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1.
The Pechinni method (A) as well as hydrothermal treatment (B) of co-precipitated CeO2-based gels with NaOH solution were used to synthesise pure CeO2, and CeO2-based solid solutions with formula Ce1−xMxO2, Ce1−x(M0.5Ca0.5)xO2 M = Gd, Sm for 0.15 < x < 0.3 nanopowders. The thermal evolution of CeO2-based precursors during heating them up to 1000 °C was monitored by thermal (TG, DTA) analysis and X-ray diffraction method. All nanopowders and samples sintered were found to be pure CeO2 or ceria-based solutions with fluorite-type structure. The microstructure of CeO2-based sintered samples at 1500 °C (A) or 1250 °C (B) was observed for 2 h under the scanning electron microscope. The electrical properties of singly Ce1−xMxO2 or doubly doped CeO2-based samples with formula Ce1−x(M0.5Ca0.5)xO2, M = Gd, Sm, 0.15 < x < 0.30 were investigated by means of the ac impedance spectroscopy method throughout the temperature range of 600-800 °C. It has been stated that partial substitution of calcium by samarium or calcium by gadolinium in the Ce1−x(M0.5Ca0.5)xO2, M = Gd, Sm solid solutions leads to ionic conductivity enhancement comparable with only samaria- or gadolina-doped ceria. The CeO2-based samples with small-grained microstructures obtained from powders synthesised by hydrothermal method exhibited better ionic conductivity than samples with the same composition obtained from powders synthesised by the Pechinii method. The stability of the electrolytic properties of selected co-doped ceria sinters in fuel gases (H2, CH4) as well as exhaust gases from diesel engine was also investigated. The co-doped Ce0.8(Sm0.5Ca0.5)0.2O2 or Ce0.85(Gd0.5Ca0.5)0.15O2 dense samples would appear be to more adequate oxide electrolytes than Ce1−xMxO2, M = Sm, Gd and x = 0.15 or 0.2 for electrochemical devices operating at temperatures ranging from 600 to 700 °C.  相似文献   

2.
Lead-free (1−x)(Ba0.85Ca0.15)(Ti0.9Zr0.1)O3xBiYbO3 [(1−x)BCTZ−xBYO] piezoelectric ceramics in the range of BYO concentrations were prepared by the conventional oxide-mixed method, and the effect of BYO content on their microstructure, crystalline structure, density and electrical properties was investigated. A dense microstructure with large grain was obtained for the ceramics with the addition of BYO. The ceramics with x=0.1% exhibit an optimum electrical behavior of d33~580 pC/N, r~10.9 Ω, kp~56.4%, and tan δ~1.12% when sintered at a low temperature of ~1350 °C. When the measuring electric field is 40 kV/cm, the well-saturated and square-like PE loops for the ceramics were observed with Pr~12.2 μC/cm2 and Ec~1.83 kV/cm.  相似文献   

3.
This paper reports the synthesis, structure, chemical stability and electrical transport properties of Ti substituted Ba3CaNb2O9 (BCN) to develop electrolytes for proton conducting solid oxide fuel cells (H-SOFCs). The powder X-ray diffraction (PXRD) of Ba3CaNb2−xTixO9−δ (x = 0.1, 0.15, 0.2, 0.25 and 0.3) and Ba3Ca1.18Nb1.82−xTixO9−δ (x = 0.15 and 0.25) showed formation of double perovskite-like structure with lattice constant comparable to that of Ba3Ca1.18Nb1.82O9−δ (BCN18). Scanning electron microscopy (SEM) showed dense and pore-free microstructure for Ba3CaNb1.75Ti0.25O8.875. PXRD and Fourier transform infrared (FTIR) spectroscopy data confirmed long-term stability of Ba3CaNb2−xTixO9−δ and Ba3Ca1.18Nb1.82−xTixO9−δ in boiling H2O and in CO2 at elevated temperatures. The AC impedance investigation showed contribution due to bulk, grain-boundary and electrode effect at low temperatures. The electrical conductivity of studied materials were measured in different medium including dry air, dry H2, wet H2, wet N2 and D2O. Increase in conductivity in wet N2 and decrease in conductivity in D2O confirmed the proton conduction in Ba3CaNb1.75Ti0.25O9-δ. Among Ti-substituted compounds investigated in this study, Ba3Ca1.18Nb1.57Ti0.25O8.605 showed the highest conductivity of 3.5 × 10−4 S cm−1 at 400 °C in wet N2 (3%H2O), which is comparable to reported values of Ba2Ca0.79Nb0.66Ta0.55O6−δ and BCN18.  相似文献   

4.
Cr and Co doped Bi1.5Zn0.92Nb1.5O6.92 pyrochlore ceramics were produced by solid state mixing of oxides. Cr and Co were doped into the Nb and Nb-Zn sites considering the compositions of Bi1.5Zn0.92Nb1.5−xCrxO6.92−x, (Bi1.5Zn0.46)(Zn0.46−3x/6Nb1.5−3x/5Crx)O6.92−x/2 for Cr doping and Bi1.5Zn0.92Nb1.5−3x/5CoxO6.92, (Bi1.5Zn0.46)(Zn0.46−3x/6Nb1.5−3x/5Cox)O6.92−x/2 for Co doping. The solubility limit of Cr in BZN was higher than that of Co and the solubility limit increased when doping was made both into Nb and Zn sites. The second phases appeared when x > 0.2 for Cr and x > 0.15 for Co doping into the Nb-Zn sites. Simultaneous Cr doping into the Nb- and Zn-sites of BZN pyrochlore gave higher dielectric constant than doping into the Nb-site of pyrochlore. However, Co doping into the Nb- and Zn-sites and only into the Nb-site of BZN gave identical dielectric results in the range of 202-218. The temperature coefficient of dielectric constant decreased with Cr doping and increased with Co doping.  相似文献   

5.
NiFe2−xBixO4 (x = 0, 0.1, 0.15) nanopowders were synthesized via sol-gel method. The precursor gels were calcined at 773 K in air for 1 h to obtain the pure nanostructured NiFe2−xBixO4 spinel phase. The crystal structure and magnetic properties of the substituted spinel series of NiFe2−xBixO4 have been investigated by means of 57Fe Mössbauer spectroscopy, transmission electron microscopy and alternating gradient force magnetometry. Mössbauer spectroscopic measurements revealed that Bi3+ cations tend to occupy octahedral positions in the structure of the substituted ferrite, i.e., the crystal-chemical formula of the as-prepared nanoparticles may be written as: (Fe)[NiFe1−xBix]O4 (x = 0, 0.1, 0.15), where parentheses and square brackets enclose cations on sites of tetrahedral and octahedral coordination, respectively. Selective area electron diffraction studies provided evidence that the samples of the NiFe2−xBixO4 series, independently of x, exhibit the cubic spinel structure. The values of the saturation magnetization and the coercive field of NiFe2−xBixO4 nanoparticles were found to decrease with increasing degree of bismuth substitution.  相似文献   

6.
Pr2O3-doped Ba0.85Ca0.15Ti0.90Zr0.10O3 (BCTZ-xPr) ceramics were prepared by the conventional solid-state method. A tetragonal phase is only observed in these ceramics, and the introduction of Pr2O3 decreases their sintering temperature without affecting negatively the piezoelectric constant. Enhanced ferroelectric properties were obtained in these BCTZ-xPr ceramics. The ceramic with x=0.06 wt% exhibits a good electrical behavior of d33∼460 pC/N, kp∼47.6%, εr∼4638, and tan δ∼0.015 when sintered at a low temperature of ∼1400 °C. As a result, the BCTZ-xPr ceramic is a promising candidate for lead-free piezoelectric ceramics.  相似文献   

7.
Solid state glass electrolyte, xLi2O-(1 − x)(yB2O3-(1 − y)P2O5) glasses were prepared with wide range of composition, i.e. x = 0.35 - 0.5 and y = 0.17 - 0.67. This material system is one of the parent compositions for chemically and electrochemically stable solid-state electrolyte applicable to thin film battery. Lithium ion conductivity of Li2O-B2O3-P2O5 glasses was studied in the correlation to the structural variation of glass network by using FTIR and Raman spectroscopy. The measured ionic conductivity of the electrolyte at room temperature increased with x and y. The maximum conductivity of this glass system was 1.6 × 10−7 Ω−1 cm−1 for 0.45Li2O-0.275B2O3-0.275P2O5 at room temperature. It was shown that the addition of P2O5 reduces the tendency of devitrification and increases the maximum amount of Li2O added into glass former without devitrification. As Li2O and B2O3 contents increased, the conductivity of glass electrolyte increased due to the increase of three-coordinated [BO3] with a non-bridging oxygen (NBO).  相似文献   

8.
New pyrochlore ceramics have been produced by doping Sm and Nd into the Bi site and Fe into the Nb site in the Bi1.5Zn0.92Nb1.5O6.92 (BZN) pyrochlore. Doped pyrochlore ceramics were produced by conventional solid state mixing of oxides at different doping levels using the compositions of Bi1.5−xSmxZn0.92Nb1.5O6.92, Bi1.5−xNdxZn0.92Nb1.5O6.92 and Bi1.5Zn0.92Nb1.5−xFexO6.92−x. The solubility limit of cations was determined as x = 0.13, 0.18 and 0.15 for Sm, Nd and Fe, respectively. While Sm and Nd increased the dielectric constant (?), Fe doping led a decrease in ?. Dielectric constant of Sm and Nd doped BZN increased to 199 at x = 0.13 (Sm) and to 219 at x = 0.18 (Nd). At low Fe dopings (x = 0.05), the dielectric constant of BZN increased to 242 but decreased to 211 at x = 0.15. The dielectric losses were lower for Sm and Nd dopings than Fe but in all cases it was lower than 0.006. The dielectric constant of Sm, Nd and Fe doped BZN ceramics was nearly independent of frequency within the frequency range between 1 kHz and 2 MHz, but decreased considerably with temperature between 20 and 200 °C. Temperature coefficient of Sm doped BZN (−354 ppm/°C) was lower than Nd and Fe doped BZN ceramics at solubility limits (−538 ppm/°C for Nd and −565 ppm/°C for Fe).  相似文献   

9.
Co-doped Li3V2−xCox(PO4)3/C (x = 0.00, 0.03, 0.05, 0.10, 0.13 or 0.15) compounds were prepared via a solid-state reaction. The Rietveld refinement results indicated that single-phase Li3V2−xCox(PO4)3/C (0 ≤ x ≤ 0.15) with a monoclinic structure was obtained. The X-ray photoelectron spectroscopy (XPS) analysis revealed that the cobalt is present in the +2 oxidation state in Li3V2−xCox(PO4)3. XPS studies also revealed that V4+ and V3+ ions were present in the Co2+-doped system. The initial specific capacity decreased as the Co-doping content increased, increasing monotonically with Co content for x > 0.10. Differential capacity curves of Li3V2−xCox(PO4)3/C compounds showed that the voltage peaks associated with the extraction of three Li+ ions shifted to higher voltages with an increase in Co content, and when the Co2+-doping content reached 0.15, the peak positions returned to those of the unsubstituted Li3V2(PO4)3 phase. For the Li3V1.85Co0.15(PO4)3/C compound, the initial capacity was 163.3 mAh/g (109.4% of the initial capacity of the undoped Li3V2(PO4)3) and 73.4% capacity retention was observed after 50 cycles at a 0.1 C charge/discharge rate. The doping of Co2+into V sites should be favorable for the structural stability of Li3V2−xCox(PO4)3/C compounds and so moderate the volume changes (expansion/contraction) seen during the reversible Li+ extraction/insertion, thus resulting in the improvement of cell cycling ability.  相似文献   

10.
SnO2-doped CaSiO3 ceramics were successfully synthesized by a solid-state method. Effects of different SnO2 additions on the sintering behavior, microstructure and dielectric properties of Ca(Sn1−xSix)O3 (x=0.5–1.0) ceramics have been investigated. SnO2 improved the densification process and expanded the sintering temperature range effectively. Moreover, Sn4+ substituting for Si4+ sites leads to the emergence of Ca3SnSi2O9 phase, which has a positive effect on the dielectric properties of CaO–SiO2–SnO2 materials, especially the Qf value. The Ca(Sn0.1Si0.9)O3 ceramics sintered at 1375 °C possessed good microwave dielectric properties: εr =7.92, Qf =58,000 GHz and τf=−42 ppm/°C. The Ca(Sn0.4Si0.6)O3 ceramics sintered at 1450 °C also exhibited good microwave dielectric properties of εr=9.27, Qf=63,000 GHz, and τf=−52 ppm/°C. Thus, they are promising candidate materials for millimeter-wave devices.  相似文献   

11.
This study reports the successful preparation of single-phase perovskite (Ba0.5Sr0.5)0.8La0.2Fe1−xMnxO3−δ (x = 0-0.2) by the citrate-EDTA complexing method. The crystal structure, thermal gravity analysis, coefficient of thermal expansion, electrical conductivity, and electrochemical performance of (Ba0.5Sr0.5)0.8La0.2Fe1−xMnxO3−δ were investigated to determine its suitability as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The lattice parameter a of (Ba0.5Sr0.5)0.8La0.2Fe1−xMnxO3−δ decreases as the amount of Mn doping increases. The coefficients of thermal expansion of the samples are in the range of 21.6-25.9 × 10−6 K−1 and show an abnormal expansion at around 400 °C associated with the loss of lattice oxygen. The electrical conductivity of the (Ba0.5Sr0.5)0.8La0.2Fe1−xMnxO3−δ samples decreases as the amount of Mn-doping increases. The electrical conductivity of the samples reaches a maximum value at around 400 °C and then decreases as the temperature increases. The charge transfer resistance, diffusion resistance and total resistance of a (Ba0.5Sr0.5)0.8La0.2Fe0.8Mn0.15O3-δ-Ce0.8Sm0.2O1.9 composite cathode electrode at 800 °C are 0.11 Ω cm2, 0.24 Ω cm2 and 0.35 Ω cm2, respectively.  相似文献   

12.
(1−x)BaTiO3xBi0.5Na0.5TiO3 (BT–BNT) ceramics were prepared by the solid-state reaction method. With an increase of BNT content, both the Curie temperature and the room temperature resistivity increased. At 1 mol% BNT addition, the sample was not semiconducting, due to Bi2O3 volatilization resulting from the decomposition of pre-calcined BNT during sintering. Appropriate extra Nb2O5 doping in the raw materials could offset Bi2O3 volatilization and neutralize the redundant acceptor Na+ ions. When the extra Nb2O5 content was 0.6 mg, the sample room-temperature resistivity was 6.3×103 Ω cm, with the Curie point about 135 °C and a high PTC effect of ∼3 orders of magnitude.  相似文献   

13.
Gd2(Zr1−xNbx)2O7+x (0 ≤ x ≤ 0.2) ceramics are prepared via the solid state reaction process at 1973 K for 10 h in air. Gd2(Zr1−xNbx)2O7+x (x = 0.1, 0.2) ceramics exhibit an ordered pyrochlore-type structure, whereas Gd2Zr2O7 has a defective fluorite-type structure. The electrical property of Gd2(Zr1−xNbx)2O7+x ceramics is investigated by electrochemical impedance spectroscopy over a frequency range of 10 Hz to 8 MHz from 623 to 923 K. The electrical conductivity obeys the Arrhenius equation. The grain conductivity of Gd2(Zr1−xNbx)2O7+x ceramics varies with doping different Nb contents, and exhibits a maximum at the Nb content of x = 0.1 in the temperature range of 623-923 K. The conductivity in hydrogen atmosphere is a little bit higher than in air in the temperature range of 723-923 K, which indicates that the doping of Zr4+ by Nb5+ can increase the proton-type conduction and reduce the oxide-ionic conduction. The conduction of Gd2(Zr1−xNbx)2O7+x is not a pure oxide-ionic conductor.  相似文献   

14.
A new series of rare earth solid solutions Sc2−xYxW3O12 was successfully synthesized by the conventional solid-state method. Effects of doping ion yttrium on the crystal structure, morphology and thermal expansion property of as-prepared Sc2−xYxW3O12 ceramics were investigated by X-ray diffraction (XRD), thermogravimetric analysis (TG), field emission scanning electron microscope (FE-SEM) and thermal mechanical analyzer (TMA). Results indicate that the obtained Sc2−xYxW3O12 samples with Y doping of 0≤x≤0.5 are in the form of orthorhombic Sc2W3O12-structure and show negative thermal expansion (NTE) from room temperature to 600 °C; while as-synthesized materials with Y doping of 1.5≤x≤2 take hygroscopic Y2W3O12·nH2O-structure at room temperature and exhibit NTE only after losing water molecules. It is suggested that the obvious difference in crystal structure leads to different thermal expansion behaviors in Sc2−xYxW3O12. Thus it is proposed that thermal expansion properties of Sc2−xYxW3O12 can be adjusted by the employment of Y dopant; the obtained Sc1.5Y0.5W3O12 ceramic shows almost zero thermal expansion and its average linear thermal expansion coefficient is −0.00683×10−6 °C−1 in the 25–250 °C range.  相似文献   

15.
Y2−xLaxW3O12 solid solutions were successfully synthesized by the solid state reaction method. The microstructure, hygroscopicity and thermal expansion property of the resulting samples were investigated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM) and thermal mechanical analysis (TMA). Results indicate that the structural phase transition of the Y2−xLaxW3O12 changes from orthorhombic to monoclinic with increasing substituted content of lanthanum. The pure phase can form for 0≤x≤0.4 with orthorhombic structure and for 1.5≤x≤2 with monoclinic one. High lanthanum content leads to a low relative density of Y2−xLaxW3O12 ceramic. Thermal expansion coefficients of the Y2−xLaxW3O12 (0≤x≤2) ceramics also vary from −9.59×10−6 K−1 to 2.06×10−6 K−1 with increasing substituted content of lanthanum. The obtained Y0.25La1.75W3O12 ceramic shows almost zero thermal expansion and its average linear thermal expansion coefficient is −0.66×10−6 K−1 from 103 °C to 700 °C.  相似文献   

16.
The LaBaCo2O5+δx wt.% Bi2O3 (LBCO-xBi2O3, x=10, 20, 30, and 40) were prepared as composite cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs) via the conventional mechanical mixing method. The effect of Bi2O3 on polarization resistance, overpotential, and long-term stability of the LBCO cathode was investigated. An effective sintering aid for LBCO cathode, Bi2O3 not only lowers its sintering temperature by ~200 °C, but also improves the electrochemical performance within the intermediate temperature range of 600–800 °C. Electrochemical impedance spectroscopy measurements showed that the addition of 20 wt% Bi2O3 to LBCO exhibited the lowest area-specific resistance of 0.020 Ω cm2 at 800 °C in air, which was about a seventh of that of the LBCO cathode at the same condition. At a current density of 0.2 A cm−2, the cathodic overpotential of LBCO-20Bi2O3 was about 12.6 mV at 700 °C, while the corresponding value for LBCO was 51.0 mV. Compared to B2O3–Bi2O3–PbO frit, the addition of Bi2O3 significantly improved the long-term stability of cathode. Therefore, LBCO-20Bi2O3 can be a promising cathode for IT-SOFCs.  相似文献   

17.
Effects of compressive stress on the ferroelectric properties of ceramics in PZT–PZN systems were investigated. (1  x)Pb(Zr1/2Ti1/2)O3(xPb(Zn1/3Nb2/3)O3 or (1  x)PZT–(x)PZN (x = 0.1–0.5) ceramics were prepared by a conventional mixed-oxide method. The ferroelectric properties under compressive stress of the PZT–PZN ceramics were observed at stress levels up to 170 MPa using a compressometer in conjunction with a modified Sawyer–Tower circuit. It was found that with increasing compressive stress the area of the ferroelectric hysteresis (P–E) loops, the saturation polarization (Psat), the remanent polarization (Pr), and the coercive field (Ec) decreased. These results were interpreted through the non-180° ferroelectric domain switching processes.  相似文献   

18.
Direct electrochemical oxidation of hydrocarbon fuels is a current development trend of solid oxide fuel cells (SOFCs) and finding new anode materials for this application is a key issue. In this study, promising candidates, Y2O3-doped SrTiO3 perovskite compounds Sr1−1.5xYxTiO3 (x = 0.02, 0.04, 0.06, 0.08, 0.10), were synthesized by solid-state reaction. The structure of the calcined powders was examined by X-ray diffraction (XRD). The sinterability and high temperature conductivity were measured by the Archimedes principle and a dc four-probe method, respectively. The effect of sintering temperature on the electrical conductivity was studied. The results indicated that the optimal sintering temperature is around 1400 °C. From 400 °C to 1000 °C, the conductivity decreased with increasing temperature. At 800 °C the highest conductivity (26.8 S/cm) was observed for x = 0.08.  相似文献   

19.
We report the investigation of boron substitution on structural, electrical, thermal, and thermoelectric properties of Ca3−xBxCo4O9 (x=0, 0.5, 0.75, and 1) in the temperature range between 300 K and 5 K. X-ray diffraction studies show that the Ca3Co4O9 phase is successfully preserved as the majority phase in the x=0.5 sample despite the small size of boron ions. Electrical transport measurements confirm that B3+ substitution for Ca2+ causes an increase in resistivity due to the decrease in carrier concentration. x=0.5 sample is found to have a Seebeck coefficient of 181 μV/K at room temperature which is ~1.5 times higher than that of the pure Ca3Co4O9. Our results indicate that the chemical pressure due to the large ionic radii difference between B3+ (0.27 Å) and Ca2+ (1 Å) enhances the thermoelectric properties as long as the unique crystal structure of Ca3Co4O9 is preserved.  相似文献   

20.
The effect of nano-sized PbO (10–30 nm) addition on the transport critical current density, Jc of (Bi1.6Pb0.4)Sr2Ca2Cu3O10 (PbO)x (x=0–0.15 wt%) was investigated. Jc of PbO added pellet samples showed the maximal value at x=0.05 wt%. Using this result, Ag-sheathed (Bi1.6Pb0.4)Sr2Ca2Cu3O10 (PbO)x/Ag tapes (x=0 and 0.05 wt %) were fabricated by the powder-in-tube (PIT) method. The tapes were sintered for 50 h and 100 h at 845 °C. The temperature dependence of Jc for the non-added and PbO added tapes in applied field was investigated. Jc of the non-added tapes was 4510 A/cm2 at 40 K and 949 A/cm2 at 77 K. Jc of (Bi1.6Pb0.4)Sr2Ca2Cu3O10 (PbO)0.05/Ag tape sintered for 100 h was 26,800 A/cm2 at 40 K and 10,700 A/cm2 at 40 K, which was higher than the tapes sintered for 50 h (8590 A/cm2 at 40 K and 1880 A/cm2 at 77 K). Nano-sized PbO added tapes sintered for 100 h showed a higher Jc (more than 10 times) under magnetic field (0–0.75 T) compared with the non-added tape. A combined effect of enhanced flux pinning and improved microstructure led to the significant increase in Jc of the nano-sized PbO added tapes.  相似文献   

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