Syntheses, structures, optical properties, and electronic structures of KBaMSe3(M = As, Sb)

Article abstract of DOI:10.1016/j.jallcom.2014.07.109

The first two members in the quaternary A/A′/M/Q (A = alkali metal; A′ = alkaline-earth metal; M = As, Sb, Bi; Q = S, Se, Te) system, namely the KBaMSe₃(M = As, Sb) selenides, have been synthesized by solid state reactions. They are isostructural and crystallize in the centrosymmetric space group P2₁/c of the monoclinic system. In the structure, the trivalent M atom (M = As, Sb) is coordinated to three Se atoms forming a trigonal pyramid with the Se atoms serving as the triangle base, showing the stereochemical activity of the ns²lone pair electron. The MSe₃(M = As, Sb) trigonal pyramids are totally isolated from each other with K⁺and Ba²⁺cations located between them. The optical band gaps of 2.26 (2) eV for KBaAsSe₃and 2.04 (2) eV for KBaSbSe₃, were deduced from the diffuse reflectance spectra. The first principles calculations were performed to study the electronic structures of KBaMSe₃(M = As, Sb) compounds and the results indicated that these two compounds are indirect band gap semiconductors.

Full text of DOI:10.1016/j.jallcom.2014.07.109

Journal of Alloys and Compounds 617 (2014) 287–291
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jalcom
Syntheses, structures, optical properties, and electronic structures
of KBaMSe3 (M = As, Sb)
Wenlong Yin a,b, Kai Feng a,c, Lei Kang a,c, Bin Kang b, Jianguo Deng b, Zheshuai Lin a, Jiyong Yao a,
,
⇑
Yicheng Wu a
a Key Laboratory of Functional Crystals and Laser Technology, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China
b Institute of Chemical Materials, China Academy of Engineering Physics, P.O. Box 919-306 Mianyang 621900, China
c University of the Chinese Academy of Sciences, Beijing 100049, China
a r t i c l e i n f o
a b s t r a c t
The first two members in the quaternary A/A0/M/Q (A = alkali metal; A0 = alkaline-earth metal; M = As, Sb,
Bi; Q = S, Se, Te) system, namely the KBaMSe3 (M = As, Sb) selenides, have been synthesized by solid state
reactions. They are isostructural and crystallize in the centrosymmetric space group P21/c of the mono-
clinic system. In the structure, the trivalent M atom (M = As, Sb) is coordinated to three Se atoms forming
a trigonal pyramid with the Se atoms serving as the triangle base, showing the stereochemical activity of
the ns2 lone pair electron. The MSe3 (M = As, Sb) trigonal pyramids are totally isolated from each other
with K+ and Ba2+ cations located between them. The optical band gaps of 2.26 (2) eV for KBaAsSe3 and
2.04 (2) eV for KBaSbSe3, were deduced from the diffuse reflectance spectra. The first principles calcula-
tions were performed to study the electronic structures of KBaMSe3 (M = As, Sb) compounds and the
results indicated that these two compounds are indirect band gap semiconductors.
Article history:
Received 28 May 2014
Received in revised form 11 July 2014
Accepted 12 July 2014
Available online 19 July 2014
Keywords:
Chalcogenides
Synthesis
Crystal structure
Optical property
Band structure
Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction
generation (SHG) responses in the IR range [7]. KBiCu2S3 exhibits
notable photoelectric behavior and has a potential application in
Over the past decades, the exploratory synthesis of new multi-
nary chalcogenides with two or more metal cations has attracted
great interest due to their amazing structural and compositional
complexity that gives rise to their fascinating physical properties
including magnetic, superconducting, thermoelectric, and nonlin-
ear optical properties [1–34]. Since the stereochemical activity of
ns2 lone pair of electrons of group 15 elements M (M = As, Sb, Bi)
has profound effects on the crystal structures, electronic struc-
tures, and hence on the properties of the resultant compounds,
the exploratory synthesis of new group 15 element-containing
multinary chalcogenides has been an active area for years and with
great efforts many chalcogenides with intriguing structures and
properties have been discovered [2–17,24–27]. For example, Ba23-
Ga8Sb2S38 features an unusual zero-dimensional structure contain-
ing totally isolated GaS4 tetrahedra and discrete SbS3 pyramids [2];
Bi3In4S10 and Bi14.7In11.3S38 contain interesting chains of Bi atoms
with alternating short Bi–Bi bonds of around 3.1 Å and longer dis-
tances of around 4.6 Å [3]; Cs5BiP4Se12 [4], Rb3Ta2AsS11 [5], La4InS-
bS9 [6], and Sm4GaSbS9 exhibit very strong second harmonic
solar cells [8].
The above significant results inspire us to synthesize new com-
pounds containing group 15 elements. As we know, in the A/M/Q
(A = alkali metal; M = As, Sb, Bi; Q = S, Se, Te) ternary system which
has been extensively studied, more than 130 compounds have
been reported and some of them have interesting structures or
physical properties. For example, CsBi4Te6 [24] and K2Bi8Se13 [25]
possess attractive thermoelectric properties; LiAsS2 [26] and
c-
NaAsSe2 [27] exhibit very strong second harmonic generation
effects. On the other hand, in the A0/M/Q (A0 = alkaline-earth metal;
M = As, Sb, Bi; Q = S, Se, Te) ternary system, to date there are also
about 20 compounds have been reported and some compounds
possess interesting structure features. For example, Sr6Sb6S17 pos-
sesses the novel discrete trisulfide S23ꢀ anions [28]. However, as to
the quaternary A/A0/M/Q (A = alkali metal; A0 = alkaline-earth
metal; M = As, Sb, Bi; Q = S, Se, Te) system, no compounds were
reported so far.
As shown in numerous explorations, the size and charge of cat-
ions have great influence on the microscopic packing of anions,
which in turn determines the overall properties in a crystal
[16,29–34]. In this paper, we utilize both the alkali and the alka-
line-earth cation as mixed cations. The different charge/size
⇑
Corresponding author. Tel./fax: +86 10 82543725.
E-mail address: jyao@mail.ipc.ac.cn (J. Yao).
http://dx.doi.org/10.1016/j.jallcom.2014.07.109
0925-8388/Ó 2014 Elsevier B.V. All rights reserved.

288
W. Yin et al. / Journal of Alloys and Compounds 617 (2014) 287–291
combination of mixed cations may have different influence on the
packing of anions, so it is more likely to isolate new phases with
interesting stoichiometries, structures, and properties. Guided by
this idea, we successfully obtained the first two compounds in
the quaternary A/A0/M/Q (A = alkali metal; A0 = alkaline-earth
metal; M = As, Sb, Bi; Q = S, Se, Te) system, namely the KBaMSe3
(M = As, Sb) selenides. In this paper, we report the syntheses, struc-
tural characterizations, experimental band gaps and electronic
structures of KBaMSe3 (M = As, Sb).
2. Experimental section
2.1. Syntheses
K (98%, Sinopharm Chemical Reagent Co., Ltd.), Ba (99%, Aladdin Co., Ltd.), As
(99.9%, Sinopharm Chemical Reagent Co., Ltd.), Sb (99.99%, Sinopharm Chemical
Reagent Co., Ltd.), and Se (99.99%, Sinopharm Chemical Reagent Co., Ltd.) were used
without further purification. The binary starting materials BaSe and Sb2Se3 were
prepared by the stoichiometric reactions of elements at high temperatures
(1123 K for BaSe and 623 K for Sb2Se3) in sealed silica tubes evacuated to 10ꢀ3 Pa,
while K2Se was prepared by the stoichiometric reactions of elements in liquid
NH3. The ternary starting material KAsSe2 was synthesized by the stoichiometric
reaction of K2Se, As, and Se in the molar ratio of K2Se:As:Se = 1:2:3 at 973 K in
sealed silica tube evacuated to 10ꢀ3 Pa. The ternary starting material KSbSe2 was
synthesized by the stoichiometric reaction of K2Se and Sb2Se3 in the molar ratio
of 1:1 at 923 K.
Fig. 1. Powder X-ray diffraction pattern of KBaAsSe3 and the simulated pattern
based on the single crystal crystallographic data. (The four peaks marked with * are
due to very small amount of As2Se3.)
2.1.1. KBaAsSe3
Crystals of KBaAsSe3 were initially obtained from the reaction between KAsSe2
and BaSe in the molar ratio of 1:3. The reaction mixture (KAsSe2 82 mg, 0.3 mmol;
BaSe 195 mg, 0.9 mmol) was ground and loaded into 12 mm inner-diameter fused-
silica tube under an Ar atmosphere in a glovebox. The tube was sealed under a
10ꢀ3 Pa vacuum and then placed in a computer-controlled furnace. The reaction
mixture was heated to 1273 K in 15 h, kept at 1273 K for 48 h, followed by slow
cooling to 473 K at a rate of 4 K/h, and finally cooled to room temperature by
switching off the furnace. The products consisted of orange single crystals of KBa-
AsSe3, which were manually selected for structure characterization. Analysis of
the crystals with an EDX-equipped Hitachi S-4800 SEM showed the presence of
K, Ba, As, and Se in the approximate ratio of 1:1:1:3. The crystals are stable in air.
2.1.2. KBaSbSe3
Fig. 2. Powder X-ray diffraction pattern of KBaSbSe3 and the simulated pattern
based on the single crystal crystallographic data. (The two peaks marked with * are
due to small amount of KSbSe2.)
Crystals of KBaSbSe3 were initially obtained from a reaction among K2Se, BaSe,
and Sb2Se3 in the molar ratio of 2:2:1. The reaction mixture (K2Se 63 mg, 0.4 mmol;
BaSe 87 mg, 0.4 mmol; Sb2Se3 96 mg, 0.2 mmol) was ground and loaded into
12 mm inner-diameter fused-silica tube under an Ar atmosphere in a glovebox.
The tube was sealed under a 10ꢀ3 Pa vacuum and then placed in a computer-
controlled furnace. The reaction mixture was heated to 1093 K in 20 h, kept at
1093 K for 50 h, followed by slow cooling to 673 K at a rate of 3 K/h, and finally
cooled to room temperature by switching off the furnace. The products consisted
of reddish orange single crystals of KBaSbSe3, which were manually selected for
structure characterization. Analysis of the crystals with an EDX-equipped Hitachi
S-4800 SEM showed the presence of K, Ba, Sb, and Se in the approximate ratio of
1:1:1:3. The crystals are stable in air.
Polycrystalline samples of KBaMSe3 (M = As, Sb) were synthesized by high-
temperature solid state reaction techniques. The mixtures of BaSe and KMSe2
(M = As, Sb) the molar ratio of 1:1 were ground and loaded into fused-silica tubes
under an Ar atmosphere in a glovebox. The tubes were sealed under a 10ꢀ3 Pa
vacuum and then placed in computer-controlled furnaces. The reaction mixtures
were heated to 823 K in 12 h, kept at that temperature for 96 h, and then the
furnaces were turned off.
2.3. Structure determination
The single crystal X-ray diffraction measurement was performed on a Rigaku
AFC10 diffractometer equipped with
a
graphite-monochromated
K
a
(k = 0.71073 Å) radiation at 153 K. The Crystalclear software [35] was used for data
extraction and integration and the program XPREP [36] was used for face-indexed
absorption corrections.
The structure was solved with Direct Methods implemented in the program
SHELXS and refined with the least-squares program SHELXL of the SHELXTL.PC suite
of programs [36]. The program STRUCTURE TIDY [37] was then employed to stan-
dardize the atomic coordinates. Additional experimental details are given in Table 1
and selected metrical data are given in Table 2. Further information may be found in
the electronic Supplementary information.
2.4. Diffuse reflectance spectroscopy
A Cary 1E UV–visible spectrophotometer with a diffuse reflectance accessory
was used to measure the spectrum of KBaMSe3 (M = As, Sb) in the range of
300 nm (4.13 eV) to 1500 nm (0.83 eV). The optical absorption spectra were
converted from diffuse–reflectance spectra using the Kubelka–Munk function,
a/S = (1 ꢀ R)2/2R, where a is the Kubelka–Munk absorption coefficient and S is the
scattering coefficient.
2.2. X-ray powder diffraction
X-ray powder diffraction analysis of the resultant powder samples was per-
formed at room temperature in the angular range of 2h = 10–60° with a scan step
width of 0.02° and a fixed counting time of 0.2 s/step using an automated Bruker
D8 X-ray diffractometer equipped with a diffracted monochromator set for Cu K
a
(k = 1.5418 Å) radiation. The experimental powder X-ray diffraction patterns were
found to be in agreement with the calculated patterns on the basis of the single
crystal crystallographic data of KBaMSe3 (M = As, Sb) (Figs. 1 and 2). Meanwhile,
the peaks in the patterns marked with * are due to small amount of As2Se3 and
KSbSe2 for KBaMSe3 and KBaMSe3, respectively.
2.5. Band structure calculation
The electronic structures for KBaMSe (M = As, Sb) were calculated using the
first-principles plane-wave pseudopotential method [38] implemented in the
CASTEP [39] program. The local density approximation (LDA) [40] is adopted to

W. Yin et al. / Journal of Alloys and Compounds 617 (2014) 287–291
289
Table 1
Crystal data and structure refinements for KBaAsSe3 and KBaSbSe3.
KBaAsSe3
KBaSbSe3
fw
a (Å)
b (Å)
c (Å)
488.24
9.369(2)
9.049(2)
9.247(2)
108.23(3)
744.6(3)
P21/c
535.07
9.386(2)
9.199(2)
9.369(2)
108.25(3)
768.3(3)
P21/c
b (°)
V (Å3)
Space group
Z
4
4
qc (g/cm3)
4.355
4.626
l
(mmꢀ1
)
24.846
0.0227
0.0569
23.246
0.0379
0.0653
R (F)a
RW (F2o )b
zb
0.02
0.018
P
P
RðFÞ ¼ kFoj ꢀ jFck= jFoj for F2o > 2
r
ðF2o Þ.
a
Fig. 3. The metal atom coordination geometry in KBaAsSe3.
1=2
P
P
RwðF2o Þ ¼ f ½wðFo2 ꢀ F2c Þ2ꢁ= wF4og
for all data. wꢀ1
¼
r2ðF2o Þ þ ðzPÞ , where
2
b
P ¼ ðMaxðF2o ; 0Þ þ 2F2c Þ=3.
Table 2
Selected interatomic distances (Å) for KBaAsSe3 and KBaSbSe3.
KBaAsSe3
Distance
KBaSbSe3
Distance
Ba–Se1
Ba–Se2
Ba–Se3
Ba–Se2
Ba–Se3
Ba–Se2
Ba–Se2
Ba–Se1
K–Se3
K–Se3
K–Se1
K–Se2
K–Se1
3.2510(9)
3.2844(8)
3.331(1)
3.3338(7)
3.3595(8)
3.3613(8)
3.4479(8)
3.578(2)
3.266(2)
3.315(2)
3.342(2)
3.523(2)
3.699(2)
3.766(2)
3.789(2)
2.3741(8)
2.3818(9)
2.439(1)
Ba–Se1
Ba–Se2
Ba–Se3
Ba–Se2
Ba–Se3
Ba–Se2
Ba–Se2
Ba–Se1
K–Se3
K–Se3
K–Se1
K–Se2
K–Se1
3.277(1)
3.3448(9)
3.338(1)
3.3900(8)
3.3727(9)
3.4097(9)
3.5362(9)
3.640(2)
3.319(2)
3.326(2)
3.403(2)
3.464(2)
3.506(2)
3.780(2)
3.712(2)
2.5344(8)
2.5449(9)
2.604(1)
K–Se1
K–Se3
As–Se3
As–Se1
As–Se2
K–Se1
K–Se3
Sb–Se3
Sb–Se1
Sb–Se2
Fig. 4. Unit cell of the KBaAsSe3 structure.
unique K atom, one Ba atom, one M (M = As, Sb) atom, and three
Se atoms. All atoms are at general positions 4e. In both structures,
the K atoms are coordinated to a distorted monocapped trigonal
prism of seven Se atoms with the K–Se distances ranging from
3.315(2) to 3.789(2) Å in KBaAsSe3 and from 3.319(2) to 3.780(2) Å
in KBaSbSe3 (Table 2), which are close to those in KHgSbSe3
(3.366–3.701 Å) [44]; the Ba atoms are surrounded by a distorted
describe the exchange–correlation (XC) functionals. The ion–electron interactions
are modeled by the ultrasoft pseudopotentials [41] for all constituent elements.
In this model, K 3s23p64s1, Ba 5s25p66s2, Se 4s24p4, As 4s24p3 and Sb 5s25p3 electrons
are treated as the valence electrons, respectively. The ultra-fine kinetic energy cut-
off of 320 eV and Monkhorst–Pack k-point meshes [42] spanning less than 0.04/Å3
in the Brillouin zone are chosen to ensure the present purposes to be sufficiently
accurate.
3. Results and discussion
3.1. Syntheses
KBaMSe3 (M = As, Sb) single crystals were grown by the tradi-
tional high-temperature solid state reactions. The powder samples
of KBaMSe3 (M = As, Sb) were successfully synthesized at 823 K
with BaSe:KMSe2 (M = As, Sb) = 1:1 in molar ratio. Efforts to syn-
thesize analogues, in the form of either single crystals or polycrys-
talline samples, with other alkali metal, alkaline-earth metal,
group 15 element, or chalcogen, were unsuccessful.
3.2. Structures
KBaMSe3 (M = As, Sb) have been obtained for the first time,
which are isostructural and crystallize in the KEuAsS3-related
structure type [43] in the centrosymmetric space group P21/c of the
monoclinic system. Only the structure of KBaAsSe3 will be discussed
here. In the asymmetric unit, there are one crystallographically
Fig. 5. Diffuse reflectance spectra of KBaMSe3 (M = As, Sb).

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W. Yin et al. / Journal of Alloys and Compounds 617 (2014) 287–291
Fig. 6. Electronic band structures of KBaMSe3 (M = As, Sb) (a) KBaAsSe3 and (b) KBaSbSe3.
bicapped trigonal prism of eight Se atoms with the Ba–Se distances
ranging from 3.2510(9) to 3.578(2) Å in KBaAsSe3 and from
3.277(1) to 3.640(2) Å in KBaSbSe3, which are in agreement with
The structure of KBaAsSe3 is illustrated in Fig. 4. The compound
features a zero-dimensional structure containing totally isolated
distorted AsSe3 trigonal pyramids with K+ and Ba2+ cations located
between them. The Se atoms of the AsSe3 trigonal pyramids are
serving as the triangle base, and the As atoms are above or below
such a plane. The distortion of the AsSe3 trigonal pyramids are
evidenced by deviations of both the AsꢀSe bond lengths
(2.3741(8)ꢀ2.439(1) Å) and the SeꢀAsꢀSe angles (98.77(4)ꢀ102.49
(3)°), which are attributable to the stereoactive lone pairs of the
As3+ cations. This pyramidal kind of coordination geometry is com-
mon for M (M = As, Sb) atoms and has been observed in many M3+
(M = As, Sb) containing chalcogenides, such as, Ba23Ga8Sb2S38 [2],
Rb3Ta2AsS11 [5], and Na3SbSe3 [9].
those in BaGa4Se7 (3.429(2)–3.861(2) Å) [45]; whereas the
M
(M = As, Sb) atoms are coordinated to a slightly distorted pyramid
of three Se atoms with the As–Se distances of 2.3741(8)–2.439(1) Å
and the Sb–Se distances of 2.5344(8)–2.604(1) Å, which are compara-
ble to those of 2.322–2.515 Å in NaAsSe2 [27] and 2.590–2.672 Å in
KHgSbSe3 [44], respectively. The metal atom coordination geometry
of KBaAsSe3 is shown in Fig. 3. Considering no Se–Se or metal–metal
bonds in the structure, the oxidation states of 1+, 2+, 3+, and 2ꢀ can
be attributed to K, Ba, M (M = As, Sb), and Se, respectively and in this
way charge balance can be achieved.
Fig. 7. DOS and PDOS of KBaMSe3 (M = As, Sb) (a) KBaAsSe3 and (b) KBaSbSe3.

W. Yin et al. / Journal of Alloys and Compounds 617 (2014) 287–291
291
Although KBaMSe3 (M = As, Sb) may be assigned to the KEuAsS3
Appendix A. Supplementary material
structure type, their structures have some differences. First, K ions
in KEuAsS3 are eight-coordinated distorted bicapped trigonal-pris-
matic geometry. In comparison, K ions in KBaMSe3 (M = As, Sb) are
coordinated to a distorted monocapped trigonal prism of seven Se.
Second, KEuAsS3 may be viewed as a two-dimensional structure
with [Eu(AsS3)]ꢀ layers, which sandwich the K atoms, while
KBaMSe3 (M = As, Sb) feature a zero-dimensional structure con-
taining isolated MSe3 (M = As, Sb) trigonal pyramids with K+ and
Ba2+ cations located between them.
The crystallographic data for KBaMSe3 (M = As, Sb) have been
deposited with FIZ Karlsruhe as CSD numbers 427690 and
427691. These data may be obtained free of charge by contacting
FIZ Karlsruhe at +49 7247808666 (fax) or crysdata@fiz-kar-
lsruhe.de (e-mail). Supplementary data associated with this article
can be found, in the online version, at http://dx.doi.org/10.1016/
j.jallcom.2014.07.109.
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3.3. Experimental band gap
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The electronic band structure of KBaMSe (M = As, Sb) along the
symmetry lines in the Brillouin zone of the unit cell is plotted in
Fig. 6. It is clear that these two crystals are indirect band gap semi-
conductors with the calculated energy band gaps of 1.52 eV and
1.67 eV for KBaAsSe and KBaSbSe respectively. The calculated
energy band gaps are smaller than the experimental values (2.46
(2) eV and 2.03 (2) eV) as we expect from the employed LDA
exchange–correlation functional. Fig. 7 displays the corresponding
total/partial density of states (DOS/PDOS) of KBaMSe (M = As, Sb),
from which several characteristics can be seen. The energy region
below ꢀ6 eV is mainly composed of the isolated inner orbitals of K
(3s) (3p), Ba (5s) (5p), Se (4s), and As (4s)/Sb (5s), which are
strongly localized deep in the valence band (VB) and have a negli-
gible influence with the neighbor atoms. The top of the VB is
mainly occupied by the p orbitals of As (4p)/Sb (5p), Se (4p) and
minor by the s orbitals of As (4s)/Sb (5s), Se (4s). The bottom of con-
duction band (CB) is mainly contributed by the orbitals of As (4p)/
Sb (5p) and Se (4s) (4p). It should be emphasized that the states on
both sides of the band gap are mainly composed of the orbitals
from the [MSe3]3ꢀ (M = As, Sb) anionic units.
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lize in the centrosymmetric space group P21/c of the monoclinic
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Acknowledgments
This research was supported by National Natural Science
Foundation of China (Nos. 91122034, 21271178, and 11274367),
Science and Technology Innovation Foundation of Institute of
Chemical Materials, China Academy of Engineering Physics
(KJCX-201308).
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