Structural simplicity and complexity of compressed calcium: electronic origin.

A simple cubic structure with one atom in the unit cell found in compressed calcium is counterintuitive to the traditional view of a tendency towards densely packed structures with an increase in pressure. To understand this unusual transformation it is necessary to assume electron transfer from the outer core band to the valence band, and an increase of valence electron number for calcium from 2 to ∼ 3.5.

The fcc-bcc Bain path in In-Sn and related alloys at ambient and high pressure.

Experimental high-pressure structural studies on an In-Sn alloy containing 8 at.% Sn reveal an isostructural transition of a face-centered tetragonal phase at pressures above 15 GPa with a switch of the axial ratio from c/a>1 to c/a<1. Such tetragonal phases in binary alloys based on In and Sn are analyzed in relation to the Bain path, i.

Structure solution in binary systems under high pressure: phase decomposition and phase synthesis.

There are binary systems (compounds) for which no structural solution can be found for a new high-pressure state by assuming a single phase. In accordance with Gibb's phase rule, an additional variable--composition--leads to an additional degree of freedom for a binary system (one more than in a one-component system). Although the bulk composition of a system may remain fixed, compositional variation between phases should be taken into account when considering phase transitions under pressure in binary compounds.