Static compression and H disorder in brucite, Mg(OH)2, to 11 GPa: a powder neutron diffraction study

Abstract

Abstract. Neutron diffraction data suitable for Rietveld refinements were collected on a powder sample of synthetic Mg(OH)2 by the Polaris time-of-flight spectrometer (ISIS spallation source, U.K.) at 10 -4, 7.8(3) and 10.9(6) GPa. The Paris-Edinburgh high-pressure cell with WC anvils was used. Pressure calibration and equation-ofstate results were attained by separate runs with an NaC1 internal standard. Interpolation of p(V) data by the fourth-order Birch-Murnagban e.o.s, yields K0=41(2 ) GPa, K0=4(2 ) and Ko'= 1.1(9) GPa -1. The bulk modulus obtained is smaller than previously reported results. Rietveld refinements (Rprof= 1.45% and 2.02% at 10 .4 and 10.9 GPa) show that H lies on the threefold axis (1/3, 2/3, z) up to 10.9 GPa, where a model with H disordered in (x, 2x, z) can be refined. In the latter case, a hydrogen bond with O-H=0.902 (7), H..O =2.026(8) A and <OHO'= 145.9(7) ~ is observed. Differences with previous results for deuterated brucite are discussed. The onset of H disorder, and a jump of the c/a ratio vs. pressure at 6-7 GPa, may be related to a second-order phase transition consistent with recently reported Raman spectroscopic results.

Functional Materials - Syntheses, Characterisation and Catalytic Applications

“…2 Table 1, prove that our syntheses were successful. Another important reflection is the (110), which represents the distance between two metal cations in the octahedral layer.…”

“…4 Only one example is known of LDH structure with monovalent cation, the LiAl 2 -LDH that is. It has been speculated that the ionic radii of M(II) and M(III) and the difference between them, 5,6 as well as the solubility products 7 of M(II)(OH) 2 and M(II)CO 3 , play roles in defining the boundaries of the range of metal cations that can form LDHs.…”

“…If the opposing OH groups lie vertically above one another; an interlayer with a trigonal prismatic arrangement is resulted, whilst an octahedral arrangement is formed if they are offset. 15 There are three possible two-layer polytypes with hexagonal stacking of the layers, denoted as 2H 1 ,2H 2 , and 2H 3 where the 2H 1 polytype has all prismatic interlayers and the 2H 2 polytype has all octahedral interlayers while both types of interlayers are present in the 2H 3 polytype. There are nine possible three-layer polytypes of which two have rhombohedral symmetry 3R 1 and 3R 2  while the remaining seven (3H 1  3H 7 ) have hexagonal symmetry.…”

“…18 Several rhombohedral space groups, a monoclinic one and the two triclinic space groups have been observed for synthetic monoanionic tetracalcium aluminates. In the rhombohedral space groups R-3 and R-3c, the water molecules linked to Ca atoms are on the straight line passing through the Ca atoms and perpendicular to the (001) plane 6 Cl · 2H 2 O, in R-3 space group.…”

“…As it is seen, the Ca(OH) 2 The average value of D was calculated from FWHM of peak (003) and (006) using the…”