressed pellet is suggested as being hopping conduction. The ESR peaks for these polymers were obtained and the ESR parameters calculated.

Electrical conductivity of the solid solutions XThO2 + (1−X)Ho2O3; 0.02≤X≤0.10

Abstract ThO 2 -doped Ho 2 O 3 systems containing 2, 5, 8 and 10 mol% ThO 2 were found to be solid solutions by X-ray techniques. The lattice parameter ( a ) was obtained by the Nelson-Riley method, and its value increased with increasing dopant content. The residual factors ( R ) obtained from X-ray intensity analysis based on the oxygen interstitial model show values in the range 0.0489–0.1207. The results of thermal analysis showed that no phase transition occurred in the temperature range used in this experiment. The electrical conductivity was measured as a function of temperature from 600 to 1100°C and of oxygen partial pressure from 1 × 10 −5 to 2 × 10 −1 atm. The exponential dependence of the conductivity on the oxygen pressure (σ ∞ P 02 1 n ) gives 1 n = 1 6 , and the main defect and charge carriers are the oxygen interstitial and electron hole, respectively.