Large-scale synthesis of isotropic single-crystalline ScF 3 cubes by hydrothermal method

Article abstract of DOI:10.1111/jace.12932

Scandium fluoride (ScF₃) belongs to one of the rare compounds which exhibit isotropic negative thermal expansion. Here, a facile and environmentally friendly hydrothermal synthesis method has been presented. High-quality single-crystalline ScF₃ cubes, with an average size of 200 nm, can be easily fabricated in a large scale. Sc(NO₃) ₃ and NH₄HF₂ were used as precursors. The as-prepared ScF₃ demonstrates cubic symmetry (Pm-3 m), which was confirmed by X-ray diffraction and selected-area electron diffraction. Its uniform morphology and size were characterized by high-resolution transmission electron microscopy. Furthermore, thermal analysis was also performed in argon gas atmosphere to investigate its thermal stability.

Full text of DOI:10.1111/jace.12932

J. Am. Ceram. Soc., 97 [5] 1386–1388 (2014)
DOI: 10.1111/jace.12932
©
2014 The American Ceramic Society
Rapid Communication
ournal
J
Large-Scale Synthesis of Isotropic Single-Crystalline ScF Cubes by
3
Hydrothermal Method
‡
Lei Hu, Jun Chen,
‡,§,†
‡
‡
‡
Zhao Pan, Jinxia Deng, Ranbo Yu, and Xianran Xing
‡,§
‡
Department of Physical Chemistry, University of Science and Technology Beijing, Beijing 100083, China
§
State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China
Scandium fluoride (ScF ) belongs to one of the rare compounds
3
Recently, the synthesis of rare-earth fluorides on precisely
controlling size and morphology has attracted intense
which exhibit isotropic negative thermal expansion. Here, a
facile and environmentally friendly hydrothermal synthesis
method has been presented. High-quality single-crystalline
research attention. By means of a La(CF
route, single-crystalline LaF triangular nanoplates has been
3 3
COO) pyrolysis
3
1
8
3+
ScF cubes, with an average size of 200 nm, can be easily fab-
3
produced. Similarly, fullerene-like nanoparticles and Ln
doped bundle like YF
pared by a hydrothermal approach.
-
ricated in a large scale. Sc(NO
precursors. The as-prepared ScF
Pm-3 m), which was confirmed by X-ray diffraction and
3
)
3
and NH
4
HF
2
were used as
3
phosphors have been successfully pre-
1
9–22
3
demonstrates cubic symmetry
In addition, CeF
3
(
nanocrystals in various forms of disks, rods, and dots have
2
3
selected-area electron diffraction. Its uniform morphology and
size were characterized by high-resolution transmission electron
microscopy. Furthermore, thermal analysis was also performed
in argon gas atmosphere to investigate its thermal stability.
been obtained in a mild ultrasound-assisted route. And a
microemulsion fabrication of hexagonal and triangular YF
3
2
4
nanocrystals has been presented. With the assistance of
organics such as surfactants or co-surfactants, these unique
methods could facilitate precisely tailoring of size and mor-
phology. However, the introduction of all kinds of organics
not only gives rise to environmental pollution but also
increase costs when it comes to practical application in huge-
scale production. So it is known that there is still a big chal-
lenge to explore a simple, environmentally friendly, and low-
cost synthesis method without templates or surfactants.
Herein, we report a simple and efficient hydrothermal
I. Introduction
ENERALLY, majority of materials expand on heating and
contract on cooling. However, an opposite phenome-
G
non that some of materials tend to expand on cooling and
thus feature negative thermal expansion (NTE) behavior has
1
,2
sparked considerable interest in the past decades. Actually,
the NTE effect of most materials is minute and anisotropic,
3
approach to prepare ScF cubes with single-crystalline nat-
3
,4
and occurs only over a limited temperature range. How-
ever, potentially technical applications require materials
revealing isotropic NTE over a large temperature zone. To
ure. The crystal structure and morphology are characterized
by X-ray diffraction (XRD) and high-resolution transmission
electron microscopy (HRTEM), respectively. The thermal
5
date, isotropic NTE materials have been documented just in
a small amount of compounds, such as ZrW
3
stability of the as-prepared ScF is also investigated.
6
,7
8
2
O
8
,
2 7
ZrV O ,
9,10
and ZrMo O .
2
Very recently, it was reported that ScF3
3
-type structure demonstrates a pronounced
8
II. Experimental Section
(1) Hydrothermal Synthesis
Scandium nitrate [Sc(NO
(NH HF ) were of analytical grade, supplied by Beijing
with a cubic ReO
isotropic NTE over a large temperature range from about 10
to 1100 K (60–110 K, a
its NTE mechanism was investigated with the assistance of
1
1,12
l
ꢀ À14 ppm/K).
Furthermore,
3 3
) ] and ammonium bifluoride
4
2
1
3
inelastic neutron diffraction. In addition, its open frame-
work structure provides an opportunity to tune thermal
expansion by substitution Sc with other ions, such as rare-
Chemical Reagent Company. All these reagents were used to
fabricate the target product without further purification.
Deionized water was prepared to dissolve these reagents.
For a typical hydrothermal synthesis method, 0.001 mol
3
+
14
earth ions. However, there are very few reports on the fab-
1
5
rication of high-quality ScF
there are two methods to prepare ScF
reaction in which Sc O and NH HF are treated as precur-
3
in a large scale. Traditionally,
3 3 4 2
Sc(NO ) and 0.0015 mol NH HF were dissolved in 30 mL
3
. One is the solid-state
deionized water in a stainless-steel autoclave lined with Teflon.
Then, the autoclave was placed in a furnace at 180°C for 10 h
after which it was allowed to cool down to room temperature.
Subsequently, precipitates in the autoclave were washed with
excess ethanol and water. After separation by centrifugation,
the sample was dried under a vacuum oven at 80°C for 10 h
and collected for the next step characterization.
2
3
4
2
sors. However, the problem is related to the synthesis of
1
6,17
ScF
other method is wet chemical reaction in which ScCl
Sc O are dissolved by hydrofluoric acid followed by dehy-
3
with the moderately high ScF2.76 impurity.
The
3
or
2
3
dration and calcination in an inert atmosphere. However, the
toxic precursor, similar to HF, makes this method unsafe
and environmentally unfriendly.
(
2) Characterization
The structure of ScF
at 40 kV and 30 mA, where k = 0.15418 nm (Rigaku D/Max
200PC diffractometer; Rigaku Corp.,Tokyo, Japan). Its
3
was characterized by XRD operating
P. Barnes—contributing editor
2
lattice parameters were calculated by PowderX (Institute of
Physics, Chinese Academy of Sciences, Beijing, China) and
TREOR software (Department of Structural Chemistry, Uni-
versity of Stockholm, Stockholm, Sweden). The size and
Manuscript No. 34124. Received November 16, 2013; approved February 24, 2014.
Author to whom correspondence should be addressed. e-mail: junchen@ustb.edu.cn
†
1386

May 2014
Rapid Communications of the American Ceramic Society
1387
morphology of the sample were determined by transmission
electron microscope (TEM, TecnaiG2 20; FEI, Hillsboro,
OR) operating at 20 kV. The microstructure of the as-pre-
pared sample was studied by selected-area electron diffraction
(
2
SAED) and HRTEM with an accelerating voltage of
00 kV. The thermal stability was also investigated in the
argon atmosphere with a ramping rate of 10°C per min by
thermogravimetric analysis and differential scanning calorime-
TM
try (DSC/TG, Labsys Evo, Setaram Corp., Lyon, France).
III. Results and Discussion
The typical diffraction peaks of the sample have been clearly
showed in the powder X-ray diffraction pattern (Fig. 1). The
sharp diffraction peaks indicate a perfect crystalline structure.
And all peaks of the sample are in good agreement with the
3
previously reported cubic structure for crystalline ScF (space
group: Pm-3m, JCPDS card 46-1243). The lattice parameters
of the as-prepared ScF sample were calculated to be
3
Fig. 3. TG-DSC trace of the as-prepared ScF cubes.
3
ꢀ
ꢀ
3
a = b = c = 4.020 A, and unit cell volume is 64.73 A .
The morphology and particle size of as-prepared ScF
ture with a crystallographic orientation [001]. The cube of
the ScF3 sample grows along the {100} crystal planes. Its
microstructure information was further characterized by
HRTEM. The distinct lattice fringes on the surface of these
cubes [Fig. 2(b)] display its good crystallization. Further-
more, the fast Fourier transform pattern [FFT, inset in
Fig. 2(b)] also confirms its single-crystalline nature. The
3
were investigated by typical TEM image. As-prepared ScF3
particles demonstrate almost uniform distribution of shape
and size. And the average size of these particles is about
200 nm [Fig. 2(a)]. The SAED pattern was also performed
on a typical individual cube of the sample [inset in Fig. 2(a)].
The sharp diffraction spots show its single-crystalline struc-
ꢀ
interplanar spacing of 0.401 A corresponds to {100} planes
of cubic ScF3.
In the simple hydrothermal reaction, the morphology of
3
as-prepared ScF is solely determined by intrinsic factors.
The faces comprising the crystal habit correspond directly
with the most energetically stable atomic planes in ScF . The
3
planes of {100} have low Miller indices in the cubic symme-
try of ScF and are often relatively stable, because they con-
3
tain densely packed arrays of strongly bonded atoms. So the
morphology of ScF3 here corresponds to the symmetry of
the Bravais lattice, and its cubic 25crystal shape is
macroscopic expression of the unit cell.
a
To study the thermal stability of the as-prepared ScF3
cubes, thermal analysis was also performed in high pure
argon gas atmosphere by TG/DSC (Fig. 3). The sample
undergoes a weight loss about 2% below 200°C. It is likely
that this weight loss arises from the evaporation of adsorbed
water and the decomposition of crystallized water. The heat
flow curve also shows a corresponding broad endothermic
peak. With the temperature increasing, the weight of ScF
almost keeps unchanged. It demonstrates that ScF would be
stable among the temperature range from 200°C to 700°C.
When the sample is heated to 700°C, its weight is inclined to
3
3
3
Fig. 1. XRD patterns of pure phase of ScF (red line) and bulk
3
ScF (black line, JCPDS card 46-1243).
(
a)
(b)
3
Fig. 2. (a) TEM image and SAED image (inset) (b) HRTEM image and FFT pattern of ScF (inset).

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Vol. 97, No. 5
6
decrease. And there also appears an endothermic peak in the
heat flow curve. With temperature further increasing, the
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2 8
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11
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This work was supported by National Natural Science Foundation of China
(Grant nos. 21322102, 21031005, 21231001), Program for Changjiang Scholars
and Innovative Research Team in University (IRT1207), the Foundation for
the Author of National Excellent Doctoral Dissertation of P.R. China
(201039), Fok Ying Tung Education Foundation (131047), and Program for
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