1H AND 19F MULTIPLE-QUANTUM NMR DYNAMICS IN QUASI-ONE-DIMENSIONAL SPIN CLUSTERS IN APATITES

The 1H multiple-quantum NMR dynamics of quasi-one-dimensional distributions of clusters of uniformly spaced proton spins in hydroxyapatite, Ca5(OH)(PO4)3, and related fluorine-containing apatites have been studied. Two different growth exponents characterizing the power-law dependence of the effective size upon preparation time are observed at short and long times for the hydroxyapatite samples. The corresponding growth exponents are 0.98 and 1.78 for the most stoichiometric sample, which suggest a possible transition from 1-D to 2-D growth at longer preparation times. A slight deficiency of hydroxyl groups in another sample of hydroxyapatite leads to a decreased rate of MQ coherence growth and a measurable decrease in the short-time growth exponent to 0.83. The 1H MQ dynamics of two fluorohydroxyapatite solid solutions, Ca5Fx(OH)1-x(PO4)3, exhibit both decreasing rates of MQ coherence growth as x increases and decreased values of the short-time growth exponent. A 1-D cluster model is developed to account...