Apatite thin films of calcium phosphate were successfully prepared by rf-magnetron sputtering, followed by postannealing, from calcium phosphate glass targets with C d P atomic ratios of 0.6 to 0.75, much lower than the stoichiometric value of 1.67 for hydroxyapatite. Using targets with low C d P ratios of 0.65 to 0.25, tricalcium and pyrocalcium phosphate thin films were obtained. The formation of these calcium phosphates phases was attributed to the phosphorus oxide losses during sputtering. H,O vapor was effective in the formation of the apatite phase at high temperatures; apatite was the exclusive phase in the ambient H,O, even when the target with the low Ca/P ratio of 0.4 was used. Based on phase stability at high temperatures, it was assumed that various kinds of apatites, such as stoichiometric and nonstoichiometric hydroxy-and Ca-deficient hydroxy-apatites were formed, depending on the composition of the glass targets.
Capacitance aging under dc field has been studied on BaTiO3-based dielectrics with X7R characteristics for multilayer ceramic capacitors with Ni internal electrodes. Capacitance change strongly depends on additives and firing conditions as well as microstructure. Aging behavior under no dc field is well explained by Richter's relaxation curve. On the other hand, aging under dc field cannot be fitted by Richter's curve. Therefore, a new model which assumes two factors that affect relaxation is proposed. According to the new model, capacitance changes in two stages, short-term and long-term relaxations. Capacitance change in short-term relaxation strongly depends on applied dc field. On the contrary, that of long-term relaxation does not depend on dc field.
We have developed the coating technology of apatite onto strong materials such as the ceramics of alumina and zirconia, and the metals of titanium and stainless steel, and recently established the method for the formation of bone-like layers of partially carbonated calcium hydroxyapatite by a reactive rf-magnetron sputtering method, which is undertaken in a mixed CO2/Ar gas ambience.Essential to this method is the use of calcium phosphate glass targets with much lower Ca/P ratios than the stoichiometric value of hydroxyapatite. It has been identified by the surface analyses of XRD, EDX, and FT-IR that CO32-ions occupied the lattice positions of PO43-in the apatite structure. The bioactivity of the coated ceramic materials was confirmed by the in vitro experiments of the bone-like crystal growth on their surfaces in a simulated body fluid.
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