Hydrogen positions and thermal expansion in lizardite-l? from Elba: A low-temperature study using Rietveld refinement of neutron diffraction

Ansrucr The structure of lizardite-lTfrom Monte Fico, Elba, was refined in space group P3lm usingneutron diffraction data, measured at 8, 150, and 294K. and full-profile Rietveld refinement techniques. The lattice parameters at & K [a : 5.3267(2), c : 7.2539(6) A], I 50 K [a : 5.3260(2), c : 7 .257 4($ A], and 29 4 K 1a : 5.3332(2), c : 7 .27 18(6) Al show nonlinear expansion, with nearly all volume change above 150 K. H positions were precisely refined at 8 K. The inner H4 atom deviates from the idealized 0,0,2 positions and is disordered over three symmetry-related positions 0.24 A away from the ternary axis. The outer H3 atom location is consistent \vith the previous single-crystal X-ray structure refinement. On the basis of the present thermal expansion data and previous compressibility measurements, the following equation of state for lizardite-I7 is proposedi Vp.r : voll + 32.8 x lO-u(r 294) 15.5 x 10-o(P 0.001)1. Accordingly, the constant volume condition requires geothermal gradients on the order of 15 'Clkm. data