Microsc. Microanal. Microstruct. 7, 225-234 (1996)
DOI: 10.1051/mmm:1996118

Order and Disorder in Boron Phases

Paola Favia¹, Tiziana Stoto¹, Michel Carrard¹, Pierre-André Stadelmann² et Libero Zuppiroli<sup>1

1</sup>  Laboratoire de Physique des Solides Semi-Cristallins, École Polytechnique Fédérale, 1015 Lausanne, Switzerland
²  Centre Interdépartemental de Microscopie Électronique, École Polytechnique Fédérale, 1015 Lausanne, Switzerland

Abstract
The complicated rhombohedral unit cell of crystalline -boron containing 105 atoms is a good approximant structure for a quasicrystal. Thus one may wonder if between the amorphous and the crystalline phases of boron, a non-metallic quasi-crystalline phase could exist. In order to examine this possibility and to characterize order and disorder in boron phases, we have performed high resolution electron microscopy (HREM) and electron energy loss spectroscopy (EELS) measurements. In the crystalline phase, the creation of large number of microtwins and stacking faults is the way that nature chooses to disorder boron. The presence of these microtwins seems to be the major obstacle towards the formation of a quasicrystal. A comparison between energy loss near edge structures and electronic density of states for different boron compounds has allowed us to identify the signature of the icosahedra in EELS measurements. In the amorphous phase, a special processing of HREM images proposed by Fan and Cowley has been applied in order to estimate the extent of local order in amorphous boron. Both techniques (HREM and EELS) have confirmed the presence of icosahedral units in the amorphous phase. This raises the question of the existence of a quasi-crystalline phase.

PACS
6140M - Structure of quasicrystals.
6180M - Channelling, blocking and energy loss of particles.
7920K - Other electron surface impact phenomena.
6170N - Grain and twin boundaries.
6170P - Stacking faults, stacking fault tetrahedra and other planar or extended defects.

Key words
boron -- electron energy loss spectra -- electron microscopy -- quasicrystals -- stacking faults -- twinning -- beta B -- quasicrystal -- order -- disorder -- high resolution electron microscopy -- electron energy loss spectroscopy -- microtwins -- stacking faults -- energy loss near edge structures -- electronic density of states -- icosahedral units -- amorphous phase -- B


© EDP Sciences 1996