The Growth and Crystallographic Properties of Calcium Fluor- and Chlorapatite Crystals

Abstract

Stoichiometric crystals of Ca5false(PO4)3F and Ca5false(PO4)3normalCl were grown by slowly cooling solutions of the polycrystalline apatites in fused CaCl2 or CaF2 . While fluorapatite is hexagonal, optical and x‐ray observations indicate that Ca5false(PO4)3normalCl has a monoclinic P21/normalb space group. All crystals of this compound are highly twinned. At about 200 °C a transition to a hexagonal phase false(P63/normalmfalse) occurs. Loss of CaCl2 from the crystals leads to a stabilization of the hexagonal phase whereas at low concentrations F ion impurities have the opposite effect. Some previous observations on the luminescence of Ca5false(PO4)3−normalxfalse(MnO4)normalxnormalCl can now be understood in terms of the lower symmetry structure.

SITE PREFERENCE OF Gd IN SYNTHETIC FLUORAPATITE BY SINGLE-CRYSTAL W-BAND EPR AND X-RAY REFINEMENT OF THE STRUCTURE: A COMPARATIVE STUDY

“…Experimental details for the synthesis of sample AP30-1 (crystals up to 1 cm in length and ≥1 mm in diameter) in a tightly covered platinum crucible (in air), using the flux method of Prener (1967), were given in Chen et al (2002a). Sample AP40-0 was synthesized by use of similar experimental procedures and starting materials, except that a mixture of ~100 mg starting materials containing ~15 wt% Gd 2 O 3 was sealed in a platinum capsule by welding.…”

“…Therefore, this substitution is controlled by the availability of such vacancies at the Ca2 site in FAp. Although the flux method of Prener (1967) is known to produce highly stoichiometric crystals of FAp (Elliott 1994), point defects such as Ca 2+ (and F -) vacancies along the c-axis channels (Serret et al 2000, Pan andFleet 2002) are expected to be readily available at ppmand sub-ppm concentrations. Therefore, the marked preference of Gd for the Ca1 site in AP30-0 and AP30-5 containing only 0.8(1) and 57(4) ppm Gd, respectively, is most likely related to the availability of Ca 2+ vacancies at these concentrations.…”

“…The maximum Ca deficiency in synthetic FAp corresponds to a loss of 10 at.% of total Ca (Mazelsky et al 1968, Elliott 1994. However, Ca 2+ vacancies in FAp crystals synthesized from CaF 2 -rich melts in tightly covered platinum crucibles (Prener 1967) and in sealed platinum capsules (e.g., AP40-0) appear to reach saturation at thousands and hundreds of ppm levels of concentrations, respectively (authors' unpubl. results).…”

Implementation of State Transfer Hamiltonians in Spin Chains with Magnetic Resonance Techniques

“…Owing to their unique geometry [116,117], nuclear spin systems in apatite crystals have emerged as a rich test-bed to probe quasi-one-dimensional (1D) spin dynamics, including transport and decoherence [12,[118][119][120].…”

Multifrequency Epr Study of Radiation-Induced Defects in Chlorapatite

“…Chlorapatite, Ca 10 (PO 4 ) 6 Cl 2 , was prepared as part of a program of syntheses for U-doped apatite-group minerals or analogues, following the fl ux method of Prener (1967). The starting materials were CaO (obtained from the decomposition of CaCO 3 at 900°C), P 2 O 5 and CaCl 2 from the Sigma-Aldrich Chemical Company, and UO 2 from Alfa Aesar, were weighed and mixed thoroughly to form the composition of chlorapatite with approximately 10 ppm U.…”