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1.
Both the formation and diffusion activation energies of single vacancy migrating intra-layer and inter-layer near the Fe [0 0 1] Σ = 5 (3 1 0) and (2 1 0) symmetric tilt grain boundaries have been calculated by using the MAEAM and a MD method. From energy minimization, the vacancy concentration in the second layer is higher than the one in the other layers for both (3 1 0) and (2 1 0) STGBs. By the diffusion activation energies of the vacancies migrating intra-layer and inter-layer, the vacancies located from the first to the eighth layers of (3 1 0) STGB as well as the ones located from the first to the tenth layers of (2 1 0) STGB are favorably migrated to the second layer. Thus there is a vacancy aggregation tendency to the second layer near the grain boundary. For the vacancy migrating intra-layer and inter-layer, the influences of the grain boundary are respectively as far as to the fifth and eighth layers for (3 1 0) STGB as well as to the sixth and tenth layers for (2 1 0) STGB. 相似文献
2.
《材料与设计》2015
In this paper, a series of Ca3 -x-ySry(PO4)2:xEu2 +, (0 ≤ x ≤ 0.075, 0 ≤ y ≤ 2.2) phosphors were prepared by flux assisted solid-state reaction method, and their photoluminescence properties were investigated. The β- to β′-phase transition of Ca3 -ySry(PO4)2 for high Sr2 + content was observed from the XRD patterns, and the corresponding optical bandgaps were obtained experimentally. Various Eu2 + emission centers were found, which generate tunable emission depending on the Sr2 + concentration. Broad and intense excitation bands exist in Eu2 + activated Ca3(PO4)2, and the introduction of Sr2 + further extends and enhances the excitation bands beyond 350 nm, which is beneficial to the applications on near ultraviolet LEDs. The morphology measurement reveals that the average size of particles with smooth surface is about 11.2 μm, which is suitable for the practical applications. These results indicate that the Ca3 -x-ySry(PO4)2:xEu2 + phosphors could be promising candidates for LEDs. 相似文献
3.
D.S. Dalafave 《Materials Chemistry and Physics》2010,119(1-2):195-200
Thermoelectric properties of Re6GaxSeyTe15?y (0 ≤ x ≤ 2; 0 ≤ y ≤ 7.5) were studied in the temperature range 90–320 K. The measurements revealed p-type semi-conductivity in all samples. Relatively high values of the Seebeck coefficients, α, were obtained in all samples. The electrical resistivities and room temperature Seebeck coefficients increased as selenium concentrations increased, for each value of x. The room temperature Seebeck coefficients and resistivities decreased as gallium content increased, for each value of y. Low carrier concentrations were found at room temperatures, in agreement with large Seebeck coefficient values. Measurements suggested hopping conduction between 150 K and 280 K for all samples. Temperature dependences of the Seebeck coefficient below 150 K were accounted for by phonon drag effect. The power factors for the samples were calculated. Theoretical discussions of dependences of the measured quantities on temperature and composition are given. Usefulness of these materials as thermoelectrics is also discussed. 相似文献
4.
《材料与设计》2015
This paper addresses for the first time two of the main challenges in the field of electroceramics. The first one is the development of a continuous, fast and reliable synthesis method for producing sub-20 nm barium titanate zirconate (BaTi1-yZryO3 with 0 ≤ y ≤ 1–BTZ) nanocrystals over the whole solid solution, while keeping a narrow size distribution. The second one concerns the processing of dense and nanostructured lead free electroceramics highlighting the size effect on the crossover from ferroelectric to relaxor, in the case of grains smaller than 100 nm. This was achieved combining the supercritical fluid technology to produce in continuous and at moderate temperature (400 °C) BTZ nanocrystals, with Spark Plasma Sintering (SPS) to prevent grain growth during the sintering. 相似文献
5.
LaMg1 ? xNixAl11O19 (x = 0, 0.25, 0.5, 0.75, 1) ceramics are fabricated by pressureless-sintering method at 1700 °C for 10 h in air. The microstructure and thermo-optical properties of LaMg1 ? xNixAl11O19 ceramics are investigated by the X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy measurements. The influence of NiO doping on structure and thermo-optical properties of LaMg1 ? xNixAl11O19 ceramics is investigated. The partial substitution of Ni2+ for Mg2+ results in a significant increase in emissivity at low wavelengths as compared with unmodified LaMgAl11O19. When the Ni2+ content increases to x = 0.75 or above, LaMg1 ? xNixAl11O19 ceramics have a high emissivity value above 0.70 at low wavelengths at 500 °C. The measured emissivity of all LaMg1 ? xNixAl11O19 ceramics shows a similar trend in the wavelength range of 6 to 14 μm. 相似文献
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7.
Hidetoshi Miyazaki Isao Ushiroda Daisuke Itomura Tsunehisa Hirashita Nobuyasu Adachi Toshitaka Ota 《Materials science & engineering. C, Materials for biological applications》2009,29(4):1463-1466
Hydroxy apatite (HAp) ceramic was synthesized using traditional sintering. Dilatometric and lattice thermal expansion properties of a HAp ceramic were evaluated at temperatures of ? 100–50 °C. In that temperature range, the dilatometric thermal expansion coefficient and the lattice thermal expansion coefficient of the HAp ceramic were, respectively, 10.6 × 10? 6/°C and 9.9 × 10? 6/°C. Furthermore, thermal expansion properties of a human tooth were measured. The thermal expansion coefficient of the horizontal direction perpendicular to the growing direction of a tooth was 15.5 × 10? 6/°C; that of the vertical direction along with the direction of tooth growth was 18.9 × 10? 6/°C at the temperature range described above. 相似文献
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9.
G. Krishna Kumari Sk. Muntaz Begum Ch. Rama Krishna D.V. Sathish P.N. Murthy P.S. Rao R.V.S.S.N. Ravikumar 《Materials Research Bulletin》2012,47(9):2646-2654
Co2+ and Ni2+ ions doped 20ZnO + xLi2O + (30 ? x) K2O + 50B2O3 (5 ≤ x ≤ 25) mol% glasses are prepared using melt quenching technique. Structural changes of the prepared glasses by addition of transition metal oxides, CoO and NiO are investigated by UV–vis–NIR, FT-IR spectroscopy and XRD. The XRD pattern indicates the amorphous nature of prepared glasses. FT-IR measurements of the all glasses revealed that the network structure of the glasses are mainly based on BO3 and BO4 units placed in different structural groups in which the BO3 units being dominant. The optical absorption spectra suggest the site symmetry of Co2+ and Ni2+ ions in the glasses are near octahedral. Crystal field and inter-electronic repulsion parameters are also evaluated. The optical band gap and Urbach energies exhibited the mixed alkali effect. Various physical parameters such as density, refractive index, optical dielectric constant, polaron radius, electronic polarizability and inter-ionic distance are also determined. 相似文献
10.
We measured the complex refractive index at the wavelength of 10.6 μm with the help of Fourier transform infrared spectroscopy for polycrystalline plates of the following compositions AgCl1−xBrx (0 ⩽ x ⩽ 1) and Ag1−xTlxBr1−xIx, where x varied from 0 to 0.05. In order to do it we chose a segment of the spectrum, which was recorded with a high resolution (0.5 cm−1) using the HgCdTe detector and which had a set of 10 identical peaks. It is shown that the real part of the refractive index rises along with increasing the substituting component fraction in the solid solution from 1.99 to 2.17 for AgCl1−xBrx and from 2.17 to 2.24 within the range of TlI mole fraction up to 0.05 for Ag1−xTlxBr1−xIx. We considered errors introduced by the spectrometer resolution and the accuracy rating of the micrometer, which was used to measure sample thickness. It is seen in the spectra, recorded for the second system with a lower resolution and using a deuterated and l-alanine doped triglycine sulfate detector, that increasing the thallium monoiodide fraction results in widening the transmission range towards bigger wavelengths. We also plan to use the obtained refractive index values for simulating mid-infrared optical fibers, the polycrystalline structure of which is close to the structure of the plates under investigation. 相似文献
11.
Cr doped ZnO (Zn1 ? xCrxO) thin films with different Cr concentrations (0.4, 1.5, and 8.9 at.%) were deposited on Si substrates using RF magnetron sputtering. Film crystal structure was characterized using X-ray diffraction, and vibrating sample magnetometer measurements were used to investigate their magnetic properties. Unstable ZnO structure is present at low Cr concentrations, while secondary phases appear at higher Cr concentrations. 8.9 at.% Zn1 ? xCrxO film exhibits room temperature ferromagnetism and high 325 K Curie temperature, even after 300 °C annealing for 1 h. This result is promising and demonstrates Cr doped ZnO film's potential use in practical applications. 相似文献
12.
Luc Huy Hoang Pham Van Hai Pham Van Hanh Nguyen Hoang Hai Xiang-Bai Chen In-Sang Yang 《Materials Letters》2011,65(19-20):3047-3050
Ti1 ? xVxO2 (x = 0.0–0.10) nanopowders were successfully synthesized by a microwave-assisted sol–gel technique and their crystal structure and electronic structure were investigated. The products were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman and UV–Vis spectroscopy. The results revealed that TiO2 powders maintained the anatase phase for calcination temperature below 600 °C, but gradually changed to the rutile phase above 800 °C. The formation of the rutile phase was completed at 1000 °C. For Ti1 ? xVxO2 (x = 0.05) powders, the phase transformation appeared at 600 °C. The absorption edge of Ti1 ? xVxO2 (x > 0) powders broadened to the visible region with increasing V concentration and a strong visible light absorption was obtained with 10% V doping. V doping and subsequent coexistence of both anatase and rutile phases in our Ti1 ? xVxO2 nanoparticles are considered to be responsible for the enhanced absorption of visible light up to 800 nm. 相似文献
13.
《材料与设计》2015
The electronic structure of Cu100−xZrx (x = 40, 50, 60) metallic glasses was investigated by ultraviolet photoelectron spectroscopy and X-ray photoemission spectroscopy, the valence band spectra of these alloys were analyzed by a large shift of the Cu d-band peaks to higher binding energies upon increasing Cu content. Photoemission experiments and first-principles calculations prove that the values of density of states at Fermi level of Cu100−xZrx metallic glasses are mainly dominated by Zr rather than Cu. This work will enlighten further research on understanding the inheritance of metallic glasses and designing new metallic glasses with unique properties. 相似文献
14.
《材料与设计》2015
The structural, electronic, magnetic and optical properties of Ga1 − xCrxAs (x = 0, 6.25%, 12.5%) have been studied by first-principles calculations based on the HSE hybrid density functional theories. The optical properties, including the complex dielectric function, optical refractive index, extinction coefficient and absorption coefficient are discussed for radiation up to 15 eV. The results predicate that the system of Ga1 − xCrxAs exhibits typical half-metallic properties, in which Cr forms deep levels in the forbidden band and reduces the energy gap, increases static dielectric constant and obviously red-shifts the absorption edge. With the increase of the fraction of Cr, the material gradually exhibits noticeable anisotropy in the photon energy range of 0–5 eV. In addition, the p-d hybridization reduces the magnetic moment of Cr from its free space charge value of 3 μB and a smaller atomic magnetic moments of As and Ga atoms are generated. 相似文献
15.
Magnetic properties of hole doped, oxygen deficient double perovskite compounds, Gd1 ? xCaxBaCo2O5.5, have been investigated. Ferromagnetic transition temperatures increase and the anti-ferromagnetic transition temperatures decrease with Ca substitution leading to stabilisation of ferromagnetisim for x ≥ 0.05. A detailed study of the ferromagnetic phase indicates the presence of double hysterisis loops for Ca fractions, 0.05 ≤ x ≤ 0.2 in the 50–200 K temperature range, suggestive of the co-existence of two ferromagnetic phases with different co-ercivities. Based on the magnetisation and transport measurements a phase diagram is proposed for Ca doped GdBaCo2O5.5. 相似文献
16.
Multiferroic Ba(FexTi1 ? x)O3 (BFT) nanorods were prepared by a chemical route using polyvinyl alcohol as surfactant. The presence of PVA in excess is responsible to convert cubic or spherical shaped nanoparticles into rodlike structure. Tetragonal phase and nano dimensions in the form of rods of BFT specimens are identified. These BFT nanorods show improvement in the coexistence of ferroelectricity and ferromagnetism of multiferroic properties than their nanoparticles. The effect of low dimensions of BFT rods to control dielectric constant with low loss up to higher frequency region has been observed. With 1% of Fe-doping BFT shows higher value of spontaneous polarization, saturation magnetization and dielectric constant than with other dopants. 相似文献
17.
P.T. Phong N.V. Khiem N.V. Dai D.H. Manh L.V. Hong N.X. Phuc 《Materials Letters》2009,63(3-4):353-356
In this study we report the effect of Al2O3 on the low field magnetoresistance (LFMR) of (1 ? x) La0.7Ca0.3MnO3 + x Al2O3 composite synthesized through a solid-state reaction method combined with an energy milling method. Based upon a spin-polarized tunneling of conduction electrons at the grain boundaries, we have proposed a phenomenological model to explain the observed electrical transport behavior over the whole temperature range (5 300 K), especially the gradual drop of metal-insulator transition temperature (Tp = Tmax) as a function of increasing Al2O3 content, while the ferromagnetic–paramagnetic transition temperature (TC) remains almost constant (TC = 250 K). 相似文献
18.
L. Deng H.A. Ma T.C. Su F.R. Yu Y.J. Tian Y.P. Jiang N. Dong S.Z. Zheng X. Jia 《Materials Letters》2009,63(24-25):2139-2141
Skutterudite compounds Co4Sb12 ? xTex with bcc crystal structure were prepared by high pressure and high temperature (HTHP) method. The study explored chemical doping with Te at the Sb site in an attempt to optimize the thermoelectric figure of merit ZT in the system Co4Sb12 ? xTex. The electrical resistivities, Seebeck coefficients and thermal conductivities of the samples were measured in the temperature range of 300–710 K. We found that the presence of Te substantially decreased the electrical resistivity without any detrimental effect on the Seebeck coefficients, which improved the power factor. Among all the samples, Co4Sb11.5Te0.5 shows the highest power factor of 35.3 µw/(cmK2) at 710 K, and the maximum ZT value reaches 0.67 at 710 K. 相似文献
19.
The novel Fe/Nb co-doped SrCo1 ? 2x(Fe,Nb)xO3 ? δ (x = 0.05, 0.10) perovskite oxides were synthesized by the solid-state method. Structural and chemical stability of the SrCo1 ? 2x(Fe,Nb)xO3 ? δ (x = 0.05, 0.10) oxides were studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and X-ray diffraction (XRD). The results demonstrated that the structural and chemical stability of the Fe/Nb co-doped SrCo1 ? 2x(Fe,Nb)xO3 ? δ (x = 0.05, 0.10) is improved significantly. The oxygen sorption properties of the SrCo1 ? 2x(Fe,Nb)xO3 ? δ (x = 0.05, 0.10) oxides were investigated between 300–900 °C in air, and the high oxygen sorption capacity of 11.5 and 10.3 mL O2 (STP)/g oxide, respectively, are obtained. 相似文献
20.
V. Sedykh G.E. Abrosimova V.Sh. Shekhtman I.M. Aristova I.I. Zverkova A.V. Dubovitskii V.I. Kulakov 《Materials Letters》2009,63(3-4):454-456
The formation of polydisperse and monodisperse structures in LaMnO3 + δ has been investigated by X-ray diffraction (XRD) analysis and transmitting electron microscopy (TEM). The sizes of LaMnO3 + δ particles have been evaluated for different types and conditions of synthesis (solid-phase synthesis and sol–gel method) and subsequent heat treatment in the controlled atmosphere. The effect of the size distribution on the correctness in the determination of particle sizes has been analyzed. 相似文献