Intermediate 4fbonding structure for samarium under pressure

Abstract

The crystal structure of the low-symmetry phase Sm{V) was studied by synchrotron x-ray di8'raction under isothermal compression at room temperature up to 77 GPa {volume fraction=0. 45). Measured lattice spacings and difFraction intensities for Sm{U) in the pressure range beyond the phase mixing show that this phase can be identi5ed as a prototype structure with 3 atoms in the hexagonal unit cell. The occurrence of this low-symmetry structure gives strong evidence for a rapid increase of 4f-electron bonding in Sm in the pressure range above 37 GPa.

Untitled

“…1, is tentatively identified as the onset of itinerant 4f character in Sm. The same d-fcc → hP3 transition is seen in Nd [17], and is similarly marked in Fig. 1.…”

“…Earlier work had noted a structural change in Nd at about 40 GPa, denoted by the open diamond in the figure [12,13]. More recent measurements report the hP3 phase from 40 to 65 GPa in Nd, however do not publish pressurevolume data [17]. Data taken to date for Pm still falls within the regular rare earth sequence, as may be seen by the highest pressure d-fcc points in Fig.…”

“…1 by the open diamonds, as a hexagonal phase with three atoms in the primitive cell (hP3). This is a rather unusual structure with open channels of roughly helical shape running along the c direction, and an approximate fourfold coordination [2,17]. An analysis of anomalies in the pressure-volume equation of state for Sm has led to the conclusion that a rapid increase of 4f bonding most likely begins with this phase [17].…”

“…This is a rather unusual structure with open channels of roughly helical shape running along the c direction, and an approximate fourfold coordination [2,17]. An analysis of anomalies in the pressure-volume equation of state for Sm has led to the conclusion that a rapid increase of 4f bonding most likely begins with this phase [17]. Thus in the last part of the Sm sequence, d-fcc → hP3 → bct, the 91 GPa transition between d-fcc and hP3, marked by the line perpendicular to the P -V curve in Fig.…”

“…[15]- [17], and Gd [18,19], where some of the more recent, higher-pressure data is plotted, with curves provided as guides to the eye. More complete references may be obtained elsewhere from recent papers dealing with systematics of the whole series [1,2].…”