Temperature dependent conductivity and structural properties of sol-gel prepared holmium doped Bi2O3 nanoceramic powder (original) (raw)
Related papers
In this study; production and characterization of Bi 2 O 3 based solid electrolytes used in medium-temperature solid oxide fuel cells (IT-SOFC) were performed. Solid electrolyte samples were obtained using compounds Eu 2 O 3 , Dy 2 O 3 and Bi 2 O 3. Stable phase which can create the highest power density δ-Bi 2 O 3 (cubic-fcc) was tried to be reached for IT-SOFC. X-ray diffractometry (XRD) and differential thermal analysis and thermal gravimeter (TG/DTA) with binary (Eu 2 O 3-Bi 2 O 3) and ternary (Eu 2 O 3-Dy 2 O 3-Bi 2 O 3) powder materials were analyzed for crystal structure identification. Bi 2 O 3-based compounds with the cubic structure have been identified in those composition regions ((Bi 2 O 3) 0,6 (Eu 2 O 3) 0,3) and ((Bi 2 O 3) 1-x-y (Dy 2 O 3) x (Eu 2 O 3) y , 0.25 ≤ x ≤ 0.35, y=0,05). Four point measurement techniques were used for electrical characterization. The conductivity of the ternary system is higher than the conductivity of the binary system. The highest conductive sample is (Bi 2 O 3) 0,7 (Dy 2 O 3) 0,25 (Eu 2 O 3) 0,05 0.3 S/cm at 800 o C.
Materials Science and Technology, 2010
In the present work, the authors have investigated the binary system of (Bi 2 O 3) 12x (Ho 2 O 3) x. For the stabilisation of the tetragonal type solid solution, small amounts of Ho 2 O 3 were doped into the monoclinic Bi 2 O 3 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) 424x Ho(II) 4x O 622x Vo (2z2x) (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 760uC (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 O 22 vacancies, which have disordered arrangements in its tetragonal crystal structure. The increase in the amount of Ho 2 O 3 doping and temperature causes an increasing degree of the disordering of oxygen vacancies and a decrease in the activation energy E a .
Journal of Power Sources, 2010
Crystalline Bi 5 NbO 10 nanoparticles have been achieved through a modified sol-gel process using a mixture of ethylenediamine and ethanolamine as a solvent. The Bi 5 NbO 10 nanoparticles were characterized by X-ray diffraction (XRD), differential scanning calorimetry/thermogravimetry (DSC/TG), fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and Raman spectroscopy. The results showed that well-dispersed 5-60 nm Bi 5 NbO 10 nanoparticles were prepared through heat-treating the precursor at 650 °C and the high density pellets were obtained at temperatures lower than those commonly employed. The frequency and temperature dependence of the dielectric constant and the electrical conductivity of the Bi 5 NbO 10 solid solutions were investigated in the 0.1 Hz -1 MHz frequency range. Two distinct relaxation mechanisms were observed in the plots of dielectric loss and the imaginary part of impedance (Z") versus frequency in the temperature range of 200-350 o C. The dielectric constant and the loss in the low frequency regime were electrode dependent. The ionic conductivity of Bi 5 NbO 10 solid solutions at 700 o C is 2.86 (Ω·m) -1 which is in same order of magnitude for Y 2 O 3 -stabilized ZrO 2 ceramics at same temperature. These results suggest that Bi 5 NbO 10 is a promising material for an oxygen-ion conductor.
A study of polymer-derived erbia-doped Bi2O3 nanocrystalline ceramic powders
Journal of Sol-Gel Science and Technology, DOI: 10.1007/s10971-013-3011-z
""In this study, erbia (Er2O3)-doped Bi2O3 ceramics were prepared from sol-gel derived nanocrystalline powders. The morphological properties were investigated by Scanning Electron Microscopy (SEM). X-Ray Diffraction (XRD) analysis was carried out in order to characterize the phase and crystal structure of the powder samples. Temperature dependent electrical properties were determined by Thermogravimetry/Differential Thermal Analyzer (TG/DTA) and 4-point probe techniques (4PPT). The stable fluorite face centered cubic -type phase was observed at room temperature from the XRD result, which was supported by the Differential Thermal Analyzer and temperature dependent electrical conductivity measurements. Electrical conductivity results indicate that there is a transition approximately at 650 °C, which can be attributed to an orderdisorder transition (ODT). The activation energy values obtained from the Arrhenius approach for heating and cooling process were presented. Two regimes, corresponding to high temperature region (HTR) and low temperature region (LTR), were observed. As a result of morphological changes during the ODT, the electrical conductivity modifies and the activation energies are different for studied sample at HTR and LTR.""
Thermo-electrical and structural properties of Gd2O3 and Lu2O3 double-doped Bi2O3
International Journal of Hydrogen Energy, 2017
Gd 2 O 3 and Lu 2 O 3 double-doped Bi 2 O 3 compounds were prepared by solid-state synthesis techniques. Eight micro crystalline samples were synthesized with compositions of (Bi 2 O 3) 1ÀxÀy (Gd 2 O 3) x (Lu 2 O 3) y , where x ¼ 0.05, 0.1 and y ¼ 0.05, 0.1, 0.15, 0.2. The structure of the ceramic materials was characterized by X-ray powder diffraction (XRD) and Thermo Gravimetry/Differential Thermal Analysis (TG/DTA). The morphology of the materials of the system was displayed by Scanning Electron Microscope (SEM). Also, the electrical conductivity of the samples was determined by the DC four-point probe technique (4PPT) in air at temperatures ranging from room temperature to 1100 C. It was observed that two samples, (Bi 2 O 3) 1ÀxÀy (Gd 2 O 3) x (Lu 2 O 3) y x ¼ 0.05e0.1, y ¼ 0.05 have mixture phases including d-phase before additional heat treatments, and that the phases of all of the samples changed to the stable fluorite type face centered cubic d-Bi 2 O 3 phase which has a high conductivity property after electrical conductivity measurements. The DTA results also showed that all samples have d-Bi 2 O 3 phases. The highest electrical conductivity was seen for the sample of the (Bi 2 O 3) 0.85 (Gd 2 O 3) 0.1 (Lu 2 O 3) 0.05 system as 9.20 Â 10 À2 (ohm.cm) À1 at 650 C. The lowest activation energy was also calculated for the sample of the (Bi 2 O 3) 0.8 (-Gd 2 O 3) 0.1 (Lu 2 O 3) 0.1 system as 0.5104 eV. The results indicated that the stable d-Bi 2 O 3 phase samples can be used as electrolyte materials in solid oxide fuel cells.
Study of electrical conductivity and phase transition in Bi2O3–V2O5 system
Phase Transitions, 2010
The solid solutions of bismuth–vanadate were prepared by the conventional solid-state reaction. The sample characterization and the study of phase transition were done by using FT-IR, X-ray diffraction (XRD) and DSC measurements. AC impedance measurements proved that the oxide ion conductivity predominantly arises from the grain and grain boundary contributions as two well-defined semicircles are clearly seen along with an inclined spike. The electrical conductivity of Bi2O3–V2O5 has been studied at different temperatures for various molar ratios. The isothermal conductivity increases with an increase in the concentration of V2O5 due to the vacancy migration phenomenon. It has been found that the conductivity of different compositions of Bi2O3–V2O5 increases and shows a jump in the temperature range 230–260°C due to the phase transition of BiVO4 from monoclinic scheelite type to that of tetragonal scheelite type. The endothermic peak in DSC at around 260°C reveals the phase transition, which is also confirmed by the XRD and FT-IR analysis. The XRD patterns confirmed the monoclinic structure of BiVO4.
Current Applied Physics, 2016
In the present work, the ternary system of (Bi 2 O 3) 1ÀxÀy (Sm 2 O 3) x (Yb 2 O 3) y was investigated. For the production and stabilization of the fcc-type solid solution, nano-Sm 2 O 3 and nano-Yb 2 O 3 were doped into nano-Bi 2 O 3 by solid-state synthesis techniques. The XRD results showed that the crystallographic structure of the samples had displayed a fluorite type face-centered cubic d-Bi 2 O 3 phase. The phase stability was also checked by the DTA measurements. The temperature dependent electrical conductivity results revealed that the maximum electrical conductivity observed for the sample of the nanostructure-(Bi 2 O 3) 0.8 (Sm 2 O 3) 0.1 (Yb 2 O 3) 0.1 system was 5.39 Â 10 À2 (ohm.cm) À1 at 650 C. The results also show that the lowest activation energy was 0.7062 eV and the lowest crystallite size was 31.62 nm for the nanostructure-(Bi 2 O 3) 0.75 (Sm 2 O 3) 0.1 (Yb 2 O 3) 0.15 system. Consequently, the face-centered cubic stable d-phase-(Bi 2 O 3) 0.8 (Sm 2 O 3) 0.1 (Yb 2 O 3) 0.1 is the optimal dopant amount due to the relatively good stability and oxygen ionic conductivity obtained, which are two of our major concerns for the electrolyte layer of solid oxide fuel cells (SOFCs).
Journal of the Serbian Chemical Society, 2009
A powder mixture of α-Bi 2 O 3 and HfO 2 , in the molar ratio 2:3, was mechanochemically treated in a planetary ball mill under air, using zirconium oxide vials and balls as the milling medium. After 50 h of milling, the mechanochemical reaction led to the formation of a nanocrystalline δ-Bi 2 O 3 phase (fluorite-type solid solution Bi 0.78 Hf 0.59 Zr 0.63 O 3.61 ), with a crystallite size of 20 nm. The mechanochemical reaction started at a very beginning of milling accompanied by an accumulation of ZrO 2 arising from the milling tools. The samples prepared after various milling times were characterized by X-ray powder diffraction and DSC analysis. The electrical properties of the as-milled and pressed Bi 0.78 Hf 0.59 Zr 0.63 O 3.61 powder were studied using impedance spectroscopy in the temperature range from 100 to 700 °C under air. The electrical conductivity was determined to be 9.43×10 -6 and 0.080 S cm -1 for the temperatures of 300 and 700 °C, respectively.
Solid State Ionics, 2011
Bi 2 O 3-Dy 2 O 3 Nano-crystalline ceramic SPS Pressureless sintering Oxide ion conductivity Using (Bi 2 O 3) 0.75 (Dy 2 O 3) 0.25 nano-powder synthesized by reverse titration co-precipitation method as raw material, dense ceramics were sintered by both Spark Plasma Sintering (SPS) and pressureless sintering. According to the predominance area diagram of Bi-O binary system, the sintering conditions under SPS were optimized. (Bi 2 O 3) 0.75 (Dy 2 O 3) 0.25 ceramics with relative density higher than 95% and an average grain size of 20 nm were sintered in only 10 min up to 500°C. During the pressureless sintering process, the grain growth behavior of (Bi 2 O 3) 0.75 (Dy 2 O 3) 0.25 followed a parabolic trend, expressed as D 2 − D 0 2 = Kt, and the apparent activation energy of grain growth was found to be 284 kJ mol − 1. Dense (Bi 2 O 3) 0.75 (Dy 2 O 3) 0.25 ceramics with different grain sizes were obtained, and the effect of grain size on ion conductivity was investigated by impedance spectroscopy. It was shown that the total ion conductivity was not affected by the grain size down to 100 nm, however lower conductivity was measured for the sample with the smallest grain size (20 nm). But, although only the δ phase was evidenced by X-ray diffraction for this sample, a closer inspection by Raman spectroscopy revealed traces of α-Bi 2 O 3 .