Structure refinement of synthetic deuterated kaolinite by Rietveld analysis using time-of-flight neutron powder diffraction data

The crystal structure of synthetic deuterated kaolinite was refined by Rietveld analysis using time-of-flight (TOF) neutron powder diffraction data. For non-hydrogen atoms, CI symmetry was assumed. Starting models were tested in which only the direction of O-D vectors was varied. The constraints were introduced to all Al-O, Si-O and O-D bonds. The refinement adopting the former gives Pl(Cl), a = 5.169(1) Angstrom, b = 8.960(2) Angstrom, c = 7.410(2) Angstrom, alpha = 91.26(2)degrees, beta = 104.99(2)degrees, gamma = 89.93(1)degrees, R(wp) = 3.17%, R(I) = 5.78% and S = 1.34 with constraints of l(Al-O) = 1.93 +/- 0.05 Angstrom, I(Si-O) = 1.62 +/- 0.03 Angstrom and l(D-O) = 0.95 +/- 0.15 Angstrom. The inner O-D vector points toward the tetrahedral sheet. All inner-surface O-D groups form H bonding with basal O atoms in the next kaolinite layers. The results agreed with those obtained from natural kaolinite.