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1.
S.Ya. Istomin A.V. Kurlov S.M. Kazakov E.V. Antipov 《Materials Research Bulletin》2012,47(5):1176-1180
Solid solution LaCr1?xMgxO3, 0 < х ≤ 0.25 was prepared by heating stoichiometric amounts of appropriate oxides in air at 1400 °C, 48 h. At room temperature it crystallizes in orthorhombically distorted GdFeO3-type structure (a ≈ √2 × aper; b ≈ √2 × ape; c ≈ 2 × aper, where aper – perovskite subcell parameter). High-temperature X-ray powder diffraction (HT XRPD) and dilatometry revealed first order phase transition to rhombohedral perovskite phase (R-3c, a ≈ √2 × aper, c ≈ 2√3 × aper) at 260–311 °C (OR phase transition). Crystal structures of room-temperature orthorhombic and high-temperature rhombohedral phases for LaCr0.75Mg0.25O3 were refined using HT XRPD data. Temperature of OR phase transition increases gradually with increasing of magnesium content. Low-temperature orthorhombic phase exhibits TEC lower in comparison with high-temperature rhombohedral one (e.g. for LaCr0.85Mg0.15O3 TEC(O) = 8.8 ppm K?1; TEC(R) = 11.6 ppm K?1). TEC for rhombohedral phase increases with increasing magnesium content from 10.4 ppm K?1 for LaCr0.95Mg0.05O3 to 12.1 ppm K?1 for LaCr0.75Mg0.25O3. 相似文献
2.
《Materials Research Bulletin》2006,41(6):1056-1062
According to thermal expansion data, O3-type phase NaxNi(1+x)/3Sb(2−x)/3O2 (x ≈ 0.8) undergoes at ca. 1270 K a reversible transition to a less dense form. The high-temperature phase quenched to liquid nitrogen belongs to P2 type, space group P63/mmc (no. 194), a = 3.0123 Å(2), c = 11.2264 Å(7) for x ≈ 0.74 at 298 K. The stabilisation of P2 versus O3-type structure at high temperatures seems to be due to alkali distribution over greater number of sites thus increasing entropy and decreasing Na+–Na+ repulsion. 相似文献
3.
The temperature dependent transport properties of molybdenum oxide (MoO3) doped N,N′-di(1-naphthyl)-N,N′-diphenylbenzidin (α-NPD) were studied over a frequency range of 100 Hz to 1 MHz. The value of trap density and mobility calculated by detailed analysis of current–voltage (I–V) characteristics are 9.43 × 1026 m?3 and 1.23 × 10?6 cm2 V?1 s?1, respectively. The relaxation time for the carriers in the bulk and in the interface region decreases with temperature. The Cole–Cole plot indicates the device can be modeled as the combination of two parallel resistor–capacitor (R–C) circuits with a series resistance of around 70 Ω. The dc conductivity shows two different regions in the studied temperature range with activation energy of Ea ~ 0.107 eV (region I) and Ea ~ 52 meV (region II), respectively. The ac conductivity follows the universal power law and the onset frequency increases with increase of temperature. The temperature dependent conduction mechanism can be explained by correlated hopping barrier (CBH) model. 相似文献
4.
Rajendra Kumar Singh A. Srinivasan 《Materials science & engineering. C, Materials for biological applications》2010,30(8):1100-1106
Fine particles of zinc ferrite (ZnFe2O4) and calcium sodium phosphate [NaCaPO4] were crystallized in bulk x(ZnO, Fe2O3)(65?x)SiO220(CaO, P2O5)15Na2O (6 ≤ x ≤ 21 mol %) glassy matrix by heat treatment. Initial magnetization curves reveal that samples with x = 6 and 9 mol % zinc–iron oxide exhibit both ferrimagnetic and paramagnetic contributions, whereas, samples with x > 9 mol % zinc–iron oxide exhibit only ferrimagnetic contribution. This observation is supported by the disappearance of the electron paramagnetic resonance (EPR) absorption line centered at g ≈ 4.3 in samples with x > 9 mol % zinc–iron oxide. Apatite-forming ability of the glass-ceramic samples was investigated by examining apatite formation on the surface of the samples treated in simulated body fluid (SBF). Increase in apatite-forming ability was observed with an increase in zinc–iron oxide content. The results obtained have been used to understand the evolution of the apatite surface layer as a function of immersion time in SBF and glass-ceramic composition. A good correlation has also been observed between the magnetic nature of the samples and their apatite-forming ability. These materials are expected to find application as thermo-seeds in hyperthermia treatment of bone cancer. 相似文献
5.
《Optical Materials》2011,33(12):1671-1675
The temperature dependence of the spectral positions and widths of the photoluminescence lines corresponding to the 5D0 → 7F0, 5D0 → 7F1 and 5D1 → 7F0 electronic transitions in Sm2+-doped SrFCl crystal was measured between 87 and 625 K at ambient pressure. The temperature dependence of the homogeneous line width Γh(T) for all these transitions in the whole temperature range used can be described by the two-phonon Raman scattering of acoustic phonons with the Debye temperature TD ≈ 230 K. Comparison of the temperature- and pressure-induced shifts revealed why all the emission lines studied show the blue temperature shifts. It is so because a greater part of the line shift is caused by the thermal expansion of the host crystal and not by enhancement of the electron–phonon coupling with increasing temperature. 相似文献
6.
Robert D. Shannon Olaf Medenbach Hiroshi Mizoguchi M.A. Subramanian Reinhard X. Fischer 《Materials Research Bulletin》2012,47(2):235-238
The refractive indices of Sc2W3O12, measured at wavelengths of 435.8–643.8 nm, were used to calculate na = 1.7331, nb = 1.7510, nc = 1.7586 at λ = 589.3 nm and n∞ values at λ = ∞ from a one-term Sellmeier equation. Mean refractive indices, 〈nD〉, and mean dispersion values, 〈A〉, are, respectively, 1.7475 and 110 × 10?16 m2. Total electronic polarizabilities, αobs, were calculated from n∞ and the Lorenz–Lorentz equation. The unusually large difference between the observed polarizability of 28.415 Å3 and the calculated total polarizability αT of 26.74 Å3 (Δ = +6.3%) is attributed to (1) a large M–O–W angle, and (2) a high degree of W 5d–O 2p and Sc nd–O 2p hybridization, where n signifies unspecified Sc d orbitals. 相似文献
7.
《Materials Research Bulletin》2013,48(11):4947-4952
60ZnCl2–20KCl–20BaCl2–xTbCl3 glasses (x = 0.10, 0.25, 0.50, 0.75, 1.00, and 1.25) were prepared by melt-quenching method, and Tb3+ fluorescence properties were investigated under 355 nm excitation. Regardless of x values, the electrons that were relaxed from the 5D3 to 5D4 level of Tb3+ ions by the multiphonon relaxation, were repressed to 28% of all the excited electrons because the ZnCl2-based glass had much lower phonon energy than oxide glasses. For 0 < x ≤ 0.34, the cross relaxation, (5D3 → 5D4) → (7F0 ← 7F6), was repressed, and consequently 72% and 28% of all the excited electrons were radiatively relaxed by the 5D3 → 7FJ (J = 6, 5, 4, 3, and 2) and 5D4 → 7FJ (J = 6, 5, 4, and 3) transitions, respectively. The lifetimes of the 5D3 and 5D4 initial levels were obtained to be 1.1 and 2.1 ms, respectively. 相似文献
8.
《Materials Research Bulletin》2006,41(11):2024-2034
The monoclinic crystal structure of (C9H15N3O2)2P2O7·H2O denoted DLTHDP [a = 14.626(1), b = 6.1990(2), c = 14.562(1) Å, β = 97.289(3)°, Z = 2, monoclinic P21, Dcal = 1.508, Dmes = 1.49 g cm−3] has been solved using direct methods and refined to a reliability factor R = 4.37% for 2079 independent reflections. The DLTHDP structure can be described by infinite polyanions [P2O7·H2O]n4n− organized in chains parallel to the b-direction and located at z = 1/2, alternating with organic cations associated in ribbons spreading along the a-direction. Multiple hydrogen bonds originating from amine, hydroxyl groups and water molecules donors [NH…O(N) and O(W)H…O] connect the different components of the lattice. The IR data of DLTHDP is reported and discussed according to the theoretical group analysis and by comparison with IR results of similar compounds. The coupled thermogravimetric analysis (TGA)–differential thermal analysis (DTA) thermal study shows the departure of one water molecule, confirming the hydrated character of this compound. 相似文献
9.
High temperature treatment in inert atmosphere proved to be an effective way to improve high temperature stability of MWNTs in ambient condition. TEM analysis of heat-treated MWNTs confirmed successful removal of impurities and formation of ordered graphene layers and internal bamboo structure. TG–DTG curves indicated that decomposition range and rate of as-received MWNTs were narrow and notably higher, respectively, than heat-treated MWNTs mainly due to presence of impurities like metal nanoparticles in the former. Non-isothermal kinetic analysis revealed that the rate determining mechanism for as-received MWNTs was random nucleation and growth of active species. However, for heat-treated MWNTs, rate controlling mechanism was chemical reaction. Higher activation energies (~203 kJ mol?1 and 280 kJ mol?1) and reaction orders (3 and 4) of MWNTs heat-treated at 1200 °C and 1800 °C in inert, respectively, indicated delayed thermal decomposition than as-received MWNTs (Ea ≈ 178 kJ mol?1; n = 1) even in oxidative atmosphere. 相似文献
10.
《Materials Research Bulletin》2006,41(5):948-954
A new indium trimesate In12O(OH)12({OH}4,{H2O}5)[btc]6·≈31H2O, called MIL-96, (btc = 1,3,5-benzenetricarboxylate or trimesate species) was hydrothermally synthesized under mild condition (210 °C, 5 h) in the presence of trimethyl 1,3,5-benzenetricarboxylate in water and characterized by single-crystal X-ray diffraction technique. The MIL-96 (In) structure exhibits a three-dimensional metal-organic framework containing isolated trinuclear μ3-oxo-bridged indium clusters and infinite chains of InO4(OH)2 and InO2(OH)3(H2O) octahedra generating a hexagonal network based on 18-membered ring. The two types of indium entities are connected to each other through the trimesate species which induce corrugated chains of indium octahedra, linked via μ2-hydroxo bonds with the specific –cis–cis–trans– sequence. The 3D framework of MIL-96 reveals three kind of cavities (two of them have estimated ≈ 400 Å3 volumes), in which are encapsulated free water molecules. The latter species are removed upon heating at 150 °C. 相似文献
11.
Xia Zhang Yongfu Liu Zhendong Hao Yongshi Luo Xiaojun Wang Jiahua Zhang 《Materials Research Bulletin》2012,47(5):1149-1152
Luminescence properties of the yellow-emitting (Ca2Lu1?xCex)(ScMg)Si3O12 (CLSM:xCe3+ x = 0.01–0.15) phosphor are investigated for various Ce3+ concentrations. Different Ce3+ emission sites and energy transfers between them are observed, resulting in a red shift of the emission spectra from 530 to 575 nm with increasing x from 0.01 to 0.15. Combining with blue (460 nm) InGaN LEDs, CLSM:Ce3+ shows excellent performances for phosphor-converted white LEDs with higher color rendering index Ra of 87.4–87.9 and lower color temperature TC of 5034–5814 K, especially for warm pcWLEDs with a high color rendering (Ra > 80) and a low color temperature (TC < 4000 K). Thermal quenching behaviors depending on Ce3+ concentrations and temperatures are discussed. 相似文献
12.
Shuangyou Bai Zhihui Xu Min Wang Yuehua Liao Jianru Liang Chaocheng Zheng Lixiang Zhou 《Materials science & engineering. C, Materials for biological applications》2012,32(8):2323-2329
In order to accurately predict the types of biogenic iron hydroxysulfate precipitates in acidic, sulfate-rich environments facilitated by Acidithiobacillus ferrooxidans, different initial concentrations of Fe2 +, K+, Na+, and NH4+ are selected and tested in batch experiments for the formation of the precipitates. The critical equations of jarosite formation in FeSO4–K2SO4–H2O system or FeSO4–(NH4)2SO4–H2O system could be described as Y = ? 22120.8077 ? 0.04257x + 0.006170x2 (R2 = 0.9979) or Y = 0.03540 ? 0.002950x + 7.407E ? 5x2 (R2 = 0.9934), respectively, where Y is the threshold or critical values of the molar ratio of Fe/K or Fe/NH4 for jarosite formation, and x (mmol/L) is the initial concentration of Fe(II). Schwertmannite is the sole biogenic secondary ferric mineral when molar ratio of Fe/K or Fe/NH4 is higher than Y in the system with a given initial Fe(II) concentration. The precipitates are an admixture of schwertmannite and jarosite, or pure jarosite when the Fe/M molar ratio is lower than Y. The crystallinity of the secondary ferric minerals increased with the increase of initial Fe(II) concentration in the medium with a fixed K+ concentration. It is observed that the capacity of monovalent cation in promoting jarosite formation is K+ > NH4+ > Na+, as exhibiting that the capacity of K+ in this process is about 75 and 200 times greater than NH4+ and Na+, respectively. Obviously, both the initial concentration of Fe(II) and molar ratio of Fe to monovalent cation determine the types of biogenic iron hydroxysulfate precipitates. 相似文献
13.
《Materials Letters》2007,61(4-5):937-941
The (Pb, La)TiO3 (PLT) ferroelectric thin films with and without a special buffer layer of PbOx have been deposited on Pt/Ti/SiO2/Si(100) substrates by RF magnetron sputtering technique at room temperature. The microstructure and the surface morphology of the films annealed at 600 °C for 1 h have been investigated by X-ray diffraction (XRD) and atomic force microscope (AFM). The surface roughness of the PLT thin film with a special buffer layer was 4.45 nm (5 μm × 5 μm) in comparison to that of 31.6 nm (5 μm × 5 μm) of the PLT thin film without a special buffer layer. Ferroelectric properties such as polarization hysteresis loop (P–V loop) and capacitance–voltage curve (C–V curve) of the films were investigated. The remanent polarization (Pr) and the coercive field (Ec) are 21 μC/cm2 and 130 kV/cm respectively, and the pyroelectric coefficient is 2.75 × 10− 8 C/cm2 K for the PLT film with a special buffer layer. The results indicate that the (Pb, La)TiO3 ferroelectric thin films with excellent ferroelectric properties can be deposited by RF magnetron sputtering with a special buffer layer. 相似文献
14.
X-band electron paramagnetic resonance (EPR) studies of Cr3+ doped lithium potassium sulphate single crystals have been done at room temperature. The Cr3+ crystal field and spin Hamiltonian parameters have been evaluated by employing resonance line positions observed in the EPR spectra for different orientations of external magnetic field. The evaluated g, D and E values are: gx = 2.0763 ± 0.0002, gy = 1.9878 ± 0.0002, gz = 1.8685 ± 0.0002 and D = 549 ± 2 × 10?4 cm?1, E = 183 ± 2 × 10?4 cm?1. Using EPR data the site symmetry of Cr3+ ion in the crystal is discussed. Cr3+ ion enters the lattice substitutionally replacing K+ site. The optical absorption study of the single crystal is also done in 195–925 nm wavelength range at room temperature. By correlating optical and EPR data the nature of bonding in the crystal is discussed. The calculated values of Racah parameters (B and C), crystal field parameter (Dq) and nephelauxetic parameters (h and k) are obtained as: B = 697, C = 3247, Dq = 2050 cm?1, h = 1.146 and k = 0.21. 相似文献
15.
《Materials Science and Engineering: B》2003,97(1):54-58
A novel low-temperature (600–850 °C), chemical vapor deposition method, involving a simple reaction between disiloxane (H3Si–O–SiH3) and ammonia (NH3), is described to deposit stoichiometric, Si2N2O, and non-stoichiometric, SiOxNy, silicon oxynitride films (5–500 nm) on Si substrates. Note, the gaseous reactants are free from carbon and other undesirable contaminants. The deposition of Si2N2O on Si (with (1 0 0) orientation and a native oxide layer of 1 nm) was conducted at a pressure of 2 Torr and at extremely high rates of 20–30 nm min−1 with complete hydrogen elimination. The deposition rate of SiOxNy on highly-doped Si (with (1 1 1) orientation but without native oxide) at 10−6 Torr was ∼1.5 nm min−1, and achieved via the reaction of disiloxane with N atoms, generated by an RF source in an MBE chamber. The phase, composition and structure of the oxynitride films were characterized by a variety of analytical techniques. The hardness of Si2N2O, and the capacitance–voltage (C–V) as a function of frequency and leakage current density–voltage (JL–V) characteristics were determined on MOS (Al/Si2N2O/SiO/p-Si) structures. The hardness, frequency-dispersionless dielectric permittivity (K), and JL at 6 V for a 20 nm Si2N2O film were determined to be 18 GPa, 6 and 0.05–0.1 nA cm−2, respectively. 相似文献
16.
Eu3+ ions incorporated Li–K–Zn fluorotellurite glasses, (70 − x)TeO2 + 10Li2O + 10K2O + 10ZnF2 + xEu2O3, (0 ⩽ x ⩽ 2 mol%) were prepared via melt quenching technique. Optical absorption from 7F0 and 7F1 levels of the Eu3+-doped glass has been studied to examine the covalent bonding characteristics, energy band gap and Judd–Ofelt intensity parameters. The emission spectra (5D0 → 7F0,1,2,3,4) of the glasses were used to estimate the luminescence enhancement, asymmetric environment in the vicinity of Eu3+ ions, stimulated emission cross section and branching ratios. The phonon side band mechanism of 5D2 level of the Eu3+ ions in the prepared glass was examined by considering the excitation and Raman spectra. The radiative lifetime calculated using Judd–Ofelt parameters was compared with the experimental lifetime to estimate the quantum efficiency of 5D0 level of Eu3+ ions in Li–K–Zn fluorotellurite glass. 相似文献
17.
Zhenyan Zhang Liming Peng Xiaoqin Zeng Penghuai Fu Wenjiang Ding 《Materials Characterization》2009,60(6):555-559
Phases in as-cast and solution-treated Mg–6Gd–4Sm–0.4Zr (wt.%) alloy have been characterized using transmission electron microscopy in this paper. The intermetallic phase in as-cast microstructure has a face centered cubic crystal structure (a = 2.2879 nm) with a composition of Mg6.2(Sm0.56Gd0.44) and was dissolved after solution treatment. A particulate phase with a face centered cubic crystal structure (a = 0.5502 nm) was found in the solution-treated microstructure and suggested to already exist in as-cast sample as the nucleus for its further growth during solution treatment. 相似文献
18.
A.Y. Polyakov N.B. Smirnov A.V. Govorkov A.V. Markov Q. Sun Y. Zhang C.D. Yerino T.-S. Ko I.-H. Lee J. Han 《Materials Science and Engineering: B》2010,166(3):220-224
Electrical properties, deep traps spectra and luminescence spectra were studied for two undoped a-plane GaN (a-GaN) films grown on r-plane sapphire using metalorganic chemical vapor deposition and differing by structural perfection. For sample A, the a-GaN film was directly deposited on AlN buffer. A two-step growth scheme was implemented for sample B, including an initial islanding growth stage and a subsequent enhanced lateral growth. Preliminary detailed X-ray analysis showed that the stacking faults density was 8 × 105 cm?1 for sample A and 1.7 × 105 cm?1 for sample B. Electrical properties of a-GaN films were largely determined by deep traps with a level near Ec ?0.6 eV, with other prominent traps having the activation energy of 0.25 eV. The Fermi level was pinned by the Ec ?0.6 eV deep traps for sample A, but shifted to the vicinity of the shallower 0.25 eV traps for sample B, most likely due to the reduced density of the 0.6 eV traps. This decrease of deep traps density is accompanied by a very pronounced improvement in the overall luminescence intensity. A correlation of the observed improvement in deep traps spectra and luminescence efficiency with the improved crystalline quality of the films is discussed. 相似文献
19.
《Materials Research Bulletin》2006,41(9):1612-1621
The simultaneous thermal decomposition and nitridation of [VO(NH2O)2Gly]·H2O complex in NH3 atmosphere at 723–973 K gives the nanocrystalline vanadium nitride (VN) having crystallite size of 8–32 nm. It shows cubic NaCl structure with lattice parameter of a = 4.137 nm. XRD pattern Rietveld analysis program for crystal structure of VN shows the space group-Fm3m. The particle sizes measured by BET and SEM techniques are in the range of 26–100 nm. The particles are spherical and distributed homogeneously and found larger than XRD crystallite size because of agglomeration of crystallites. The fundamental IR absorption of VN material is found at 995 cm−1 which gives the force constant of 634.3 Nm−1. The electrical resistivity and magnetic studies show the superconducting to normal transition (Tc) at 9.2 K. Thermal decomposition of VN is carried out in O2 atmosphere which goes through the formation of an oxynitride (V–Np–Oq) intermediate phase up to 913 K. Finally, nanocrystalline V2O5 is formed at 973 K. The V2O5 has orthorhombic structure with lattice parameters of a = 11.537, b = 3.568 and c = 4.380 Å and the XRD crystallite size of 10 nm. 相似文献
20.
《Materials Research Bulletin》2006,41(5):1001-1007
The crystal structure of the 1222-type ruthenocuprate RuSr2Nd0.9Y0.2Ce0.9Cu2O10 has been studied by time-of-flight neutron diffraction at temperatures 100–160 K and pressures up to 5 GPa. The structure has tetragonal I4/mmm symmetry throughout (e.g. a = 3.8104(2) Å and c = 28.125(3) Å at 160 K and 5.1 GPa) with no significant distortions observed at the 140 K Ru spin ordering transition. The strongly bonded Cu–O and Ru–O network leads to a bulk modulus of 145 GPa which is high for layered cuprates, with a low anisotropy in the cell compressibility (kc/ka = 1.32). The Cu–O–Cu buckling angle and the tilting of the CuO5 square pyramids decreases with pressure, but the in-plane rotation of the RuO6 octahedra increases. 相似文献