Substitution Of Sr For Ca Research Articles

Phonons in Ca2-xSrxCuO3 (x=0, 0.2 and 0.4): Raman and infrared spectroscopy, and lattice dynamics calculation

The polarized Raman spectra of Ca2CuO3, Ca1.8Sr0.2CuO3 and Ca1.6Sr0.4CuO3 single crystals and the IR transmission spectra of Ca2CuO3 and Ca1.6Sr0.4CuO3 have been measured. The frequencies of all Gamma -point phonons of Ca2CuO3 have been determined on the basis of assignment of the one-phonon Raman (Ag) and IR lines to definite normal modes and calculations of the lattice dynamics. The line assignment is consistent with earlier results for Ca1.8Sr0.2CuO3 as well as with the line shifts upon substitution of Sr for Ca. The intensive broad lines in the (bb)-polarized Raman spectra of both Sr-free and Sr-substituted samples (in addition to the two Ag lines already assigned) have been attributed to resonantly enhanced two-phonon scattering involving modes related to motions of Cu and/or O(2) atoms. A coincidence has been found between most of the line frequencies and half-widths in the (bb)-polarized Raman spectra and some of the maxima in the two-phonon density of states as obtained from lattice dynamics calculations.

Substitution of calcium for strontium in the SrCuO 2 structure : The solid solution Sr 1−xCa xCuO 2

The study of the substitution of calcium for strontium in SrCuO 2 is of capital importance for the understanding of superconductivity in layered cuprates. We describe here a large solid solution Sr 1−xCa xCuO 2 for 0≤x≤0.7, which is single phase to x=0.6. The parameters of the orthorhombic cell (a=3.576 to 3.401Å, b=16.335 to 16.033Å, c=3.895 to 3.857Å) are strongly affected by the Ca-Sr substitution. The HREM study of this phase shows lamellar character and the existence of disoriented domains formed through coherent boundaries.

Substitution effects of Ca for Sr in Pb-based layered copper oxides, (Pb (1+x)/2Cu(1−x)/2Sr2(Y 1−xCa x)Cu 2O 7+δ

(Pb/Cu)-1212 cuprates in which Sr sites are partially substituted by Ca, (Pb (1+x)/2Cu (1−x)/2)(Sr 1−yCa y) 2(Y 1−xCa x)Cu 2O 7+δ, are synthesized and characterized. While single-phase samples are obtained only in the range of 0≦ ×≦ 0.35 for y=0, partial substitution of Ca for Sr stabilizes the (Pb/Cu)-1212 compounds which contain Ca in the Y sites with x>0.35. For x = 0.5, nearly single-phase samples are obtained for y = 0.05 and 0.1. Superconductivity transition temperature as high as 80 K is measured for the sample with x = 0.5 and y = 0.1.

Synthesis, structure, and properties of a new T* structure copper-oxychloride of MLnCuO 3Cl ( M = Ca, Sr and Ln =Nd, Sm, Eu, Gd)

The syntheses of a new copper oxychloride with the general formula of MLnCuO 3Cl ( M = Ca, Sr and Ln =Nd, Sm, Eu, Gd) are reported. These compounds are shown to have the T* structure where the copper atoms are coordinated by a square pyramidal geometry with a chloride ion in the apical position. This structure is supported by the X-ray powder patterns and lattice parameters of the new oxychlorides. The substitution of Sr for Ca in Ca 1− x Sr xLnCuO 3Cl with Ln =Nd, Sm was performed, and the substitution is discussed in terms of the size requirements of the T* structure. Alternating current impedance measurements for CaSmCuO 3Cl and Ca 0.72Sr 0.28NdCuO 3Cl from 100 to 600°C are presented; when annealed in oxygen, CaSmCuO 3Cl showed semiconducting behavior with an activation energy of 0.12 eV. When these two samples were annealed in argon, ionic conductivity from oxygen vacancies was observed. Magnetic susceptibility measurements for CaSmCuO 3Cl and Ca 0.72Sr 0.28NdCuO 3Cl from 2 to 400 K show similarity to the magnetic results for Sm 2CuO 4 and Nd 2CuO 4, respectively. The resistivity and magnetic measurements indicate that the properties of these compounds are similar to those of their parent copper oxides, Ln 2CuO 4, and not to their parent oxychlorides, M 2CuO 2Cl 2 ( M =Ca, Sr).

Specific heat of the ceramic superconductor Bi 2Sr 2CuO 6 from 0.4 to 20 K

Specific heat, C p, data in the range 0.4 to 20 K for three polycrystalline specimens of Bi 2Sr 2CuO 6 (2:2:0:1 phase, T c ≈ 8 K) are reported and compared with similar measurements made on Bi 2Sr 1.33Ca 0.67CuO 6 ( T c ≈ 20 K) which is also of the 2:2:0:1 phase, but with partial substitution of Ca for Sr. No anomaly in C p at T c is observed in any of the specimens. Below ≈ 2 K, an upturn in C p/ T is observed in all specimens. The coefficient of the linear term in C p, γ 0, is non-zero in all specimens, and is in the range 3 to 10 mJ / (mol K 2). A limiting value for the Debye temperature, θ 0 D, of 220±8 K is obtained.

Characterization of Ca-doped Bi2 +xSr2 –xCuOz

The ‘R’ phase in the Bi–Sr–Cu–O system, which is actually a solid solution of formula Bi2 +xSr2 –xCuOz, forms an extensive solid solution by partial substitution of Ca for Sr. This has formula, Bi2 +xSr2 –x–yCayCuOz, with 0 < y≲ 0.45 and 0.15 ≲x≲ 0.40 at 800 °C. Lattice parameters of the solid solutions are given; pseudotetragonal symmetry is retained throughout but the incommensurate superstructure becomes less marked with increasing contents of both Ca and Bi. The excess oxygen content of the solid solutions, determined by iodometry, is unchanged by replacement of Sr by Ca, but for a given composition, can be varied by heating at 750 °C in different atmospheres.

Na-Ca exchange and tension development in guinea-pig aorta.

1. In guinea-pig aorta, removal of external K produced contraction which reached maximum (about 1 g) after about 3 h. Excess K (65.4 mM) produced contraction (about 1 g) at a faster rate of increase than was observed in K-free solution. 2. Verapamil, nifedipine and diltiazem (10−7–10−5 M) and the raising of [Mg]0 (8–32 mM) had no effect on the contraction induced by K-free solution, although they relaxed the contraction induced by high-K solution. Verapamil (10−6 M) also relaxed the contractions induced by other depolarizing agents, TEA (40 mM) and Ba (15 mM). 3. Following incubation in Ca- and K-free solution for 3 h, the readdition of Ca produced contraction at a faster rate of increase than in a K-free normal Ca containing solution. Verapamil (10−6 M) and Mg (16 mM) had exhibited little effect on these Ca-induced contractions. The Ca-induced contractions in high-K solution, on the other hand, were significantly suppressed in the presence of verapamil (10−6 M) and Mg (16 mM). 4. After incubation of the muscle in K-free solution for 1 h, Na depletion caused a more rapid and greater contraction than was seen in untreated muscle. This tension development was also unaffected by verapamil (10−6 M) and Mg (16 mM). 5. Substitution of Sr for Ca produced contraction in K-free or high-K solution. Sr-induced contraction in K-free solution was scarcely affected by verapamil (10−6 M), while Sr-induced contraction in high-K solution was inhibited. 6. 45Ca entry into smooth muscle during the contractions was measured by the modified “La method”. The 45Ca uptake was markedly increased both in K-free and high-K solutions. Verapamil (10−6 M) and Mg (16 mM) had no significant effect on the 45Ca uptake increase clicited by K-free solution, whereas they significantly inhibited the 45Ca uptake increased by high-K solution. 7. It is suggested that the contraction induced by K-free solution is initiated by a mechanism different from that underlying the depolarization-induced contraction, and that it is produced by an influx of Ca through Na-Ca exchange mechanism. The data also suggest that the Ca binding site on the Na-Ca exchange carrier is occupied by Sr ions but not by Mg ions. It is likely that such a carrier system is not influenced by organic “Ca antagonists”.

Onset of Mechanical Activation of Mammalian Heart Muscle in Calcium- and Strontium-Containing Solutions

The time course of the relationship between force, shortening velocity, and length during shortening was examined in mammalian heart muscle in calcium (Ca)-containing solutions and solutions with strontium (Sr) substituted for Ca by imposing load clamps of various amplitudes at various times during external shortening. The onset of this force-velocity-length relationship was measured by abruptly unloading the muscle at different times to nearly zero external load--by zero load clamping the muscle--under conditions of optimal damping; the subsequent unloaded active muscle shortening velocity was then analyzed with respect to time and length. In Ca- containing solution, the unloaded velocity in the length range around 90% of L max rose within 16% of the time required to reach peak isometric force to a maximum level appropriate to a given contractile state. Subsequently, the force-velocity-length relationship was independent of time at any load over a well-determined portion of external shortening. In Sr-containing solution, unloaded active velocity rose much slower to reach a steady state after 30-35% of the time to peak force, and the time independence of the force-velocity-length relationship was delayed until after this time. In Na-free Sr-containing solution, maximum unloaded shortening velocity and the time-independent portion of the force-velocity-length relationship were achieved again within 20% of the time to peak force. The effects of substitution of Sr for Ca thus resemble those of caffeine on mammalian heart muscle. These findings suggest a close relationship between the time course of the force-velocity-length relationship and the degree of activation.

Abstract of alkaline phosphatases in fixed plant cells : M. H. Ross and J. O. Ely ( Experimental Cell Research, 2, 339 (1951))

Neutron diffraction, 23Na and 31P NMR, and FTIR spectroscopy have been used to investigate the structural effects of substituting CaO with SrO in a 40P2O5·(16-x)CaO·20Na2O·24MgO·xSrO glass, where x is 0, 4, 8, 12 and 16 mol%. The 31P solid-state NMR results showed similar amounts of Q1 and Q2 units for all of the multicomponent glasses investigated, showing that the substitution of Sr for Ca has no effect on the phosphate network. The M-O coordinations (M = Mg, Ca, Sr, Na) were determined for binary alkali and alkaline earth metaphosphates using neutron diffraction and broad asymmetric distributions of bond length were observed, with coordination numbers that were smaller and bond lengths that were shorter than in corresponding crystals. The Mg-O coordination number was determined most reliably as 5.0(2). The neutron diffraction results for the multicomponent glasses are consistent with a structural model in which the coordination of Ca, Sr and Na is the same as in the binary metaphosphate glass, whereas there is a definite shift of Mg-O bonds to longer distance. There is also a small but consistent increase in the Mg-O coordination number and the width of the distribution of Mg-O bond lengths, as Sr substitutes for Ca. Functional properties, including glass transition temperatures, thermal processing windows, dissolution rates and ion release profiles were also investigated. Dissolution studies showed a decrease in dissolution rate with initial addition of 4 mol% SrO, but further addition of SrO showed little change. The ion release profiles followed a similar trend to the observed dissolution rates. The limited changes in structure and dissolution rates observed for substitution of Ca with Sr in these fixed 40 mol% P2O5 glasses were attributed to their similarities in terms of ionic size and charge.Phosphate based glasses are extremely well suited for the delivery of therapeutic ions in biomedical applications, and in particular strontium plays an important role in the treatment of osteoporosis. We show firstly that the substitution of strontium for calcium in bioactive phosphate glasses can be used to control the dissolution rate of the glass, and hence the rate at which therapeutic ions are delivered. We then go on to examine in detail the influence of Sr/Ca substitution on the atomic sites in the glass, using advanced structural probes, especially neutron diffraction. The environments of most cations in the glass are unaffected by the substitution, with the exception of Mg, which becomes more disordered.