Interpenetration of covalent and noncovalent networks in the crystal structures of {[M(4,4′-bipyridine)2(NO3)2]⋅2p-nitroaniline}n where M=Co, 1, Ni, 2, Zn, 3

The synthesis and crystal structures of {[M(4,4′-bipyridine)₂(NO₃)₂]⋅2p-nitroaniline}_n, M=Co, 1, Ni, 2, Zn, 3, are described. 1, 2 and 3 crystallize in the form of compounds that can be described as interpenetrating covalent and noncovalent networks. Analysis of the crystal packing in these compounds reveals that the p-nitroaniline molecules form a noncovalent network that is complementary from a topological perspective with [M(4,4′-bipyridine)₂(NO₃)₂] networks, which exist as square grids. These structures are interpreted in the broader perspective of crystal engineering strategies and development of new hybrid materials.     

Efficient reverse converter design for the new four-moduli set {22n, 2n + 1, 2n/2 + 1, 2n/2 – 1}

Abstract

This paper presents a new four-moduli set {2²ⁿ, 2ⁿ + 1, 2^n/2 + 1, 2^n/2 – 1} (n even). According to new Chinese remainder theorem 1, an efficient algorithm is derived for converting four residue numbers to binary. Then, the converter architecture is designed using shorter bit-width carry propagate adders to improve the hardware performance considerably. Compared with existing converters for related four-moduli sets, the proposed converter shows higher speed and lower power consumption. The proposed converter design with 64-bit width has been implemented on the basis of the Taiwan Semiconductor Manufacturing Company 90-nm CMOS process. The chip area is 1622 × 1657 μm², and the working frequency is 116 MHz. The experimental results show that the proposed design achieves more than 26.9 and 18.4% savings in delay and power consumption, respectively. The converter also saves at least 39% in AD² (area × delay²).     

Synthesis,structure, and magnetic properties of n=2 Ruddlesden–Popper manganates

Low-field magnetoresistance is observed both below and above the three-dimensional Curie temperature of the intrinsically layered Ruddlesden–Popper manganates Sr_2−xLa_1+xMn₂O₇. Significant differences from the more extensively investigated n=∞ three-dimensional perovskites include a much more rapid suppression of ferromagnetic ordering as the size of the lanthanide cation is reduced and more complex magnetic and structural behaviour in the manganese oxidation state range which produces charge ordering in the n=1 and n=∞ homologues. Control of chemical imperfections, such as intergrowth and phase co-existence, is required to allow understanding of the physical properties of this system.     

Impact of annealing temperature on structural,optical, and Mössbauer properties of nanocrystalline NiFe2O4

In this paper, we have investigated the effect of annealing temperature on the structural, optical, and Mössbauer properties of nanocrystalline (NC) nickel ferrites (NFOs) synthesized by the sol–gel auto-combustion method. The NFOs were characterized by X-Ray diffraction (XRD), Raman spectroscopy, Diffusion reflectance spectroscopy (DRS), and Mössbauer spectroscopy techniques. The XRD results show that the average crystallite size increases from 27.5 to 54.3 nm when increasing the annealing temperature from 200 to 1000 °C. The Ultraviolet–Visible Diffuse Reflectance Spectroscopy (UV-DRS) measurement is used to find the optical band gap observed between 1.92 and 1.75 eV for NFOs annealed at 200 and 1000 °C, respectively. The Mössbauer study confirmed that the structure transforms from mixed spinel to inverse spinel structure when moving to higher annealing temperature.

     

Subsolidus Phase Relations in the Systems M2 +O–M2+O–V2O5(M+ = Li, Na, K, Rb, Cs; M2+ = Mg, Ca)

Subsolidus phase relations in the M₂O(M₂CO₃)–MgO–V₂O₅ and M₂O(M₂CO₃)–CaO–V₂O₅ (M = Li, Na, K, Rb, Cs) systems are studied. Twenty mixed vanadates are obtained, of which Rb₂CaV₂O₇, Cs₂CaV₂O₇, LiMg₄(VO₄)₃, RbCaVO₄, and CsCaVO₄ are identified for the first time. Structural data are summarized for all of the mixed vanadates: the space group and lattice parameters are indicated for 14 compounds (for 6 compounds, such data are obtained for the first time), and I and d data are presented for 8 compounds. Partial series of Ca₃(VO₄)₂-based solid solutions with the general formula Ca_{3 – x} M_2x (VO₄)₂ (M = Na, K, Rb, Cs) are identified in the range 0 < x 0.14. Six phase diagrams (M⁺ = Li, Rb, Cs; M²⁺ = Mg, Ca) are investigated and are compared with the phase diagrams of the other ternary systems in question. The key features of the ternary phase diagrams and, hence, the reactivity of the constituent oxides are shown to vary systematically in going from Li₂O to Cs₂O and from MgO to SrO, which is interpreted in terms of the variation in the ionic radius of the alkali and alkaline-earth metals.     

Fluctuation-Induced Conductivity of Cu0.5Tl0.5Ba2Ca2Cu2M1O10−δ (M = Si, Sn, Ge) Superconductors

Fluctuation-induced conductivity of Cu_0.5Tl_0.5Ba₂Ca₂Cu₂M₁O_10−δ (M = Si, Sn, Ge) superconductors has been studied from the resistivity vs. temperature data. The logarithmic plots of excess conductivity (Δσ) vs. reduced temperatures [ε=(T−T _c ^mf )/T _c ^mf ] show two crossover temperatures with three exponents. A distinct crossover from two-dimensional to three-dimensional conductivity in accordance with the 2D, 3D Aslamazov–Larkin equations has been observed in all the samples. Another crossover from 2D to 0D fluctuations has also been witnessed. FIC data analysis has been found to be quite useful in explaining the superconducting properties of the samples. Si and Sn doped samples have shown almost similar characteristics, while in Ge doped sample diverse behavior is observed.     

Crystal structure and anisotropy of iodine-intercalated Bi2Sr2Ca n−1Cu n O x

The electronic state and structural configuration of the intercalated iodine species in stage-1, I-Bi₂Sr₂Ca _n?1Cu _n O _x (n = l, 2), have been studied through polarization-resolved Raman and¹²⁹I Mössbauer spectroscopy. The polarization dependence of the Raman spectra and the Mössbauer measurement confirmed the dominant species to be triiodide ions, I ₃ ^? , with alignment of these linear molecules either along thea- orb-axis in the host crystals. Transport measurements such as thermoelectric power and Hall coefficient clearly indicated that hole carriers are doped into the CuO₂ planes upon intercalation, by whichT _c of the host superconductor is changed. Furthermore, based on resistivity measurements in a magnetic field, we suggest that the iodine intercalation leads to a decrease of the anisotropy both in normal and superconducting states, suppressing the extremely two-dimensional character of the Bi₂Sr₂Ca _n?1Cu _n O _x systems.     

Properties of n × n square arrays of proximity effect bridges

We have studied the I-V characteristics, the dc resistance at the origin R(T), and the critical current I _c (T) of arrays consisting of n × n (n = 10, 20, 30, and 40) In squares separated by Au/In regions. The superconducting squares have side d _s (In) from 7.5 to 15 m and d _N (Au/In) from 2.5 to 11 m. These devices show two transition temperatures in their R(T) curve; one at T _cG near T _c (In) and another one at T _c ^* above T _c (Au/In). The I-V curves for each temperature region resemble recent published results on NbN granular films. These arrays follow a formalism proposed by Wolf, Gubser, and Imry to describe the transition to a resistanceless state at T _c ^*. The measured values of I _c (T) are larger than expected from n noninteracting Bardeen-Johnson junctions in parallel, although the exponential behavior in temperature is followed. They are compatible with the idea of bands in the quasiparticle spectrum in the Au/In regions. Deviations in I _c (T) from an exponential behavior in T near T _c ^* have been analyzed by applying to SNS arrays ideas developed for phase transitions in SIS arrays. Evidence that at T _c ^* we may be observing a phase transition at T _cJ due to the Josephson coupling between In squares exists but it needs the development of theoretical work to be put on more solid grounds.Supported by the Swiss National Science Foundation.     

Thermal expansion behaviour of M′Ti2P3O12 (M′=Li,Na, K,Cs) and M″Ti4P6O24 (M″=Mg,Ca, Sr,Ba) compounds

The [NZP] family has been attracting considerable attention because of its potential in thermal shock-resistant applications. The compounds MTi₂P₃O₁₂ (M=Li, Na, K, Cs) and MTi₄P₆O₂₄ (M=Mg, Ca, Sr, Ba) belong to this new family of low-expansion materials. The results of a systematic study undertaken to investigate the thermal expansion behaviour of these materials are reported. A correlation between the ionic size and lattice expansion was also attempted, and compounds possessing lowest bulk thermal and low anisotropy were identified.     

Effect of (n, γ) and (n, α) reactions of framework atoms on the (n, γ) recoils in Ba and Cs cations in high-silica zeolites

The effects of (n, γ) and (n, α) reactions of framework atoms on the fate of (n, γ) recoil species ¹³¹Ba²⁺ and ¹³⁴Cs⁺ from Ba²⁺ and Cs⁺ loaded in high-silica aluminosilicate and borosilicate zeolites (boron-zeotypes) have been studied. Studies were made of the recoil from “open to locked-in” and “locked-in to open” sites. In open to locked-in recoil, target ions were eluted with efficiencies of 90% where only (n, γ) processes were in operation, but in the presence of (n, γ) and (n, α) reactions, the efficiency fell to 80%. For locked-in to open site recoil, the corresponding efficiencies were in the ranges 50–60% and 40–50%. The effect of calcination temperature on the exchange of cations present was also ascertained. The high-silica zeolites used were synthesized according to published methods and were characterized by XRD, i.r., SEM, and t.g.-d.t.g./d.s.c. techniques, and all were found to be crystalline. In boron-zeotype materials, the magnitude of (n, α) damage was increased by the use of ¹⁰B isotope.     

Net Holes and Superconductivity in the Members with n ≥ 3 of Homologous Series, Tl- and Hg-m2(n-l)n

All the Tl- and Hg-based superconducting cuprates can be classified as members of Tl/Hg-m2(n-l)n homologous series, with m being 1 or 2, and n increasing even up to 7. In the phases with n 3, holes may be inhomogeneously distributed between outer (Coordination Number = 5) and inner (CN = 4) CuO₂ planes. In each series T _c increases as n increases from 2 to 3, and then either saturates or slowly decreases with n > 3, proposing that the CuO₂ planes predominantly controlling the value of T _c are different in the n 3 phases from those in the structures with n = 1 (CN = 6) or 2 (CN = 5). Estimation of the distribution of holes between the inequivalent CuO₂ planes utilizing existing crystallographic data and a bond-valence-sum calculation method, results in a somewhat surprising conclusion that the holes are confined in the innermost CuO₂ planes. On the other hand, the result agrees with the empirical believe that the flatter the CuO₂ planes the higher the T _c..      

Influence of Ti on MC Carbide in M2 Steel

Influence of Ti on MC carbide of M2 high speed Steel was investigated by experimental observation, thermodynamic calculation and crystallographic calculation. With addition of Ti into M2 steel, large quantities of dispersed TiC particles formed in the steel melt at higher temperature than that of the formation of MC carbide. TiC can act as heterogeneous nuclei for the crystallization of MC carbide particles, and therefore promote the formation of blocky MC carbide.     

Synthesis of cubic boron nitride using Mg and pure or M′-doped Li3N,Ca3N2 and Mg3N2 with M′=Al,B, Si,Ti

The growth pressure-temperature region of cubic boron nitride (cBN) in the systems Mg-BN and MxNy-BN (MxNy=Li₃N, Ca₃N₂, Mg₃N₂) has been redetermined using well-crystallized hexagonal BN (hBN) with low oxygen content (0.2%) as the starting material. The data on the MxNy-BN systems are compatible with the existence of two growth regions: a high-temperature region where cBN grows from a liquid phase, and a low-temperature region where cBN forms from solid-solid reactions. Previous data are discussed according to this model and possible solid-state reactions are proposed on the basis of thermodynamic considerations. The results for the Mg-BN system confirm the effect of the O₂ content of the starting BN on the cBN growth region. The systems (MxNy + M)-BN (M=Al, B, Si, Ti) have been shown to produce cBN crystals of increased size and improved morphology (more compact and perfect) compared to those obtained with the MxNy-BN systems. Their colour is dark or black and their size reaches 0.6 mm. The effect of the relative proportions of M and MxNy on the growth region and yield has been determined and is discussed on the basis of the chemical reactions likely to occur.     

Self-doping Effects on the Superconducting Properties of Cu0.5Tl0.25M0.25Ba2Ca2Cu3O10−δ (M = Bi, Hg, Nb, Pd, Li, Na, K)

The effect of self-doping and substitution of elements of higher and lower electronegativity, such as Bi, Hg, Nb, Pd, Li, Na, K, on the superconducting properties of Cu_0.5Tl_0.5−x M _x Ba₂Ca₂Cu₃O_10−δ with x=0.25 is investigated. These experiments demonstrated that the elements of lower electronegativity such as Li, Na, and K can easily liberate their outer most s-electron that could be supplied to the conducting CuO₂ planes of Cu_0.5Tl_0.5−x M _x Ba₂Ca₂Cu₃O_10−δ superconductor, and as a result, we get enhanced superconducting properties. However, highly electro-negative elements hinder the transfer of carriers from charge reservoir layer to the conducting CuO₂ planes and promote inferior superconducting properties. In the present studies, we have investigated the effect of post-annealing in nitrogen and oxygen atmospheres for optimizing the carriers in conducting CuO₂ planes of Cu_0.5Tl_0.5−x M _x Ba₂Ca₂Cu₃O_10−δ (M=Bi,Hg,Nb,Pd,Li,Na,K) superconductor. These studies are important since the density of carriers in the conducting CuO₂ planes determines the Fermi-vector k _F and Fermi velocity v _F of the carriers, which ultimately brings about the final superconducting state of the system.      

Determination of the Alfvén Oscillation Location in the TUMAN-3M Tokamak Plasma

The Alfvén oscillations have been studied in ohmically heated deuterium discharges with LH-transition in the TUMAN-3M tokamak in order to clarify their location in a plasma column. The Alfvén oscillation location was determined by comparison of the oscillation frequency measured with magnetic probes and that calculated from local density assuming the typical dispersion relation for Alfvén waves f = (2π)^?1k_||v _A , where v _A is the Alfvén velocity and k_|| is the the parallel wave number in the direction of the magnetic field. It was found that they are localized in central part of plasma column inside r/a < 0.5 region. Candidate sets of mode numbers have been determined.     

Synthesis and Properties of La2(Mo1 – x M x )2O9 (M = Nb, Ta) Ionic Conductors

La₂(Mo_{1 – x} M _x )₂O₉ (M = Nb, Ta; 0 < x 0.2) solid solutions were prepared, and their physicochemical and electrical properties were studied. Second harmonic generation measurements indicate that the solid solutions have a noncentrosymmetric structure and undergo a structural phase transition accompanied by a sharp increase in ionic conductivity, similar to that of La₂Mo₂O₉. The transition temperature is found to decrease with increasing Nb or Ta content. The introduction of 5 wt % Nb increases the 800°C conductivity of the material.     

(Ba,Mg,Sr)O·nAl2O3:M(n=4.6,M=Ce,Tb)的合成及发光性质研究

采用高温固相反应合成(Ba,Mg,Sr)O·nAl2O3M(n=4.6,M=Ce,Tb)发光材料.经X射线衍射分析,属六方晶系,与JSPDS标准卡完全一致.用同步辐射实验室真空紫外光谱站设备进行了光谱分析,在(Ba,Mg,Sr)O·nAl2O3Ce(n=4.6)的激发光谱中,产生160nm和260nm的激发峰,分别由基质和铈离子的吸收引起的.在(Ba,Mg,Sr)O·nAl2O3Tb(n=4.6)的激发光谱中,产生160、190和234nm的激发峰,其中160nm和234nm的激发峰是宽带峰,分别是由基质吸收和铽离子的4f-5d吸收引起的;190nm峰是铽离子的特征吸收引起的.由于铽离子的特征吸收和基质吸收产生较大的交迭,因此基质对铽离子具有能量传递.     

Infrared spectra of bismuth family of superconductors Bi2Sr2Can−1CunO4+2n+y

FTIR spectra of bismuth family of superconductors are studied. Polycrystalline samples of bismuth superconductors are prepared choosing an off-stoichiometric composition for phase stabilisation and reproducibility. Vibrational modes are strongly affected by the holes introduced into the CuO planes. Mid IR spectra of the Bismuth system was recorded using Bruker IFS 66v and the high frequency oxygen vibrations of the system is discussed based on the factor group analysis for both symmorphic and non-symmorphic space groups I4/mmm, F_mmm and A_maa of different structures based on the modulated superstructure.