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1.
A spin model of quasi-one-dimensional LiCu2O2 compound with ground state of ellipsoidal helical structure has been adopted. The helical axis is along the diagonal of CuO4 squares. By taking into account the interchain coupling and exchange anisotropy, the exotic magnetic properties and ferroelectricity induced by spiral spin order have been studied by performing Monte Carlo simulation. The simulation results qualitatively reproduce the main characters of ferroelectric and magnetic behaviors of LiCu2O2 compound and confirm the low-temperature noncollinear spiral ordering. Furthermore, by performing the calculations of spin structure factor, we systematically investigate the effects of different exchange couplings on the lower-temperature magnetic transition, and find that the spiral spin order depends not only on the ratio of nearest and next-nearest neighbor inchain spin coupling but also strongly on the exchange anisotropy. 相似文献
2.
J. Feng B. Xiao J.C. Chen C.T. Zhou Y.P. Du R. Zhou 《Solid State Communications》2009,149(37-38):1569-1573
AgCuO2 and Ag2Cu2O3 are new types of semiconductor materials. A theoretical study is presented for both the electronic and optical properties of these new photovoltaic materials in the framework of density functional theory (DFT). The calculated cohesive energy is −3.606 eV/atom and −3.723 eV/atom for Ag2Cu2O3 and AgCuO2, respectively. Electronic calculations indicate that AgCuO2 is a small band gap semiconductor and Ag2Cu2O3 is metallic in nature. The valency state of Cu is divalent in Ag2Cu2O3 and trivalent in AgCuO2. The largest absorption coefficient of CuO2 is 332 244, which is significantly greater than that of CuInSe2, CdTe, GaAs, etc. 相似文献
3.
Incommensurate modulations in Ba2TiSi2O8, Sr2TiSi2O8, and Ba2TiGe2O8 are compared based on their corresponding electron diffraction patterns. The dependence of the modulations on chemical composition provides a suitable model system for the investigation of incommensurations in framework structures using high-resolution transmission electron microscopy (HRTEM). A widening of quantitative HRTEM utilising the concept of rigid units is proposed allowing for a determination of atomistic displacements responsible for the formation of incommensurately modulated structures. 相似文献
4.
Mixtures of AgI and PbI2 cooled from the melt result in the peritectic formation of a fast ion conducting phase centred about Ag4PbI6, which is face centred cubic with a = 6.33(5)A; this phase exhibits high electrical conductivity. On cooling to about 125°C, dissociation occurs to γAgI and PbI2, accompanied by the transient formation of another phase, centred about Ag2PbI4. A modified form of the T-x section of the equilibrium phase diagram at AgI concentrations greater than 60 mole % and below 300°C is proposed. 相似文献
5.
By means of neutron diffraction we found for MnTa2O6S1S2 S3S4 with a magnetic unit which is the same as the chemical. Whereas the chemical unit of CoNb2O6 is doubled in c-direction; all spins in the chemical unit are parallel. Therefore the orthorhombic symmetry of the crystal structure cannot be maintained. In both compositions are the spins parallel to the a-axis. 相似文献
6.
Magnetic properties of BaMn2V 2O8 are investigated by means of susceptibility, magnetization, and heat capacity measurements. Our experimental results show that BaMn2V 2O8 is a one-dimensional canted antiferromagnet. The antiferromagnetic transition at a relatively high TN of 37 K may be due to an enhancement of interchain interaction in the system, since Mn2+ ions have large spin moment of S=5/2. Weak ferromagnetism in BaMn2V 2O8 may be due to Dzyaloshinskii-Moriya interactions arising from its noncentrosymmetric crystal structure. 相似文献
7.
The dielectric, optical and non-linear optical properties of Ba6Ti2Nb8O30 single crystals were examined from room temperature up to the Curie temperature of 245°C. The spontaneous polarization at room temperature was estimated as 0·22±0·01 C/m2. The linear electrooptic constants were measured as r33T=(1·17±0·02)×10?10 and r13T=(0·42±0·01)×10?10 m/V. The non-linear optical coefficients were d33=(15·1±2·0)×10?12 and d31=(11·0±2·0)×10?12 m/V, which are comparable to those of Ba4Na2Nb10O30. Temperature dependences of δ33 and δ31 (Miller's δ) were found to be proportional to that of Ps. 相似文献
8.
A. Fontana G. Mariotto E. Cazzanelli G. Carini M. Cutroni M. Federico 《Physics letters. A》1983,93(4):209-212
In this letter we refer on the Raman-scattering measurements in superionic glasses (AgI)x(Ag2O nB2O3)1-x where 0 ? x ? 0.5. The behaviour of the low-frequency Raman spectra, Δν < 250 cm?1, has been interpreted as due to a vibrational density of states mainly due to the silver halide. Nonlinear increase of the Raman efficiency with the increase of AgI concentration has been found: a phenomenological explanation is presented. 相似文献
9.
T. Miyatake K. Yamaguchi T. Takata S. Gotoh N. Koshizuka S. Tanaka 《Physica C: Superconductivity and its Applications》1989,160(5-6):541-544
Samples of YBa2Cu4O8 are prepared by means of a new high oxygen pressure technique employing oxygen-HIP. Both magnetization and resistivity measurements show the superconductivity transition at 82.5 K. The lower and upper critical fields of YBa2Cu4O8 are obtained from the magnetization measurements. The Ginzburg-Landau parameters, ζ(0)=17 Å, λ(0)=2400 Å, are estimated from these results. 相似文献
10.
Dapeng Xu Yipeng Gu Liang Li Hongzhi Shen Hang Yang Qiang Zhou Zhan Shi Hongming Yuan Tian Cui 《Journal of Physics and Chemistry of Solids》2014
A high-quality ZnNb2O6 single-crystal grown by optical floating zone method has been used as a research prototype to analyze the optoelectronic parameters by measuring the absorption coefficient and transmittance spectra along the b-axis from 200 nm to 1000 nm at room temperature. The optical interband transitions of ZnNb2O6 have been determined as a direct transition with a band gap of 3.84 eV. The refractive index, extinction coefficient, and real and imaginary parts of the complex dielectric constants as functions of the wavelength for ZnNb2O6 crystal are obtained from the measured absorption coefficients and transmittance spectra. In the Urbach tail of 3.16–3.60 eV, the validity of the Cauchy–Sellmeier equation has also been evaluated. Using the single effective oscillator model, the oscillator energy Eo is found to be 4.77 eV. The dispersion energy Ed is 26.88 eV and ZnNb2O6 crystal takes an ionic value. 相似文献
11.
Ag3PO4/Ag/Ag2Mo2O7 composite photocatalyst was successfully prepared via an in situ precipitation method. The as-prepared Ag3PO4/Ag/Ag2Mo2O7 nanocomposite included Ag3PO4 nanoparticles (NPs) as well as Ag NPs assembling on the surface of Ag2Mo2O7 nanowires. Under visible light irradiation (λ>420 nm), the Ag3PO4/Ag/Ag2Mo2O7 composite degraded rhodamine B (Rh B) efficiently and showed much higher photocatalytic efficiency than pure Ag3PO4, Ag2Mo2O7, or Ag3PO4/Ag2Mo2O7. It was elucidated that the excellent photocatalytic performance of Ag3PO4/Ag/Ag2Mo2O7 for the degradation of Rh B under visible light could be ascribed to the high specific surface area, the extended absorption in the visible light region resulting from the Ag3PO4/Ag loading, and the efficient separation of photogenerated electrons and holes through the ternary heterostrucure composed of Ag3PO4, Ag and Ag2Mo2O7. 相似文献
12.
Praveen Khatri 《Journal of Physics and Chemistry of Solids》2009,70(2):385-29
Polycrystalline sample of Ca3Nb2O8 was prepared by a high-temperature solid-state reaction technique. X-ray diffraction (XRD) analysis confirms the formation of single-phase compound of hexagonal (rhombohedral) crystal structure at room temperature. Scanning electron micrograph of the material showed uniform grain distribution on the surface of the sample. Detailed studies of dielectric properties of the compound, studied in a wide frequency range (102-106 Hz) at different temperatures (25-500 °C), exhibit a dielectric anomaly suggesting phase transition of ferroelectric-paraelectric and structural type at 300 °C. Electrical properties of the material were analyzed using a complex impedance technique. The Nyquists plot showed the presence of bulk effect in the material in the studied temperature range. Studies of electrical conductivity over a wide temperature range suggest that the compound has negative temperature coefficient of resistance behavior. 相似文献
13.
Bismuth-borate glasses doped with some rare earth ions were studied with respect to the density, molar volume and the elastic moduli, Poisson’s ratio, Debye temperature, microhardness, softening temperature, acoustic impedance, diffusion constant and latent heat of melting. Ultrasonic velocities were measured by the pulse echo overlap technique at a frequency of 10 MHz and at room temperature. From these velocities and density values, various elastic moduli were calculated. The correlation of elastic stiffness, the cross link density, and the fractal bond connectivity of these glasses are discussed. The derived experimental values of shear modulus, bulk modulus, Young’s modulus, and Poisson’s ratio for our glasses are compared with the theoretically calculated values in terms of the bond compression model and Makishima-Mackenize theory. 相似文献
14.
Thermal evaporation, flash evaporation and rf-sputtering techniques were applied to the preparation of amorphous films of superionic conducting glasses in the systems AgIAg2MoO4 and AgIAg2OB2O3. The flash-evaporated films were amorphous and showed very high conductivities, about 2 × 10?2S/cm for the AgIAg2MoO4 and about 5 × 10?3S/cm for the AgIAg2OB2O3 at room temperature, and gave a Ag+ transport number of unity. The thermal evaporation method produced crystalline-phase included films. The rf-sputtered films were amorphous by X-ray diffraction and the transport number of Ag+ ions was smaller than unity (about 0.9). Thus flash evaporation was concluded to be the most suitable method for preparing amorphous films of superionic conducting glasses. 相似文献
15.
This paper reports on the influence of the sintering temperature and atmosphere and transition-metal doping on the magnetic properties of nanocrystalline and bulk In2O3. Undoped nanocrystalline In2O3 is diamagnetic whatever the sintering temperature and atmosphere. All single-phase transition-metal-doped In2O3 samples are paramagnetic, with a paramagnetic effective moment originating from weakly interacting transition metal ions. No trace of ferromagnetism has been detected even with samples sintered under argon, except extrinsic ferromagnetism for samples with magnetic dopant concentrations exceeding the solubility limit. 相似文献
16.
C. Petitjean 《Applied Surface Science》2009,255(17):7700-7702
Ag2Cu2O3 films were deposited on glass substrates by reactive sputtering of a composite silver-copper target. The deposited films were annealed in air at 100, 200 and 300 °C. The structure of the films was studied using X-ray diffraction (XRD), their surface morphology was characterised using scanning electron microscopy (SEM) and their electrical resistivity at room temperature was measured using the four point probe method. The 100 °C annealing did not modify either the film structure or the film morphology. On the other hand, Ag2Cu2O3 films were partially decomposed into Ag and CuO after a 200 °C annealing. The decomposition was complete for a 300 °C annealing. The evolution of the film surface morphology as a function of the annealing temperature was discussed in connection to the evolution of the molar volume of the phases constituting the films. 相似文献
17.
Electronic,optical properties,surface energies and work functions of Ag8SnS6: First-principles method
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Ternary metal chalcogenide semiconductor Ag8Sn S6,which is an efficient photocatalyst under visible light radiation,is studied by plane-wave pseudopotential density functional theory.After geometry optimization,the electronic and optical properties are studied.A scissor operator value of 0.81 e V is introduced to overcome the underestimation of the calculation band gaps.The contribution of different bands is analyzed by virtue of total and partial density of states.Furthermore,in order to understand the optical properties of Ag8Sn S6,the dielectric function,absorption coefficient,and refractive index are also performed in the energy range from 0 to 11 e V.The absorption spectrum indicates that Ag8Sn S6has a good absorbency in visible light area.Surface energies and work functions of(411),(4 13),(21 1),and(112)orientations have been calculated.These results reveal the reason for an outstanding photocatalytic activity of Ag8Sn S6. 相似文献
18.
Rietveld refinements of X-ray powder diffraction data have confirmed the crystal structure of BaCa2MgSi2O8 prepared by a standard solid-state method. The final reliable factors were Rwp=10.91%, Rp=8.10%, RI=2.71%, and RF=1.14%. BaCa2MgSi2O8 crystallizes in the trigonal space group P3¯m1 (no. 164) with a=5.430(3) Å and c=6.807(2) Å. The oxide has a layered structure constructed from the unit layers built up by corner-sharing MgO6 octahedra and SiO4 tetrahedra. Ba and Ca atoms occupy the distinct crystallographic sites; Ba atom is sited in the interlayer space and Ca atom is embedded in the layer framework. This structure was not disrupted by doping of Eu2+ ions.The Eu2+-doped BaCa2MgSi2O8 exhibited an intense blue emission based on 5d-4f electron transitions of Eu2+ ions under 254 nm excitation. This emission has a sufficient chromaticity as a blue phosphor. An additional analysis of the emission spectra using an empirical formula indicates that Eu2+ is distributed into both Ba and Ca sites. 相似文献
19.
Jin-Ah Park 《Physica B: Condensed Matter》2008,403(4):639-643
The effect of Al2O3 on the electrical properties of ZnO-Pr6O11-based ceramics is investigated in this work. The average grain size of ZnO increased as the Al2O3 content increased from 10.3 to 13.5 μm. It was found that a sample doped with Al2O3 of 0.005 mol% showed the highest nonlinear current-voltage characteristics with a nonlinear exponent of 43.8 and a leakage current of 0.66 μA. When the Al2O3 content was increased, the donor concentration was increased from 0.51×1018/cm3 to 1.59×1018/cm3, but the barrier height was decreased from 1.01 to 0.87 eV. The best electrical stability against aging stress was obtained by doping Al2O3 of 0.001 mol%. 相似文献
20.
Ab initio band structure calculations were performed for the low-temperature modifications of the silver chalcogenides β-Ag2Se, β-Ag2Te and the ternary compound β-Ag3AuSe2 by the local spherical wave (LSW) method. Coordinates of the atoms of β-Ag2Se and β-Ag3AuSe2 were obtained from refinements using X-ray powder data. The structures are characterized by three, four and five coordinations of silver by the chalcogen, a linear coordination of gold by Se, and by metal-metal distances only slightly larger than in the metals. The band structure calculations show that β-Ag3AuSe2 is a semiconductor, while β-Ag2Se and β-Ag2Te are semimetals with an overlap of about 0.1-0.2 eV. The Ag 4d and Au 5d states are strongly hybridized with the chalcogen p states all over the valence bands. β-Ag2Se and β-Ag2Te have a very low DOS in the energy range from about −0.1 to +0.5 eV. The calculated effective mass β-Ag2Se is about 0.1-0.3 me for electrons and 0.75 me for holes, respectively. 相似文献