Shape-controlled growth and single-crystal XRD study of submillimeter-sized
single crystals of SnO†
Y. Q. Guo,
*
a
R. Q. Tan,
b
X. Li,
c
J. H. Zhao,
a
Z. L. Luo,
d
C. Gao
d
and W. J. Song
a
Received 14th December 2010, Accepted 5th July 2011
DOI: 10.1039/c0ce00949k
Submillimeter-sized single crystals of SnO exhibiting well-defined
symmetric shapes of four-armed star and square plate were
successfully synthesized through a mild surfactant-free hydro-
thermal reaction. Crystal structures, refined by single-crystal X-ray
diffraction, and Raman scattering investigations performed on an
individual SnO single crystal are reported.
Recently, the native p-type conductivity and large hole mobility of
SnO have attracted much attention to this oxide. A number of
investigations have focused on the p-type conductivity of SnO
films.
1–4
However, the strain, microstructure, surface, and film/
substrate interface would inevitably affect the transport properties of
thin films. In addition, anisotropic behaviors in the physical prop-
erties of layered SnO are expected due to the structural anisotropy.
Theoretical studies have predicted that the carrier effective masses
and the p-type conductivity are anisotropic.
5,6
The latest discovery of
superconductivity in polycrystalline SnO under high pressure makes
this oxide much more fascinating.
7
However, there are no reports on
the conductivity of SnO single crystals and its anisotropy has not
been confirmed by experiments due to the lack of large high-quality
single crystals. Consequently, high-quality, sizable single crystals of
SnO are highly desirable to achieve a more accurate study of their
transport properties and anisotropic behaviors. The preparation of
SnO is relatively difficult because disproportionation or oxidation of
SnO can readily occur. There are a few reports on single crystal
growth of SnO via high-temperature thermal evaporation or room-
temperature solution methods.
8–14,21
These methods need high
temperature or long reaction time, and the shapes of crystals were
basically diskett e, plate, or truncat ed bipyramid on the micrometre
scale. With the introduction of tri-sodium citrate and CTAB, the
shape control of single crystalline SnO platelets with edge length of
about 10 mm was achieved in solution.
14
However, shape-controlled
synthesis of large high-quality single crystals of SnO through a mild
and surfactant-free method still remains a challenge.
The crystal structure of SnO has been investigated by powder
X-ray diffraction and neutron diffraction experiments on
powdered SnO, revealing a tetragonal symmetry with space group of
P4/ nmm.
15–17
Raman spectra of SnO films and polycrystalline SnO
have been reported.
18,19
Up to now, neither single-crystal X-ray
diffraction nor Raman scattering studies on a single crystal of SnO
have been reported in the literature, due to the difficulties in obtaining
suitable single crystals.
In this communication, we report a facile surfactant-free hydro-
thermal route for the synthesis of SnO single crystals with large size
and controlled shape. By using this approach, high-quality SnO single
crystals have been obtained and successfully used to acquire single-
crystal XRD data and Raman scattering data. In addition, we report,
for the first time, the well-defined star-like crystals of SnO with four
symmetric arms.
The synthesis was carried out via a facile one-pot hydrothermal
method employing SnCl
2
$2H
2
O and NaOH as the source materials
(experimental details in the ESI†). The shape control of the crystals is
an intriguing factor in this study. Fig. 1 shows SEM images of crystals
grown at different temperatures. The product obtained by aging at
room temperature mainly consists of three-dimensional flower-like
structures assembled by interpenetrating plates with a thickness of
about 10 mm, even though some plates are also observed (Fig. 1a, e).
A groove on the top surface of an individual petal-like plate which
could interpenetrate other petals was clearly shown (Fig. S1a in the
ESI†). In contrast, highly truncated bipyramids of 40–100 mmin
width and 15–40 mm in thickness, star-shaped crystals with lateral
dimensions of about 0.8–1.3 mm, and crystals of square plate shape
of 0.3–0.6 mm in side length and 30–60 mm in thickness were acquired
at hydrothermal temperatures of 60
C, 100
C, and 180
C,
respectively (Fig. 1b-1d, 1f–1h). Interestingly, the novel star-shaped
crystals have four symmetric arms extending radially from the center
and one cross-like protuberance rising and locating diagonally on the
top surface (Fig. 1c,g). Different to the smooth surface morphology
of star-shaped and square plate crystals, a feature of truncated
bipyramids is that the surfaces are not smooth but assembled
from small standing nanosheets (Fig. S1b,c,d in the ESI†). From
the viewpoint of crystallography, the shape of crystals is in fact the
outside embodiment of the intrinsic crystal structure. Due to the
a
Ningbo Institute of Material Technology and Engineering, Chinese
Academy of Sciences, Ningbo, 315201, China. E-mail: yqguo@nimte.ac.
cn; Fax: +86-574-86685164; Tel: +86-574-86685164
b
College of Information Science and Engineering, Ningbo University,
Ningbo, 315211, China
c
Faculty of Materials Science and Chemical Engineering, Ningbo
University, Ningbo, 315211, China
d
National Synchrotron Radiation Laboratory, University of Science and
Technology of China, Hefei, 230029, China
† Electronic supplementary information (ESI) available: experimental
details, surface morphology of truncated bipyramids and
crystallographic data in .cif format. See DOI: 10.1039/c0ce00949k
This journal is ª The Royal Society of Chemistry 2011 CrystEngComm, 2011, 13, 5677–5680 | 5677
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