共查询到20条相似文献,搜索用时 15 毫秒
1.
F.M. Pontes L.S. Santos D.S.L. Pontes E.R. Leite A.J. Chiquito 《Journal of Physics and Chemistry of Solids》2008,69(11):2796-2803
Single-phase perovskite structure Pb1−xBaxTiO3 thin films (x=0.30, 0.50 and 0.70) were deposited on Pt/Ti/SiO2/Si substrates by the spin-coating technique. The dielectric study reveals that the thin films undergo a diffuse type ferroelectric phase transition, which shows a broad peak. An increase of the diffusivity degree with the increasing Barium contents was observed, and it was associated to a grain decrease in the studied composition range. The temperature dependence of the phonon frequencies was used to characterize the phase transition temperatures. Raman modes persist above tetragonal to cubic phase transition temperature, although all optical modes should be Raman inactive. The origin of these modes was interpreted in terms of breakdown of the local cubic symmetry by chemical disorder. The absence of a well-defined transition temperature and the presence of broad bands in some interval temperature above FE-PE phase transition temperature suggested a diffuse type phase transition. This result corroborates the dielectric constant versus temperature data, which showed a broad ferroelectric phase transition in these thin films. The leakage current density of the PBT thin films was studied at different temperatures and the data follow the Schottky emission model. Through this analysis the Schottky barrier height values 0.75, 0.53 and 0.34 eV were obtained to the PBT70, PBT50 and PBT30 thin films, respectively. 相似文献
2.
E.A MahmoudM.M El-Samanoudy A.S Abd Rabo 《Journal of Physics and Chemistry of Solids》2002,63(11):2003-2010
Optical absorption at room temperature and electrical conductivity at temperatures between 283 and 333 K of vacuum evaporated GexFexSe100−2x (0≤x≤15) amorphous thin films have been studied as a function of composition and film thickness. It was found that the optical absorption is due to indirect transition and the energy gap increases with increasing both Ge and Fe content; on the other hand, the width of the band tail exhibits the opposite behavior. The optical band gap Eopt was found to be almost thickness independent. The electrical conductivity show two types of conduction, at higher temperature the conduction is due to extended states, while the conduction at low temperature is due to variable range hopping in the localized states near Fermi level. Increasing Ge and Fe contents were found to decrease the localized state density N(EF), electrical conductivity and increase the activation energy for conduction, which is nearly thickness independent. Variation of the atomic densities ρ, molar volume V, glass transition temperature Tg cohesive energy C.E and number of constraints NCo with average coordination number Z was investigated. The relationship between the optical gap and chemical composition is discussed in terms of the cohesive energy C.E, average heat of atomization and coordination numbers. 相似文献
3.
Electroresistance (ER) effects were investigated for a full series of manganite ceramics La1−xCaxMnO3 (0<x<1), synthesized by solid state reaction. The results indicate that while the ER effects are large only in the presence of electrically active, high E-field boundaries, the equilibrium or metastable electronic-magnetic states in the adjoining domains are also significant, as a large ER occurs only at x=0.51 and x=0.17; those compositions are both near a two-phase coexistence region, i.e. close to a compositional regime where equilibrium insulating/metallic phase domains and interfaces would occur spontaneously. 相似文献
4.
5.
R.T.A. Khan 《Solid State Communications》2006,137(3):110-114
Static computer simulation techniques have been employed for structural investigation of the La1−xSrxVO3 series. Potential parameters for V3+-O2− and V4+-O2− have been derived which reproduces the crystal structures of end members with sufficient accuracy. Variations of lattice parameters and bond distances with Sr concentration have been studied. The calculated lattice parameters decrease with increase in the Sr concentration. A structural phase transition from orthorhombic to cubic is observed at 50% Sr doping level. 相似文献
6.
Toshimitsu Kanai 《Journal of Physics and Chemistry of Solids》2003,64(3):391-397
We have prepared a series of (PLZT)x(BiFeO3)1−x transparent thin films with thickness of 300 nm by a thermal pyrolysis method. Only films with x≦0.10 formed a single phase of perovskite structure. The film where x=0.10 exhibited both ferromagnetic and ferroelectric properties at room temperature with spontaneous magnetization and coercive magnetic fields of 0.0027μB and 5500 G, respectively. The remanent electric polarization and coercive electric field for the film where x=0.10 were 3.0 μC/cm2 and 24 kV/cm, respectively. Additionally, films with 0.02≦x≦0.10 showed both magneto-optical effects and the second harmonic generation of transmitted light. 相似文献
7.
O. Vigil-Galán F. Cruz-Gandarilla E. Sánchez-Meza G. Contreras-Puente 《Journal of Physics and Chemistry of Solids》2009,70(2):365-7370
Bismuth telluride thin films have been grown by close space vapor transport (CSVT) technique as a function of substrate temperature (Tsub). Both N- and P-type samples can be obtained by this method which is a relatively simple procedure, which makes the method interesting for technological applications. The samples were deposited onto amorphous glass and polycrystalline CdTe film substrates in the substrate temperature range 300-425 °C, with a fixed gradient between source and substrate of 300 °C. The influence of the type of substrate and substrate temperature in the CSVT chamber on the physical properties of the films is presented and discussed. 相似文献
8.
A.K. Diab M.M. Wakkad E.Kh. Shokr W.S. Mohamed 《Journal of Physics and Chemistry of Solids》2010,71(9):1381-1387
Physical properties of In35Sb45Se20−xTex thin films with different compositions (x=2.5, 5, 7.5, 10, 12.5 and 15 at %) prepared by electron beam evaporation method are studied. X-ray diffraction results indicate that the as-evaporated films depend on the Te content and the crystallized compounds consist mainly of Sb2Se3 with small amount of Sb2SeTe2. Transmittance and reflectance of the films are found to be thickness dependent. Optical-absorption data indicate that the absorption mechanism is direct transition. Optical band gap values decrease with increase in Te content as well as with increase in film thickness. 相似文献
9.
V.B. Nalbandyan 《Journal of Physics and Chemistry of Solids》2004,65(6):1201
The irreproducibility of electrical properties of Na0.88Li0.12NbO3 solid solution on thermal cycling reported by M.A.L. Nobre and S. Lanfredi is explained by gradual decomposition of the supersaturated solid solution below ca. 800 °C. 相似文献
10.
CuIn(SxSe1−x)2 thin polycrystalline films were grown by the chemical spray pyrolysis method on the glass substrate at 280-400°C. The alloy composition in the film was studied with relation to that in the splay solution. Films were characterized by X-ray diffraction, optical absorption, Raman spectroscopy, resistivity and surface morphology. The CuInSe2-rich alloy films grown at high substrate temperature had chalcopyrite structure, while, the CuInS2-rich films grown at low substrate temperature exhibited sphalerite structure. Optical-gap energies were smaller than that of the bulk crystal by 0.1-0.2 eV for CuInS2-rich films. Raman spectra exhibited both CuInSe2-like and CuInS2-like A1 modes, and their relative changed systematically with alloy composition. 相似文献
11.
K. Ishii T. Inami K. Kuzushita Y. Murakami S. Ishihara S. Maekawa Y. Moritomo 《Journal of Physics and Chemistry of Solids》2005,66(12):2157-2162
We report a resonant inelastic X-ray scattering (RIXS) study on perovskite manganese oxides La1−xSrxMnO3 (x=0, 0.2, and 0.4) at Mn K-absorption edge. Hole-doping effect on the electronic excitations in the strongly correlated electron systems is elucidated by comparing with undoped LaMnO3. The scattering spectra of metallic La0.6Sr0.4MnO3 show that a salient peak appears in low energies indicating the persistence of the Mott gap. At the same time, the energy gap is partly filled by doping holes and the spectral weight shifts toward lower energies. Though the peak position of the excitations shows weak dispersion in momentum dependence, RIXS intensity changes as a function of the scattering angle (2θ), which is related to the anisotropy. Furthermore, anisotropic temperature dependence is observed in La0.8Sr0.2MnO3 which shows a metal-insulator transition associated with a ferromagnetic transition. We consider that the anisotropy in the RIXS spectra is possibly attributed to the correlation of the orbital degrees of freedom. The anisotropy is large in LaMnO3 with long-range orbital order, while it is small but finite in hole-doped La1−xSrxMnO3 which indicates persistence of short-range orbital correlation. 相似文献
12.
S.T. Mahmud M.M. Saber H.S. AlagozJ. Jung K.H. Chow 《Journal of Physics and Chemistry of Solids》2013
We experimentally investigate the role of geometry on the current and current density dependencies of the intrinsic electroresistance of Sm1−xSrxMnO3 of two compositions (x=0.40 and x=0.45). It is found that for each composition, the plot of the intrinsic electroresistance versus current density for samples with different dimensions and resistances coincide whereas this does not happen in the case of the electroresistance versus the magnitude of the current. These results confirm that the current density is indeed the relevant “universal” parameter for controlling the intrinsic electroresistance of these manganites. 相似文献
13.
Y. G. Zhao R. C. Srivastava P. Fournier V. Smolyaninova M. Rajeswari T. Wu Z. Y. Li R. L. Greene T. Venkatesan 《Journal of magnetism and magnetic materials》2000,220(2-3)
We report on the growth of La0.8Ce0.2MnO3 thin films on (0 0 1) LaAlO3 substrates by pulsed laser deposition. CeO2 as an impurity is present in both the bulk and film samples. The electrical transport and magnetic properties of the films are similar to that of the divalent cation-doped or La deficient LaMnO3, which show colossal magnetoresistance. Thermopower measurements indicate that the carriers are holes. The results are explained in terms of a La site deficiency due to the existence of CeO2. 相似文献
14.
The amorphous silicon oxide SiO2−x thin films were prepared by the plasma-assisted pulsed laser deposition (PLD) method. X-ray diffraction spectrometry (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-VIS-NIR scanning spectrophotometry and ellipsometry were used to characterize the crystallinity, microscopic morphology and optical properties of obtained thin films. The influences of substrate temperatures, oxygen partial pressures and oxygen plasma assistance on the compositions of silicon oxide (SiO2−x) thin films were investigated. Results show that the deposited thin films are amorphous and have high surface quality. Stoichiometric silicon dioxide (SiO2) thin film can be obtained at elevated temperature of 200 °C in an oxygen plasma-assisted atmosphere. Using normal incidence transmittance, a novel and simple method has been proposed to evaluate the value of x in transparent SiO2−x thin films on a non-absorbing flat substrate. 相似文献
15.
《Journal of Physics and Chemistry of Solids》2002,63(5):781-792
The synthesis of LaNi1−xMnxO3+δ samples with different oxygen contents has been performed. Structural characterization was carried out by X-ray and neutron powder diffraction. The crystallographic structure of stoichiometric samples, δ=0, evolves from an orthorhombic (LaMnO3) to a rhombohedral (LaNiO3) unit cell. Oxygen excess, δ>0, seems to stabilize the rhombohedral unit cell. For instance, the unit cells at room temperature are orthorhombic and rhombohedral for LaNi0.1Mn0.9O3.0 and LaNi0.1Mn0.9O3.13, respectively. The X-ray patterns show the coexistence of both phases for LaNi0.5Mn0.5O3+δ at room temperature. This coexistence is not ascribed to chemical inhomogeneities, but to a structural phase transition. Neutron patterns collected from 1.5 to 300 K show a continuous evolution except for LaNi0.5Mn0.5O3.08 and LaNi0.1Mn0.9O3.13, which show a phase transition at around 290 and 220 K, respectively. The neutron patterns suggest the presence of an ordered arrangement of Ni and Mn atoms in the crystallographic unit cell. Such arrangement indicates that LaNi0.5Mn0.5O3 could be considered as a double perovskite (nominal formula, La2NiMnO6). 相似文献
16.
O. Chaix-Pluchery B. ChenevierV. Aubry-Fortuna I. Matko 《Journal of Physics and Chemistry of Solids》2002,63(10):1889-1900
X-ray diffraction experiments have been combined with Raman scattering and transmission electron microscopy data to analyze the result of rapid thermal annealing (RTA) applied to Zr films, 16 or 80 nm thick, sputtered on Si1−xGex epilayers (0≤x≤1). The C49 Zr(Si1−xGex)2 is the unique phase obtained after complete reaction. ZrSi1−xGex is formed as an intermediate phase. The C49 formation temperature Tf is lowered by the addition of Ge in the structure. Above a critical Ge composition close to x=0.33, a film microstructure change was observed. Films annealed at temperatures close to Tf are continuous and relaxed. Annealing at T>Tf leads to discontinuous films: surface roughening resulting from SiGe diffusion at film grain boundaries occurred. Grains are ultimately partially embedded in a SiGe matrix. A reduction in the lattice parameters as well as a shift of Raman lines are observed as T exceeds Tf. Both Ge non-stoichiometry and residual stress have been considered as possible origins for these changes. However, as Ge segregation has never been detected, even by using very efficient techniques, it is thought that the changes originate merely from residual stress. The C49 grains are expected to be strained under the SiGe matrix effect and shift of the Raman lines would indicate the stress is compressive. Some simple evaluations of the stress values indicate that it varies between −0.3 and −3.5 GPa for 0≤x≤1 which corresponds to a strain in the range (−0.11, −1.15%). X-ray and Raman determinations are in good agreement. 相似文献
17.
Lina Sun Peng Wu Jingtao Liu Huang Zhou Shengyong Jin Jiangying Wang 《Journal of Physics and Chemistry of Solids》2011,72(10):1147-1151
Microstructure, phase transformation behavior and dielectric properties of BaTi1−x(Al1/2Nb1/2)xO3 (0.01≤x≤0.40) ceramics were investigated. A high level of (Al1/2Nb1/2)4+ substitution for Ti4+ ions was not conducive to the stability of the perovskite structure and resulted in the formation of BaAl2O4. As x was increased, lattice constants and unit cell volume decreased, reached a minimum at x=0.10 and then increased. The BaTi1−x(Al1/2Nb1/2)xO3 ceramics at room temperature experienced a transformation from ferroelectric to paraelectric phase with increasing (Al1/2Nb1/2)4+ concentration. Meanwhile, permittivity of the BaTi1−x(Al1/2Nb1/2)xO3 ceramics was markedly reduced, while Q value was slightly increased. Frequency dispersion of dielectric peak was obviously increased as x was increased from 0.01 to 0.10. It is of great interest that a dielectric abnormity represented by a broad dielectric peak at 200-400 K was observed for the composition with x=0.40. 相似文献
18.
Ethylene glycol solutions of La-Mn(II) and La-Ca-Mn(II) citric complexes has been used as a starting material for spray-pyrolysis deposition of LaMnO3 and La1−xCaxMnO3 thin films on β-quartz, fused quartz, Si(0 0 1) and SrTiO3(1 0 0) substrates heated during the deposition at 380 °C. At suitable post-deposition heating conditions highly uniform films, 0.1-1 μm in thickness, with good crystal structure were obtained. Highly textured LaMnO3 films are obtained on SrTiO3(1 0 0) substrate. Interaction between the layer and Si-containing substrates is observed during the post-deposition heating in static air. 相似文献
19.
Thin amorphous As-Se films were prepared by pulsed laser deposition (PLD) and by classical thermal evaporation techniques. Raman spectra and optical properties (optical gap, Egopt, index of refraction, n, third-order non-linear susceptibility, χ(3)) of prepared films and their photo- and thermally induced changes were studied. The structure of laser deposited films was close to the corresponding bulk glasses contrary to thermal evaporated films. The composition of PLD films was practically unchanged during the process of deposition. The optically and thermally induced changes of n and of Egopt in PLD films are different from the changes in thermally deposited films. The differences are discussed. 相似文献
20.
B. Munirathinam M. Krishnaiah M. Manivel Raja 《Journal of Physics and Chemistry of Solids》2010,71(12):1763-1767
Lanthanum based mixed valence manganite system La1−xCax−0.08Sr0.04Ba0.04MnO3 (LCSBMO; x=0.15, 0.24 and 0.33) synthesized through the sol-gel route is systematically investigated in this paper. The electronic transport and magnetic susceptibility properties are analyzed and compared, apart from the study of unit cell structure, microstructure and composition. Second order phase transition is observed in all the samples and significant difference is observed between the insulator to metal transition temperature (TMI) and paramagnetic (PM) to ferromagnetic (FM) transition temperature (TC). In contrast to the insulating FM behaviour usually observed in La1−xCaxMnO3 (LCMO) for x=0.15, a clear insulator to metal transition is observed for LCSBMO for the same percentage of lanthanum. The temperature dependent resistivity of polycrystalline pellets, when obeying the well studied law ρ=ρo+ρ2T2 for T<TMI, is observed to differ significantly in the values of ρo and ρ2, with the electrical conductivity increasing with x. The variable range hopping model has been found to fit resistivity data better than the small polaron model for T>TMI. AC magnetic susceptibility study of the polycrystalline powders of the manganite system shows the highest PM to FM transition of 285 K for x=0.33. 相似文献