A family of mixed-layer type bismuth compounds

Existence of a family of mixed-layer type bismuth compounds with the general formula Bi₄A_2m?1B_2m+1O_6m+9, where A is Na(1+), Sr(2+), Bi(3+), etc., B is Ti(4+), Nb(5+), W(6+), etc. and m is an integer as 1,2, or 3, was confirmed. Following new compounds, each of which has an orthorhombic cell, were found: Bi₅TiNbWO₁₅ and Na_0.5Bi_4.5Nb₂WO₁₅ for m=1, Bi₇Ti₄TaO₂₁, SrBi₆Ti₃Nb₂O₂₁ and BaBi₆Ti₃Nb₂O₂₁ for m=2 and BaBi₈Ti₇O₂₇ and PbBi₈Ti₇O₂₇ for m=3. An extensive study for thermal phase transitions was made by both DTA method and dielectric measurement.     

Preparation of bismuth nanoparticles in opal matrices through reduction of bismuth compounds with supercritical isopropanol

Bismuth nanoparticles have been produced in pores of opal matrices by reducing bismuth salts and oxide compounds with supercritical isopropanol. According to transmission electron microscopy data, the diameter of the SiO₂ spheres in the opal matrices is about 260 nm, and that of the bismuth nanoparticles does not exceed 80 nm.     

Low-temperature specific heat of layered compounds

Specific heat measurements in the temperature range from 1 to 10 K and in magnetic fields up to 1.2 T have been made on a number of layered transition metal dichalcogenide crystal complexes. The thermodynamic critical fieldH _c and the Ginzburg-Landau coherence length and penetration depth have been calculated. For TaS₂ (pyridine)_1/2 and TaS_1.6Se_0.4 (pyridine)_1/2, the coherence length perpendicular to the layers is slightly less than the interlayer separation.Research at Stanford supported by Air Force Office of Scientific Research, Air Force Systems Command, USAF, under grant AFOSR 73-2435B.     

离子型层状化合物制备及应用研究

简单介绍离子型和非离子型两类层状化合物的结构和性能,重点概括了以 LDH为代表的阴离子型层状化合物和以α 磷酸盐为代表的阳离子型层状化合物的制备以及研究进展。     

The effectiveness of the exciton mechanism in superconducting layered compounds

The excitonic interaction resulting from an array of adsorbed dyes on a plane conducting metallic sheet is considered. We show that only with the appropriate choice of dye and with certain constraints on the structure and properties of the metallic system can this interaction be strong enough to influence the superconducting properties of the sheet.     

Synthesis and structural characterization of Ce-doped bismuth titanate

Ce-modified bismuth titanate nanopowders Bi_4−xCe_xTi₃O₁₂ (x ≤ 1) have been synthesized using a coprecipitation method. DTA/TG, FTIR, XRD, SEM/EDS and BET methods were used in order to investigate the effect of Ce-substitution on the structure, morphology and sinterability of the obtained powders. The phase structure investigation revealed that after calcinations at 600 °C powder without Ce addition exhibited pure bismuth titanate phase; however, powders with Ce (x = 0.25, 0.5 and 0.75) had bismuth titanate pyrochlore phase as the second phase. The strongest effect of Ce addition on the structure was noted for the powder with the highest amount of Ce (x = 1) having a cubic pyrochlore structure. The presence of pure pyrochlore phase was explained by its stabilization due to the incorporation of cerium ions in titanate structure. Ce-modified bismuth titanate ceramic had a density over 95% of theoretical density and the fracture in transgranular manner most probably due to preferable distribution of Ce in boundary region.     

Nonlinear optical activity in Bridgman growth layered compounds

Layered semiconductor compound CdI₂ has been grown with the Bridgman technique and studied by nonlinear transmittance spectroscopy. The optical absorption in CdI₂ shows a nonlinear transmission of the incident laser power (P₀) within a lower power limit. The transmission, however, is found to saturate at high powers, giving a clamped output. The value of the incident power (P_0C) at which clamping starts is also found to depend on the crystal temperature (T_L). The values of P_OC ranges from 55 to 65 MW cm⁻² for T_L = 4.2–180 K. The dynamic range (D_R) as a function of T_L is calculated and the values are found to range from D_R = 2 to 1.6. The optical limiting mechanisms are discussed. The two-photon absorption (TPA) coefficient (β) of the optical nonlinear process in CdI₂ is estimated. The values are found to be within a range from β = 47 to 25 cm GW⁻¹ and be decreasing with increasing T_L. As expected for the TPA process, the experimental data within a certain range follows the linear relation: log (P₀/P_T) = A_G + Ω(P₀ − P_T), where P_T is the transmitted power, A_G is the absorbance of the ground state and Ω is a constant depending on the absorption cross-section and the relaxation time. The values of A_G and Ω estimated from the fits to the measured data vary with T_L. The findings resulting from this investigation might have potential applications in optical sensors protection.     

Deformation of layered structural elements in a temperature-radiation field

The paper considers the neutron irradiation effect on the deformation of viscoelastoplastic layered structural elements under the action of thermal-force loads. A general formulation of the boundary-value problem is proposed. A numerical solution for a three-layered metal-polymeric rod is given.Translated from Problemy Prochnosti, No. 6, pp. 111–118, November–December, 2004     

Possible coexistence of superconductivity and magnetism in layered compounds

The possibility of a coexistent superconducting and magnetic phase in layered transition metal dichalcogenides of the type MX ₂ A _x is investigated (M =transition metal; X = S, Se; A = magnetic ion; x 0.25). Describing such systems with a model in which a highly anisotropic electron gas interacts with a quasi-two-dimensional Heisenberg magnet, we find the following conditions for coexistence: (1) The coupling between adjacent layers of ferromagnetically ordered magnetic ions needs to be antiferromagnetic (S ^z = 0) in order to have no pair-breaking internal fields. (2) The exchange interaction between conduction electrons and magnetic ions must be very small ( 0.003 eV), since otherwise, due to the high concentration of localized magnetic moments, spin-flip scattering processes and spin fluctuations would destroy superconductivity. The theoretical prediction for the persistence of superconductivity up to concentrations of x 0.25 of magnetic ions is compared with recent experiments on Eu-intercalated TaS ₂ and NbS ₂ and related compounds showing a tendency for ferromagnetically ordered layers of Eu impurities and antiferromagnetic coupling between neighboring layers but no superconductivity for x exceeding a few percent. Reasons for the quick disappearance of superconductivity in these systems and criteria for possible observation of high-magnetic-impurity-concentration superconductivity in other layered compounds are given.     

Charge bag model of superconductivity in intercalated layered compounds

In certain layered compounds the superconducting transition temperature (T _c ) is enhanced on intercalation. The superconductivity in these materials arises over a charge density wave background. To explain this enhancement inT _c we propose the charge bag model analogous to the spin bag model proposed earlier by Schrieffer as a mechanism for highT _c superconductivity.     

Effect of metal electrode on thermoelectric power in bismuth telluride compounds

The measurements of apparent effective Seebeck coefficients S _a, thermoelectric powers E and I-V characteristics were made on a copper-semiconductor-metal contact junction, where the semiconductor is consisted of the p- and n-type bismuth telluride compounds. The S _a measured by heating either of copper and metal alternatively to produce the temperature differences of T = ±6 K changed slightly with the kind of metal electrodes, but it changed very little when the direction of the temperature gradient was reversed. The averaged S _a values over all kinds of metal electrodes agreed closely with the Seebeck coefficients S measured by the conventional technique using two alumel-chromel thermocouples as an electrode. The thermoelectric power E generated by imposing the temperature differences of T = ±6 K on a thermoelement tended to increase with increase of S _a and reached large values in noble metal electrodes of Ag and Au. The E was found to achieve enhancements of up to 10% or even more, when one end of a thermoelement contacts with Au electrode and the external electrical resistance is zero. Thus, the selection of the optimal metal electrode is necessary to make the thermoelectric conversion efficiency as high as possible.     

Electrical behavior of lithium intercalated layered In-Se compounds

InSe and In₂Se₃ was lithium intercalated by mean of a spontaneous intercalation reaction. The electrical conductivity was studied and was found to be altered by 3-orders of magnitude with respect to non-intercalated samples. An interesting time dependent anisotropy appeared during intercalation, associed to the initial non-uniform Li distribution and the movement of Li concentration kinks.     

Nuclear magnetic resonance in layered high T c compounds

Using the completed anisotropic Eliashberg equations valid for layered compounds, we have calculated numerically the temperature dependent nuclear magnetic resonance rate. The calculations fully include anisotropy and quasiparticle damping effects represent an extension of previous work in which anisotropy was included approximately through an ansatz. The calculations largely confirm previous work which showed reasonable agreement.     

Preparation, sintering, and microstructures of strontium barium bismuth tantalate layered perovskite ceramics

The solid solutions of Ba-doped SrBi₂Ta₂O₉ layered perovskite ceramic powders have been successfully prepared via a two-step process using BiTaO₄ as a precursor. The lattice constants of the solid solutions monotonically increase with increasing barium-ion content. The sinterability of (Sr_1–xBa_x)Bi₂Ta₂O₉ powders is significantly improved by increasing the barium-ion content. When the specimens with high barium-ion contents are sintered at 1100°C, they thermally decompose to form rod-like grains and the matrix expands, leading to a lower density. The addition of barium ions to SrBi₂Ta₂O₉ also results in significant variation in the morphology of the sintered specimens and the occurrence of c-axis preferred orientation which is ascribed to the anisotropic growth of plate-like grains. The precise control of the barium-ion content as well as the sintering conditions is critical for obtaining densified barium-ion doped SrBi₂Ta₂O₉ ceramics with a pure, layered perovskite structure.     

Change in the structural properties of bismuth and its alloys as a result of irradiation

It is shown that the intensities of certain diffraction lines characterizing bismuth and bismuth-lead alloy single crystals and polycrystalline aggregates change after these materials have been irradiated with electrons or protons.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol.21, No.6, pp. 1105–1107, December, 1971.     

Magnetic orders in copper hydroxide n-alkylsulfonate layered compounds

Anhydrous copper(II) hydroxide alkanesulfonates, Cu₂(OH)₃(C_nH_2n+1SO₃) (n=8 and 10), were synthesized and investigated by means of dc and ac magnetic susceptibility measurements. As a result, a long-range magnetic order, with both antiferromagnetic and ferromagnetic interactions, was revealed in the novel compounds.