High-pressure P2₁/c-C2/c phase transitions in clinopyroxenes; influence of cation size and electronic structure

Amorphization in natural omphacite and its implications

“…There is also the possibility that there is an order/disorder transformation from their high temperature origin (Deer et al, 1978) or ultrahigh pressure origin (Wu et al, 2002). The low-clinopyroxenes are known to undergo a first order phase transition from P2 1 /c to C2/c with increasing pressure (Angel et al, 1992;Arlt et al, 1998;Ross and Reynard, 1999). For omphacite the transition of order/disorder displays a hysteresis ultrahigh pressure origin (Wu et al, 2002).…”

The (Na,Li)FeGe2O6 clinopyroxene-type series: a temperature-dependent single-crystal X-ray diffraction and 57Fe Mössbauer spectroscopic study

“…Artl and Angel (2000) figured out a HT-C2/c ⇔ P2 1 /c ⇔ HP-C2/c phase transition sequence for ZnSiO 3 , and a HT-C2/c ⇔ P2 1 /c transition was also reported for LiAlSi 2 O 6 by the same authors; hightemperature HT and high-pressure HP-C2/c structures represent distinct phases (Hugh-Jones et al 1994;Artl and Angel 2000) and mainly differ in the kinking state of the tetrahedral chains and the coordination of the atom at the M2 site. The HP-C2/c structure is characterized by strong chain kinking with bridging angles around 140° (e.g., Arlt et al 1998;Artl and Angel 2000;Nestola et al 2004), while the HT-C2/c structure has more extended chains with kinking angles ~170-180° (e.g., Redhammer and Roth 2004a). LiAlGe 2 O 6 is a synthetic Ge pyroxene, which shows a slightly different structure type with P2 1 /n symmetry (Redhammer et al 2012a).…”

Compressibility trends of the clinopyroxenes, and in-situ high-pressure single-crystal X-ray diffraction study of jadeite

“…In addition, new high-pressure X-ray diffraction data are reported for jadeite. Clinopyroxenes have been the subject of many recent highpressure single-crystal X-ray diffraction studies (Hugh-Jones and Angel 1994;Hugh-Jones et al 1997;Zhang et al 1997;Arlt et al 1998;Yang et al 1999;Arlt and Angel 2000;Hattori et al 2000;Tribaudino et al 2000;Origlieri et al 2003;Gatta et al 2005;Bindi et al 2006;Downs and Singh 2006;Nestola et al 2006a). Many of the clinopyroxenes have been found to undergo phase transitions with pressure, changing symmetry between C2/c and P2 1 /c.…”