Structural Characterization of Na0.96Ho9.04(SiO4)6Cl0.02O1.98 Apatite Prepared by Mechanical Milling

Abstract  

In this paper we report the synthesis and structural characterization of Na_0.96Ho_9.04(SiO₄)₆Cl_0.02O_1.98 apatite prepared by mechanical milling at room temperature, in which well crystallized sample was obtained after heating the sample at 1123 K. The crystal structure study was carried out by synchrotron radiation diffraction. This apatite crystallizes in the hexagonal space group P6 ₃ /m (No. 176) with cell parameters a = 9.3444(1) ?, c = 6.7611(1) ?, unit cell volume of 511.27(1) ?³ and Z = 1. As in other rare-earth orthosilicate apatites, it was found that sodium cations are mixed with holmium occupying the 4f position at the center of tricapped trigonal prisms; while holmium fully occupies the 6h position at the center of a seven-coordinated polyhedron. No vacancies are present in the two crystallographic sites available for holmium atoms. The chemical composition was established by wavelength dispersive spectroscopy.