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1.
In this paper we present the growth of La0.5Sr0.5CoO3 (LSCO) films on MgO, quartz, and silicon substrates by pulsed laser deposition (PLD) using a Ti:sapphire laser (50 fs, 800 nm wavelength). The morphology and the structure of the films were studied by X-ray diffraction, atomic force microscopy, and scanning electron microscopy. The films were polycrystalline and exhibit a good adherence to the Si substrate. Different deposition parameters such as substrate temperature, oxygen pressure, and laser fluence were varied to achieve good surface quality and low resistivity crystalline films. We also defined the optimum conditions in which the deposited film surface is particulate free. The best films (droplets free) were grown at 625 °C, in an ambient oxygen pressure of 6 mbar, with an incident laser fluence of 0.19 J/cm2. This is a mandatory step in the complex work of fabricating La0.5Sr0.5CoO3/BaTiO3/La0.5Sr0.5CoO3 heterostructures for the development of thin film capacitors for non-volatile ferroelectric access memory devices. PACS 81.15 Fg; 42.62-b; 68.65.Ac  相似文献   

2.
PbZr0.4Ti0.6O3/La0.5Sr0.5CoO3 heterostructures have been grown on Pt/Ti/SiO2/Si substrates by chemical solution routes. Optical properties of the PbZr0.4Ti0.6O3/La0.5Sr0.5CoO3 heterostructures were studied by infrared spectroscopic ellipsometry (IRSE) in the spectral range of 2.5–12.5 m. The optical constants of PbZr0.4Ti0.6O3 and La0.5Sr0.5CoO3 thin films were determined by fitting the IRSE data using a classical dielectric model and a Drude dielectric model, respectively. For PbZr0.4Ti0.6O3 thin films, the refractive index decreases and the extinction coefficient increases as the wavelength increases. For La0.5Sr0.5CoO3 thin films, the refractive index and the extinction coefficient increase as the wavelength increases. The absorption coefficient of La0.5Sr0.5CoO3 thin films is greater than 104 cm-1 for the wavelength range of 2.5–12.5 m. The absorption coefficient of PbZr0.4Ti0.6O3 thin films on a La0.5Sr0.5CoO3/Pt/Ti/SiO2/Si substrate is smaller than that on a Pt/Ti/SiO2/Si substrate by a factor of two. PACS 77.84.Dy; 78.20.Ci; 81.20.Fw  相似文献   

3.
The phase equilibria of the La-Me-Co-O systems (Me = Ca, Sr and Ba) were studied in air at 1100 °C. Two types of solid solution of general composition La1−xMexCoO3−δ and (La1−y Mey)2CoO4 were found to exist in the systems. The limiting composition of La1−xMexCoO3−δ lies at x=0.8 for Me = Sr, Ba and between 0.3–0.5 for Me = Ca. It is shown that the rhombohedral distortion of the perovskite type La1−xMexCoO3−y decreases while x increases. La1−xMexCoO3−δ (Me = Sr, Ba) shows an ideal cubic structure at x=0.5. The stability range of (La1−yMey)2CoO4 was found to be 0.25≤y≤0.35 for Me = Ca, 0.3≤y≤0.55 for Me = Sr and 0.3≤y≤0.375 for Me = Ba. All phases have tetragonal K2NiF4-type crystal structure. Based on the XRD and neutron diffraction patterns of quenched samples, the phase diagrams (Gibbs triangles) are constructed for all systems. The phase equilibrium at low oxygen pressure is shown for the example of the La-Sr-Co-O system. The decomposition mechanism of La1−xSrxCoO3−δ at 1100 °C for the samples with 0.5<x<0.8 within the oxygen pressure range −0.678>log(Po2)>−2.25 can be written as follows: La1−x′ Srx′CoO3−δ′=n La1−x″Srx″CoO3−δ″+m SrCoO2.5+q/2 O2 where x′>x″. The decomposition mechanism of La1−xSrxCoO3−δ for the samples with x < 0.5 within the oxygen pressure range −2.25>log(Po2)>−3.55 changes and can be written as follows: La1−xSrxCoO3−δ′=r La1−x′Srx′CoO3−δ″+w (La1−y′Sry′)2CoO4+v CoO+f/2 O2. The results are shown in “logPo2-composition” diagrams. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.  相似文献   

4.
Lead-free (Bi0.98−x La0.02Na1−x )0.5Ba x TiO3 ceramics have been prepared by an ordinary sintering technique and their structure, ferroelectric and piezoelectric properties have been studied. The results of X-ray diffraction show that La2+ and Ba2+ diffuse into the Bi0.5Na0.5TiO3 lattices to form a new solid solution with a pure perovskite structure, and a morphotropic phase boundary (MPB) exists at 0.04<x<0.10. Compared with pure Bi0.5Na0.5TiO3 ceramics, the (Bi0.98−x La0.02Na1−x )0.5Ba x TiO3 ceramics possess much smaller coercive field E c and larger remanent polarization P r. Because of the low E c (3.38 kV/mm), large P r (46.2 μC/cm2) and the formation of the MPB of rhombohedral and tetragonal phases, the piezoelectric properties of the ceramics are significantly enhanced at x=0.06: d 33=181 pC/N and k p=36.3%. The depolarization temperature T d reaches a minimum value near the MPB. The ceramics exhibit relaxor characteristic, which is probably a result from the cation disordering in the 12-fold coordination sites. The temperature dependences of the ferroelectric and dielectric properties suggest that the ceramics may contain both polar and non-polar regions at the temperatures above T d.  相似文献   

5.
The energy structure and temperature evolution of the magnetic excitation spectra of Pr0.5Sr0.5CoO3 are studied by inelastic neutron scattering. The measurements are performed on a polycrystalline sample of Pr0.5Sr0.5CoO3 and its non-magnetic analogue La0.5Sr0.5CoO3 on the high intensity time-of-flight spectrometer IN4 (ILL, Grenoble) in the temperature range 10 K < T < 300 K. The crystal electric field parameters in Pr0.5Sr0.5CoO3 are calculated and the splitting scheme of the 4f ground multiplet of Pr3+ ions is determined based on the experimental data.  相似文献   

6.
Sr1−x La x Zn x Fe12−x O19/poly(vinylpyrrolidone) (PVP) (0.0≤x≤0.5) precursor nanofibers were prepared by the sol–gel assisted electrospinning method from starting reagents of metal salts and PVP. Subsequently, the Sr1−x La x Zn x Fe12−x O19 nanofibers with diameters of around 100 nm were obtained by calcination of the precursor at 800 to 1000°C for 2 h. The precursor and resultant Sr1−x La x Zn x Fe12−x O19 nanofibers were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometer and vibrating sample magnetometer. The grain sizes of Sr0.8La0.2Zn0.2Fe11.8O19 nanofibers are in a nanoscale from 40 to 48 nm corresponding to the calcination temperature from 800 to 1000°C. With La–Zn substitution content increase from 0 to 0.5, the grain size and lattice constants for the Sr1−x La x Zn x Fe12−x O19 nanofibers obtained at 900°C show a steady reduction trend. With variations of the ferrite particle size arising from the La–Zn substitution, the nanofiber morphology changes from the necklace-like structure linking by single elongated plate-like particles to the structure building of multi-particles on the nanofiber cross-section. The specific saturation magnetization of Sr1−x La x Zn x Fe12−x O19 nanofibers initially increases with the La–Zn content, reaching a maximum value 72 A m2 kg−1 at x=0.2, and then decreases with a further La–Zn content increase up to x=0.5, while the coercivity exhibits a continuous reduction from 413 (x=0) to 219 kA m−1 (x=0.5). The mechanism for the La–Zn substitution and the nanofiber magnetic property are analyzed.  相似文献   

7.
The sensing characteristics of an amperometric NOx sensor with yttria-stabilized zirconia and a La-based perovskite-type oxide sensing electrode were examined. La1-xSrxMO3 (M = Co, Mn, x = 0, 0.2, 0.4, 0.6) were synthesized using the spray pyrolysis method. The NO2 response of a sensor fabricated with La1-xSrxMnO3 increased with increasing amount of Sr, and the trend was in contrast to that of the sensors fabricated with La1-xSrxCoO3. LaSr0.2MnO3 was determined to be the most appropriate material for the sensor in terms of a high NO2 response and low O2 current. In order to discuss the effects of Sr addition to La-based perovskite oxides for the sensor, NO adsorption and desorption properties of oxides and the relationship between the oxidation number of the B-site cation and Sr substitution were examined using temperature-programmed desorption and X-ray photoelectron spectroscopy, respectively.  相似文献   

8.
(La0.5Sr0.5)CoO3 (LSCO) thin films have been fabricated on silicon substrate by the pulsed laser deposition method. The effects of substrate temperature and post-annealing condition on the structural and electrical properties are investigated. The samples grown above 650°C are fully crystalline with perovskite structure. The film deposited at 700°C has columnar growth with electrical resistivity of about 1.99×10−3 Ω cm. The amorphous films grown at 500°C were post-annealed at different conditions. The sample post-annealed at 700°C and 10−4 Pa has similar microstructure with the sample in situ grown at 700°C and 25 Pa. However, the electrical resistivity of the post-annealed sample is one magnitude higher than that of the in situ grown sample because of the effect of oxygen vacancy. The temperature dependence of resistivity exhibits semiconductor-like character. It was found that post-annealing by rapid thermal process will result in film cracks due to the thermal stress. The results are referential for the applications of LSCO in microelectronic devices.  相似文献   

9.
Rectifying and photovoltaic properties of a La0.7Sr0.3CoO3−σ /Si heterostructure have been experimentally studied. The heterostructure exhibits a rectifying behavior, similar to that of the traditional diode. A photovoltaic effect is observed when the heterostructure is exposed to the laser with a wavelength of 532 nm and a power of 6 mW/mm2. It is interesting to note that the peak photovoltages initially increase with decreasing temperature, followed by a decrease at T<220 K. This reveals that the photovoltaic effect can be modulated by the intrinsic properties of the La0.7Sr0.3CoO3−σ layer.  相似文献   

10.
Srikiran  J. S.  Shinde  A. B.  Krishna  P. S. R. 《Pramana》2004,63(2):221-226
The structure and the magnetic properties of the doped rare earth cobaltite systems are of recent interest owing to the CMR phenomenon that occur in them. In this paper, we investigate the structure and magnetic properties of Tb0.5Sr0.5CoO3 solid solution, for the first time, using neutron powder diffraction technique. The sample Tb0.5Sr0.5CoO3 is found to crystallize in orthorhombic (Pbnm) symmetry. The unit cell volume and Co—O bond length reduce with temperature. The calculatede g bandwidth obtained from structural parameters turns out to be 0.989 eV. Low temperature neutron diffraction profiles exhibit a magnetic contribution to the fundamental Bragg peaks indicating a ferromagnetic ordering belowT c. The results are compared with Co—O—Co bond angles and Co—O bond length of La0.5Sr0.5CoO3, highlighting the ionic size effects on substitution of Tb ion for La in the compound.  相似文献   

11.
Two kinds of ZnO nanotubes, including taper-like and flat-roofed tubes, have been successfully fabricated using a simple aqueous solution route by changing the experimental conditions. All the obtained nanotubes have a uniform size of 500 nm in diameter, 10–50 nm in wall thickness, and 2–5 μm in length. The growth mechanism of two kinds of ZnO nanotubes was investigated. Field emission measurements showed that tapering nanotubes have the good field emission performance with a low turn-on field of ∼ 2.1 V μm-1 and a low threshold field of ∼ 3.8 V μm-1, which suggests the possible applications of the ZnO tubular structures in field emission microelectronic devices. PACS 73.61.Ga; 73.63. Fg; 85.45.Db  相似文献   

12.
La0.5Sr0.5CoO3 (LSCO) films have been grown on Si (100) by a metalorganic chemical liquid deposition (MOCLD) technique using lanthanum acetate, strontium acetate and cobalt acetate as the starting materials. Subsequent PbZr0.5Ti0.5O3 (PZT) films were deposited onto LSCO films by a modified sol-gel method. Field-emission scanning electron microscopy and X-ray diffraction analysis show that PZT and LSCO films are polycrystalline and entirely perovskite phase. At an applied electric field of 250 kV/cm, the Pt/PZT/LSCO capacitor shows no polarization fatigue after 3×109 switching cycles and an internal electric field; the remnant polarization Pr and the coercive field Ec are about 22 μC/cm2 and 73 kV/cm, respectively. The dielectric constant of PZT films is 650 at a frequency of 1 kHz. Received: 20 February 2001 / Accepted: 6 June 2001 / Published online: 30 August 2001  相似文献   

13.
Ni-Ti films prepared at 10 W and 70 W by rf magnetron sputtering are investigated as the oxygen diffusion barrier layer, it is found that crystallinity of Ni-Ti film does not greatly depend on the deposition power. X-ray photoelectron spectroscopy indicates that Ni is still in the form of metallic state from the binding energies of both Ni 2p3/2 and Ni 2p1/2 spectra for the sample with 10 W prepared Ni-Ti, however, Ni is oxidized for 70 W prepared Ni-Ti film. Moreover, the (La0.5Sr0.5)CoO3/Pb(Zr0.40Ti0.60)O3/(La0.5Sr0.5)CoO3 capacitor grown on high power prepared Ni-Ti film is leaky, however, the capacitor on low power prepared Ni-Ti film possesses very promising physical properties (i.e. remnant polarization of ∼27 μC/cm2 at 5 V and maximum dielectric constant of 940). Leakage current density of the capacitor grown on low power prepared Ni-Ti film is further investigated, it meets ohmic behavior (<1.0 V) and agrees well with the space-charge-limited current theory (>1.0 V).  相似文献   

14.
Materials that contain a photocatalyst have a semi-permanent capacity for removing harmful gases from the ambient air. It is the purpose of this study to investigate the photocatalytic activity of commercial paints containing TiO2 nanoparticles towards NO and NO2. Experiments were carried out in a stainless steel (30 m-3) walk-in type environmental chamber (Indoortron), under “real world setting” conditions of temperature, relative humidity, irradiation and pollutant concentrations. Two types of nanoparticle TiO2-containing paints were tested for their depolluting properties: a mineral silicate paint and a water-based styrene acrylic paint. The results showed a significant effect of TiO2-materials in reducing NOx. It was found that up to 74% of NO and 27% of NO2 were photo-catalytically degraded by the mineral silicate paint, while degradation percentage using the styrene acrylic paint reached 91% and 71% for NO and NO2, respectively. The photo-catalytic rate of NO on the mineral and styrene acrylic paint was calculated to 0.11 μg m-2 s and 0.18 μg m-2 s, respectively, indicating higher photocatalytic performance of the organic based material. The effect of relative humidity (RH) was also investigated. An increase of RH from 20% to 50% inhibited the NOx photocatalysis on the surface of the samples. PACS 81.16.Hc; 81.65.Mq; 82.33.Tb; 82.50.Hp; 82.65.+r  相似文献   

15.
The atomic and magnetic structures of La0.5Ca0.5CoO3 cobaltite have been studied by the neutron diffraction technique at high pressures of up to 4 GPa in the 10- to 300-K temperature range. The pressure dependences of the structural parameters have been obtained. The Curie temperature increases with the pressure with the coefficient dT C/dP = 1 K/GPa, demonstrating the stability of the ground ferromagnetic (FM) state. The pressure dependence of the ground FM state in La0.5Ca0.5CoO3 is in drastic contrast with that for La1 − x Ca x CoO3 at a lower calcium content (x < 0.3). For the latter compound, the pressure suppressed the ground FM state and a large negative pressure coefficient of the Curie temperature (dT C/dP ∼ −10 K/GPa) was observed. The nature of such a phenomenon is analyzed in the framework of the double exchange model also taking into account the changes in the electron configuration of Co3+ ions.  相似文献   

16.
K. Kammer 《Ionics》2009,15(3):325-328
La2 − x Sr x NiO4 +  δ materials were investigated as cathodes for the electrochemical reduction of oxygen on a Ce1.9Gd0.1O1.95 (CGO10) electrolyte using cone-shaped electrodes together with electrochemical impedance spectroscopy. The area-specific resistance (ASR) of the La2 − x Sr x NiO4 +  δ nickelates towards the reduction of oxygen is equal to the ASR of perovskites; however, it is not as low as for the best Fe–Co-based perovskites. The lowest ASR is found for the compound La1.75Sr0.25NiO4 +  δ with an ASR of 23.8 Ωcm2 measured on a cone-shaped electrode in air at 600 °C. It is suggested that difference in oxide ionic conductivity of the nickelates is the main cause for the different activity of the nickelates towards the electrochemical reduction of oxygen.  相似文献   

17.
Mn-doped (Bi0.5Na0.5)TiO3-BaTiO3 (BNBMT) thin film with the composition near the morphotropic phase boundary was grown on (La0.6Sr0.4)CoO3-electroded SrTiO3 single-crystal substrate by using pulsed laser deposition method. Ascribed to the crystal structure and lattice similarity, (100)-oriented BNBMT film with pure single-phase perovskite structure was obtained through carefully controlling the growth conditions. Enhanced ferroelectric and dielectric properties were obtained with large remanent polarization P r of ~21 μC/cm2, coercive field E c of ~7.4 kV/mm and dielectric constant $\varepsilon_{33}^{T}/\varepsilon_{0}$ of ~750 at 1 kHz. The excellent global electrical properties of the BNBMT film are promising for environmentally friendly ferroelectric devices.  相似文献   

18.
This paper reports on the electrochemical properties and chemical stability of a recently developed Ca2+ and Sm3+-doped oxide ion conducting electrolyte, Ce0.85Ca0.05Sm0.1O1.9 (CCS), employed in an intermediate temperature solid oxide fuel cell (IT-SOFC) using conventional Sm0.5Sr0.5CoO3 (SSC) and La0.8Sr0.2MnO3 (LSM) cathodes in air at elevated temperatures. The materials were prepared by conventional solid-state reactions using their corresponding metal oxides and salts in the temperature range of 1,200–1,450 °C in air. Powder X-ray diffraction (PXRD) and impedance spectroscopy were employed for phase formation, chemical compatibility, and electrochemical characterization. PXRD studies on 1:1 weight ratio of heat-treated (1,000 °C for 3 days) mixtures of SSC or LSM and CCS revealed the presence of fluorite-type and perovskite-like phases. The area-specific resistance (ASR) value in air was lower for SSC cathodes (4.3–0.15 Ω cm2) compared to those of LSM (407–11 Ω cm2) over the investigated temperature range of 600–800 °C. As expected, a significant increase in ASR was observed in Ar as compared to air.  相似文献   

19.
The structural, magnetic and transport properties of La0.5Sr0.5MnO2.88 and La0.5Sr0.5Mn0.5Ti0.5O3 samples have been investigated systematically. Indeed, this series has been considered to understand the influence of physical parameters such as oxygen deficiency and titanium doping effect in undoped La0.5Sr0.5MnO3 sample. Ceramic material based on La0.5Sr0.5MnO2.88 exhibits interesting behaviours of charge-ordering (CO), ferromagnetic (FM) states and a good conductivity down to the lowest temperatures. The substitution of Ti for Mn destroyed drastically the CO, damaged the motion of itinerant eg electrons and changed the local parameters of perovskite cell. A change of the structure from tetragonal to rhombohedral symmetry is observed causing a weakening of double-exchange interaction. The experiment results show that the suppression of the CO is sensitive to the variety of Mn3+/Mn4+ ratio. In a field of 8 T at 10 K, FM and CO phase can be evaluated to be ∼20:80 according to the μexpcal ratio for La0.5Sr0.5MnO2.88, whereas the CO state is suppressed for La0.5Sr0.5Mn0.5Ti0.5O3 sample, FM and anti-ferromagnetic (AFM) phase are coexisted and evaluated to be ∼54:46, respectively.  相似文献   

20.
The short- and long-range order correlations of the crystal structure in the distorted perovskites La1−xSrxCoO3 and La1−xBaxCoO3 (0.0?x?0.5) have been studied by the neutron powder diffraction (NPD) and the Co K-edge X-ray absorption spectroscopy (XAS) measurements. The results of XAS and NPD indicate a local distortion around the Co3+ ions in LaCoO3 at room temperature. The substitution of the La3+ ions by the Sr2+(Ba2+) ions leads to a gradual increase of the Co-O-Co angle and is accompanied by an increase of the mean square relative displacement (MSRD) of the Co-O bond. These results correlate with an increase of the oxygen amplitude vibration in the direction perpendicular to the Co-O bond. The possible explanation of the observed changes of the crystal and electronic structures in the above-mentioned cobaltites is discussed.  相似文献   

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