A new high‐pressure form of KAlSi₃O₈ under lower mantle conditions

Abstract

[1] In situ X-ray diffraction measurements have been made on KAlSi 3 O 8 hollandite using diamond anvil cell and multianvil apparatus combined with synchrotron radiation. Both of the measurements with different techniques demonstrated that K-hollandite transforms to a new highpressure phase (hollandite II) at $22 GPa upon increasing pressure at room temperature. The X-ray diffraction peaks of the new phase were reasonably indexed on the basis of a monoclinic cell with I2/m space group. Hollandite II was also confirmed to be formed at high temperatures to 1200°C and pressures to 35 GPa, which was quenched to room temperature under pressure but converted back to hollandite at about 20 GPa on release of pressure. The present result is contradictory to earlier studies based mainly on quench method, which concluded that hollandite is stable up to 95 GPa at both room temperature and high temperatures up to 2300°C.

A first-principles study of the phase transition from Holl-I to Holl-II in the composition KAlSi3O8

“…Previous studies have generally reached good agreements on the phase relations of the composition KAlSi 3 O 8 up to the pressure of 128 GPa (Urakawa et al 1994;Yagi et al 1994;Tutti et al 2001;Akaogi et al 2004;Sueda et al 2004;Nishiyama et al 2005;Liu 2006;Ferroir et al 2006;Yong et al 2006;Liu and El Goresy 2007;Hirao et al 2008;Liu et al 2010). First, Or (KAlSi 3 O 8 ) breaks down to a three-phase assemblage (wadeitetype K 2 Si 4 O 9 + kyanite-type Al 2 SiO 5 + SiO 2 ) at around 6 GPa and 600-1400 °C.…”

“…As demonstrated by some high-P experiments up to about 24 GPa (Irifune et al 1994), the proportion of its high-P form, mainly KAlSi 3 O 8 -hollandite, could volumetrically account for one third of the phase assemblages of the subducted upper continental crust composition, so that its importance in the geodynamic process in the deep interior of the Earth cannot be overestimated. Orthoclase (Or; KAlSi 3 O 8 ) is one of the major end-members in the feldspar family, and its high-P behavior is of great interest to many investigators (e.g., Yamada et al 1984;Zhang et al 1993;Urakawa et al 1994;Yagi et al 1994;Tutti et al 2001;Akaogi et al 2004;Sueda et al 2004;Nishiyama et al 2005;Liu 2006;Ferroir et al 2006;Yong et al 2006;Liu and El Goresy 2007;Hirao et al 2008;Liu et al 2009). …”

“…Finally, Holl-II possibly remains thermodynamically stable up to 128 GPa. Mainly due to its unquenchable nature during decompression, Holl-II was difficult to detect within experimental products generated by traditional high-P quench methods, so that some discrepancy in the phase transition from Holl-I to Holl-II was reported (Tutti et al 2001;Sueda et al 2004;Nishiyama et al 2005;Ferroir et al 2006).…”

“…Holl-I has tetragonal symmetry I4/m (Ringwood et al 1967;Yamada et al 1984), whereas Holl-II has monoclinic symmetry * E-mail: xi.liu@pku.edu.cn I2/m (Sueda et al 2004;Nishiyama et al 2005;Ferroir et al 2006). Paired edge-sharing (Si,Al)O 6 octahedra form double chains running parallel to the c-axis, and four of the double chains are linked to delimit a large squared open tunnel to host the K cation.…”

Recent advances of high-pressure generation in a multianvil apparatus using sintered diamond anvils

“…The size of the SD anvil has been extended in the 1990s from a 5e10-mm to 14-mm edge length and this highpressure technique has been developed and applied to study mineral properties and phase transitions in the MAA by using the traditional quenched method (Ito et al, 1998), or by combining with the synchrotron X-ray diffraction technique (Kato et al, 1992;Kondo et al, 1993;Funamori et al, 1996aFunamori et al, , 1996b. High-pressure generation using SD anvils has been extended significantly, especially in the last decade, including the Earth Science research field with many studies carried out (Ito, 2000;Ono et al, 2000Ono et al, , 2001Irifune, 2002;Irifune et al, 2002;Ito and Kubo, 2002;Kubo et al, 2003;Yamazaki and Irifune, 2003;Ito et al, 2004;Ohtani, 2004;Sueda et al, 2004;Ito et al, 2005;Ito, 2006;Yamazaki et al, 2006;Ito, 2007;Stewart et al, 2007;Kubo et al, 2008;Shinmei et al, 2008;Tange et al, 2008;Ito et al, 2009Ito et al, , 2010Katsura et al, 2009;Sueda et al, 2009;Yamazaki et al, 2011). In this paper we review the advances of high-pressure generation in the MAA by adopting the SD cubic anvil and we also discuss the problems and perspectives of this technique.…”