SIMPLE HEXAGONAL AND TETRAGONAL BODY-CENTERED STRUCTURES: EFFECT OF PRESSURE AND ELECTRON CONCENTRATION
V. Degtyareva 1
and W.B. Holzapfel 2
1Institute of Solid State Physics,
Russian Academy of Sciences, Chernogolovka, Moscow
district, 142432 Russia, E-mail: degtyar@ issp.ac.ru
2FB 6 Physik, Universität-GH-Paderborn,
33095 Paderborn, Germany
Keywords: structural transformations, high
pressure, electron concentration
A structural transformation from a simple hexagonal (hP1)
to body-centered tetragonal (tI 2)
phase was observed under pressure in a Sn-Hg alloy (10 at.% Hg)
by X-ray diffraction with diamond anvil cells and synchrotron
radiation [1]. A comparison with previous data on the occurrence
of these structures shows that they are typical for metals and
alloys with nearly four valence electrons, i. e. with
electron concentrations ne~ 4.
Obvious features of these structures are special values of the
lattice parameter ratios which depend on either composition or
pressure.
The hP1 structure of the Sn-Hg alloy with an axial
ratio c/a = 0.930 at ambient pressure shows a
slight increasing of c/a under pressure, in agreement with
previous observations on Al-Ge [2] and Cd-Sb [3] alloys. The
trend of the axial ratio to increase was also noted with
decreasing ne in
binary hP1 alloys of various composition [4] providing a
common reason for more symmetrical atomic coordinations by either
increasing pressure or decreasing electron concentration.
A tetragonal structure with small distortion from a body-centered
cubic structure was observed previously under pressure on tin
[5] and recently on III-V compound InBi [6]. The tI 2 structure shows in all
three cases under pressure an initial increase in c/a with
a saturation at a specific value of c/a depending on ne: c/a<= 0.96
with ne = 4
for Sn and InBi and c/a <= 0.92 with ne = 3.8 for the Sn-Hg
alloy.
The concept of Brillouin zone - Fermi sphere
interaction relates the structural stability and pressure
behaviour for both the hP1 and tI 2
phases to special values in ne.
1. V.F. Degtyareva, O. Degtyareva, M.
Winzenick, and W.B. Holzapfel (to be published)
2. V.F. Degtyareva, F. Porsch, E.G.
Ponyatovskii, and W.B. Holzapfel, Phys. Rev. B 53
(1996) 8337-8339.
3.V.F. Degtyareva, I. Bdikin, S.S. Khasanov, Fiz. Tverd. Tela
39, (1997) 1509-1512 [Phys. Solid State 39
(1997) 1341-1344]
4. R.H.Kane, B.C. Giessen and N.J. Grant, Acta met. 14,
(1966) 605-609
5. H. Olijnyk and W.B. Holzapfel, J. de Phys. 45,
C8 (1984) 153-155
6. V.F. Degtyareva, M. Winzenick, and W.B. Holzapfel, Phys.Rev.B
57 (1998) 4975-4978