Chemical and Hydrostatic Pressure in Natrolites: Pressure Induced Hydration of an Aluminogermanate Natrolite

Journal Article · Fri Sep 24 04:00:00 EDT 2010 · Journal of Physical Chemistry C

DOI:https://doi.org/10.1021/jp106964j· OSTI ID:1001328

Lee, Y; Kao, C; Parise, J B; Vogt, T

The ambient structure and pressure-induced structural changes of a synthetic sodium aluminogermanate with a natrolite (NAT) framework topology (Na-AlGe-NAT) were characterized by using Rietveld refinements of high-resolution synchrotron X-ray powder diffraction data at ambient and high pressures. Unlike a previously established model for Na{sub 8}Al{sub 8}Ge{sub 12}O{sub 40} {center_dot} 8H{sub 2}O based on a single-crystal study, the ambient structure of the Na-AlGe-NAT is found to adopt a monoclinic space group Cc (or Fd) with a ca. 6% expanded unit cell. The refined ambient structure of Na{sub 8}Al{sub 8}Ge{sub 12}O{sub 40} {center_dot} 12H{sub 2}O indicates an increased water content of 50%, compared to the single-crystal structure. The unit-cell volume and water-content relationships observed between the two Na-AlGe-NAT structures at ambient conditions with 8 and 12 H{sub 2}O respectively seem to mirror the ones found under hydrostatic pressure between the Na{sub 8}Al{sub 8}Ge{sub 12}O{sub 40} {center_dot} 8H{sub 2}O and the parantrolite phase Na{sub 8}Al{sub 8}Ge{sub 12}O{sub 40} {center_dot} 12H{sub 2}O. Under hydrostatic pressures mediated by a pore-penetrating alcohol and water mixture, the monoclinic Na-AlGe-NAT exhibits a gradual decrease of the unit-cell volume up to ca. 2.0 GPa, where the unit-cell volume then contracts abruptly by ca. 4.6%. This is in marked contrast to what is observed in the Na-AlSi-NAT and Na-GaSi-NAT systems, where one observes a pressure-induced hydration and volume expansion due to the auxetic nature of the frameworks. Above 2 GPa, the monoclinic phase of Na-AlGe-NAT transforms into a tetragonal structure with the unit-cell composition of Na{sub 8}Al{sub 8}Ge{sub 12}O{sub 40} {center_dot} 16H{sub 2}O, revealing pressure-induced hydration and a unit cell volume contraction. Unlike in the Na-Al,Si-paranatrolite phase, however, the sodium cations in the Na-AlGe-NAT maintain a 6-fold coordination in the monoclinic structure and only become 7-fold coordinated at higher pressures in the tetragonal structure. When comparing the pressure-induced hydration in the observed natrolite-type zeolites, Na-AlGe-NAT appears to have a nonauxetic framework and reveals the highest onset pressure for complete superhydration.

• Research Organization: Brookhaven National Laboratory (BNL) National Synchrotron Light Source
• Sponsoring Organization: DOE - Office Of Science
• DOE Contract Number: AC02-98CH10886
• OSTI ID: 1001328
• Report Number(s): BNL--94413-2010-JA; KC0401030
• Journal Information: Journal of Physical Chemistry C, Journal Name: Journal of Physical Chemistry C Journal Issue: 44 Vol. 114; ISSN 1932-7455; ISSN 1932-7447
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALCOHOLS
CATIONS
CONTRACTION
DIFFRACTION
HYDRATION
HYDROSTATICS
MIRRORS
SODIUM
SPACE GROUPS
SYNCHROTRONS
TOPOLOGY
WATER
ZEOLITES
national synchrotron light source