Characterization of NH4-phlogopite (NH4) (Mg-3) [AISi(3)O(10)] (OH)(2) andND4-phlogopite (ND4) (Mg-3) [AISi(3)O(10)] (OD)(2) using IR spectroscopy and Rietveld refinement of XRD spectra

A synthesis technique is described which results in > 99% pure NH4-phlogopi te (NH4) (Mg-3) [AlSi3O10] (OH)(2) and its deuterium analogue ND(4)(-)phlog opite (ND4) (Mg-3) [AlSi3O10] (OD)(2). Both phases are characterised using both IR spectroscopy at 298 and 77 K as well as Rietveld refinement of thei r X-ray powder diffraction pattern. Both NH4+ and ND4+ are found to occupy the interlayer site in the phlogopite structure. Absorption bands in the IR caused by either NH4+ or ND4+ can be explained to a good approximation usi ng Td symmetry as a basis. Rietveld refinement indicates that either phlogo pite synthesis contains several mica polytypes. The principle polytype is t he one-layer monoclinic polytype (1 M), which possesses the space group sym metry C2/m. The next most common polytype is the two-layer polytype (2M(1)) with space group symmetry C2/c. Minor amounts of the trigonal polytype 3T with the space group symmetry P3(1)12 were found only in the synthesis run for the ND4-phlogopite. Electron microprobe analyses indicate that NH4-phlo gopite deviates from the ideal phlogopite composition with respect to varia ble Si/Al and Mg/Al on both the tetrahedral and octahedral sites, respectiv ely, due to the Tschermaks substitution Mg-VI(2+) + Si-IV(4+) <----> Al3+ Al-IV(3+) and with respect to vacancies on the interlayer site due to the e xchange vector (XII)(NH4)(+) +(IV) Al3+ <----> (XII) square +Si-IV(4+).