Wide band gap design of new chalcogenide compounds: KSrPS4 and CsBaAsS4

Article abstract of DOI:10.1039/c7ra01142c

Recently, the exploration of infrared nonlinear optical (IR NLO) materials has mainly focused on chalcogenide compounds. However, their practical applications are often hampered by the low laser damage thresholds (LDTs). It is known that wide band gaps ca

Full text of DOI:10.1039/c7ra01142c

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Wide band gap design of new chalcogenide
compounds: KSrPS and CsBaAsS †
4
4
Cite this: RSC Adv., 2017, 7, 38044
a
a
bd
b
c
Jianqiao Jiang,
and Yuandong Wu
Dajiang Mei,* Pifu Gong, Zheshuai Lin, Junbo Zhong
a
Recently, the exploration of infrared nonlinear optical (IR NLO) materials has mainly focused on
chalcogenide compounds. However, their practical applications are often hampered by the low laser
damage thresholds (LDTs). It is known that wide band gaps can significantly enhance the LDTs of
materials, and the introduction of alkali and alkaline earth cations would broaden the band gap.
Accordingly, in this work two new compounds KSrPS
cations were synthesized successfully. Both compounds crystallize in the space group Pnma (62) of the
orthorhombic system, and the structures consist of isolated PnS
4 4
and CsBaAsS with both alkali and alkaline earth
4
(Pn ¼ P, As) tetrahedra with the
Received 25th January 2017
Accepted 19th July 2017
interstices occupied by K (or Cs) and Sr (or Ba) atoms, respectively. The band gaps of compounds were
determined by different methods. The UV-visible diffuse reflectance spectra revealed that the band gaps
DOI: 10.1039/c7ra01142c
of KSrPS
4
and CsBaAsS
4
are larger than 3.62 eV and 2.86 eV, respectively. The band gaps are primarily
rsc.li/rsc-advances
determined by the PnS
4
tetrahedra.
band gap of material can be enlarged through the introduction
Introduction
24,25
of the Ge or Si element.
(ref. 2) with 1.8 eV, the band gaps of AgGaSiSe
Ga SiSe (ref. 25) are broadened to 2.63 eV and 2.30 eV,
And compared to the band gap of
It is well known that coherent IR lasers have been widely applied AgGaSe
in civil and military elds such as laser guidance, signal and Ag
2
4
(ref. 24)
3
3
8
communication and industrial processing. A number of NLO respectively. The introduction of alkali or alkaline earth cations
materials have been applied to generate IR lasers. The which usually are electropositive elements also contributes to
2
6–28
commercial IR NLO materials are mainly focused on chalco- broaden band gap of materia.
For example, the band gaps of
(ref. 27) increased to 3.54 eV and
been applied in optoelectronic and thermoelectric areas because 4.15 eV, respectively, compared to that of AgGaS with 2.75 eV.
(ref. 27) increased to
these materials suffer from the low LDTs, which limits their 2.64 eV and 3.34 eV, respectively, compared to that of AgGaSe
further application in various areas. Here, the low LDT is prin- with 1.8 eV. And with the introduction of both alkali and alkaline
cipally caused by the relatively small band gap of the material. earth cations, the band gap of Na BaGeS (ref. 29) reached
1,2
genide compounds, such as AgGaS
2
and AgGaSe
2
,
which have BaGa S (ref. 26) and LiGaS
4 7 2
2
3–8
4 7 2
of their diverse structures and physical properties. However, Those of BaGa Se (ref. 28) and LiGaSe
2
2
4
Materials with higher LDTs can be obtained based on broader 3.7 eV. Wherefore in this work, we attempted to simultaneously
band gaps. Numerous research has been conducted to search for introduce the alkali and alkaline earth cations to broaden the
novel, promising mid-IR NLO materials that exhibit broad band band gap of material. Meanwhile the introduction of PnS
4
9–29
gaps and strong NLO responses.
Ag
In our previous research for (Pn ¼ P, As) groups are conducive to improve the NLO proper-
30
3 3 8 4
Ga SiSe and AgGaSiSe
compounds, it mentioned that the ties. Through the combination of alkali and alkaline earth
cations with the PnS
A/AL/Pn/S (A ¼ alkali cations, AL ¼ alkaline earth cations)
system, and fortunately, the two new compounds KSrPS and
CsBaAsS were successfully synthesized. The syntheses, crystal
4
groups, we conducted the research to the
a
College of Chemistry and Chemical Engineering, Shanghai University of Engineering
4
Science, Shanghai 201620, P. R. China. E-mail: meidajiang718@pku.edu.cn
b
4
Center for Crystal Research and Development, Key Laboratory of Functional Crystals structures, electronic structures and optical properties of the
and Laser Technology, Chinese Academy of Sciences, Beijing 100190, P. R. China
materials were also investigated.
c
Key Laboratory of Green Catalysis of Higher Education Institutes of Sichuan, College
of Chemistry and Environmental Engineering, Sichuan University of Science and
Engineering, Zigong 643000, P. R. China
d
Experimental section
Synthesis
University of Chinese Academy of Sciences, Beijing 100190, P. R. China
Electronic supplementary information (ESI) available: Crystallographic data in
CIF format for KSrPS and CsBaAsS . CCDC 1502143 and 1503947. For ESI and
crystallographic data in CIF or other electronic format see DOI:
0.1039/c7ra01142c
†
4
4
The compound KSrPS
4 2 3
was prepared by combining K S
1
(prepared by stoichiometric reaction of the K (Sinopharm
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chemical Reagent Co., Ltd., 98%) and S (Sinopharm chemical in the range of 80–100 mm. Similar size of AgGaS
2
was chosen as
Reagent Co., Ltd., 99.5%) elements in liquid NH ), SrS the reference.
3
(prepared by stoichiometric reaction of Sr (Sinopharm chemical
Reagent Co., Ltd., 99%) and S elements), Nd (Sinopharm Laser damage threshold test
2 5
chemical Reagent Co., Ltd., 99.9%), P S (Sinopharm chemical
The laser damage thresholds of title compounds were evaluated
Reagent Co., Ltd., 99%) and additional S (Sinopharm chemical
Reagent Co., Ltd., 99.5%) in the molar ratio 2 : 1 : 1 : 1 : 6. The
sample was heated in a computer-controlled furnace to 973 K,
then kept there for 5 d, then cooled to 373 K at the rate of 3 K
on powder sample with a pulsed YAG laser (1.06 mm, 10 ns, 10
32
2
Hz). Similar size of AgGaS was chosen as the reference.
Structure determination
ꢀ1
h
. The resulting melts were washed with dimethylformamide
The structure model was obtained by direct methods and was
(DMF) and acetone in turn. The product consisted of colorless
rened by full-matrix least-squares renement based on F2
transparent platelet KSrPS . This compound was stable in dry
4
33
using the Shelxtl package. The positions were standardized
air for several days.
34
with the Structure Tidy program within the Platon package.
The compound CsBaAsS
prepared by stoichiometric reaction of the Cs (Alfa Aesar,
9.8%) and S (Sinopharm chemical Reagent Co., Ltd., 99.5%)
elements in liquid NH ), BaS (Sinopharm chemical Reagent Co.,
4 2 3
was prepared by combining Cs S
The nal renement converged with a residual factor of
(
9
wR ¼ 0.095 (all data). Technical details of the data acquisition
2
as well as some renement results are summarized in Table 1.
3
Ltd., 99%), Nd (Sinopharm chemical Reagent Co., Ltd., 99.9%),
As S (Sinopharm chemical Reagent Co., Ltd., 99%) and addi-
The rst-principles calculations
2
3
tional S (Sinopharm chemical Reagent Co., Ltd., 99.5%) in the The rst-principles calculations for the KSrPS and CsBaAsS4
4
molar ratio 2 : 0.5 : 1 : 1 : 6. The sample was heated in crystals are performed by the plane-wave pseudo potential
a computer-controlled furnace to 973 K, then kept there for 5 d, method implemented in the CASTEP package based on the
ꢀ
1
35
then cooled to 373 K at the rate of 3 K h . The resulting melts density functional theory (DFT). The ion–electron interactions
were washed with DMF and acetone in turn. The product con- are modeled by the optimized normal-conserving pseudo
sisted of yellow transparent platelet crystal of CsBaAsS
compound was stable in dry air for several days.
4
. This potentials for all elements. The adopted density functional
method is exchange-correlation (XC) functional of local density
36
approximation (LDA). The kinetic energy cutoffs of 800 eV and
37
Energy dispersive X-ray uorescence test
Monkhorst–Pack k-point meshes with density of (2 ꢁ 3 ꢁ 2)
and (1 ꢁ 3 ꢁ 3) points in the Brillouin zone are chosen for
KSrPS and CsBaAsS crystals, respectively. Our tests reveal that
The analysis of the compounds was carried out with Shimadzu
EDX-720 Energy Dispersive X-ray Fluorescence spectrometer.
The tests for each compound were performed with 5 times, and
the spectra of number 1 and 6, as shown in Fig. 1 (the rest of the
number 2–5 and 7–10 spectra are shown in the ESI†), man-
ifested the presence of K, Sr, P, S and Ca, Ba, As, S in the
approximate molar ratio of 1 : 1 : 1 : 4 and 1 : 1 : 1 : 4,
respectively.
4
4
the above computational set ups are sufficiently accurate for the
present purposes.
Results and discussion
4 4
The two compounds KSrPS and CsBaAsS crystallize in space
group Pnma (62) of the orthorhombic system and adopt the
TlEuPS (ref. 38) structure type, As shown in Fig. 2. The struc-
4
Single crystal data collection
tures consist of isolated PnS (Pn ¼ P, As) tetrahedra separated
4
Single crystal X-ray diffraction data were collected with graphite- by the K (or Cs) and Sr (or Ba) atoms, and the atoms locate in the
˚
monochromatized Mo K radiation (l ¼ 0.71073 A) at 220 K on tunnel formed by the tetrahedra, respectively. The asymmetric
a STOE Imaging Plate Diffraction System (IPDS-1).
units for both compounds contain one crystallographically
independent K (or Cs) atom, one independent Sr (or Ba) atom,
one independent P (or As) atom and three independent S atoms.
UV-vis diffuse reectance test
For KSrPS
4
, K atom is coordinated to a bicapped trigonal
UV-vis diffuse reectance spectroscopy test was performed on
a Shimadzu UV-3600 spectrophotometer. The samples and
prism of eight S atoms with K–S distances ranging from 3.336(1)
˚
˚
to 3.603(2) A, which is close to those of 3.2058(14)–3.5239(14) A
BaSO
4
(totally reected) were ground together at room
˚
for K–S distances in KBiSiS
K–S distances in KBiGeS
atoms with Sr–S distances ranging from 2.992(1) to 3.685(1) A˚ ,
4
(ref. 39) and 3.194(3)–3.601(3) A for
temperature. Then the mixture was prepared as a at specimen,
and in UV/vis range, the resolution was 0.1 nm. The data were
collected at 200–800 nm.
39
4
.
The Sr atom is coordinated to 9 S
˚
which is close to those of 2.928–3.242 A for Sr–S distances in
40
Sr
2
ZnS
3
.
Each P atom is bonded to four S atoms to form
Second harmonic generation test
a slightly distorted tetrahedron, with the bond lengths ranging
˚
The optical second harmonic generation test was performed on from 2.023(2) to 2.049(8) A, similar to those of 2.010(1)–2.090(1)
˚
41
the powder sample of KSrPS and CsBaAsS by means of the A for P–S distances in LiZnPS . Since S–S bonds are not
4
4
4
31
Kurtz–Perry method, with a 1.06 mm Q-switch laser. The observed in the structure, the oxidation states of 1+, 2+, 5+,
samples were ground and sieved by using a series of mesh sizes 2ꢀ can be distributed to K, Sr, P and S, respectively.
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4 4
Fig. 1 (a) Energy dispersive X-ray fluorescence spectra of KSrPS , (b) energy dispersive X-ray fluorescence spectra of CsBaAsS .
42
For CsBaAsS
4
, Cs atom is bonded to 10 S atoms with Cs–S Cs
3
Bi(AsS
4
)
2
.
While Ba is coordinated to 9 S atoms with Ba–S
˚
˚
distances ranging from 3.468(2) to 3.895(1) A, which is close to distances ranging from 3.182(2) to 3.588(0) A, similar to those of
43
˚
˚
those of 3.4022(10)–4.0982(13)
8 2 38
A for Cs–S distances in 2.896(2)–3.331(2) A for Ba–S distances in Ba23Ga Sb S . Each
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Table
CsBaAsS
1
Crystal data and structure refinement for KSrPS
4
and the structure, the oxidation states of 1+, 2+, 5+, 2ꢀ can be
distributed to Cs, Ba, As and S, respectively.
4
For these compounds, the larger content of alkali cations (K,
KSrPS
4
CsBaAsS
4
Cs) and alkaline cations (Ba, Sr) is, the sparser the PS and AsS4
4
ꢀ
1
F
a (A)
b (A)
c (A)
w
(g mol
)
285.93
473.41
tetrahedra connectivity will be, which can be referred to our
previous work on Ba Al Se and Ba Ga Se . And the tetrahedra
5 2 8 5 2 8
would be completely separated from each other by the K (or Cs)
and Sr (or Ba) atoms.
From the UV-visible diffuse reectance spectra of the
compounds in Fig. 3(a), the absorption edges are about 343 nm
˚
45
16.8214(9)
6.6274(5)
6.5585(4)
731.16(8)
Pnma (62)
4
11.9066(6)
6.9184(5)
10.0338(5)
826.53(8)
Pnma (62)
4
˚
˚
3
˚
V (A )
Space group
Z
Index ranges
ꢀ21 # h # 22
ꢀ15 # h # 15 and 434 nm for KSrPS and CsBaAsS , respectively. The band
4
4
ꢀ
8 # k # 8
8 # l # 8
ꢀ9 # k # 9
ꢀ13 # l # 12
2.65–28.08
1029
gaps of KSrPS and CsBaAsS obtained by direct extrapolation
4
4
ꢀ
46
method with baseline tangents were 3.62 and 2.86 eV,
respectively. To correctly compared the band gaps of different
compounds, the measurement methods need to be consistent.
And in the Fig. 3(b), the direct extrapolation method with upper
tangents were carried out on the spectra, and the results showed
that the band gaps of compounds are 4.23 eV and 3.25 eV,
respectively. These two compounds band gaps are signicantly
Theta range
2.42–28.08
873
Number of reection collected
ꢀ
3
r
c
(g cm
)
2.598
91.84
0.0292
0.0770
3.804
140.24
0.0309
0.0775
) ¼ {P
ꢀ
1
m (cm
R(F)
R
)
a
2
o
b
w
(F
)
P
P
a
2
2
o
b
2
o
2
o
R(F) ¼ rrF
o
r ꢀ rF
c
rr/ rF
for all data.
o
r for F
o
> 2s(F
).
R
w
(F
[w(F
ꢀ
P
2
2
4 1/2
F
c
) ]/ wF
o
}
larger than that of the commercial materials AgGaS (ref. 1) with
2
2
.75 eV and AgGaSe
KSrPS and CsBaAsS
6) with 3.54 eV and BaGa
2
(ref. 2) with 1.8 eV. The band gaps of
are also larger than that of BaGa (ref.
Se (ref. 28) with 2.64 eV, respectively,
4
4
4 7
S
As atom is bonded to four S atoms to form a slightly distorted
tetrahedron, with the As–S bond lengths ranging from 2.153(4)
2
4
7
˚
˚
indicated that compounds with large band gaps were obtained.
According to the single crystal growth experiment results, the
colors for KSrPS and CsBaAsS crystals are colorless and yellow
to 2.161(1) A, which is similar to those of 1.918(3)–2.390(3) A for
˚
As–S distances in Cs
distances in Cs Ta AsS11
3
Bi(AsS
4
)
2
and 2.229(2)–2.266(2) A for As–S
Since S–S bonds are not observed in
4
4
4
4
3
2
.
Fig. 2 (a) Unit cell structure of KSrPS
4
, (b) PS
4
tetrahedron in KSrPS
4
structure, and (c) AsS
4
4
tetrahedron in CsBaAsS structure.
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Fig. 3 Diffuse spectra of KSrPS
hy) versus hy; (d) the spectra of (F(R) hy) versus hy.
4
and CsBaAsS
4
: (a) the spectra with upper tangents; (b) the spectra with baseline tangents; (c) the spectra of (F(R)
2
0.5
damage thresholds of KPSrS
that of AgGaS . The optical second harmonic generation test
was performed on KSrPS and CsBaAsS with a 1.06 mm Q-
switch laser. The compounds KSrPS and CsBaAsS did not
4 4
and CsBaAsS are above 5 times of
2
4
4
4
4
give any second harmonic generation signal because of their
centrosymmetric structure.
The electronic band structures of the KSrPS and CsBaAsS4
4
crystals are shown in Fig. 5. The calculations with sX-LDA
functional were carried out to investigate the experimental
values of band gaps and the results showed the values of 3.58 eV
and 2.73 eV for KSrPS
The partial density of state (PDOS) projected on the consti-
tutional atoms of the KSrPS and CsBaAsS are shown in Fig. 6,
4 4
and CsBaAsS , respectively.
4 4
Fig. 4 The single crystals of KSrPS and CsBaAsS compounds.
4
4
from which several electronic characteristics are shown: (i) the
region lowered than ꢀ5 eV consist of the isolated inner-shell
states with K 2s2p (or Cs 5s5p), Sr 4s4p (or Ba 5s5p), P 3s2p
(
see in Fig. 4), respectively, which was in good accordance with
the UV-visible reectance spectra. In the Fig. 3(c) and (d), the
direct and indirect band gaps are measured by Tauc–Davis Mott
expressions. The measurement of direct band gap indicated
that KSrPS and CsBaAsS is 3.92 eV and 2.97 eV, respectively.
And the measurement of indirect band gap indicated that
KSrPS and CsBaAsS is 3.84 eV and 2.91 eV, respectively.
The laser damage test was performed on the powder sample
with a pulsed YAG laser (1.06 mm, 10 ns, 10 Hz). AgGaS was
served as the reference. The results showed that both the laser
(
or As 4s3p) and S 3s2p orbitals, which have little interaction
with neighbor atoms. (ii) The upper part of the valence band
about ꢀ4 eV) is mainly composed of the p orbitals of P 3p (As
p) and S 3p orbitals, but the extra top of the VB is occupied by
47
4
4
(
4
4
4
the S 3p orbitals. (iii) Although all the elements contribute to
the states on the bottom of conduct band, states on the bottom
of conduct band mostly come from the S and P (As) atoms.
2
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4 4
Fig. 5 (a) The band structure of KSrPS , and (b) band structure of CsBaAsS .
4 4
Fig. 6 (a) The PDOS of KSrPS , and (b) PDOS of CsBaAsS crystals.
In summary, the upper part of valence band and the bottom
of conduct band are principally determined by the P (As) and S tures and properties of the compounds, the contours of elec-
elements, which indicated that the optical absorption is mostly tronic density difference on the PS and AsS groups were drawn
To further investigate the relationship between the struc-
4
4
3
ꢀ
determined by (PnS4) (Pn ¼ P, As) groups.
for the title compounds in Fig. 7, which illustrate charge
redistribution due to the formation of chemical bonds. It is
obvious that more charges are located on the P–S bonds than on
the As–S bonds, indicating the much stronger covalent char-
acteristic of the former chemical bonds.
Conclusions
To obtain compounds with wide band gaps, in this work,
introduction of both the alkali and alkaline earth cations was
carried out. Two new compounds KSrPS and CsBaAsS were
4
4
successfully synthesized. The compounds crystallize in space
group Pnma (62) of the orthorhombic system and adopt the
Fig. 7 (a) The electronic charge density difference plotting on the PS
4
groups, and (b) AsS
4
groups.
TlEuPS
structure type. The band gaps of compounds were
4
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determined by four methods. The results revealed that the band 15 H. Lin, L. Chen, L. J. Zhou and L. M. Wu, J. Am. Chem. Soc.,
gaps of KSrPS4 and CsBaAsS4 are larger than 3.62 eV and 2013, 135, 12914.
.86 eV, respectively, which imply that the band gaps of 16 Y. Kim, I. S. Seo, S. W. Martin, J. Baek, P. S. Halasyamani,
2
compounds were successfully broadened compared with the
N. Arumugam and H. Steinnk, Chem. Mater., 2008, 20,
commercial materials AgGaS
2
and AgGaSe
2
, respectively. The
6048.
band gaps are primarily determined by the PnS
4
(Pn ¼ P, As) 17 Z. H. Kang, J. Guo, Z. S. Feng, J. Y. Gao, J. J. Xie, L. M. Zhang,
tetrahedra. Such compounds may arouse further interest in
exploring new IR NLO materials with wide band gaps, through
introducing the alkali or alkaline earth cations.
V. Atuchin, Y. Andreev, G. Lanskii and A. Shaiduko, Appl.
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Acknowledgements
2
This research was supported by the National Natural Science
Foundation of China (No. 51502169), China “863” project (No.
2
2
2015AA034203), Opening Project of Key Laboratory of Green
Catalysis of Sichuan Institutes of High Education (No. LZJ1503),
Shanghai University of Engineering Science “Innovation
Training Project of Undergraduate” (No. cs1504002) and
Shanghai University of Engineering Science “Scientic Research
Training Project of Undergraduate” (No. HZJY20160029).
2
2
2
5 D. Mei, P. Gong, Z. Lin, K. Feng, J. Yao, F. Huang and Y. Wu,
CrystEngComm, 2014, 16, 6836.
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