共查询到20条相似文献,搜索用时 62 毫秒
1.
J. Agostinho Moreira A. Almeida M.R. Chaves J.M. Machado da Silva S.M.F. Vilela 《Solid State Communications》2011,151(5):368-371
This work reports an experimental investigation of the ferroelectric character of magnetic phases of the orthorhombic Eu1−xY xMnO3 system at low temperatures. The temperature dependence of the polarization curves clearly reveals the existence of a re-entrant improper ferroelectric phase for x=0.2, 0.3 and 0.5. A ferroelectric phase is also stable for x=0.4, and we have no experimental evidence for its vanishing down to 7 K. From these and early results obtained using other experimental techniques, the corresponding (x,T) phase diagram was traced, yielding significant differences with regard to the ones previously reported. 相似文献
2.
R. Sathyamoorthy P. SudhagarR. Saravana Kumar P. MatheswaranRanjith G. Nair 《Physica B: Condensed Matter》2011,406(4):715-719
CdSexTe1−x nanocrystals (x=0.25, 0.40, 0.50, 0.60 and 0.75) were synthesized using thioglycerol as a stabilizing agent. The composition of the CdSexTe1−x nanocrystals was precisely controlled by tuning the precursor (Se/Te) ratio. The structural, morphological and optical properties of the nanocrystals were analyzed using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), diffused reflectance spectroscopy (DRS) and photoluminescence (PL) measurements. It is found that the Se/Te ratio significantly affects the properties of the resultant CdSexTe1−x nanocrystals. XRD pattern of the CdSexTe1−x nanocrystals revealed cubic, hexagonal and mixed phases depending on the ratio of Se:Te. Surface morphology of the CdSexTe1−x nanocrystals showed nanoclusters of sizes ∼50 nm, with the adjacent cluster interlinking each other. DRS revealed the size dependence band gap energy prevailing in the CdSexTe1−x nanocrystals from 1.52 to 2.66 eV due to the optical bowing effect. PL measurements exhibited band edge emission in the visible spectral region, and are red shifted with increase in Se concentration. The facile route employed in the present work to synthesis the CdSexTe1−x nanocrystals in an aqueous medium is simple and controllable, and the strategy presented will be handy in preparing diverse semiconducting nanocrystals. 相似文献
3.
Structural, electronic and optical properties of Cd1−xSrxO (0≤x≤1) are calculated for the first time using density functional theory. Our results show that these properties are strongly dependent on x. The bond between Cd and O is partially covalent and the covalent nature of the bond decreases as the concentration of Sr increases from 0% to 100%. It is found that Cd1−xSrxO is an indirect bandgap compound for the entire range of x and the bandgap of the alloy increases from 0.85 to 6.00 eV with the increase in Sr concentration. Frequency dependent dielectric functions ε1(ω), ε2(ω), refractive index n(ω) and absorption coefficient α(ω) are also calculated and discussed in detail. The peak value of refractive indices shifts to higher energy regions with the increase in Sr. The striking feature of these alloys is that Cd0.5Sr0.5O is an anisotropic material. The larger value of the extraordinary refractive index confirms that the material is positive birefringence crystal. The present comprehensive theoretical study of the optoelectronic properties of the material predicts that it can be effectively used in optoelectronic applications in the wide range of spectrum; IR, visible and UV. 相似文献
4.
Luminescence characteristics of Ca1−xSrxS:Ce (x = 0, 0.25, 0.50, 1) nanophosphors have been investigated. XRD of all the samples show a single cubic phase of Ca1−xSrxS:Ce. TEM micrographs exhibit the rod like structure of the samples with a decrease in diameter with decreasing amount of Ca. The results of TEM were found to be in good agreement with the XRD results. The photoluminescence spectrum comprises of a main peak in the range 480-510 nm with a shoulder in the range 530-565 nm, which may be ascribed to transitions from 5d-4f levels of cerium in the mixed host lattice. The red shift in the emission wavelength with increasing Ca content may be correlated with the change in crystal field of mixed host lattice for different Ca and Sr concentrations. We have also investigated TL response of Ca1−xSrx:Ce to 60Co-γ rays. All the samples with different Sr and Ca contents show different TL response. TL response for the sample with x = 0.75 shows the simplest TL glow curve with the maximum TL intensity, for which we have calculated the activation energy using glow curve deconvolution functions. 相似文献
5.
U. Sondermann 《Journal of magnetism and magnetic materials》1980,21(3):228-232
The magnetic susceptibility of Hg1?xMnxSe semimetals for x ? 0.031 and 2.3 ? T ? 250 K is presented. The samples show Curie-Weiss behaviour in several temperature regions. Seff at high temperatures exceeds that at low temperatures. θp is antiferromagnetic (θp < 0) for all x at low T, but θp is positive at high T for low x. The coupling mechanism considered is long-range and caused by virtual band transitions across the zero-gap. 相似文献
6.
The influence of the Mg concentration and lattice temperature on the carrier recombination dynamics in Zn1−xMgxO alloys has been studied by time-resolved photoluminescence for different emission and excitation energies. Carrier localization effects are found to play a significant role, becoming increasingly important for lower temperatures and higher Mg concentrations. Emission energy dependent dynamics were analyzed by the application of the theoretical model, yielding a characteristic localization energy of 60±15 meV for the sample with the highest Mg concentration of x=0.21. 相似文献
7.
D.K. Hohnke 《Journal of Physics and Chemistry of Solids》1980,41(7):777-784
As x in Zr(In)O2?x is increased from 0.08 to 0.16 (9–19 mole per cent In2O3) the activation energy E(x) for ionic conduction increases from 1.05 to 1.51 eV; the concuctivity decreases from 2 × 10?5 to 3 × 10?6Ω?1cm?1at 400°C, is composition-independent at about 580°C, and increases from 1 × 10?2 to 4 × 10?2Ω?1cm?1 at 800°C. The pre-exponential term of the Boltzmann-type conductivity equation depends exponentially on E(x), a much stronger dependence on x than theoretically expected with a model for ionic conductivity that includes nearest-neighbor defect interactions. Analysis of reported conductivity data for Zr(M)O2?x (M = Sc, Y, Ca and rare earth metals) and other doped oxide electrolytes with fluorite-type structure reveals that the same relationship is observed with these materials when x γ0.08. It is shown that ionic conduction in these oxides is consistent with nearest neighbor vacancy-cation defect interaction forx < 0.08 but that an additional complex interaction with composition-dependent free energy ΔG(x) occurs when xγ 0.08.The lattice constant of Zr(In)O2?x with the cubic fluorite-type structure is independent of composition, 5.114 ± 0.002 Å, in agreement with ionic size considerations. 相似文献
8.
The structure, magnetic property and magnetocaloric effect of GdCo2−xAlx (x=0, 0.06, 0.12, 0.18, 0.24, 0.4) compounds have been investigated by X-ray diffraction (XRD) and magnetic measurement techniques. The experimental results show that the GdCo2−xAlx (x≤0.4) compounds are single phase with a Laves-phase MgCu2-type structure. The Curie temperature Tc initially increases, and then decreases with increasing Al content. The maximum value of Tc, 418 K, is reached for the compound with x=0.06. The magnetic entropy change, which is determined from the temperature and field dependence of the magnetization by the Maxwell relation, decreases almost linearly with increasing Al content. 相似文献
9.
Measurements of the reflection spectra of polycrystalline CdxSr1−xO alloys (0 ? x ? 0.9) at 85 and 300 K in the spectral range of lattice vibrations (200–600 cm−1) are reported. By Kramers-Kronig analysis the optical constants and the LO-mode frequencies were evaluated. The samples showed essentially one-mode behaviour with marked fine structure of the low-temperature absorption for intermediate values of x. Up to now, applying the cluster model of Verleur and Barker has not yielded a tentative explanation. 相似文献
10.
P.S.R. MurthyK.R. Priolkar P.A. BhobeA. Das P.R. SarodeA.K. Nigam 《Journal of magnetism and magnetic materials》2011,323(6):822-828
The perovskite solid solutions of the type La2xSr2−2xCo2xRu2−2xO6 with 0.25≤x≤0.75 have been investigated for their structural, magnetic and transport properties. All the compounds crystallize in double perovskite structure. The magnetization measurements indicate a complex magnetic ground state with strong competition between ferromagnetic and antiferromagnetic interactions. Resistivity of the compounds is in confirmation with hopping conduction behaviour though differences are noted especially for x=0.4 and 0.6. Most importantly, low field (50 Oe) magnetization measurements display negative magnetization during the zero field cooled cycle. X-ray photoelectron spectroscopy measurements indicate the presence of Co2+/Co3+ and Ru4+/Ru5+ redox couples in all compositions except x=0.5. Presence of magnetic ions like Ru4+ and Co3+ gives rise to additional ferromagnetic (Ru-rich) and antiferromagnetic sublattices and also explains the observed negative magnetization. 相似文献
11.
The ferroelectric compounds Pb2Na1−xLaxNb5−xFexO15 and Pb0.5(5−x)LaxNb5−xFexO15 (0≤x≤1) with the tungsten bronze type structure have been investigated using Raman spectroscopy. The evolution of the spectra as a function of composition at room temperature is reported. In the frequency range 200-1000 cm−1 three main A1 phonons around 240 (υ1), 630 (υ2) and 816 (υ3) cm−1 were observed. The broadening of the Raman lines for high values of x originates from a significant structural disorder. This is in good agreement with the relaxor character of these compositions. The lowest-frequency part of the spectra, below 180 cm−1, reveals a structural change in the studied solid solutions. The behaviour of the Raman shift of the υ1 mode confirms that in Pb2Na1−xLaxNb5−xFexO15, a clear anomaly occurs in the vicinity of x=0.4. 相似文献
12.
M.A. AliA.K.M.A. Islam 《Physica B: Condensed Matter》2012,407(6):1020-1026
The structural, elastic, electronic and optical (x=0) properties of doped Sn1−xBixO2 and Sn1−xTaxO2 (0≤x≤0.75) are studied using the first-principles pseudopotential plane-wave method within the local density approximation. The independent elastic constants Cij and other elastic parameters of these compounds have been calculated for the first time. The mechanical stability of the compounds with different doping concentrations has also been studied. The electronic band structure and density of states are calculated and the effect of doping on these properties is also analyzed. It is seen that the band gap of the undoped compound narrowed with dopant concentration, which disappeared for x=0.26 for Bi doping and 0.36 for Ta doping. The materials thus become conductive oxides through the change in the electronic properties of the compound for x≤0.75, which may be useful for potential application. The calculated optical properties, e.g. dielectric function, refractive index, absorption spectrum, loss-function, reflectivity and conductivity of the undoped SnO2 in two polarization directions are compared with both previous calculations and measurements. 相似文献
13.
Prashant SinghMoshiour Rahaman Abhijit Mookerjee 《Journal of magnetism and magnetic materials》2011,323(20):2478-2482
We present a mean-field study of the magnetic phase diagram of Ni1−xMox and Ni1−xWx alloys. The pair energies that enter the internal energy part of the free energy are obtained from a first-principles calculation. We try to understand why spin-glass phase is not observed in these alloys. 相似文献
14.
Sung-Ho Han Falah S. Hasoon Allen M. Hermann 《Journal of Physics and Chemistry of Solids》2005,66(11):1895-1898
Spectroscopic ellipsometry measurements of CuInSe2 (CIS) and CuIn1−xGaxSe2 (CIGS) over a range of Cu compositions reveal that there are important differences in electronic and optical properties between α-phase CIS/CIGS and Cu-poor CIS/CIGS. We find a reduction in the imaginary part of the dielectric function ?2 in the spectral region, 1-3 eV. This reduction can be explained in terms of the Cu-3d density of states. An increase in band gap is found for Cu-poor CIS and CIGS due to the reduction in repulsive interaction between Cu-3d and Se-4p states. We also characterize the dielectric functions of polycrystalline thin-film α-phase CuIn1−xGaxSe2 (x=0.18 and 0.36) to determine their optical properties and compare them with similar compositions of bulk polycrystalline CuIn1−xGaxSe2. The experimental results have important implications for understanding the functioning of polycrystalline optoelectronic devices. 相似文献
15.
Duc-Phuong Nguyen N. Regnault R. Ferreira G. Bastard 《Solid State Communications》2004,130(11):751-754
We show that the large band offsets between GaN and InN and the heavy carrier effective masses preclude the use of the virtual crystal approximation to describe the electronic structure of Ga1−xInxN/GaN heterostructures, while this approximation works very well for the Ga1−xInxAs/GaAs heterostructures. 相似文献
16.
The structural parameters and the energetics of the Ni2+xMn1−xGa alloys have been investigated by the first-principles Exact Muffin Tin Orbital-Coherent Potential Approximation (EMTO-CPA) for 0.10<x<0.30. The difference in total energies (δE) between the low-temperature tetragonal phase and the high-temperature cubic phase has been considered as a qualitative indicator of the martensitic transformation temperature Tm. The qualitative behavior of δE with variation of x has been found to be in agreement with the experimentally observed variation of Tm with x. The elastic constants for the entire range of x have also been calculated and the determination of a relationship between δE and the elastic shear modulus has been attempted. It is seen that δE varies linearly with elastic shear modulus C′, qualitatively similar to the relation between Tm and C′. The energetics calculated with the EMTO method agrees quite well with the all-electron full-potential results ensuring the accuracy of the method. These results show that the EMTO-CPA method is one of the most reliable and accurate first-principles methods, in the context of off-stoichiometric alloys which undergo martensitic phase transformations. 相似文献
17.
Wenxia Feng Shouxin Cui Haiquan Hu Guiqing Zhang Zengtao Lv 《Physica B: Condensed Matter》2011,406(19):3631-3635
The structural, electronic and elastic properties of TiCxN1−x, ZrxNb1−xC and HfCxN1−x alloys have been investigated by using the plane-wave pseudopotential method within the density-functional theory. The calculations indicate that the variations of the equilibrium lattice constants and bulk modulus with the composition are found to be linear. The calculated elastic constants C44 and shear constants as a function of alloy concentration reveal the anisotropic hardness of these compounds. The partial and total density of states (DOS) for the binary and ternary compounds had been obtained, and the metallic behavior of these alloys had been confirmed by the analysis of DOS. 相似文献
18.
A series of phosphors with the composition Y3−xMnxAl5−xSixO12 (x=0, 0.025, 0.050, 0.075, 0.150, 0.225, 0.300) were prepared with solid state reactions. The X-ray powder diffraction analysis of samples shows that the substitution of Mn2+ and Si4+ does not change the garnet structure of phosphors, but makes the interplanar distance decrease to a certain extent. The emission spectra show that Mn2+ in Y3Al5O12 emits yellow-orange light in a broad band. With the increment of substitution content, the emission intensity of the phosphors increases firstly then decreases subsequently, and the emission peak moves to longer wavelength. Afterglow spectra and decay curves show that all the Mn2+ and Si4+ co-doped samples emit yellow-orange light with long afterglow after the irradiation of ultraviolet light. The longest afterglow time is 18 min. Thermoluminescence measurement shows that there exist two kinds of traps with different depth of energy level and their depth decreases with the increment of substitution content. 相似文献
19.
J.H Jung S.A SeoT.W Noh P.A Sharma N Hur S.-W Cheong 《Solid State Communications》2003,126(4):175-179
We measured reflectivity spectra of polycrystalline Mg1−xB2 samples, which show a metal-insulator transition with x. After performing the Kramers-Kronig analysis, the obtained optical conductivity spectra σ(ω) of MgB2 show a narrow Drude peak in the far-infrared region and a broad peak in the mid-infrared region. As x increases, the spectral weight of the Drude peak is strongly suppressed and that of the broad peak becomes enhanced a little. The existence of the broad mid-infrared peak in the insulating sample suggests that this peak might not be related to the free carriers in MgB2. In the far-infrared region, we also observe that the low energy dielectric constant of Mg1−xB2 diverges near the metal-insulator phase boundary (i.e. x=0.08). This result implies the possibility of a phase separation and a percolative metal-insulator transition in Mg1−xB2. 相似文献
20.
Thin films of amorphous indium selenide compounds (a-InxSe1−x) are important, e.g. for photovoltaics. The feature of merit in such applications is also the real part of refractive index n of this material. The data on n in literature are divergent. In this paper, the results of investigations on n in the bulk as well as in the interface layers of thin films of a-InxSe1−x are presented. The measurements had been performed using optical transmittance and reflectance in spectral range from 1.24 to 1.96 eV of linear polarized radiation that hit the samples with angles of incidence from 0° to 80°. Investigations had been done for sample temperatures from 80 to 340 K. It was found that the refractive index for areas at the free surface nf is bigger than the refractive index nb at the interface of thin film-substrate. The averaged over thin film thickness value of real part refractive index have the biggest value in all spectral range. Values of these coefficients increase with increasing the temperature. 相似文献