Characterization of NH 4 -phlogopite (NH 4 ) (Mg 3 ) [AlSi 3 O 10 ] (OH) 2 and ND 4 -phlogopite (ND 4 ) (Mg 3 ) [AlSi 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-phlogopite (NH4) (Mg3) [AlSi3O10] (OH)2 and its deuterium analogue ND4-phlogopite (ND4) (Mg3) [AlSi3O10] (OD)2. Both phases are characterised using both IR spectroscopy at 298 and 77 K as well as Rietveld refinement of their 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 using Td symmetry as a basis. Rietveld refinement indicates that either phlogopite synthesis contains several mica polytypes. The principle polytype is the one-layer monoclinic polytype (1M), which possesses the space group symmetry C2/m. The next most common polytype is the two-layer polytype (2M1) with space group symmetry C2/c. Minor amounts of the trigonal polytype 3T with the space group symmetry P3112 were found only in the synthesis run for the ND4-phlogopite. Electron microprobe analyses indicate that NH4-phlogopite deviates from the ideal phlogopite composition with respect to variable Si/Al and Mg/Al on both the tetrahedral and octahedral sites, respectively, due to the Tschermaks substitution VIMg2++IVSi4+↔VIAl3++IVAl3+ and with respect to vacancies on the interlayer site due to the exchange vector XII(NH4)++IVAl3+↔XII□+IVSi4+.