Two examples of Cu-II/Ca-II-diphosphonate coordination polymers, [Cu-2(L)(H2O)(2)](n) 1 and {[Ca(L-H-2)](2)center dot 2H(2)O}(n) 2 (H4L =3D H2O3PCH2N(C4H8)NCH2PO3H2), L-H-2 =3D O3PCH2HN(C4H8)NHCH2PO3), N,N'-piperazinebis(methylenephosphonic acid)), have been hydrothermally synthesized and characterized by elemental analysis, FT-IR, PXRD, TGA and single-crystal X-ray diffractions. Compound 1 possesses a 2-D inorganic-organic alternate arrangement layer structure, in which ligand H4L shows a never reported multi-dentate coordination mode. Compound 2 possesses a 3-D open-framework structure with 1-D channel built from 44-atom rings. Results of fluorescent measurements indicate the maximum emission band centered at 435 nm of 1 should be due to the coordination effect with metal(II) ions, and the high energy emission peaks (383, 298 nm for 1 and 378, 300 nm for 2) could be derived from the intraligand pi*-> n transition station of H4L (382, 310 nm, lambda(ex) =3D 235 nm). Magnetism analysis of 1 indicated antiferromagnetic interactions being from the 1-D magnetic chain with the binuclear unit [Cu2O2].
We have investigated the static (omega = 0) and frequency-dependent nonlinear optical (NLO) properties of the M@C(N) endohedrals (M = Li, Ca, Sc, N = 60 and 70) using the SSH (Su-Schrieffer-Heeger) approximation and sum-over-state (SOS) approach. Also, we study the effects of displacement and alkali, alkaline earth and lanthanide metal atoms and type of cage on the hyperpolarisabilities of the M@C(N) endohedrals. The hyperpolarisability magnitudes and spectra are in agreement with experiment and the work of others using the SSH approximation. Our results indicate that the cage-type effect on the NLO spectra of M@C(N) endohedrals is dramatic. Also, atom type has little effect on the highest peak value. These relationships between the atom and cage type and hyperpolarisability values may be beneficial to experimentalists when designing new NLO materials with large NLO responses.
Several silicon alloys Mg 2Si and MSi 2 (M=Ca,Fe) in powder form have been tested as possible anodes in two electrode cells. These alloys react with lithium to form Li-Si alloys as detected by the X-ray diffraction. However, the initial uptake of lithium is poorer than expected, corresponding to 690, 250 and 100 mAh/g for the Mg, Ca and Fe systems, respectively. All the electrodes exhibit a drastic capacity fade upon cycling. X-ray diffraction analysis correlated to the galvanostatic tests indicating that there is a mechanical disintegration of the electrode due to the impressive volume changes upon cycling and the lack of a suitable matrix to absorb the mechanical stress. Finally, we have observed that the lithium diffusion coefficients, calculated by the potentiostatic method, are of the order of 10 -9 cm 2/s in the initial reduction step of all the systems which is not a limiting factor for using Mg 2Si and MSi 2 (M=Ca, Fe) alloys as possible negative electrodes for Li-ion cells
The influence of the nature of M(n)O(m) and treatment temperature of zirconia-based systems M(n)O(m)-ZrO(2) (M = Ca, Ba, Sm, Yb) of approximately equimolar composition on their phase composition and dispersity has been studied. The samples are shown to contain solid solutions based on cubic ZrO(2). Besides, CaZrO(3) perovskite is present in the CaO-ZrO(2) system, and a solid solution based on Sm(2)O(3) is present in the Sm(2)O(3)-ZrO(2) system. The particle sizes in the corresponding solid solutions vary from 25 to 150 Angstrom while in the perovskite phase they are in the 300-500 Angstrom range, with the treatment temperature increasing from 623 to 1273 K.
Hu, Junhua
Kato, Akihiko
Sadoh, Taizoh
Maeda, Yoshuhito
Galkin, K. N.
Turchin, T. V.
Tatsuoka, Hirokazu
Single phase M(2)Si (M = Mg, Ca, Sr) silicides were grown using Si substrates, by thermal treatment of the substrates in the vapors of the metallic sources, M, and the electronic structures and optical property of the silicides were investigated. The electronic band structures of the silicides were calculated using the first-principles total-energy calculation program in pseudopotential schemes with plane-wave basis functions. The calculated optical reflectance spectra were also deduced from the theoretical band structures, and roughly agreed with the experimental results except for the low reflectance intensity around 2 eV. This suggests that the energy band gap of the silicides roughly agree with the calculated values of 0.15, 0.31 and 0.35 eV for Mg(2)Si, Ca(2)Si and Sr(2)Si respectively, within the underestimation of the band gap by the density functional calculation. The optical property of the silicides is also discussed in relation to the morphological structures of the silicides.
The crystal structure of LaBa1−x MxCuFeO5+δ (M = Sr, Ca, Mg; 0 < x ≤ 0.5) solid solutions has been studied by x-ray diffraction and IR absorption spectroscopy, and their thermal stability, thermal expansion, and electrical conductivity have been determined in air between 290 and 1270 K. The structure of LaBa1−x SrxCuFeO5+δ has been shown to change from cubic to tetragonal at x ≃ 0.4−0.45, whereas the LaBa1−x MxCuFeO5+δ (M = Ca, Mg) solid solutions have a cubic structure up to x = 0.5. The composition dependences of structural parameters and physicochemical properties for LaBa1−x SrxCuFeO5+δ show anomalies at x = 0.25, which suggests ordering of the La3+, Ba2+, and Sr2+ cations in the structure of La(Ba,Sr)CuFeO5+δ, leading to the formation of a new chemical compound, LaBa3/4Sr1/4CuFeO5+δ.
Duan, C. J.
Otten, W. M.
Delsing, A. C. A.
Hintzen, H. T.
Mn2+-doped M2Si5N8 (M = Ca, Sr, Ba) phosphors have been prepared by a solid-state reaction method at high temperature and their photoluminescence properties were investigated. The Mn2+-activated M2Si5N8 phosphors exhibit narrow emission bands in the wavelength range of 500-700 nm with peak center at about 599, 606 and 567 nm for M = Ca, Sr, Ba, respectively, due to the T-4(1)((4)G) --> (6)A(1)(S-6) transition of Mn2+. The long-wavelength emission of Mn2+ ion in the host of M2Si5N8 is attributed to the effect of a strong crystal-field of Mn2+ in the nitrogen coordination environment. Also it is observed that there exists energy transfer between M2Si5N8 host lattice and activator (Mn2+). The potential applications of these phosphors have been pointed out. (C) 2008 Elsevier Inc. All rights reserved.