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1.
S. Benmokhtar A. El Jazouli J.P. Chaminade M. Menetrier 《Materials Research Bulletin》2007,42(5):892-903
A new titanium oxyphosphate Mg0.50TiO(PO4) has been synthesized and characterized by several physical techniques: X-ray diffraction, 31P MAS-NMR, Raman diffusion, infrared absorption and diffuse reflectance spectroscopy. It crystallizes in the monoclinic system with unit cell parameters: a = 7.367(9), b = 7.385(8), c = 7.373(9) Å, β = 120.23(1), with the space group P21/c (no. 14), Z = 4. The crystal structure has been refined by the Rietveld method using X-ray powder diffraction. The conventional R indices obtained are Rwp = 0.138, Rp = 0.096 and RB = 0.0459. The structure of Mg0.50TiO(PO4) consists of infinite chains of corner-shared [TiO6] octahedra parallel to the c-axis, crosslinked by corner-shared [PO4] tetrahedra. These infinite chains have alternating short (1.74 Å) and long (2.26 Å) TiO bonds and are similar to those found in titanium oxyphosphate MII0.50TiO(PO4) (M2+ = Fe2+, Co2+, Ni2+, Cu2+, Zn2+). The magnesium atom is located in an antiprism between two [TiO6] octahedra. 31P MAS NMR showed only a single 31P resonance line, in a good agreement with the crystal structure. Raman and IR spectra show strong bands respectively at 765 and 815 cm−1, attributed to the vibration of TiOTiO bonds in the infinite chains. The gap due to the Oxygen-Titanium(IV) charge transfer is 3.37 eV. 相似文献
2.
151Eu-Mössbauer spectroscopic and powder X-ray diffraction (XRD) study has been performed for the EuyM1−yO2−x (M = Th and U) systems over the entire composition range of 0 ≤ y ≤ 1.0. The XRD results of the Eu-Th system showed that a very wide defect-fluorite (DF) type phase in which oxygen vacancies (VO) are disordered (x = y/2) is formed for 0 ≤ y < 0.5 and that two-phase regions sandwitching a narrow C-type (C) single phase around y ≈ 0.8 appear for 0.5 < y < 0.8 (DF + C) and 0.82 < y < 1.0 (C + B-type (monoclinic) Eu2O3). The Mössbauer results show that the isomer shifts (ISs) of Eu3+ in this system smoothly increase with Eu composition, y. The decrease of average coordination number (CN) of O2− around Eu3+ with increasing y (CN = 8 − 2y) (x = y/2) results in the decrease of the average EuO bond length, which is due to the decrease of repulsion force between O2− anions. This result confirms that the IS of Eu3+ correlates well with the average EuO bond length in oxide systems. For the Eu-U system, the lattice parameter, a0, of the system decreases almost linearly with y, in accordance with the calculated a0 versus y curve for the oxygen-stoichiometric (i.e. x = 0) fluorite-type dioxide (CN = 8). The ISs of Eu3+ in this composition range remain almost constant around 0.5 mm/s, which is comparable to those of pyrochlore oxides (Eu2Zr2O7 and Eu2Hf2O7 (y = 0.5)) with O2−-eight-fold coordinated Eu3+(CN = 8). 相似文献
3.
Gel formation was realized by adding citric acid to a solution of La(NO3)3·5H2O, Ca(NO3)2·4H2O, and Fe(NO3)2·9H2O. Perovskite-type (La1−xCax)FeO3 (0 ≤ x ≤ 0.2) was synthesized by firing the gel at 500 °C in air for 1 h. The crystallite size (D1 2 1) decreased with increasing x, while the specific surface area was 6.8-9.4 m2/g and independent of x. The XPS measurement of the (La1−xCax)FeO3 surface indicated that the Ca2+ ion content increased with increasing x, while the Fe ion content was independent of x. Catalytic activity for CO oxidation increased with increasing x. 相似文献
4.
CdSexTe1−x (0 ≤ x ≤ 0.4) ternary thin films have been deposited on quartz substrates at room temperature by a single source thermal evaporation. X-ray diffraction patterns and transmission electron microscope micrographs of these films showed that the films were of polycrystalline texture over the whole range studied and exhibit predominant cubic (zinc blende) structure with strong preferential orientation of the crystallites along (1 1 1) direction. Linear variation of the lattice constant with mole fraction x is observed obeying Vegard's law. The dependence of the optical constants, the refractive index n and extinction coefficient k, of the films on the mole fraction x was studied in the spectral range of 400-2500 nm. The normal dispersion of the refractive index of the films could be described using the Wemple-DiDomenco single-oscillator model. CdSexTe1−x thin films of different composition have two direct and indirect transitions corresponding to energy gaps and . The variation in either or with x indicates that this system belongs to the amalgamation type. The variation follows a subquadratic dependence and the bowing parameters were found to be 0.36 and 0.48 eV for the direct, and indirect energy gaps, respectively. Direct linear variation of the ratio N/m* with x is observed. 相似文献
5.
Sintering behavior, microstructure and microwave dielectric properties of Li2+xTiO3 (0 ≤ x ≤ 0.2) ceramics have been studied by X-ray diffraction (XRD), scan electron microscopy (SEM), Raman spectra, dilatometery and microwave resonant measurement in this research. Homogeneous non-stoichiometric composition with rock salt structure existed for Li2+xTiO3 (0 ≤ x ≤ 0.2) ceramics. The sintering temperature was successfully reduced and highly densified sample could be obtained with appropriate excessive amount of lithium (x = 0.08). A transient reactive liquid phase sintering mechanism was proposed. The preferred orientation of grain growth and micro-cracks existed in the Li2TiO3 (x = 0) sample disappeared in the lithium excessive samples with x ≥ 0.08. The microwave dielectric properties varied significantly with the excessive amount of lithium. Optimized microwave dielectric properties were obtained for the x = 0.08 composition: ?r = 24.6, Q × f = 66,000 GHz, and τf = 22.1 ppm/°C. 相似文献
6.
C. GuarnerosB. Rebollo-Plata R. Lozada-Morales J.E. Espinosa-RosalesJ. Portillo-Moreno O. Zelaya-Angel 《Thin solid films》2012,520(16):5463-5465
By means of electron gun evaporation Ge1 − xSix:N thin films, in the entire range 0 ≤ x ≤ 1, were prepared on Si (100) and glass substrates. The initial vacuum reached was 6.6 × 10− 4 Pa, then a pressure of 2.7 × 10− 2 Pa of high purity N2 was introduced into the chamber. The deposition time was 4 min. Crucible-substrate distance was 18 cm. X-ray diffraction patterns indicate that all the films were amorphous (a-Ge1 − xSix:N). The nitrogen concentration was of the order of 1 at% for all the films. From optical absorption spectra data and by using the Tauc method the energy band gap (Eg) was calculated. The Raman spectra only reveal the presence of SiSi, GeGe, and SiGe bonds. Nevertheless, infrared spectra demonstrate the existence of SiN and GeN bonds. The forbidden energy band gap (Eg) as a function of x in the entire range 0 ≤ x ≤ 1 shows two well defined regions: 0 ≤ x ≤ 0.67 and 0.67 ≤ x ≤ 1, due to two different behaviors of the band gap, where for x > 0.67 exists an abruptly change of Eg(x). In this case Eg(x) versus x is different to the variation of Eg in a-Ge1 − xSix and a-Ge1 − xSix:H. This fact can be related to the formation of Ge3N4 and GeSi2N4 when x ≤ 0.67, and to the formation of Si3N4 and GeSi2N4 for 0.67 ≤ x. 相似文献
7.
Differential scanning calorimetry (DSC), infrared (IR) and direct current (DC) conductivity studies have been carried out on (100 − 2x)TeO2-xAg2O-xWO3 (7.5 ≤ x ≤ 30) glass system. The IR studies show that the structure of glass network consists of [TeO4], [TeO3]/[TeO3+1], [WO4] units. Thermal properties such as the glass transition (Tg), onset crystallization (To), thermal stability (ΔT), glass transition width (ΔTg), heat capacities in the glassy and liquid state (Cpg and Cpl), heat capacity change (ΔCp) and ratios Cpl/Cpg of the glass systems were calculated. The highest thermal stability (237 °C) obtained in 55TeO2-22.5Ag2O-22.5WO3 glass suggests that this new glass may be a potentially useful candidate material host for rare earth doped optical fibers. The DC conductivity of glasses was measured in temperature region 27-260 °C, the activation energy (Eact) values varied from 1.393 to 0.272 eV and for the temperature interval 170-260 °C, the values of conductivity (σ) of glasses varied from 8.79 × 10−9 to 1.47 × 10−6 S cm−1. 相似文献
8.
Boron tungsten bronzes BxWO3 (0.01 ≤ x ≤ 0.08) were synthesized by hybrid microwave method from mixtures of WO3 and amorphous boron powder. With the increase of boron content, the crystal structure of BxWO3 transforms from orthorhombic (x = 0.01) to tetragonal α (x = 0.048) and then to tetragonal β (0.07 ≤ x ≤ 0.08). The average size of crystallites is in the range of 1-10 μm. All samples show semiconducting behaviour in their temperature dependence of resistivity. The conduction behaviour above 80 K for samples with x = 0.01 and 0.08 can be explained using the variable-range hopping and thermally activated mechanism, respectively. Comparative experiments showed that boron bronze phases cannot be obtained by the microwave heating of pure WO3 powder or a mixture of B2O3 and WO3 under the same conditions. 相似文献
9.
The new oxyarsenate Li0.5Ni0.25TiOAsO4 has been synthesized and studied by a combination of X-ray powder diffraction, neutrons powder diffraction and vibrational spectroscopy. Li0.5Ni0.25TiOAsO4 crystallizes in the monoclinic P21/c space group with the unit cell parameters: a = 6.5854(3) Å, b = 7.4665(4) Å, c = 7.4969(4) Å, β = 89.884(6)°, V = 368.62(1) Å3 and Z = 4. The structure has been determined at room temperature from neutrons diffraction by the Rietveld method analysis. It is formed by a 3D network of TiO6 octahedra and AsO4 tetrahedra sharing corners. Structural refinement shows a partial and a statistical occupancy of 2a and 2b sites by Li+ and Ni2+ ions. TiO6 octahedra are linked together by corners and form infinite chains along c-axis. Raman and infrared studies confirm the existence of -TiOTi- chains. Diffuse reflectance spectrum indicates the presence of octahedrally coordinated Ni2+ ions. 相似文献
10.
Perovskite structure-based ceramic precursors have a characteristic property of substitution in the ‘A’ site of the ABO3 structure. This makes them a potential material for nuclear waste management in synthetic rock (Synroc) technology. In order to simulate the mechanism of rare earth fixation in perovskite, PrxCa1−xTiO3 (where x = 0.1) has been synthesized through ceramic route by taking calculated quantities of oxides of Ca, Ti and Pr as starting materials. The ceramic phase has been characterized by its powder diffraction pattern. The Rietveld analysis of the X-ray diffraction data has been carried out using GSAS software to achieve the convergence which gives the Rp = 5.74% and Rwp = 8.17%. The (h, k, l) values for different lattice planes have been calculated. The praseodymium substituted perovskite crystallizes in orthorhombic symmetry with space group: Pbnm, Z = 4. The unit cell parameters at room temperature are a = 5.39609(31) Å, b = 5.44869(30) Å and c = 7.6565(5) Å. The calculated and observed values of the corresponding intensities, 2θ and density of the polycrystalline powder show good agreement. GSAS-based calculation for bond distances TiO, CaO and bond angles OTiO, OCaO has been reported. 相似文献
11.
The grain size and the density of the Zn1 − xSnxO (0 ≤ x ≤ 0.05) samples decreased with increasing SnO2 content. The addition of a small amount of SnO2 (x ≤ 0.01) to ZnO led to an increase in both the electrical conductivity and the absolute value of the Seebeck coefficient, resulting in a significant increase in the power factor. The thermoelectric power factor was maximized to a value of 1.25 × 10−3 Wm−1 K−2 at 1073 K for the Zn0.99Sn0.01O sample. 相似文献
12.
Cadmium substituted strontium hydroxy- and fluoro-apatites, Sr(10−x)Cdx(PO4)6Y2 (Y = OH and F), have been prepared as single phases in the 0 ≤ x ≤ 4 interval for the former and 0 ≤ x ≤ 6 for the latter compound, respectively. The refinements of the X-ray full powder patterns allowed the structure determination of nine samples, and showed a preference of cadmium atoms for the M(1) site in fluoroapatite samples. IR investigation gave information about the nature of the metal oxygen interactions. The obtained results are used for a comparative discussion about the factors which drive the mutual substitution of Ca, Sr, Cd and Pb in apatites. The important role of electronegativity and polarisability, as well as of ionic radii, is evidenced. 相似文献
13.
The Gd2(TixZr1 − x)2O7 (x = 0, 0.25, 0.50, 0.75, 1.00) ceramics were synthesized by solid state reaction at 1650 °C for 10 h in air. The relative density and structure of Gd2(TixZr1 − x)2O7 were analyzed by the Archimedes method and X-ray diffraction. The thermal diffusivity of Gd2(TixZr1 − x)2O7 from room temperature to 1400 °C was measured by a laser-flash method. The Gd2Zr2O7 has a defect fluorite-type structure; however, Gd2(TixZr1 − x)2O7 (0.25 ≤ x ≤ 1.00) compositions exhibit an ordered pyrochlore-type structure. Gd2Zr2O7 and Gd2Ti2O7 are infinitely soluable. The thermal conductivity of Gd2(TixZr1 − x)2O7 increases with increasing Ti content under identical temperature conditions. The thermal conductivity of Gd2(TixZr1 − x)2O7 first decreases gradually with the increase of temperature below 1000 °C and then increases slightly above 1000 °C. The thermal conductivity of Gd2(TixZr1 − x)2O7 is within the range of 1.33 to 2.86 W m− 1 K− 1 from room temperature to 1400 °C. 相似文献
14.
R.V.K. Mangalam 《Materials Research Bulletin》2009,44(3):576-36
The ferromagnetic metallic oxide, SrRuO3 (TC ∼ 165 K) undergoes structural, magnetic and metal-insulator transitions upon substitution of Cu at the Ru-site. For x = 0.2 in SrRu1−xCuxO3, the structure becomes a tetragonal with the space group I4/mcm and there is a signature of both ferromagnetic (TC = 65 K) and antiferromagnetic (TN = 32 K) ordering due to possible magnetic phase separation. The antiferromagnetism arises due to short range ordering of Cu- and Ru-moments. Jahn-Teller distortion of (Ru,Cu)-O6 octahedra indicates that the copper ions are in 2+ oxidation state with 6t2g3eg electronic configuration. For x ≥ 0.1, narrowing of Ru-4d bandwidth by the substitution of Cu ions results in semiconducting behavior. For x = 0.3, the ac and dc susceptibility measurements indicate a spin glass behavior. The origin of spin glass behavior has been attributed to competing ferromagnetic and antiferromagnetic interactions. 相似文献
15.
Zhanqiang Liu Fuqiang Huang Junkang Sun 《Materials Science and Engineering: B》2011,176(16):1313-1316
Li3 − xFe2 − xTix(PO4)3/C (x = 0-0.4) cathodes designed with Fe doped by Ti was studied. Both Li3Fe2(PO4)3/C (x = 0) and Li2.8Fe1.8Ti0.2(PO4)3/C (x = 0.2) possess two plateau potentials of Fe3+/Fe2+ couple (around 2.8 V and 2.7 V vs. Li+/Li) upon discharge observed from galvanostatic charge/discharge and cyclic voltammetry. Li2.8Fe1.8Ti0.2(PO4)3/C has higher reversibility and better capacity retention than that of the undoped Li3Fe2(PO4)3/C. A much higher specific capacity of 122.3 mAh/g was obtained at C/20 in the first cycle, approaching the theoretical capacity of 128 mAh/g, and a capacity of 100.1 mAh/g was held at C/2 after the 20th cycle. 相似文献
16.
Up to 10 at.% of copper readily substitutes for cerium in ceria. It is found that at oxygen partial pressures between 0.21 atm and 10−5 atm, CuxCe1−xO2−δ (0 ≤ x ≤ 0.10) solid solution behave as an oxide-ion electrolyte. Interestingly, Cu0.10Ce0.90O2−δ exhibits the oxide-ion conductivity of ca. 10−4 Ω−1 cm−1 at 600 °C at an oxygen partial pressure of 10−5 atm. 相似文献
17.
Abdul Samee Fawzi 《Materials Research Bulletin》2010,45(8):1000-1007
The structural, electrical, dielectric, magnetic and magnetoelectric properties of (x)Ni0.8Zn0.2Fe2O4 + (1 − x)Pb0.93La0.07(Zr0.60Ti0.40)O3 (x = 0, 0.15, 0.30, 0.45 and 1) have been studied by means of various experimental techniques. Polycrystalline samples of this series have been prepared by the double sintering ceramic method. X-ray diffraction data analysis revealed purity of the composites. Microstructural analysis using scanning electron microscopy mode depicts the presence of two phases in contact with each other. Dielectric properties were studied at and well above room temperature. Temperature dependent variation of the dielectric constant show diffused phase transition which can be well described by fitting the Lorentz-type relation, . Observation of well-saturated ferroelectric hysteresis loop and magnetic hysteresis loop for composites indicates that ferroelectric and magnetic ordering exist simultaneously at room temperature. The static value of magneto electric voltage coefficient (αE) has been studied as a function of magnetic field at room temperature for all the composites. The maximum value of αE is 7.53 mV/(cm Oe) for 85% PLZT-15% NZFO composites. 相似文献
18.
This paper reports the structural and dielectric properties of Ba(Ti1 − xZrx)O3 (x = 0-0.3) ceramics. Single-phase solid solutions of the samples were determined by X-ray diffraction. Microscopic observation by scanning electron microscope revealed dense, single-phase microstructure with large grains (20-60 μm). The evolution of dielectric behavior from a sharp ferroelectric peak (for x ≤ 0.08) to a round dielectric peak (for 0.15 ≤ x ≤ 0.25) with pinched phase transitions and successively to a ferroelectric relaxor (for x = 0.3) was observed with increasing Zr concentration. Compared with pure BaTiO3, broaden dielectric peaks with high dielectric constant of 25,000-40,000 and reasonably low loss (tanδ: 0.01-0.06) in the Ba(Ti1 − xZrx)O3 ceramics have been observed, indicating great application potential as a dielectric material. 相似文献
19.
Zhong Chen Xiao Xia LiNan Chen Guoping Du Yangsheng LiGuihua Liu Andy Y.M. Suen 《Materials Science and Engineering: B》2012,177(3):337-340
Zn1−xMgxS (0 ≤ x ≤ 0.55) quantum dots (QDs) were successfully synthesized by precipitation method. The crystal structures, microstructures, and optical properties of the Zn1−xMgxS QDs were investigated using X-ray diffraction, scanning electron microscopy, and ultraviolet-visible and photoluminescence (PL) spectroscopy. The Zn1−xMgxS QDs were found to have a cubic crystal structure and an average crystallite size of 6.40-7.96 nm. It has been shown that an increase in doping Mg2+ concentration in Zn1−xMgxS QDs led to a gradual widening of the band gap and a weakening in the PL intensity of the Zn1−xMgxS QDs. 相似文献
20.
Nanocrystalline La1−xCdxFeO3 (0.0 ≤ x ≤ 0.3) solid solutions have been synthesized by a single-step solution combustion method at a relatively low temperature of 400 °C. The combustion-synthesized solid solutions were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and magnetic measurements. The crystal structure examined by XRD indicates that the samples were single-phase, and crystallize in an orthorhombic (space group, Pbnm no. 62) structure. The parent and doped compounds showed canted antiferromagnetic behavior associated with an increase in magnetic moment with Cd doping. The changes in magnetic properties of the materials are correlated to the changes in structural features resulting from the Rietveld structural refinement of the materials. 相似文献