Crystal Structure Studies of Human Dental Apatite as a Function of Age

Studies of the average crystal structure properties of human dental apatite as a function of the tooth-age in the range of 5-87 years are reported. The crystallinity of the dental hydroxyapatite decreases with the tooth-age. The a-lattice constant that is associated with the carbonate content in carbonate apatite decreases with the tooth-age in a systematic way, whereas the c-lattice constant does not change significantly. Thermogravimetric measurements demonstrate an increase of the carbonate content with the tooth-age. FTIR spectroscopy reveals both, B and A-type carbonate substitutions with the B-type greater than the A-type substitution by a factor up to ~5. An increase of the carbonate content as a function of the tooth-age can be deduced from the ratio of the v2 CO3 to the v1 PO4 IR modes.Comment: 17 page

Ca doped YBCO on the Ba site

The effect of partial, nominal replacement of Ba with Ca on the properties of the YBa2Cu3O6+gd superconductor varies with the concentration of Ca. For nominal concentrations in Ca up to 50% a two phase system is formed: the known superconducting phase Y1-yCayBa2Cu3O6+δ and a new, non superconducting phase of composition Y1.14Ca1.58Cu3.27O6.45. The x-ray diffraction pattern of this new phase matches the Bragg peaks, as well as the commensurate and incommensurate peaks of a partially indexed pattern of the phase Y2-xCa2+xCu5O10. For nominal Ca concentrations 40 and 50%, microprobe analysis shows that the superconducting phase becomes a mixture of Y1-yCayBa2Cu3O6+° and YBa1.8Ca0.2Cu3O6.5, where Ca enters the structure in the Ba site. The microraman spectra indicate a small substitution of Ba by Ca, while the new phase shows novel characteristics. © 1995 Plenum Publishing Corporation

Effect of Ca substitutions on the properties of YBa2Cu3O6+d

We study the effect of Ca substitutions on the structural and superconducting properties of the system of nominal composition YCaxBa2-xCu3O6+d. The system remains superconducting up to x=1.00 and the critical temperatures vary between 92 and 80K. A new, non superconducting phase of stoichiometry Y1.14Ca1.58Cu3.27O6.45 appears with concentrations that increase with the nominal concentration of Ca. For x=0.80 and x=1.00 we observe a substitution of the Ba with Ca in crystallites of the form YBa1.8Ca0.2Cu3O6.5. © 1994