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1.
Thermal expansion behavior of Th(MoO 4) 2, Na 2Th(MoO 4) 3 and Na 4Th(MoO 4) 4 was studied under vacuum in the temperature range of 298–1123 K by high temperature X-ray diffractometer. Th(MoO 4) 2 was synthesized by reacting ThO 2 with 2 mol of MoO 3, at 1073 K in air and Na 2Th(MoO 4) 3 and Na 4Th(MoO 4) 4 were prepared by reacting Th(MoO 4) 2 with 1 and 2 mol of Na 2MoO 4, respectively at 873 K in air. The XRD data of Th(MoO 4) 2 was indexed on orthorhombic system where as XRD data of Na 2Th(MoO 4) 3 and Na 4Th(MoO 4) 4 were indexed on tetragonal system. The lattice parameters and cell volume of all the three compounds, fit into polynomial expression with respect to temperature, showed positive thermal expansion (PTE) up to 1123 K. The average value of thermal expansion coefficients for Th(MoO 4) 2, Na 2Th(MoO 4) 3 and Na 4Th(MoO 4) 4 were determined from the high temperature data. 相似文献
2.
In Na–U(IV)–Mo–O system, two quaternary compounds Na 2U(MoO 4) 3 and Na 4U(MoO 4) 4 were prepared by solid state reactions of Na 2MoO 4, UMoO 5 and MoO 3 in the required stoichiometric ratio at 500 °C in evacuated sealed quartz ampoules. The crystal structure of both the compounds were derived from X-ray powder diffraction data in the tetragonal system by Rietveld profile method. Na 2U(MoO 4) 3 has scheelite structure, whereas Na 4U(MoO 4) 4 has scheelite superlattice structure. TG curves of Na2U(MoO4)3 and Na4U(MoO4)4 did not show any significant weight change up to 750 °C in an inert atmosphere. During the heating cycle in an inert atmosphere, DTA curves of Na2U(MoO4)3 and Na4U(MoO4)4 showed endothermic peaks due to the melting of the compounds at 740 °C and 730 °C, respectively. Na2U(MoO4)3 and Na4U(MoO4)4, when heated in air atmosphere at 1200 °C, decomposed to form Na2U2O7 which was confirmed by weight loss calculation and XRD. 相似文献
3.
A new mixed-valence iron phosphate Na 1.25Mg 1.10Fe 1.90(PO 4) 3 has been synthesized as single crystals by a flux technique and its structure has been refined from X-ray data to a residual R1 = 0.032. The compound crystallizes in the monoclinic space group C2/ c with the parameters: a = 11.7831(3) Å, b = 12.4740(3) Å, c = 6.3761(2) Å, β = 113.643(2)° and Z = 4. The structure belongs to the alluaudite structural type, and thus it obeys to the X(2)X(1)M(1)M(2) 2(PO 4) 3 general formula. The X(2) and X(1) sites are occupied by sodium while the M(1) and M(2) sites feature a statistical distribution of iron and magnesium. Additional information about the cation distribution has been extracted from a Mössbauer spectroscopy study which confirmed the mixed valency of the compound. A magnetic susceptibility study has also been undertaken and has shown the compound to be antiferromagnetic with a Neel temperature of about 35 K. 相似文献
4.
Crystal structures from two new phosphates Na 4NiFe(PO 4) 3 ( I) and Na 2Ni 2Fe(PO 4) 3 ( II) have been determined by single crystal X-ray diffraction analysis. Compound (I) crystallizes in a rhombohedral system (S. G: R-3c, Z = 6, a = 8.7350(9) Å, c = 21.643(4) Å, R1 = 0.041, wR2=0.120). Compound ( II) crystallizes in a monoclinic system (S. G: C2/ c, Z = 4, a = 11.729(7) Å, b = 12.433(5) Å, c = 6.431(2) Å, β = 113.66(4)°, R1 = 0.043, wR2=0.111). The three-dimensional structure of ( I) is closely related to the Nasicon structural type, consisting of corner sharing [(Ni/Fe)O 6] octahedra and [PO 4] tetrahedra forming [NiFe(PO 4) 3] 4+ units which align in chains along the c-axis. The Na + cations fill up trigonal antiprismatic sites within these chains. The crystal structure of ( II) belongs to the alluaudite type. Its open framework results from [Ni 2O 10] units of edge-sharing [NiO 6] octahedra, which alternate with [FeO 6] octahedra that form infinite chains. Coordination of these chains yields two distinct tunnels in which site Na +.The magnetization data of compound (I) reveal antiferromagnetic (AFM) interactions by the onset of deviations from a Curie-Weiss behaviour at low temperature as confirmed by Mössbauer measurements performed at 4.2 K. The corresponding temperature dependence of the reciprocal susceptibility χ−1 follows a typical Curie-Weiss behaviour for T > 105 K. A canted AFM state is proposed for compound (II) below 46 K with a field-induced magnetic transition at H ≈ 19 kOe, revealed in the hysteresis loop measured at 5 K. This transition is most probably associated with a spin-flop transition. 相似文献
5.
Dense aluminum nitride ceramics were prepared by Spark Plasma Sintering at a lower sintering temperature of 1700 °C with Sm 2O 3 as sintering additives. The effect of Sm 2O 3 content on the density, phase composition, microstructure and thermal conductivity of AlN ceramics was investigated. The results showed that Spark Plasma Sintering could fabricate dense AlN ceramics with superior thermal properties in a very short time. Sm 2O 3 not only facilitated the densification via the liquid-phase sintering mechanism but also improved thermal conductivity by decreasing oxygen impurity. Thermal conductivity decreased with increasing amount of Sm 2O 3 and the highest thermal conductivity was obtained for the AlN ceramics with 2 wt.% Sm 2O 3 content. During Spark Plasma Sintering process, only 2–3 wt.% sintering additives was enough to fabricate dense AlN ceramics, and the microstructures played a key role in controlling the thermal conductivity of AlN ceramics. 相似文献
6.
The effects of co-doping with Ta- and Li-ions on the microstructure, crystal structure, ferroelectric, and electric field-induced strain properties of Bi 1/2(Na 0.82K 0.18) 1/2TiO 3 (BNKT) ceramics were investigated. Li substitution into Na-sites led to a ferroelectric-nonpolar phase transition and a large accompanying normalized strain ( Smax/ Emax) of 727 pm/V near the phase boundary, when 2.5 mol% Li and 2.5 mol% Ta were co-doped on A- and B-sites, respectively. The phase transition-related strain was thought to be induced by a decrease in the tolerance factor of the perovskite structure. 相似文献
7.
Carbon-coated Li 3V 2(PO 4) 3 cathode materials for lithium-ion batteries were prepared by a carbon-thermal reduction (CTR) method using sucrose as carbon source. The Li 3V 2(PO 4) 3/C composite cathode materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical measurement. The results show that the Li 3V 2(PO 4) 3 samples synthesized using sucrose as carbon source have the same monoclinic structure as the Li 3V 2(PO 4) 3 sample synthesized using acetylene black as carbon source. SEM image exhibits that the particle size is about 1 μm together with homogenous distribution. Electrochemical test shows that the initial discharge capacity of Li 3V 2(PO 4) 3 powders is 122 mAh·g −1 at the rate of 0.2C, and the capacity retains 111 mAh−g −1 after 50 cycles. 相似文献
8.
Spherical Li 3V 2(PO 4) 3 was synthesized by using N 2H 4 as reducer. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that single-phase, spherical and well-dispersed Li 3V 2(PO 4) 3 has been successfully synthesized in our experimental process. Electrochemical behaviors have been characterized by charge/discharge measurements. The initial discharge capacities of Li 3V 2(PO 4) 3 were 123 mAh g −1 in the voltage range of 3.0–4.3 V and 132 mAh g −1 in the voltage range of 3.0–4.8 V. 相似文献
9.
Two kinds of rare earth cerium oxides Gd 2Ce 2O 7 and (Gd 0.9Ca 0.1) 2Ce 2O 6.9 were prepared by solid state reaction method at 1600 °C for 10 h. The phase compositions, microstructures, and their thermal conductivities of these materials were investigated. XRD results revealed that single phase Gd 2Ce 2O 7 and (Gd 0.9Ca 0.1) 2Ce 2O 6.9 with fluorite structure were synthesized. Results of SEM and EDS showed that the microstructures of these materials were dense and no other phases existed among grains. Because of phonon scattering resulted by the oxygen vacancies and difference in atomic mass between substitutional atoms and host atoms, thermal conductivities of Gd 2Ce 2O 7 and (Gd 0.9Ca 0.1) 2Ce 2O 6.9 are lower than that of 8YSZ at 800 °C, and thermal conductivity of (Gd 0.9Ca 0.1) 2Ce 2O 6.9 is lower than that of Gd 2Ce 2O 7. These results imply the Gd 2Ce 2O 7 and (Gd 0.9Ca 0.1) 2Ce 2O 6.9 can be used as novel candidate materials for thermal barrier coatings in the future. 相似文献
10.
The effects of La 2O 3 addition on thermal conductivity, phase stability and thermal cycle life of Y 2O 3 stabilized ZrO 2 plasma sprayed coatings were investigated. Although low thermal conductivity as well as high resistance to sintering was achieved by La 2O 3 addition, it tended to also result in lower phase stability and thermal cycle life of the coatings. Optimization of the composition and structure of the coatings improved these properties, and the optimized coatings showed prolonged thermal cycle life. 相似文献
11.
K 3Lu(PO 4) 2:Ce single crystals have been studied under gamma, X-ray, VUV, and UV excitation. For all of the excitation forms, the luminescence of these materials is dominated by the d–f emission bands of Ce 3+. The shape and position of these bands, however, depends on the form of the excitation and on temperature due to crystallographic structural phase changes and multiple types of Lu 3+ ions sites in the which the Ce 3+ ion can substitute for Lu. The highly efficient and fast scintillation of these materials is based on radiative recombination of electron-hole pairs via Ce ions, and the scintillation characteristics identify K 3Lu(PO 4) 2:Ce as a promising fast and efficient scintillator. 相似文献
12.
The polycrystalline ceramic samples of Pb 1−xSm x(Zr 0.55Ti 0.45) 1−x/4O 3 ( x = 0.00, 0.03, 0.06 and 0.09) were prepared by solid-state reaction technique at high temperature. Electric impedance ( Z) and modulus ( M) properties of the materials have been investigated within a wide range of temperature and frequency using complex impedance spectroscopy (CIS) technique. The complex impedance analysis has suggested the presence of mostly bulk resistive (grain) contributions in the materials. This bulk resistance is found to decrease with the increase in temperature. It indicates that the PSZT compounds exhibit a typical negative temperature coefficient of resistance (NTCR) behavior. The bulk contribution also exhibits an increasing trend with the increase in Sm 3+ substitution to PZT. The complex modulus plots have confirmed the presence of grain (bulk) as well as grain boundary contributions in the materials. Both the complex impedance and modulus studies have suggested the presence of non-Debye type of relaxation in the materials. 相似文献
13.
Magnesium sodium hydrogen monophosphate, Na 3MgH(PO 4) 2, crystallizes in the triclinic cell
. The crystal morphology is related to the synthesis temperature and the evaporation rate. Samples were characterized through X-ray diffraction and chemical analysis, examined by IR and Raman vibrational spectroscopy and impedance and modulus spectroscopy techniques. The conductivity relaxation parameters associated with some H · conduction have been determined from an analysis of the M″/ Mmax″ spectrum measured in a wide temperature range. Transport properties in this material appear to be due to an H · ion hopping mechanism. 相似文献
14.
In this work, we report on the Pb(Mg 1/3Nb 2/3)O 3-Pb(Zn 1/3Nb 2/3)O 3-Pb(Zr 0.52Ti 0.48)O 3 (PMN-PZN-PZT) ceramics with Ba(W 0.5Cu 0.5)O 3 as the sintering aid that was manufactured in order to develop the low-temperature sintering materials for piezoelectric device applications. The phase transition, microstructure, dielectric, piezoelectric properties, and the temperature stability of the ceramics were investigated. The results showed that the addition of Ba(W 0.5Cu 0.5)O 3 significantly improved the sintering temperature of PMN-PZN-PZT ceramics and could lower the sintering temperature from 1005 to 920 °C. Besides, the obtained Ba(W 0.5Cu 0.5)O 3-doped ceramics sintered at 920 °C have optimized electrical properties, which are listed as follows: ( Kp = 0.63, Qm = 1415 and d33 = 351 pC/N), and high depolarization temperature above 320 °C. These results indicated that this material was a promising candidate for high-power multilayer piezoelectric device applications. 相似文献
15.
Kinetics for lithium ion transfers in the fast ionic conductor Li 2.8(V 0.9Ge 0.1) 2(PO 4) 3 prepared by solid-state reaction method has been studied by electrochemical impedance spectroscopy (EIS) at various temperatures and the results were correlated with observed cathodic behavior. The specific conductivities of Li x(V 0.9Ge 0.1) 2(PO 4) 3 ( x = 0.9–2.8) versus temperatures were analyzed from blocking-electrodes by Wagner's polarization method and the activation energy was calculated. It was observed that electronic conductivities of Li x(V 0.9Ge 0.1) 2(PO 4) 3 increased with lithium contents in the materials. The compounds show a reversible capacity of 131 mAh g −1 at low current density (13 mA g −1). Modeling the EIS data with equivalent circuit approach enabled the determination of charge transfer and surface film resistances. The Li ion diffusion coefficient ( DLi+) versus voltage plot shows three valleys during the first charge cycle coinciding with the irreversible plateau of the voltage versus lithium content profiles reflecting the irreversible phase change in the compound. The obtained DLi+ from EIS varies within 10 −8 to 10 −7 cm 2 s −1, so Li 2.8(V 0.9Ge 0.1) 2(PO 4) 3 shows excellent chemical diffusion performance. 相似文献
16.
The mechanical and thermal properties of single crystal Tb 2(MoO 4) 3 have been systematically studied. The result of microhardness measurement indicates that the crystal belongs to the soft materials category. The thermodynamic parameters obtained from DTA analysis were used for determining the type of liquid-solid interface during crystal growth. Negative thermal expansion along the c-axis was observed, and this behavior was attributed to the bent Tb-O-Mo bonds. The specific heat of the crystal was measured to be 0.122 cal g −1 K −1 at 293.15 K. The thermal conductivity of Tb 2(MoO 4) 3 at room temperature was found to be smaller than that of representative ferroelectric LiNbO 3. 相似文献
17.
分别采用固相-水热法和球磨法制备磷酸亚铁锂-磷酸钒锂复合正极材料(LiFePO4-Li3V2(PO4)3)。电化学性能测试表明,LiFePO4-Li3V2(PO4)3复合正极材料的电化学性能远远高于 LiFePO4和 Li3V2(PO4)3单独作为正极材料的性能,并且以固相-水热法制备的复合材料性能优于以球磨法制得的复合材料。研究发现 LiFePO4-Li3V2(PO4)3复合材料有 4 个氧化还原峰,相当于 LiFePO4 和 Li3V2(PO4)3 氧化还原峰的叠加。采用固相-水热法制备的LiFePO4-Li3V2(PO4)3 复合材料形貌较为规则,且有新相物质产生,这是导致其电化学性能较好的原因。 相似文献
18.
Eu 2+-doped Sr 3La(PO 4) 3 phosphors were synthesized by solid-state reaction method. Their luminescent properties were investigated. The phosphor could be excited by ultraviolet light effectively. The emission spectra exhibit two emission peaks located at 418 nm and 500 nm, respectively. These two peaks originated from two different luminescent centers, respectively. One is nine-coordinated Eu(I) center, other is six-coordinated Eu(II) center. It was found that the doping concentration of Eu 2+ ions affected the shape of emission spectra. As the doping concentration increasing, Eu 2+ ions are more likely to form Eu(I) luminescent centers and emit purple light. 相似文献
20.
Ba(Zr 1−xCe x) 0.9Y 0.1O 2.95/NaCl ( x = 0.1, 0.2 and 0.3) composite electrolyte materials were fabricated with ZnO as sintering aid. The effect of ZnO on the properties of Ba(Zr 1−xCe x) 0.9Y 0.1O 2.95 matrix were investigated. The phase composition and microstructure of samples were characterized by XRD and SEM, respectively. The electrochemical performances were studied by three-probe conductivity measurement and AC impedance spectroscopy. XRD results showed that Ba(Zr 1−xCe x) 0.9Y 0.1O 2.95 with 2 mol% of ZnO was perovskite structure. The relative density of this sample was above 95% when sintered at 1450 °C for 6 h. By adding 10 mol% of NaCl to Ba(Zr 1−xCe x) 0.9Y 0.1O 2.95 with 2 mol% of ZnO that was sintered at 1400 °C for 6 h, the conductivity was increased. The electrical conductivity of 1.26 × 10 −2 S/cm and activation energy of 0.23 eV were obtained when tested at 800 °C in wet hydrogen. 相似文献
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