Effect of Manganese (II) Oxide on microstructure and ionic transport properties of nanostructured cubic zirconia (original) (raw)
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Doping effect and vacancy formation on ionic conductivity of zirconia ceramics
Journal of Physics and Chemistry of Solids, 2008
Doping effect and vacancy formation on ionic conductivity of ZrO 2 ceramics doped with RENbO 4 (RE ¼ Yb, Er, Y, Dy) were investigated using X-ray diffractometry, scanning electron microscope and corresponding ionic conductivity were evaluated using impedance spectroscopy in this work. The results show that defect distribution can be correlated with the phase transformation behavior modified by ionic radius of dopants. The total conductivity of 5 mol% RENbO 4 -doped ZrO 2 (3Y) comprises the intragrain and grain boundary (GB) conductivity. The intragrain conductivity of 5 mol% RENbO 4 -doped ZrO 2 (3Y) are lower than 3 mol% Y 2 O 3 -doped ZrO 2 (3Y-TZP) and 8 mol% Y 2 O 3 -doped ZrO 2 (8YSZ). The additions of Nb 2 O 5 to ZrO 2 (3Y) increase average lattice binding energy and activation energy, and the amount of oxygen vacancies was decreased. The average radius of oxygen vacancies of 5 mol% RENbO 4doped zirconia (3Y) were smaller than that of 8YSZ identified using hard-sphere model. The results imply that a specific doping content in zirconia which contributes a maximum content of non-interfering oxygen vacancies, the average radius of doping ions close to that of Zr 4+ and average binding energy as smaller as possible help obtain the highest conductivity of zirconia. To acquire an appropriate operation condition in the application of solid oxide fuel cell, electrical properties, phase transformation behavior and related mechanical properties need to be compromised. r
Journal of Materials Science, 2009
Zirconia stabilized with various concentrations of rare earth oxides of Yb, Sm and Y with different effective ionic radii ratio between the dopant and host cations was studied. In particular, structure, phase composition, compositional range for existence of cubic solid solutions and their phase transformations, stabilization degree of high-temperature phases and the crystal chemistry and type of solid solutions were investigated. These findings were related to the measured material characteristics, namely the electrical conductivity, microhardness and effective elastic modulus, to elucidate various effects important for practical applications, such as an increase of electrical conductivity due to the pyrochlore phase occurrence or an increase of microhardness arising from the effect of dynamic strain ageing.
Ionic and electronic conductivity of 3mol% Fe2O3-substituted cubic Y-stabilized ZrO2
Solid State Ionics, 2012
The effect of the addition of a small amount of iron oxide (3 mol%) in Y-stabilized ZrO 2 has been investigated. The aging of the obtained compound has been studied and the sintering temperature has been determined. The bulk and total conductivities of (ZrO 2 ) 0.90 -(Y 2 O 3 ) 0.07 -(Fe 2 O 3 ) 0.03 have been studied by means of impedance spectroscopy in the temperature range from 425 K to 775 K. The electronic conductivity has been studied by the Hebb-Wagner technique using a blocking Pt microelectrode. The investigation has been carried out in a wide range of oxygen activity, 10 −25 b a O 2 b 10 3 , and from 770 K to 1020 K. These data have been compared to the compound without iron oxide, YSZ (ZrO 2 ) 0.90 -(Y 2 O 3 ) 0.10. This study demonstrates that the addition of a small amount of Fe 2 O 3 decreases the sintering temperature and increases the stability of the compound without increasing the electronic conductivity.
Solid State Ionics, 2014
Scandia-stabilized zirconia (ScSZ) electrolytes exhibit the highest ionic conductivity among all ZrO 2 -based materials. However, a phase transition occurs around 650°C from cubic to rhombohedral β-phase which is unique for Sc-stabilized zirconia and leads to reduced conductivity. The occurrence of this β-phase can be suppressed by co-doping ScSZ. The aims of this study are to confirm the influence of a small amount of Fe 2 O 3 doping on both the stabilization of the cubic phase and the decrease of the sintering temperature and to investigate the influence of this co-doping on the ionic and electronic conductivity of ScSZ. Therefore (ZrO 2 ) 0.90 -(Sc 2 O 3 ) 0.07 -(Fe 2 O 3 ) 0.03 powder has been prepared by precipitation in aqueous solution and sintered at 1380°C to obtain ceramic. The electrical properties (ionic and electronic conductivities) of this ceramic are compared to the ones of Fe-doped YSZ.
Electrical Conductivity of Er2O3-Doped c- ZrO2 Ceramics
Journal of Materials Engineering and Performance, 2014
"The effect of Er2O3 addition on electrical conductivity of c-ZrO2 was investigated by analyzing the impedance spectra of undoped and various amounts of Er2O3-doped cubic zirconia (c-ZrO2). The undoped and 1-15 wt% Er2O3-doped c-ZrO2 powders were prepared via colloidal process. The doped powders were then pelletized under a pressure of 200 MPa. In addition, the undoped and Er2O3-doped c-ZrO2 specimens were sintered at 1500 C for 1 h. The electrical conductivity of the specimens was measured using a frequency response analyzer in the frequency range of 100 mHz-13 MHz, in the temperature range of 300- 800 C. Electrical conductivity results indicate an increase in the conductivity with increase in the test temperature. The addition of 1 wt% Er2O3 into c-ZrO2 led to an increase in the grain interior, grain boundary, and total conductivities. The distortion caused by the addition of Er3+ cations in the c-ZrO2 lattice leads to an increase in the concentration of oxygen vacancies in the c-ZrO2 matrix, resulting in an enhancement in the electrical conductivities."
Chemical Vapor Deposition, 2012
Dense, crack-free thin films (<5 mm) of the nanostructured scandia-zirconia system (Sc 2 O 3 :ZrO 2 ) stabilized in the cubic-fluorite phase (c-ZrO 2 ) are deposited through conventional low-pressure metal-organic(LP-MO) CVD by using b-diketonate metal complexes as precursors [(Zr(tmhd) and Sc(tmhd) 3 , with -tmhd ¼ 2,2,6,6-tetramethyl-3,5-heptanedionate]. The compositional (energy dispersive X-ray spectroscopy -EDX), structural (X-ray diffraction -XRD) and morphological (field emission gunenvironmental scanning electron microscopy -FEG-ESEM) analyses, confirmed the growth of dense partially and fully stabilized ZrO 2 , a suitable electrolyte for solid oxide fuel cells (SOFC). Results of impedance spectroscopy, which investigates the electrical conductivity of coating, deposited as thin as possible to guarantee the uniform covering of a porous substrate, are reported. Results of thin films of yttria-zirconia system (Y 2 O 3 :ZrO 2 ), deposited with the same method, are also reported for comparison.
Investigation of the electrical conductivity of sintered monoclinic zirconia (ZrO 2 )
Ceramics International, 2017
High-density monoclinic ZrO 2 was manufactured through sintering at~1200°C by using nanosized powders. Then, the electrical conductivity was measured at a range of high temperatures (700-900°C) by electrical impedance spectroscopy (EIS). For the as-sintered monoclinic ZrO 2 , the measured electrical conductivity was 3.2×10 −5 s/cm (for 80% TD) and 4.4×10 −5 s/cm (for 89% TD) at 900°C. After aging at 900°C for 100 h, the electrical conductivity of the monoclinic ZrO 2 of 80%-TD decreased by more than 50%. However, after reheating at 1200°C for 1 h, approximately 80% of the conductivity was recovered compared to the value of the assintered monoclinic ZrO 2. The pure monoclinic crystal structure was retained despite the aging and reheating treatment. Based on microstructural observations of the aged and reheated monoclinic ZrO 2 , the changes in electrical conductivity after aging and reheating were explained by the formation and recovery of micro-cracks, respectively.
Solid State Ionics, 1995
In the system ZQ-In203, the In,O,-doped ZrQ phases (cubic, tetragonal and t') exhibit high ionic conductivity and the Z&doped Inz03 high electronic conductivity. These phases are in thermodynamic equilibrium at high temperatures. The ionic conductivity of Zr02 depends on the crystal symmetry having the same In203 concentration. At lOOO"C, the highest conductivities were obtained for cubic ZQ doped with 25 molW InO,._ At lower concentrations, the ionic conductivity of cubic-Zr02 decreases due to a first-order phase transformation to the tetragonal (t') form. Single-phase In203 doped with ZrOz is an n-type electronic conductor with a conductivity of up to 7 x lo4 S/m in air. Point defect models for electronic conduction in In203 doped with ZrOz are discussed. Two maxima in the electronic conductivity have been found: one in the two-phase region and one in the In0,,5 single phase region. In the heterogeneous two-phase material cubic-ZrQ+InO ,.s, the electronic conductivity increases abruptly up to 10" S/m with increasing In0 1.5 concentration. This material is a three-dimensional composite of ionand electron-conducting phases. The origin of the maximum in electrical conductivity in the heterogeneous two-phase region is discussed.
Electrochemical characterization of nanostructured zirconias
Solid State Ionics, 2009
Redox stability of cubic nanostructured zirconia ceramics, free of any secondary phases, has been investigated experimentally as a function of grain size. Pure 8 mol% Y 2 O 3 -doped ZrO 2 powders were synthesized by a spray pyrolysis process and then compacted by uniaxial pressing, followed by cold isostatic pressing. Using appropriate thermal treatments, average grain sizes ranging from 25 to 242 nm and relative densities from 71% up to 98% were obtained. An electrochemical characterization was performed with comparison on ceramics of 3.2 and 7.6 μm and 98% of theoretical density starting from commercial YSZ powder.