Synthesis and structures of new ternary aluminum chalcogenides: LiAlSe2, α-LiAlTe2, and β-LiAlTe2

Article abstract of DOI:10.1021/ic000210c

The synthesis and crystal structures of new ternary aluminum chalcogenides, LiAlSe₂, α-LiAlTe₂, and β-LiAlTe₂, are reported. These compounds are synthesized by solid-state reaction at 800 °C. The single-crystal X-ray structures of these compounds have been determined. LiAlSe₂: a = 6.8228(9) A, b = 8.266(1) A, c = 6.5236(7) A, Pna2₁ (No. 33, Z = 4). α-LiAlTe₂: a = 6.5317(4) A, c = 11.6904(9) A, I42d (No. 122, Z = 4). β-LiAlTe₂: a = 4.4810(6) A, c = 7.096(1) A, P3m1 (No. 156, Z = 1). These ternary compounds are formed by fusion of AlQ₄ (Q = Se, Te) tetrahedra. LiAlSe₂ shows β-NaFeO₂ structure type, which can be viewed as a wurtzite superstructure. α-LiAlTe₂ adopts chalcopyrite structure type. In LiAlSe₂ and α-LiAlTe₂, AlQ₄ (Q = Se, Te) tetrahedra share four corners to build three-dimensional structures and Li atoms are located in the tetrahedral sites between the chalcogen layers. β-LiAlTe₂ has polar layers formed by three-corner shared AlTe₄ tetrahedra, and Li cations are in the distorted antiprisms between the layers. ⁷Li MAS NMR studies show that chemical shifts of Li in these ternary chalcogenides are nearly identical regardless of different chemical environments.

Full text of DOI:10.1021/ic000210c

3
092
Inorg. Chem. 2000, 39, 3092-3097
Synthesis and Structures of New Ternary Aluminum Chalcogenides: LiAlSe2, r-LiAlTe2,
and â-LiAlTe2
Joonyeong Kim and Timothy Hughbanks*
Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842-3012
ReceiVed February 25, 2000
The synthesis and crystal structures of new ternary aluminum chalcogenides, LiAlSe2, R-LiAlTe2, and â-LiAlTe2,
are reported. These compounds are synthesized by solid-state reaction at 800 °C. The single-crystal X-ray structures
of these compounds have been determined. LiAlSe2: a ) 6.8228(9) Å, b ) 8.266(1) Å, c ) 6.5236(7) Å, Pna21
(
4
(
No. 33, Z ) 4). R-LiAlTe2: a ) 6.5317(4) Å, c ) 11.6904(9) Å, I 4h 2d (No. 122, Z ) 4). â-LiAlTe2: a )
.4810(6) Å, c ) 7.096(1) Å, P3m1 (No. 156, Z ) 1). These ternary compounds are formed by fusion of AlQ4
Q ) Se, Te) tetrahedra. LiAlSe2 shows â-NaFeO2 structure type, which can be viewed as a wurtzite superstructure.
R-LiAlTe2 adopts chalcopyrite structure type. In LiAlSe2 and R-LiAlTe2, AlQ4 (Q ) Se, Te) tetrahedra share
four corners to build three-dimensional structures and Li atoms are located in the tetrahedral sites between the
chalcogen layers. â-LiAlTe2 has polar layers formed by three-corner shared AlTe4 tetrahedra, and Li cations are
7
in the distorted antiprisms between the layers. Li MAS NMR studies show that chemical shifts of Li in these
ternary chalcogenides are nearly identical regardless of different chemical environments.
Introduction
building blocks that share four corners to form three-dimensional
nets; the only difference is the stacking sequence of anions. As
a result, â-NaFeO2 can be viewed as a wurtzite superstructure
based on hexagonal closed stacking of oxygen, whereas the
chalcopyrite (CuFeS2) structure is regarded as a zinc blende
I
III
Ternary chalcogenides with the general formula A M Q2 (A
)
Li, Cu, Ag; M ) Al, Ga, In; Q ) S, Se, Te) are usually
semiconductors with energy gaps that vary between 0.9 and 4.0
eV. These materials have attracted much attention because of
their optoelectronic applications in light emitting diodes (LED),
(ZnS) superstructure in which sulfur atoms have a cubic closed
packing eutaxy.
detectors, solar energy converters, and nonlinear optical (NLO)
Most research has focused on compounds containing Cu or
devices.1
-15
These ternary compounds usually crystallize in
I
Ag as the monovalent cation, A . Much less is known about
tetragonal chalcopyrite (CuFeS2) or orthorhombic â-NaFeO2
ternary lithium chalcogenides perhaps because of crystal growth
difficulties and air sensitivity of this class of compounds.
However, ternary lithium chalcogenides are also of interest
because they have larger energy gaps than corresponding
structure types.1
6-22
Both structures incorporate tetrahedral
*
To whom correspondence should be addressed. E-mail: trh@
mail.chem.tamu.edu. Phone: (979) 845-0125. Fax: (979) 847-8860.
(
(
(
1) Rinc o´ n, C.; Wasim, S. M.; Mar ´ı n, G.; Huntzinger, J. R.; Galibert, J.;
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23-26
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Solids 1998, 56, 1015-1019.
characterization of ternary lithium chalcogenides of gallium and
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(
4) Soliman, H. S. J. Phys. D: Appl. Phys. 1998, 31, 1516-1521.
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1-25
chemistry is lacking.
Several classes of ternary aluminum
(
5) Bottomley, D. J.; Mito, A.; Niki, S.; Yamada, A. J. Appl. Phys. 1997,
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2, 817-824.
chalcogenides were reported: A3AlQ3 (A ) Na, K; Q ) S, Se,
Te), AAlQ2 (A ) Na for Q ) Se, Te; A ) K for Q ) Te), and
(
(
(
(
6) Bottomley, D. J.; Mito, A.; Fons, P. J.; Niki, S.; Yamada, A. IEEE J.
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2
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KAlQ2 (Q ) Se, Te).
Isolated [AQ3 ) A2Q4Q4/2] dimers
1997, 38, 233-244.
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81-483.
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7
(
(
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743-748.
(
(
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1
0.1021/ic000210c CCC: $19.00 © 2000 American Chemical Society
Published on Web 06/17/2000

LiAlSe2, R-LiAlTe2, and â-LiAlTe2
Inorganic Chemistry, Vol. 39, No. 14, 2000 3093
formed by sharing two corners of two AlQ4 tetrahedra are found
in the first class of compounds. The second possesses one-
analyzed, a well-characterized compound or pure element is used as a
standard. Crystals of ternary compounds were mounted on the top of
sample holders with double-sided carbon tape. For each compound,
measurements were performed at least three times for independent
crystals, and analyses were processed through the Cameca PAP full-
1
-
-
dimensional [AlQ2 ) AlQ4/2 ] chains built up by edge-
∞
sharing of AlQ4 tetrahedra, and alkali metals sit in the square
1
-
antiprisms between ∞[AlQ4/2 ] chains. The last class of com-
46
quantitative matrix correction program.
2
-
pounds has two-dimensional [AlQ6Q4/2 ] layers (Q ) Se,
7
∞
Room temperature Li MAS NMR spectra were recorded on a Bruker
Te) formed by the fusion of adamantane-like Al4Q10 super-
tetrahedra.
ACP-300 spectrometer at 116.59 MHz and 4.3 kHz spinning rate.
Samples were placed into Zirconia (o.d. 7 mm) rotors and spun using
a Bruker supplied solid-state accessory. The lithium spectra were
referenced to a 1 M LiCl aqueous solution.
Our previous systematic investigations in Li-Mn-Q (Q )
Se, Te) systems revealed new ternary compounds, LiMnQ2 (Q
2
∞
-
Synthesis. Unless otherwise indicated, all ternary aluminum chal-
cogenides were synthesized by the use of Nb tubes that were in turn
)
Se, Te) with polar layers, [MnQQ3/3 ], though crystal-
lographic data was inadequate to determine the lithium positions
-
4
sealed in evacuated (∼10 Torr) silica tubes. LiAlSe
2
was synthesized
in the (likely) presence of lithium disorder.3
6-39
Li ions may
by mixing Li, Al Se , and Se in a stoichiometric ratio. The temperature
2
3
occupy octahedral sites (as in NaMnQ2; Q ) Se, Te) or
was uniformly raised from room temperature to 250 °C over 12 h, held
at that temperature for 2 days, raised to 800 °C over 48 h, held at that
temperature for 10 days, then cooled to 350 °C at a rate of 2 °C/h, and
finally quenched to room temperature. Products contained colorless
transparent single crystals suitable for X-ray crystallography.
Pale-gray transparent R-LiAlTe was synthesized directly using Li,
2
Al, and Te combined in a 1:1:2 ratio. The temperature of the reaction
vessel was uniformly raised to 500 °C over 2 days, maintained at 500
2
∞
-
tetrahedral sites between the [MnQQ3/3 ] layers or in both
III
sites. Since the Al radius is not much smaller than the effective
III
radius that we observe for Mn , it is plausible that analogous
aluminum compounds could be prepared.40
Our investigations in Li-Al-Q (Q ) Se, Te) systems yielded
new ternary aluminum chalcogenides, LiAlSe2, R-LiAlTe2, and
â-LiAlTe2, for which we report the synthesis and characteriza-
tion.
°
C for 2 days, uniformly increased to 800 °C over 2 days, maintained
at that temperature for 10 days, then cooled to room temperature.
â-LiAlTe was synthesized by mixing Li, Al Te , and Te in a 2.4:
2
2
3
Experimental Section
1:1.2 molar ratio. The temperature was uniformly raised to 500 °C over
2
days, maintained at 500 °C for 2 days, uniformly increased to 800
Materials and Instrumentation. Because the compounds described
herein are sensitive to both moisture and oxygen, experimental
operations were carried out under an atmosphere of either nitrogen or
argon. Elemental starting materials Al (99.95%, Aldrich), Te (99.997%
Aldrich), Se (99.999%, Aldrich), and Li (99.9%, Aldrich) were used
°
C for 2 days, maintained at that temperature for 10 days, cooled to
50 °C at a rate of 2 °C/h, and then quenched. The X-ray powder pattern
of the final product showed the existence of â-LiAlTe (ca. 60%) with
Li Te and unknown phases. Pale-brown transparent crystals suitable
for X-ray studies could be physically separated.
Microprobe analyses on selected crystals from each compound
showed approximate compositions Li Al Se , Li Al Te , and
3
2
2
as received. Li
described in the literature.
and Al Se were prepared in silica tubes as described in the literature.
2
S, Li
2
Se, and Li
2
Te were synthesized in liquid NH
3
as
41,42
Binary starting materials Al Te , Al Te10,
2
3
7
4
3-45
2
3
x
1.06(8)
2
x
0.97(1)
2
After syntheses, the purity of these starting binary chalcogenides was
monitored by examination of Guinier X-ray powder patterns. Atomic
absorption (AA) measurements were performed on a Varian SpectrAA
Li
other elements heavier than Na, including Nb, were found. AA mea-
2
surements gave the compositions Li1.07(2)Al0.96(5)Se , Li0.95(3)Al0.98(4)Te ,
and Li1.11(5)Al1.05(3)Te
tively.
x
Al1.06(9)Te
2
2 2 2
for LiAlSe , R-LiAlTe , and â-LiAlTe , respectively. No
2
2
50 Plus instrument after dissolution of products in 20% (w/w) nitric
2
2 2 2
for LiAlSe , R-LiAlTe , and â-LiAlTe , respec-
acid. Samples for AA measurements were gathered by selecting crystals
from the reaction products. Standard solutions for AA measurements
were purchased from Aldrich. For each element, measurements on at
least three standard solutions were taken with different concentrations
to obtain a linear calibration plot. Wavelength-dispersive X-ray
spectrometry (WDS) analyses were performed using a Cameca SX 50
electron microprobe equipped with four WDS spectrometers. Each
spectrometer contains an X-ray diffraction crystal as a monochromator
and a gas-flow proportional ionization detector. For each element
X-ray Crystallography. X-ray diffraction data for LiAlSe
2
, R-
LiAlTe , and â-LiAlTe were collected on a Siemens R3m/V diffrac-
2
2
tometer with graphite monochromated Mo KR radiation (λ ) 0.710 73
Å) at 20 °C. Cell constants and an orientation matrix for each compound
were obtained from a least-squares refinement using the setting angles
from at least 15 centered reflections from the rotational photograph.
Cell parameters were refined by centering on at least 24 reflections in
the range 15 e 2θ e 45°. Three check reflections were monitored every
97 reflections throughout the data collection process in each compound.
The data were corrected for absorption using the ψ-scan technique based
(
(
(
(
(
(
(
30) Eisenmann, B.; Hofmann, A. Z. Kristallogr. 1991, 197, 173-174.
31) Eisenmann, B.; Hofmann, A. Z. Kristallogr. 1991, 197, 151-152.
32) Eisenmann, B.; Hofmann, A. Z. Kristallogr. 1991, 197, 161-162.
33) Eisenmann, B.; Hofmann, A. Z. Kristallogr. 1991, 197, 171-172.
34) Eisenmann, B.; Hofmann, A. Z. Kristallogr. 1991, 197, 141-142.
35) Kim, J.; Hughbanks, T. J. Solid State Chem. 2000, 149, 242-251.
36) Wang, C.; Kim, J.; Hughbanks, T. In Materials Research Society
Symposium Proceedings; Jacobson, A., Davies, P., Vanderah, T.,
Torardi, C., Eds.; Materials Research Society: Boston, MA, 1997;
Vol. 453, pp 23-28.
2
on at least five reflections. Structure refinements were based on F
with the use of the SHELX-93 package of programs.47 Reported cell
parameters were refined from Guinier powder diffraction patterns using
Si as an internal standard.
2
A colorless transparent crystal of LiAlSe having approximate
dimensions 0.08 mm × 0.06 mm × 0.06 mm was mounted in a glass
capillary. A hemisphere of data ((h, +k, (l) was collected by use of
θ-2θ scans with 2θ < 51°. A total of 374 reflections are unique, and
(37) Kim, J.; Wang, C.; Hughbanks, T. Inorg. Chem. 1998, 37, 1428-
2
95 reflections with I > 2σ(I) were used in the refinements. Systematic
absences, Guinier X-ray diffraction data, and elemental analysis
suggested that LiAlSe is isostructural with the known compound
(orthorhombic space group Pna2 ), so the atomic positions of
were used to begin refinement of the LiAlSe
gave 3.07 and 6.42% for final R(F)
1429.
(38) Kim, J.; Wang, C.; Hughbanks, T. Inorg. Chem. 1999, 38, 235-242.
(39) Kim, J.; Hughbanks, T. J. Solid State Chem. 1999, 145, 217-225.
(40) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell
University Press: Ithaca, New York, 1960.
2
LiInSe
LiInSe
2
1
22
2
2
structure. Final
(
41) Feher, F. In Handbuch der Pr a¨ paratiVen Anorganischen Chemie;
Brauer, G., Ed.; Ferdinand Enke Verlag: Stuttgart, Germany, 1954.
42) Klemm, W.; Sodomann, H.; Langmesser, P. Z. Anorg. Allg. Chem.
anisotropic refinement of LiAlSe
and wR2(F ) with I > 2σ(I). The largest remaining peaks in the final
2
2
(
1
939, 241, 281-304.
(
(
43) Nesper, R.; Curda, J. Z. Naturforsch 1987, 42b, 557-564.
44) Conrad, O.; Schiemann, A.; Krebs, B. Z. Anorg. Allg. Chem. 1997,
(46) Pouchou, J. L.; Pichoir, F. Rech. Aerosp. 1984, 3, 13-38.
(47) (a) Sheldrick, G. M. SHELXTL-93 User Guide; Crystallography
Department, University of G o¨ ttingen: G o¨ ttingen, Germany, 1993. (b)
SHELXTL-93 User Guide, version 3.4; Nicolet Analytical X-ray
Instruments: G o¨ ttingen, Germany, 1993.
6
23, 1006-1010.
45) Schneider, V. A.; Gattow, G. Z. Anorg. Allg. Chem. 1954, 277, 49-
9.
(
5

3094 Inorganic Chemistry, Vol. 39, No. 14, 2000
Kim and Hughbanks
Table 1. Crystallographic Data for LiAlSe
â-LiAlTe
2
, R-LiAlTe
2
, and
Table 2. Atomic Coordinates and Equivalent Isotropic
Displacement Parameters
2
a
2
3
chemical formula
LiAlSe2
6.8228(9)
8.266(1)
6.5236(7)
367.90(8)
4
R-LiAlTe2
â-LiAlTe2
4.4810(6)
atom position
x
y
z
U
eq (Å × 10 )
a, Å
b, Å
c, Å
6.3517(4)
LiAlSe
2
Se1
Se2
Al
4a
4a
4a
4a
0.0637(2) 0.1152(2) 0.6337(7)
0.4067(2) 0.1371(2) 0.1131(7)
0.0735(5) 0.1256(7) 0.0
10(1)
10(1)
9(1)
11.6904(9)
471.64(6)
4
7.096(1)
123.39(3)
1
3
V, Å
Z
fw
Li
0.085(4) 0.619(5) 0.003(5)
26(6)
191.84
289.12
289.12
R-LiAlTe
0.0
2
space group
temp, °C
λ, Å
Pna21 (No. 33) I 4h 2d (No. 122) P3m1 (No. 156)
20
0.710 73
3.463
20.061
Li
Al
Te
4b
4a
8d
0.0
0.0
0.5
0.0
1/8
29(7)
15(1)
17(1)
20
20
0.0
0.710 73
4.072
12.340
0.710 73
3.891
11.793
3
0.2308(1) 1/4
Fcalcd, g/cm
-
1
µ, mm
â-LiAlTe2
1/3
a
b
R1 , wR2 [I g 2σ(I)] 0.0307, 0.0642 0.0193, 0.0424 0.0199, 0.0378
R1 , wR2 (all data)
Te1
Te2
Al
1c
1b
1b
1a
2/3
1/3
1/3
0.0
0.1257(9)
0.6173(9)
0.0
27(1)
27(1)
28(1)
42(1)
a
b
0.0477, 0.0690 0.0210, 0.0433 0.0262, 0.0433
2/3
2/3
0.0
a
b
2
2
- F 2
2
R
1
(F) ) ∑(|F
o
| - |F
c
|)/∑(|F
o
|). wR2(F ) ) [∑|w(F
o
c
) |/
Li
0.400(6)
2
2
1/2
2
2
2
2
∑
+
|w(F
o
) |] , w ) 1/[σ (F
o
) + (xP) + yP] where P ) (max(F
o
,0)
2
a
2F
c
)/3. x ) 0.024 and y ) 0.0 for LiAlSe
2
, x ) 0.028 and y ) 0.0
Equivalent isotropic U defined as one-third of the trace of the
orthogonalized Uij tensor.
for R-LiAlTe
2
, and x ) 0.0 and y ) 0.5387 for â-LiAlTe .
2
3
reaction between the Nb container and Se occurs at 900 °C, as
Fourier difference map were 1.122 e/Å located close to Se1 (0.99 Å)
in the framework of the structure.
39
was discussed in a previous paper. Nb containers are otherwise
preferred for easy recovery and higher purity of products, as
indicated in powder patterns of the products. Attempts to find
other phases in the Li-Al-Se system by changing loading
stoichiometry nevertheless yielded LiAlSe2 as the major ternary
phase.
Our investigations have uncovered two polymorphs of
LiAlTe2 (R and â). R-LiAlTe2 was first synthesized directly
from elemental starting materials Li, Al, and Te in sealed Nb
tubes at 800 °C. Careful investigations of X-ray patterns revealed
that the reaction products contain R-LiAlTe2 as a major
compound and a small amount (ca. 5-10%) of unknown phase
that was later identified as â-LiAlTe2. After structural charac-
2
A pale-gray transparent crystal of R-LiAlTe with approximate
dimensions 0.10 mm × 0.10 mm × 0.30 mm was selected and mounted
in a glass capillary. Data were collected in one quadrant (+h, +k, (l)
in the θ-2θ scanning mode for reflections with 7 e 2θ e 51°. Data
for which h + k + l ) 2n + 1 were systematically absent, consistent
with a body-centered tetragonal space group. A total of 138 reflections
were unique, and 126 reflections with I > 2σ(I) were used in the
refinements. R-LiAlTe
positions of LiInTe were used to begin refinement. Final anisotropic
refinement gave 1.93 and 4.24% for final R(F) and wR2(F ) with I >
σ(I). The largest residual peak in the final Fourier difference map
2 2
is isostructural with LiInTe , so the atomic
21
2
2
2
3
was 0.885 e/Å , located close to Te in the framework of the structure.
A pale-brown transparent crystal of â-LiAlTe with approximate
2
dimensions 0.10 mm × 0.10 mm × 0.10 mm was selected and mounted
in a glass capillary. Intensity data were collected in the θ-2θ scanning
mode for reflections with 5 e 2θ e 60°. One hemisphere of data (+h,
terization of R-LiAlTe , further reactions were conducted to
2
optimize the yield of â-LiAlTe2 in which several parameters
were varied (starting materials, reaction temperatures, cooling
speed, reaction containers). Silica tubes were reactive toward
starting materials (Li2Te and Li) and sometimes did not survive
the reactions. Therefore, the syntheses of ternary lithium
aluminum tellurides were conducted in Nb containers. Surpris-
ingly, we observed that the use of Li, Al Te , and Te as starting
2 3
materials produced â-LiAlTe2 as a major product (60%) with
(
k, (l) was collected. A total of 170 reflections were unique and used
in the refinements. An initial structural model for refinement was found
by direct methods. Isotropic refinement of the structure with all Li,
Al, and Te positions fully occupied resulted in a residual (R) of 5.13%.
In the last cycle, the structure was refined anisotropically to yield
2
respective residuals of 1.99 and 3.78% for R(F) and wR2(F ) for data
with I > 2σ(I). The largest remaining peak in the final Fourier difference
3
map was 1.384 e/Å located near Te1 (0.65 Å) in the framework of
Li2Te and some unknown phases. However, several subsequent
the structure. A summary of crystal and data collection parameters of
attempts to produce pure â-LiAlTe were unsuccessful. To
understand this polymorphism (R- and â-LiAlTe2), we inves-
2
LiAlSe
2
, R-LiAlTe
2
2
, and â-LiAlTe is listed in Table 1 and final atomic
coordinates are shown in Table 2.
tigated the factors controlling the formation of the two different
compounds. The results are summarized in Scheme 1.
When elemental starting materials were used, Al7Te10 (a
Results and Discussion
II
II
43
Syntheses. LiAlSe2 was first obtained from reactions intended
compound in which an Al -Al bond is present) was
identified as a major intermediate phase in the synthesis of pure
R-LiAlTe2. Al7Te10 was observed by quenching the reaction
after 100 h at 800 °C (Scheme 1a). When Al2Te3, Li, and Te
were used as starting materials, Al2Te3 and Li2Te were found
as the intermediate phases in the synthesis of â-LiAlTe2 (Scheme
1b), as determined by quenching the reaction after 100 h at 800
°C. Thus, different products are formed via different intermedi-
ates when the starting materials are different. Syntheses of
R-LiAlTe2 and â-LiAlTe2 were reproduced by use of intermedi-
ate phases as the starting materials: Li2Te, Al7Te10, and Te for
R-LiAlTe2 and Li2Te and Al2Te3 for â-LiAlTe2 (see Scheme
1). As was shown for ternary manganese tellurides,38 elemental
Te can react with Nb containers to form binary phases (NbTe
and Nb5Te4), which favors the formation of a Te-deficient binary
intermediate such as Al7Te10 rather than Al2Te3 for the synthesis
of R-LiAlTe2. We therefore suspect that R-LiAlTe2 is Te-
39
to produce a compound isostructural with LiMnSe2. A 2:1:1
mixture of Li, Al2Se3, and Se was reacted in a Nb container at
7
00 °C for 4 days. Guinier X-ray powder patterns showed that
the products were mixtures of the major product LiAlSe2 and
minor unknown phases. To optimize conditions for LiAlSe2
synthesis, starting materials (several combinations of elements
Li, Al, Se and binaries Li2Se, Al2Se3), reaction temperatures
(700, 800, and 900 °C), cooling speed (from quenching at
reaction temperature to slow cooling (2 °C/h)), and reaction
containers (Nb and silica) were varied. Several experiments
revealed that the most important factors for the successful
synthesis of LiAlSe2 are reaction time and temperature. Longer
reaction times (>10 days) and appropriate reaction temperatures
(800 °C) are required to yield pure white LiAlSe2. Lower
reaction temperature (700 °C) and short reaction time (<5 days)
gave significant amounts of unknown phases. Undesirable

LiAlSe2, R-LiAlTe2, and â-LiAlTe2
Inorganic Chemistry, Vol. 39, No. 14, 2000 3095
Scheme 1
deficient (R-LiAlTe2-δ), although such a deficiency must be
too small to be detected in elemental analyses (WDS and AA)
or by X-ray crystallography. However, the conversion of
R-LiAlTe2 to â-LiAlTe2 by adding excess Te in either silica
tubes or Nb containers at 800 °C was not achieved. â-LiAlTe2,
along with Li2Te and unknown phases, is preferably formed
from binary tellurides (Li2Te and Al2Te3), which are less reactive
toward Nb containers. Despite several thermal treatments at 800
2
Figure 1. (a) [100] projection of thermal ellipsoid plot of LiAlSe .
°
C over several days in either silica or Nb containers, inter-
7
0% probability ellipsoids are shown. (b) Polyhedral representation of
conversion of R-LiAlTe2 and â-LiAlTe2 was not observed.
Interestingly, AgAlS2-I and AgAlS2-II (high-pressure phase)
are isostructural with R-LiAlTe2 and â-LiAlTe2, respec-
2
LiAlSe viewed down the a axis, where bonds between Li and Se were
removed for clarity, white open circles are Se atoms, and shaded circles
are Li atoms.
1
0,12,13,48
tively.
Tetragonal AgAlS2-I is converted to hexagonal
Table 3. Important Interatomic Distances (Å) and Bond Angles
AgAlS2-II at 350 °C and 25 kbar.
(deg) for LiAlSe
2
, R-LiAlTe
2
, and â-LiAlTe
2
These ternary aluminum chalcogenides are quite air- and
moisture-sensitive. LiAlSe2 decomposes to form malodorous
H2Se and red elemental Se on contact with air. H2Te and black
elemental Te are formed on the decomposition of both R- and
â-LiAlTe2.
Structure. Thermal ellipsoid and polyhedral representations
of LiAlSe2 (â-NaFeO2-type structure) are projected down the
a axis in Figure 1. Selected interatomic distances and angles
are listed in Table 3. This structure is a superstructure of wurtzite
with quadrupled cell volume. The metrical relationships between
the hexagonal structure of wurtzite and the ideal orthorhombic
superstructure of LiAlSe2 are
LiAlSe
2
AlsSe1
AlsSe1
LisSe1
AlsSe2 (×2)
LisSe2 (×2)
LisSe1
2.392(5)
2.366(5)
2.55(2)
2.387(4)
2.55(4)
2.57(3)
Se2sAlsSe1
Se1sAlsSe1
Se2sAlsSe1
Se2sAlsSe1
Se2sAlsSe2
Se1sAlsSe2
109.0(2)
109.1(2)
109.7(2)
112.8(2)
109.1(2)
107.2(2)
R-LiAlTe
2
AlsTe (×4)
LisTe (×4)
2.6087(4)
2.7534(4)
TesAlsTe (×4)
108.29(1)
111.87(1)
TesAlsTe (×2)
â-LiAlTe
2
AlsTe1 (×3)
AlsTe2
2.741(2)
2.716(6)
3.23(3)
3.01(2)
Te1sAlsTe1 (×3)
109.7(1)
109.3(1)
Te1sAlsTe2 (×3)
LisTe1 (×3)
LisTe2 (×3)
a ) c /
x
8/3 ) ao/ 3 ) b /2
x
w
o
o
in the other possible tetrahedral or octahedral holes were
unsuccessful.
where aw is the a axis of wurtzite and co, ao, and bo are cell
parameters of the orthorhombic lattice of the LiAlSe2 structure.
In the true LiAlSe2 structure, the b axis is somewhat elongated
Thermal ellipsoid and polyhedral depictions of R-LiAlTe2
viewed down the b axis are shown in Figure 2, and selected
interatomic distances and angles are listed in Table 3. R-LiAlTe2
adopts the chalcopyrite (CuFeS2) structure type, consisting of
fairly regular AlTe4 tetrahedral building blocks (d(Al-Te) )
(3.5%) in comparison with the ideal wurtzite structure. In
LiAlSe2, AlSe4 tetrahedra are slightly distorted and each
tetrahedron shares four corners with four adjacent tetrahedra in
forming the three-dimensional structure (Figure 1). Al-Se
distances range from 2.366(5) to 2.392(5) Å, and angles are
between 107.2(2) and 112.8(2)°. Li cations sit in the tetrahedral
holes in the same layers of aluminum with Li-Se distances
ranging between 2.55(2) and 2.57(3) Å. Attempts to locate Li
2
1
.6087(4) Å (×4) and ∠ (Te-Al-Te) ) 108.29(1)° (×4),
11.87(1)° (×2)). Each Te atom is two-coordinate with respect
to Al, and the [AlTe2] network is, once again, three-dimensional.
Li cations occupy tetrahedral holes (d(Li-Te) ) 2.7534(4) Å
(
×4)) within this network. While selenium atoms are hexago-
nally close packed in LiAlSe2, tellurium atoms form a cubic
closed packing in R-LiAlTe2. Factors determining structural
choice between â-NaFeO2 (LiAlSe2) type and chalcopyrite (R-
(
48) Range, K.; Engert, G.; Weiss, A. Z. Naturforsch. 1974, 29b, 186-
189.

3096 Inorganic Chemistry, Vol. 39, No. 14, 2000
Kim and Hughbanks
2
∞
-
[
AlTeTe3/3 ] with d(Al-Te1) ) 2.741(2) Å (×3) and d(Al-
Te2) ) 2.716(6) Å. Li atoms are located in the distorted trigonal
antiprisms between layers, having Li-Te distances 3 × 3.23(2)
Å (Te1) and 3 × 3.01(3) Å (Te2). The structure of â-LiAlTe2
may also be viewed as inverse ScCuS2 and AgAlS2-II (high-
pressure phase) where Cu and Ag are in the tetrahedral sites
and Sc and Al occupy the octahedral sites.
I
I
III
III
48,63
The shortest
Te-Te contact in â-LiAlTe2 is 4.4810(6) Å.
Li positions in â-LiAlTe2 are unambiguously determined,
which contrasts with the situation for LiMnTe2 (where it was
not possible to determine Li positions). A possible explanation
for the difference may be that the bigger manganese atoms
produce larger tetrahedral and octahedral holes between the
layers. This enlarged volume may enable mobility of Li cations
or engender static disorder over both octahedral and tetrahedral
sites.
Room temperature 7Li MAS NMR measurements were
performed for ternary lithium aluminum chalcogenides. Chemi-
cal shifts in the spectra have often proved to provide charac-
teristic information regarding local environments of lithium
6
4-67
atoms.
Unfortunately, chemical shifts of lithium atoms in
ternary and binary chalcogenides are relatively insensitive to
both the coordination number and chalcogen atoms coordinated.
7
The Li spectra for LiAlSe2, R-LiAlTe2, and â-LiAlTe2 show a
single resonance at 1.26, 2.23, and 0.50 ppm, respectively. These
chemical shifts are comparable to 2.06 (Li2S), 1.69 (Li2Se), and
0
.95 ppm (Li2Te) for lithium chalcogenides.
Concluding Remarks
Figure 2. [100] projection of thermal ellipsoid plot (a) and polyhedral
. 70% probability ellipsoids are shown.
Bonds between Li and Te were removed for clarity. White open circles
are Se atoms, and shaded circles are Li atoms in part b.
representation (b) of R-LiAlTe
2
The ternary aluminum chalcogenides LiAlSe2, R-LiAlTe2, and
â-LiAlTe2 have been synthesized and characterized by the use
of single-crystal and powder X-ray diffraction, microprobe
7
analyses, atomic absorption measurements, and Li MAS NMR
spectroscopy. All these ternary compounds possess different
structures despite being built with the same AlQ4 (Q ) Se, Te)
tetrahedra. Structural investigations on ternary lithium chalco-
genides of aluminum and manganese show that chalcogen atoms
are stacked with either ccp (R-LiAlTe2) or hcp (LiMnQ2 (Q )
III
III
Se, Te), LiAlSe2, and â-LiAlTe2) eutaxies. Al and Mn are
located in the tetrahedral holes between the chalcogen layers,
(
49) Eckerlin, V. P.; Rabenau, A.; Nortmann, H. Z. Anorg. Allg. Chem.
967, 353, 114-121.
50) Wintenberger, M.; Marchand, R.; Maunaye, M. Solid State Commun.
1
(
1
977, 21, 733-735.
(
(
(
(
51) Pfister, V. H. Acta Crystallogr. 1958, 11, 221-224.
52) Folberth, V. O. G.; Pfister, H. Acta Crystallogr. 1961, 14, 325-326.
53) Abrahams, S. C.; Berstein, J. L. J. Chem. Phys. 1971, 55, 796-803.
54) Honle, W.; von Schnering, H. G. Z. Kristallogr. 1981, 155, 319-
320.
(
(
(
55) Grigorovici, R.; M a˜ n a˜ il a˜ , R. Acta Crystallogr. 1968, B24, 535-541.
56) Levalois, M.; Allais, G. Phys. Status Solidi. 1988, 109a, 111-119.
57) Abrahams, S. C.; Berstein, J. L. J. Chem. Phys. 1970, 52, 5607-
2
Figure 3. Thermal ellipsoid plot of â-LiAlTe along the c axis. 70%
probability thermal ellipsoids are shown.
5613.
(
58) Wintenberger, M.; Guyader, J.; Maunaye, M. Solid State Commun.
972, 11, 1485-1488.
LiAlTe2) are not clear, but apparently the size of chalcogenides
is important. The same trends are seen in ternary indium
chalcogenides LiInQ2 (Q ) S, Se, Te) in which sulfide and
1
(
59) Wintenberger, M.; Tcheou, F. Z. Naturforsch. 1980, 35b, 604-608.
(60) Vaipolin, A. A.; Grryunnova, N. A.; Kleshchinskii, L. I.; Loshakova,
G. V.; Osmanov, E. O. Phys. Status Solidi. 1968, 29, 435-443.
selenide adopt the â-NaFeO2 structure type, but the telluride
(
(
61) Wintenberger, M. Mater. Res. Bull. 1973, 8, 1049-1054.
62) Lind, M. D.; Grant, R. w. J. Chem. Phys. 1973, 58, 357-362.
shows a chalcopyrite structure.1
4,21-23,25
This trend is also
II IV
V
evident in the ternary pnictide family A B C 2 (A ) Be, Mg,
Mn, Cd, Zn; B ) Si, Ge, Sn; C ) N, P, As) in which ternary
nitrides adopt â-NaFeO2 (LiAlSe2) type while phosphides
and arsenides adopt the chalcopyrite (R-LiAlTe2) structure
type.1
(63) Dismukes, J. P.; Smith, R. T. J. Phys. Chem. Solids 1971, 32, 913-
922.
(64) Menetrier, M.; Rougier, A.; Delmas, C. Solid State Commun. 1994,
90, 439-442.
(65) Eckert, H.; Zhang, Z.; Kennedy, J. H. Chem. Mater. 1990, 2, 273-
6,19,20,49-62
279.
(66) Lee, J. Y.; Wang, F.; Grey, C. P. J. Am. Chem. Soc. 1998, 120, 12601-
The crystal structure of â-LiAlTe2 is shown in Figure 3, and
selected interatomic distances and angles are listed in Table 3.
Like the isostructural LiMnTe2, â-LiAlTe2 has polar layers,
12613.
(67) Stewart, F. F.; Stebbins, J. F.; Peterson, E. S.; Farnan, I.; Dunham, S.
O.; Adams, E.; Jennings, P. W. Chem. Mater. 1995, 7, 363-367.

LiAlSe2, R-LiAlTe2, and â-LiAlTe2
Inorganic Chemistry, Vol. 39, No. 14, 2000 3097
+
7
and Li is in either tetrahedral holes (LiAlSe2 and R-LiAlTe2)
microprobe analyses, atomic absorption measurements, and Li
MAS NMR studies.
or octahedral holes (â-LiAlTe2).
Acknowledgment. This research was generously supported
by the Texas Advanced Research Program through Grant
10366-097. The R3m/V single-crystal X-ray diffractometer and
crystallographic computing system were purchased from funds
provided by the National Science Foundation (Grant CHE-
Supporting Information Available: Figures S1 and S2 showing
Li MAS NMR spectra for ternary and binary lithium chalcogenides,
7
0
and CIF files containing data for the structures of LiMnSe
2
, R-LiAlTe
2
,
and â-LiAlTe . This material is available free of charge via the Internet
2
at http://pubs.acs.org.
IC000210C
8
513273). We thank Dr. Renald Guillemette, Dr. Anatoly
Bortun, and Dr. Robert Taylor for their assistance with the