Transitions under pressure

A metal complex Pt(bqd)2 exhibited an insulator-metal-semiconductor transition under pressure [72, 73]. A continuous color change was observed in bis (diphenylglyoximato)Pt(ll), Scheme 5 [81] under pressure and thus has been used as a pressure indicator. For these cases it is not clear that n-d orbital mixing is critical for the transport. 

The dimer structure in Sm2 78C70 also causes a unique structural phase transition under pressure at 1.5 GPa [89]. The volume compressibility of the... 

F. Zipoli, M. Bernasconi, and R. Martohak (2004) Constant pressure reactive molecular dynamics simulations of phase transitions under pressure The graphite to diamond conversion revisited. Eur. Phys. J. B 39, p. 41... 

Voigtmann, Th. (2008) Idealized Glass Transitions under Pressure Dynamics versus Thermodynamics, Phys. Rev. Lett. 101, 095701... 

Xiao P, Cheng J-G, Zhou J-S, Goodenough JB, Henkelman G (2013) Mechanism of the Calr03 post-perovskite phase transition under pressure. Phys Rev B 88 144102... 

The nature of the 4f electrons in lanthanides and their compounds may be broadly characterized as being either localized or itinerant and is held responsible for a wide range of physical and chemical properties of both the elements and compounds. The localized states are marked by tightly bound shells or narrow bands of highly correlated electrons near the Fermi level and are observed at ambient conditions for all of the lanthanide elements. The pressure variable has a dramatic effect on the electronic structure of lanthanides, which in turn, drives a sequence of structural phase transitions under pressure. A very important manifestation of this change is the pressure-induced s to d electron transfer that is known to give rise to the... 

Phase transitions under pressure are best researched for Cs. Here the following succession of transformations has been established (the pressures of transitions in GPa are shown above the arrows, the volume changes in per cent under the arrows and Ac in parentheses) ... 

Generally speaking, an increase in density can occur upon a polymorph transformation even without change in coordination of the nearest atoms in the structure. An example of such densiflcation is presented by the SiOz modifications, where a more compact packing of silicon-oxygen tetrahedra reduces the molar volumes in the succession cristobalite (25.9cm ) keatite (24,0cm ) quartz (22.7 cm ) -> coesite (20.0cm ). However, the transition under pressure from coesite (Nc=4) to stishovite (Nc = 6) reduces this volume much more drastically, to 13.8 cm. ... 

Both above-mentioned particularities of actinides with itinerant electrons, high density and low-symmetry structures, can be induced in actinides and lanthanides with localized f electrons by the action of pressure. Compression leads to hybridization and overlapping of f electron orbitals and, thus, generates also in these regular metals states which are similar to those found in U, Np, and Pu at ambient pressure. Phase transitions under pressure to low-symmetry structures have up to now been reported in Am, Cm, Bk, and Cffor the actinides, and inC Pr, Nd, and Sm for the lanthanides. 

Phase transitions under pressure were observed in UP2, UAs2, and UAsS. These... 

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