Function Of Ca Concentration Research Articles

Electromechanical properties of sol-gel derived Ca-modified PbTiO3 films

Piezoelectric coefficients and electric field-induced strains are investigated in Ca-modified PbTiO3 (PCT) films deposited by sol-gel technique. The microstructural evolution and related electromechanical properties are studied as a function of Ca content and porosity of the films. The porosity is tailored by changing the heating rate during the final crystallization anneal. It is found that piezoelectric properties of porous films heated at slow rates are superior to those of dense films crystallized using higher heating rates. This is explained as a result of the constraining effect of the substrate, which apparently reduces the piezoelectric and strain responses in dense films. Electromechanical properties are also improved with Ca addition due to the decrease of tetragonality and ease of 90° domain rotation. Charge piezoelectric coefficients in porous films are close to those of PCT ceramics of the same composition. These results, combined with the low dielectric constant, make PCT films an attractive material for microelectromechanical applications.

Partitioning of trace elements between clinopyroxene and garnet: data from mantle eclogites

Concentrations of REE, Ba, Sr, Y and Zr have been measured by ion microprobe (SIMS) for garnet and clinopyroxene in a suite of eclogite xenoliths from the Roberts Victor kimberlite pipe in South Africa. The xenoliths have a restricted set of temperatures of formation estimated at 1100 ± 100°C at 5 GPa, but span a wide range of compositions; garnet Ca/(R 2+) ratios range from 0.08 to 0.50, whilst the associated clinopyroxenes also show increasing jadeite solid solution as their Ca/(R 2+) ratios increase. The cpx/grt partition coefficients ( D i ) for REE, Sr and Y decrease progressively as Ca/(R 2+ in the minerals increase; in the LREE this change amounts to approximately three orders of magnitude. Evidence for such large changes in partition coefficients as a function of Ca content is also seen in other data for mantle eclogites from South Africa and Siberia. Cpx and grit with low Ca/(R 2+ ratios have ( D i ) for HREE which are similar to those implied by mineral/liquid data for basic-ultrabasic melts. Poor correlations of Ba, La and Lu partition coefficients with cpx-grt Ca contents in the present dataset, are the result of late-stage partial alteration and relatively large errors of measurement associated with low concentrations. Zr partition coefficients show only a weak correlation with mineral Ca/(R 2+). Strong correlations are demonstrated between cpx/grt D i (calculated on a ppm or molar basis) and molar cpx/grt D Ca for most REE, Sr and Y. These may be expressed in the form: In D i ∗ cpx grt =A ln D Ca ∗ cpx grt + B B (Eq. (1)), where A and B are empirical constants for each element and vary with ionic radius in the REE. The partitioning of a given trace element progressively favours garnet rather than pyroxene as increasing amounts of Ca are more strongly partitioned into garnet than clinopyroxene; and the magnitude of this effect increases with ionic radius in the REE. The empirical linear calibrations (Eq. (1)) given for REE, Y and Sr allow calculation of the ( D i ) of a cpx-grt pair from their Ca contents (for 1100 ± 100°C, ∼ 5 GPa). Using the well-documented R 3+ Al [4] Ca −1Si −1 (YAG-type) substitution relationship for REE and Y in garnets as the basis of an exchange reaction, it is suggested that the A term in empirical Eq. (1) may be related to variations in activity coefficients as the major element (Ca) composition changes, whilst term B is largely dependent on the standard state free energy.

Superconductivity of (Hg 0.7Tl 0.3) 2 Ba 2Y 1− xCa xCu 2O 8−δ (0 ≦ x ≦ 0.8) with a wide range of doping state

(Hg, Tl)-based cuprates with the nomial compositions of (Hg 0.7Tl 0.3) 2Ba 2Y 1− x Ca x Cu 2O 8−δ (0 ≦ x ≦ 1.0, every 0.1 step) were prepared under high pressure, and nearly single phases were obtained for the samples with 0 ≦ x ≦ 0.8. We systematically investigated their unit cell dimensions, DC susceptibility, electrical resistivity, oxygen content and copper valence as a function of Ca content, x. For the samples with x=0–0.4, T c, which was determined by DC susceptibility, increased from 12 K to 84 K with increasing x, while the samples with x = 0.5 – 0.8 exhibited a T c decrease from 84 K to 40 K. This result indicates that the doping state of the samples can be extensively varied from underdoped to overdoped states by the Ca substitution. This variation in the doping states was also supported by the systematic change in the temperature dependence of the electrical resistivity. Oxygen analysis revealed that the copper valence gradually increased from 2.12 to 2.26 with increasing x from 0 to 0.8. The copper valence with the maximum T c of 84 K in these samples was determined to be 2.18–2.19, which is comparable to the value for the optimum T c in other high- T c cuprates.

Hydrogen storage properties of Ml1−xCaxNi5 pseudobinary intermetallic compounds

The hydrogen storage properties of the pseudobinary intermetallic compounds Ml1−xCaxNi5 (where Ml is La-rich mischmetal and x varies from 0 to 0.9) were investigated over the temperature range of 25–80°C, It was found in experiment that with increasing x in Ml1−xCaxNi5 the incubation time for its first hydrogenation shortened, the first hydrogen absorption rate accelerated, the hysteresis lowered, and the dissociation pressure of the hydrides (25°C) increased when x < 0.3 but decreased in the range of x = 0.3 to 0.9. Considering the effect of the geometrical and electric factors, we deduced an equation for the dissociation pressure as a function of Ca content x. The equation agrees well with the test results.Owing to the lower cost and favourable properties of Ml0.8Ca0.2Ni5, a metal hydride container of 30 N m3 hydrogen capacity was designed and built to supply hydrogen for the hydrogen-gasoline hybrid fuel for an automobile engine.

Effect of Ca-substitution for yttrium on positron lifetime and superconductivity of YBa 2Cu 4O 8 ceramics

The results of positron lifetime measurements as a function of Ca-substitution for Y 1 − x Ca x Ba 2Cu 4O 8 ( x = 0−0.15) materials are presented. A significant dependence of the positron parameters on the Ca content was observed and the positron annihilation characteristic identified. The local electron density n e and defect concentration C v are evaluated as a function of Ca content. The correlation between lifetime parameters and superconductivity is also discussed.

Superconducting and electrical properties of Ca-substituted YBa 2Cu 3O 6

Superconducting properties of sintered Y 1− x Ca x Ba 2 Cu 3 O 6 (0 < x ≦ 0.31)have been investigated. Measurements of resistivity, Hall effect and X-ray diffraction as a function of Ca content x were carried out. It was found that Y 1- x Ca xBa 2Cu 3O 6 becomes superconducting above x ≦ ∼ 0.2, as had been reported previously, and T c shows a maximum at x ∼ 0.26 and declines at larger x. By increasing the Ca content, the carrier number in the CuO 2 plane increased suddenly in the range x ∼ 0.2, where samples were superconducting. A part of the carrier introduced by Ca substitution, however, was localized at Cu sites forming CuO chains. About 40% of the doped carrierr was conductive in x < ∼ 0.2 and ∼ 80% was conductive in x ≧ ∼ 0.2 at room temperature and these results agree fairly well with the analysis for the results of the iodometric titration measurement. Finally, we pointed out that slight oxidation for these samples brought about the release of carrier localization at low temperatures and a remarkable rise of T c, indicating the crucial importance of the CuO chain or orthorhombicity for high T c in YBa 2Cu 3O 6+ z .

Enhancement of the irreversibility line in Y 1− xCa xSrBaCu 2.7Co 0.3O 6+ z

The imaginary part of the AC susceptibility of Y 1− x Ca x SrBaCu 2.7Co 0.3O 6+ z ( x = 0,0.1 and 0.2) is measured as a function of applied static field in the presence of an AC field of 0.1 Oe at a frequency of 1500 Hz. The irreversibility line established from such measurements shows a strong enhancement as a function of Ca concentration. Possible causes are discussed.

Internal magnetic fields at μ+ sites and the magnetic phase diagram of Bi2Sr2Y1−xCaxCu2Oy system studied by the μSR method

Abstract The magnetic properties of the Bi 2 Sr 2 Y 1− x Ca x Cu 2 O y system have been studied by positive muon spin rotation or relaxation methods. The magnetic phase diagram has been obtained as a function of Ca content x and temperature T . A long-range magnetic ordering (probably antiferromagnetic) has been observed in Bi 2 Sr 2 Y 1− x Ca x Cu 2 O y with Ca content x ranging from 0.0 to about 0.3. The Neel temperature T N decreases with increasing Ca content; T N is above 300 K for x =0.0, 200–250 K for x =0.2 and drops abruptly to 10–20 K for x =0.3. Superconductivity sets in around the same Ca content ( x ≈0.5) where the magnetic ordering disappears completely. The magnetic phase diagram of the Bi 2 Sr 2 Y 1− x Ca x Cu 2 O y system is thus similar to that of YBa 2 Cu 3 O x or La 2− x A x CuO 4−δ (A=Sr or Ba) and suggests a common origin of the superconductivity in all these oxide superconductors. The temperature dependence of the internal magnetic field at μ + in Bi 2 Sr 2 YCu 2 O y is also discussed.

Electrical Properties and Microstructure of Ca Modified PbTiO3 Ceramics

The (Pb1-x, Cax)TiO3, (x=0.12 to 0.5) ceramics were sintered, and the relationship between dielectric, piezoelectric properties and microstructure were classified as a function of Ca content. There existed no phase boundaries over the range of Ca content of 0.12 to 0.5 mol. However, the ratio of kt and kp was drastically changed as a function of Ca content. These changes were related with the appearance of 90° domains and superlattice.

Xanes analysis on pyroxenes with different ca concentration in M2 site

X-ray Absorption Near-Edge Structure (XANES) analysis of the calcium K-edge of a series of natural pyroxenes is reported. The samples belong to the solid solution series diopside (CaMgSi2O6) — jadeite (NaAlSi2O6). In diopside, the M2 site is occupied by Ca only, but along the join Na substitutes Ca in this position. From XANES analysis of different samples we found a distortion of the polyhedron around the M2 site varying as a function of Ca content. This is probably due to compression of the site in a selected direction with an unchanged average distance, so that the coordination around the Ca atom changes from the 4-2-2 configuration typical of the diopside structure to the 6-2 configuration typical of Na in the jadeite structure. Intermediate pyroxenes exhibit both configurations, and acquire therefrom the structural order as already detected by X-ray diffraction techniques.

Calcium and cardiac relaxing substance: significance for excitation and inotropy

The action of soluble cardiac relaxing substance (RS) on the Mg-stimulated actomyosin ATPase of cardiac myofibrils was studied as a function of Ca concentration. Though 2.5 x 10–6 m soluble Ca inhibits skeletal relaxing substance, between 8 x 10–6 and 1 x 10–3 m ionized Ca were without effect on cardiac relaxing substance. It is concluded that the mechanism by which cardiac RS influences ATP hydrolysis involves more than simple chelation of ionized Ca. If these experiments describe the in vivo behavior of cardiac RS it seems likely that the particulate relaxing factor functions in excitation-contraction coupling and the soluble relaxing factor solely as a control of contractile strength.