Pressure-induced incommensurate-to-incommensurate phase transition in antimony

O. Degtyareva, M. I. McMahon, and R. J. Nelmes

Phys. Rev. B 70, 184119 – Published 19 November 2004

Abstract

An incommensurate composite phase with a monoclinic host-guest structure, designated $Sb − IV$ , is found between the previously known $Sb − I$ and $Sb − II$ phases, and an incommensurate to incommensurate transition between phases II and IV is described. The monoclinic $Sb − IV$ phase is observed on both pressure increase between 8.2 and $9.0 GPa$ and on pressure decrease between 8.0 and $6.9 GPa$ . The full structure of $Sb − IV$ , including a determination of the structural modulations of the host and guest components, is reported from x-ray powder diffraction data. The high-pressure phase of arsenic, $As − III$ , is shown to have the same monoclinic composite structure.

Received 19 December 2003

DOI:https://doi.org/10.1103/PhysRevB.70.184119

Authors & Affiliations

O. Degtyareva^*, M. I. McMahon, and R. J. Nelmes

School of Physics and Centre for Science at Extreme Conditions, The University of Edinburgh, Mayfield Road, Edinburgh, EH9 3JZ, United Kingdom

^*Now at: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road N.W., Washington, D.C. 20015, USA. Electronic address: o.degtyareva@gl.ciw.edu

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Vol. 70, Iss. 18 — 1 November 2004

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Images

Figure 1
Diffraction profiles of $Sb$ collected on pressure increase $(bottom \to top)$ , showing profiles from the $Sb − I$ , $Sb − IV$ , and $Sb − II$ phases. The asterisks in the $8.2 GPa$ profile denote the remaining reflections from the $Sb − I$ phase. $g$ denotes a very weak diffraction peak from the gasket.Reuse & Permissions
Figure 2
Powder profiles of $Sb$ collected on pressure decrease $(top \to bottom)$ . The tick marks below the $6.9 GPa$ profile indicate the positions of the main host and guest reflections, some of which are indexed. The inset enlarges the low-angle regions of the single-phase $Sb − II$ and $Sb − IV$ patterns obtained at 8.9 and $6.9 GPa$ , respectively. The tick marks indicate the positions of (a) the main reflections, and (b) first-order and (c) second-order modulation reflections. (The magnification is so great that the modulation reflections are not visible in the main profile.) The filled triangles mark the clearly visible $022 \bar{2}$ and $\bar{2} 02 \bar{2}$ second-order modulation reflections. Arrows indicate the splitting of some peaks at the transition from $Sb − II$ to $Sb − IV$ . [Two of those derived from the $311 \bar{1}$ peak of $Sb − II$ lie under the (2110) and (3100) main reflections.] The asterisks in the main $6.9 GPa$ profile and inset mark the appearance of the three strongest peaks from the $Sb − I$ phase.Reuse & Permissions
Figure 3
Rietveld refinement of $Sb − IV$ at $6.9 GPa$ . The tick marks beneath the profile indicate the positions of the main host and guest reflections. The inset shows the splitting of the strongest host reflection of $Sb − II$ at $8.9 GPa$ , (2110), into four reflections of $Sb − IV$ at $6.9 GPa$ .Reuse & Permissions
Figure 4
The equation of state of $Sb$ to $65 GPa$ . Data from the present study are plotted using solid symbols, while the compression data of Bridgman (Ref. 21) are plotted with open symbols. The inset shows an enlarged view of the compression of $Sb − IV$ and $Sb − II$ in the region of the transition. The solid curves through the data points represent the equations of state fitted using the second-order Birch-Murnaghan equation with the resulting values of $K_{0} = 39.7 (5) GPa$ and $V ∕ V_{0} = 1$ for $Sb − I$ , $K_{0} = 71 (2) GPa$ and $V ∕ V_{0} = 0.891 (5)$ for $Sb − IV$ and $Sb − II$ , and $K_{0} = 74 (3) GPa$ and $V ∕ V_{0} = 0.861 (5)$ for $Sb − III$ , with $V_{0} = 30.20 (2) Å$ [3] and $K_{0}^{'} = 4$ for all phases.Reuse & Permissions
Figure 5
Rietveld refinement of $As − III$ at $50.0 GPa$ . The tick marks beneath the profile indicate the positions of the main reflections. The left-hand inset shows the group of the strongest host reflections and the right-hand inset shows the first order modulation reflections with their $h k l_{1} l_{2}$ indices. The tick marks indicate the positions of (a) the main reflections and (b) the first-order modulation reflections. Asterisks indicate reflections from the $As − II$ phase with simple cubic structure.Reuse & Permissions

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