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1.
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
2.
Solid polymer electrolytes (SPE) based on poly-(vinyl alcohol) (PVA)0.7 and sodium iodide (NaI)0.3 complexed with sulfuric acid (SA) at different concentrations were prepared using solution casting technique. The structural
properties of these electrolyte films were examined by X-ray diffraction (XRD) studies. The XRD data revealed that sulfuric
acid disrupt the semi-crystalline nature of (PVA)0.7(NaI)0.3 and convert it into an amorphous phase. The proton conductivity and impedance of the electrolyte were studied with changing
sulfuric acid concentration from 0 to 5.1 mol/liter (M). The highest conductivity of (PVA)0.7(NaI)0.3 matrix at room temperature was 10−5 S cm−1 and this increased to 10−3 S cm−1 with doping by 5.1 M sulfuric acid. The electrical conductivity (σ) and dielectric permittivity (ε′) of the solid polymer electrolyte in frequency range (500 Hz–1 MHz) and temperature range (300–400) K were carried out.
The electrolyte with the highest electrical conductivity was used in the fabrication of a sodium battery with the configuration
Na/SPE/MnO2. The fabricated cells give open circuit voltage of 3.34 V and have an internal resistance of 4.5 kΩ. 相似文献
3.
D. P. Kozlenko S. V. Trukhanov E. V. Lukin I. O. Troyanchuk B. N. Savenko 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):361-365
The crystal and magnetic structures of the oxygen deficient manganites
La0.7Sr0.3MnO3-d (d = 0.15, 0.20) have been studied by means
of powder neutron diffraction over the 0–5.2 GPa pressure and 10–290 K
temperature ranges. La0.7Sr0.3MnO2.85 exhibits a coexistence
of rhombohedral
and tetragonal (I4/mcm) crystal structures and below
Tg ~ 50 K a spin glass state is formed.
La0.7Sr0.3MnO2.80 exhibits a tetragonal (I4/mcm) crystal structure.
Below Tg ~ 50 K a phase separated magnetic state is formed,
involving coexistence of C-type AFM domains with spin glass domains. In both
compounds the crystal structure and magnetic states remain stable upon
compression. The factors leading to the formation of different magnetic
states in La0.7Sr0.3MnO3-d (d = 0.15, 0.20) and their specific
high pressure behavior, contrasting with that of the stoichiometric
A0.5Ba0.5MnO3 (A = Nd, Sm) compounds showing pressure-induced
suppression of the spin glass state and the appearance of the FM state, are analysed. 相似文献
4.
V. A. Cherepanov L. Ya. Gavrilova L. Yu. Barkhatova V. I. Voronin M. V. Trifonova O. A. Bukhner 《Ionics》1998,4(3-4):309-315
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
5.
Y. B. Lin Z. G. Huang Y. M. Yang S. Wang S. D. Li F. M. Zhang Y. W. Du 《Applied Physics A: Materials Science & Processing》2011,104(1):143-147
(La0.7Sr0.3MnO3)
x
/(YBa2Cu3O7)
y
composites were prepared by mixing La0.7Sr0.3MnO3 powders and the sol–gel-derived YBa2Cu3O7 matrix, followed by high-temperature calcinations. Their structural, magnetic properties and magnetoresistance effect have
been investigated systematically. A giant positive magnetoresistance (PMR) at low magnetic field is observed at low temperatures.
In the case of (La0.7Sr0.3MnO3)1/(YBa2Cu3O7)9 composite, the PMR achieves 260% under a magnetic field of 5800 Oe. However, the PMR value sharply decreases with increasing
temperature and no magnetoresistance effects are found above metal-insulator transition temperature. The enhancement of spin-dependent
scattering at the grain boundaries should be responsible for the observed PMR. In addition, the temperature dependence of
resistance under magnetic field could be explained by the competition between diamagnetism and paramagnetism in YBCO phase.
At low temperature, the diamagnetism is predominant over paramagnetism and the interface scattering between LSMO grains is
enhanced correspondingly. As a result, the low-temperature resistance increases and large PMR appears. 相似文献
6.
Mandy?Grobosch Kathrin?D?rr Ramesh?B.?Gangineni Martin?Knupfer 《Applied Physics A: Materials Science & Processing》2009,95(1):95-99
We have studied the energy level alignment at interfaces between clean ferromagnetic La0.7Sr0.3MnO3 and two archetype organic semiconductors, α-sexithiophene and copper-phthalocyanine, by combined X-ray and ultraviolet photoelectron spectroscopy. We observe the formation
of a large interface dipole at both studied interfaces and small hole injection barriers. In addition, our results indicate
a small chemical interaction between the organic materials and the La0.7Sr0.3MnO3 surface which leads to a pinning of the Fermi level and the relatively small hole injection barriers. 相似文献
7.
采用脉冲激光沉积技术制备了Ti/Pr0.7Ca0.3MnO3/Pt和Ti/Pr0.7Ca0.3MnO3/La0.67Sr0.33MnO3/Pt异质结并研究了La0.67Sr0.33MnO3功能插层对异质结电致电阻特性的影响. 实验结果表明La0.67Sr0.33MnO3功能层的引入有效提高了器件的电阻转变特性,尤其是电阻转变率和疲劳性得到了极大的改善. 对La0.67Sr0.33MnO3插层改善电致电阻转变特性的机理进行了定性的分析.
关键词:
电致电阻效应
电阻转变比率
疲劳特性 相似文献
8.
A. Maignan Ch. Simon V. Caignaert B. Raveau 《Zeitschrift für Physik B Condensed Matter》1995,99(1):305-310
The exploration of the magnetic and transport properties of four series of manganese perovskites, Pr0.7Ca0.34−xAxMnO3−δ (A=Sr, Ba), Pr0.7−xLaxCa0.3 MnO3−δ and Pr0.66Ca0.34−x
SrxMnO3−δ has allowed four phases with colossal magnetoresistive (CMR) properties to be isolated: Pr0.7Ca0.25Sr0.025MnO3−δ and Pr0.66Ca0.26Sr0.08MnO3−δ that exhibit a variation of resistance of 2.5. 107% and 109% at μ0 H=5 T for T=88 K and 50 K respectively, Pr0.58La0.12Ca0.3 MnO3−δ that exhibits a variation of 6.106% for μ0 H=5 T at T=80 K and Pr0.7Ba0.025Ca0.275MnO3−δ for which a resistance variation of 5.109%, at T=50 K, for μ0 H=5 T is evidenced. for each compound of this series except the barium phase, one observes that the temperature Tmax, which corresponds to the resistance maximum on the R(T) curves in zero magnetic field, increases dramatically as the mean
size of the interpolated cations increases, and that the CMR effect correlatively decreases dramatically. The comparison of
the two series Pr0.7Ca0.3−xSrxMnO3−δ and Pr0.66Ca0.34−xSrxMnO3−δ shows also the crucial role of the hole carrier density: for a same mean ionic radius of the interpolated cation Tmax is decreased of about 50 K by introducing 0.034 hole per Mn mole. 相似文献
9.
A. A. Voronkov B. P. Gorshunov V. S. Nozdrin E. S. Zhukova T. Matsuoka K. Tanaka S. Miyasaka S. Tajima M. Dressel 《JETP Letters》2012,94(9):708-713
The spectra of the conductivity and dielectric constant of La1.87Sr0.13CuO4 cuprate have been directly measured in the frequency range of 0.3 to 1.2 THz (10–40 cm−1) and the temperature range of 5 to 300 K in the E | c polarization (the electric field vector of radiation is perpendicular to the copper-oxygen planes). Excitation has been observed
in the superconducting phase, and its nature has been attributed to the transverse optical excitation of the condensate of
Cooper pairs, which appears because Josephson junctions between CuO planes are modulated due to in-plane magnetic and charge
stripes. Additional quasiparticle absorption of unknown origin has been detected at frequencies below ≈15 cm−1 at liquid helium temperatures. 相似文献
10.
The Tl2S compound was prepared in a single crystal form using a special local technique, and the obtained crystals were analysed
by X-ray diffraction. For the resultant crystals, the electrical properties (electrical conductivity and Hall effect) and
steady-state photoconductivity were elucidated in this work. The electrical measurements extend from 170 to 430 K, where it
was found that σ
⊥ = 8.82 × 10−5 Sm−1 when current flow direction makes right angle to the cleavage plane of the crystals. In the same range of temperatures, it
was found that σ
‖ = 4.73 × 10−5 Sm−1 when the current flow is parallel to the cleavage plane. In line with the investigated range of temperatures, the widths
of the band gaps were calculated and discussed as also the results of the electrical conductivity and Hall effect measurements.
In addition, the anisotropy of the electrical conductivity (σ
⊥/σ
‖) for the obtained crystals was also studied in this work. Finally the photosensitivity was calculated for different levels
of illumination as a result of the photoconductivity measurements, which showed that the recombination process in Tl2S single crystals is a monomolecular process.
相似文献
11.
N. O. Golosova D. P. Kozlenko V. I. Voronin V. P. Glazkov B. N. Savenko 《Physics of the Solid State》2006,48(1):96-101
The atomic and magnetic structures of the La0.7Sr0.3CoO3 cobaltite are investigated using neutron diffraction at high pressures up to 4.2 GPa in the temperature range 16–300 K. The
structural parameters are determined as functions of the pressure. It is revealed that the effect of high pressure leads to
a decrease in the Curie temperature: dT
C/dP = −8.3(8) K/GPa. It is established that, under high pressure, the decrease in the Curie temperature T
C is associated with the transition of a number of Co3+ ions from the intermediate-spin state (t
2g
5
e
g
1
, S = 1) to the low-spin state (t
2g
6
, S = 0). 相似文献
12.
Nanosecond (ns) photoelectric effects have been observed in all-oxide p-n junctions of La0.9Sr0.1MnO3/SrNb0.01Ti0.99O3 for the first time. The rise time was about 23 ns and the full width at half maximum was about 125 ns for the open-circuit
photovoltaic pulse when the La0.9Sr0.1MnO3 thin film in the p-n junction was irradiated by a laser of ≈20 ns pulse duration and 308 nm wavelength. The photovoltaic
sensitivity was 80 mV/MJ for a 308 nm laser pulse. 相似文献
13.
L. Fruchter Z. Z. Li H. Raffy 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,65(2):213-217
The time-averaged and low-frequency noise transport properties were investigated in the vicinity of the superconductor-insulator
transition for a Bi2Sr2-x
La
x
CuO6+δ (x = 0.3) thin film. The results are consistent with a superconductor (metal) embedded in a strong insulator, the latter showing
two-dimensional variable range hopping properties. The weak insulator behavior - if any - is attributed to the metallic inclusions
only. 相似文献
14.
T.D. ThanhL.H. Nguyen D.H. ManhN.V. Chien P.T. Phong N.V. KhiemL.V. Hong N.X. Phuc 《Physica B: Condensed Matter》2012,407(1):145-152
A systematic investigation of the structural, magnetic and electrical properties of a series of nanocrystalline La0.7SrxCa0.3−xMnO3 materials, prepared by high energy ball milling method and then annealed at 900 °C has been undertaken. The analysis of the XRD data using the Win-metric software shows an increase in the unit cell volume with increasing Sr ion concentration. The La0.7SrxCa0.3−xMnO3 compounds undergo a structural orthorhombic-to-monoclinic transition at x=0.15. Electric and magnetic measurements show that both the Curie temperature and the insulator-to-metal transition temperature increase from 259 K and 253 K correspondingly for La0.7Ca0.3MnO3 (x=0) to 353 K and 282 K, respectively, for La0.7Sr0.3MnO3 (x=0.3). It is argued that the larger radius of Sr2+ ion than that of Ca2+ is the reason to strengthen the double-exchange interaction and to give rise to the observed increase of transition temperatures. Using the phenomenological equation for conductivity under a percolation approach, which depends on the phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions, we fitted the resistivity versus temperature data measured in the range of 50-320 K and found that the activation barrier decreased with the raising Sr2+ ion concentration. 相似文献
15.
N. A. Babushkina A. N. Taldenkov A. V. Kalinov L. M. Fisher O. Yu. Gorbenko T. Lorenz D. I. Khomskii K. I. Kugel’ 《Journal of Experimental and Theoretical Physics》2010,111(2):189-193
The effect of 16O → 18O oxygen isotope substitution has been studied for (Pr1−y
Eu
y
)0.7Ca0.3CoO3 cobaltites (0.12 < y < 0.26). A pronounced isotope shift has been found for the spinstate transition temperature, which increases with the oxygen
isotope mass. In contrast, the ferromagnetic transition temperature has slightly lower values for the samples with heavier
oxygen. The observed phenomena and constructed phase diagram confirm the results reported previously for (Pr1 − y
Sm
y
)0.7Ca0.3CoO3 in [G. Y. Wang, X. H. Chen, T. Wu, et al., Phys. Rev. B 74, 165113 (2006)]. The measurements of the specific heat have been performed for (Pr1 − y
Eu
y
)0.7Ca0.3CoO3 with the main emphasis on the analysis of the isotope effect. The contributions to the isotope effect coming from the lattice
and magnetic components of the specific heat have been separated. The mechanisms underlying the large isotope effect are discussed. 相似文献
16.
The preparation of (La9.33−2x/3Sr
x
□0.67−x/3)Si6O24O2 (0 ≤ x ≤ 2) samples with different amounts of cation vacancies is reported. Structure and unit-cell parameters were deduced by Rietveld
analysis of XRD patterns. Structural features that enhance oxygen conductivity in Sr-doped apatites are discussed. Up to three
components were detected in 29Si MAS-NMR spectra which change with the amount and distribution of cation vacancies. In general, oxygen conductivity increases
with the amount of vacancies at La1 (6h) sites, passing through a maximum for x = 0.4. In the case of activation energy, a minimum is detected near x = 1.2, indicating that entropic and enthalpic change in different ways. The presence of cation vacancies should enhance oxygen
hopping along c-axis; however, the analysis of the frequency dependence of conductivity suggests that oxygen motions are produced along three
axes. 相似文献
17.
Shufang Wang Huiling Li Kun Zhao Songqing Zhao Mingjing Chen Jingchun Chen Jianglong Wang Guangsheng Fu 《Applied Physics A: Materials Science & Processing》2011,105(2):407-410
A heterojunction was fabricated by growing a layer of Bi2Sr2Co2O
y
thin film on the 0.7 wt% Nb-doped SrTiO3 substrate. Such heterojunction showed good rectifying characteristics over a wide temperature range, and its transport mechanism
under the forward bias can be attributed to a space charge limited conduction mechanism via defects near the interface of
the heterojunction. Photovoltaic properties of the heterojunction were studied by using both continuous-wave and pulsed irradiations
and the results can be well explained by the photovoltaic effect of a p–n junction. 相似文献
18.
The vibration frequencies of unstable ferroelectric and antiferrodistortion modes and the dependences of the energy on the
ion displacement amplitude have been calculated within the generalized Gordon-Kim model for distortions along eigenvectors
of these modes in the mixed compounds Sr1 − x
A
x
Ti1 − x
/4□
x/4O3 and Sr1 − y
A
2y
/3□
y/3TiO3 (A = Sc3+, In3+, La3+, Bi3+; □ is the vacancy). To compensate an excess positive charge, vacancies are introduced into the Ti4+ or Sr2+ site. Calculations have been performed in the “daverage” crystal approximation for impurity concentrations of 0.25 and 0.50.
To this end, a set of 40 atomic superlattices with various orderings of heterovalent ions Sr2+ and impurity A
3+ has been considered. It has been found that each impurity type, independently of charge balance, induces ferroelectric instabilities
in doped compounds. In the case of doping with In3+ and La3+ for concentration x = 0.25, the possibility of rotating the polarization vector has been shown. 相似文献
19.
The interfaces in complex La2 − x
Sr
x
CoO4 oxides (0.1 < x < 1.5) obtained by the ceramic method were studied in detail. To determine the chemical composition of the interfaces and
their effect on the properties of ceramics, the magnetic and electric properties were investigated and X-ray phase and micro
X-ray analyses were performed. It was found that the mechanical stability of the samples is determined by the presence of
lanthanum in the surface layer. 相似文献
20.
Recently there has been substantial interest in optimising perovskite type ceramics as mixed ionic-electronic conductors (MIECs)
for use in ceramic oxygen generators and solid oxide fuel cells. However these materials suffer from thermomechanical deficiencies
and therefore there is a need to develop alternative materials.
Using the IEDP/SIMS technique the La2−xSrxNi1−yFeyO4+δ series of compounds has been investigated and the oxygen tracer diffusion and surface exchange coefficients determined. It
has been found that the oxide ion diffusivity of the x and y=0 material is very close to that of the fast oxide ion conducting
perovskites such as La1−xSrxCoO3 (LSC) but on acceptor doping with Sr a considerable decrease in the oxygen tracer diffusion coefficient was observed. Further
studies on the effects of B site doping, where y>0, indicate that this has very little effect on the transport properties.
Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999. 相似文献