Synthesis, structure, and characterization of a new one-dimensional tellurite phosphate, Ba2TeO(PO4)2

Article abstract of DOI:10.1016/j.jssc.2006.01.045

A new one-dimensional tellurite phosphate, Ba₂TeO(PO₄)₂ has been synthesized by standard solid-state reaction techniques using BaCO₃, TeO₂, and (NH₄)H₂PO₄ as reagents. The structure of Ba₂TeO(PO₄)₂ was determined by single-crystal X-ray diffraction. Ba₂TeO(PO₄)₂ crystallizes in the triclinic space group P-1 (No. 2), with a = 6.9461 ( 16 ) A, b = 7.3970 ( 17 ) A, c = 8.887 ( 2 ) A, α = 76.843 ( 4 ) °, β = 79.933 ( 4 ) °, γ = 75.688 ( 4 ) °, V = 427.40 ( 17 ) A³, and Z = 2. Ba₂TeO(PO₄)₂ has a novel one-dimensional chain structure that is composed of PO₄ tetrahedra and TeO₅ polyhedra. Te⁴⁺ cations are in asymmetric coordination environments attributable to their lone pairs. The lone pairs on the Te⁴⁺ cations point in the [100] and [-100] direction and interact with the Ba²⁺ cations. Infrared, Raman, and UV-Vis diffuse reflectance spectroscopy, thermogravimetric analysis, and dipole moment calculations are also presented.

Full text of DOI:10.1016/j.jssc.2006.01.045

ARTICLE IN PRESS
Journal of Solid State Chemistry 179 (2006) 1345–1350
www.elsevier.com/locate/jssc
Synthesis, structure, and characterization of a new one-dimensional
tellurite phosphate, Ba2TeO(PO4)2
Ã
Kang Min Ok, P. Shiv Halasyamani
Department of Chemistry and Center for Materials Chemistry, University of Houston, 136 Fleming Building, Houston, TX 77204-5003, USA
Received 9 December 2005; received in revised form 20 January 2006; accepted 22 January 2006
Available online 24 February 2006
Abstract
A new one-dimensional tellurite phosphate, Ba2TeO(PO4)2 has been synthesized by standard solid-state reaction techniques using
BaCO3, TeO2, and (NH4)H2PO4 as reagents. The structure of Ba2TeO(PO4)2 was determined by single-crystal X-ray diffraction.
˚
˚
˚
Ba2TeO(PO4)2 crystallizes in the triclinic space group P-1 (No. 2), with a ¼ 6:9461ð16Þ A, b ¼ 7:3970ð17Þ A, c ¼ 8:887ð2Þ A,
3
˚
a ¼ 76:843ð4Þ1, b ¼ 79:933ð4Þ1, g ¼ 75:688ð4Þ1, V ¼ 427:40ð17Þ A , and Z ¼ 2. Ba2TeO(PO4)2 has a novel one-dimensional chain
structure that is composed of PO4 tetrahedra and TeO5 polyhedra. Te4+ cations are in asymmetric coordination environments
attributable to their lone pairs. The lone pairs on the Te4+ cations point in the [100] and [ꢀ100] direction and interact with the Ba2+
cations. Infrared, Raman, and UV–Vis diffuse reflectance spectroscopy, thermogravimetric analysis, and dipole moment calculations are
also presented.
r 2006 Elsevier Inc. All rights reserved.
Keywords: Synthesis; Tellurite; Phosphate; One-dimensional structure
1. Introduction
combined with octahedral or tetrahedral moieties, a
number of interesting framework architectures are possible.
In addition with transition metal oxyphosphate com-
pounds, a wide variety of structural topologies such as
one-dimensional chains [1,20], two-dimensional layers
[21–23], and three-dimensional frameworks [24–26] have
been observed. Thus, combining these building blocks,
Te4+ polyhedra and oxyphosphate groups, would result in
interesting structural topologies. With these ideas in mind,
we investigated materials in the Ba–Te–P-oxide system.
With respect to tellurite phosphate oxides, a few materials
have been reported, namely, Te2O3(HPO4) [27,28], Te8O10
(PO4)4 [29], A2TeMo2O6(PO4)2 (A ¼ K, Rb, Cs, or Tl) [30],
and BaTeNbO4(PO4) [31]. Structurally the materials are
different; BaTeNbO4(PO4) contains two-dimensional layers;
whereas, Te2O3(HPO4), Te8O10(PO4)4, and A2TeMo2O6
(PO4)2 exhibit three-dimensional structures consisting of
asymmetric TeO4 and TeO5 polyhedra that are linked
through oxygen atoms. In this paper, we report the
synthesis, structure, and characterization of a uni-dimen-
sional material, Ba2TeO(PO4)2, representing a new qua-
ternary tellurite phosphate with a novel crystal structure.
Mixed metal tellurites exhibit varying structural topolo-
gies owing to the nonbonded electron pair on the Te4+
cation [1–4]. Attributable to this lone pair, a local acentric
coordination environment is also observed. In fact, lone
pair cations such as Te4+, not only exhibit asymmetric
coordination environments, but these environments influ-
ence the material’s properties [5–7]. The asymmetric
coordination environment and lone pair are thought to be
result of a second-order Jahn–Teller (SOJT) distortion
[8–13]. A SOJT distortion reduces the energy between the
highest occupied (HOMO) s-orbital and the lowest
unoccupied (LUMO) p-orbital through s–p mixing
[14–17]. The observed coordination numbers for Te4+
cations are three, four, and five, which result in various
structural geometries such as distorted trigonal pyramidal,
seesaw, and distorted square pyramidal, respectively [18,19].
Furthermore, when this distorted coordination geometry is
Ã
Corresponding author. Fax: +1 713 743 0796.
E-mail address: psh@uh.edu (P. Shiv Halasyamani).
0022-4596/$ - see front matter r 2006 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2006.01.045

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K.M. Ok, P. Shiv Halasyamani / Journal of Solid State Chemistry 179 (2006) 1345–1350
1346
2. Experimental
2.1. Synthesis
Table 1
Crystal data for Ba2TeO(PO4)2
Empirical formula
Formula weight
Crystal system
Space group
Z
Ba2TeO(PO4)2
608.22
BaCO3 (Aldrich, 99+%), TeO2 (Aldrich, 99+%), and
(NH4)H2PO4 (Aldrich, 98+%) were used as received.
Single-crystals of Ba2TeO(PO4)2 were prepared by using
excess amount of TeO2 in order to promote crystal growth.
0.197 g (1.00 mmol) of BaCO3, 0.115 g (1.00 mmol) of
(NH4)H2PO4, and 0.319 g (2.00 mmol) of TeO2 were mixed
with an agate mortar and pestle and introduced into a
platinum crucible. The crucible was heated to 650 1C for
15 h and then cooled down to 500 1C at a rate of 6 1C hꢀ1
before being quenched to room temperature. Colorless
block-shaped crystals of Ba2TeO(PO4)2 (42% yield based
on tellurium) were recovered from the crucible with TeO2.
Pure polycrystalline Ba2TeO(PO4)2 was synthesized
through standard solid-state reaction. A stoichiometric
mixture of BaCO3 (1.316 g, 6.66 mmol) with TeO2 (0.532 g,
3.33 mmol) and (NH4)H2PO4 (0.767 g, 6.66 mmol) was
thoroughly ground with an agate mortar and pestle and
pressed into a pellet, which was introduced into an alumina
crucible. The pellet was heated to 650 1C at a rate of
5 1C minꢀ1, held for 48 h, and cooled to room temperature
(5 1C minꢀ1) with an intermediate regrinding. Powder
X-ray diffraction (XRD) on the resultant white powder
indicated a single-phase product, and was in a good
agreement with the calculated pattern from the single-
crystal structure (see supporting information).
Triclinic
P-1 (No. 2)
2
6.9461(16)
˚
a (A)
˚
b (A)
˚
c (A)
7.3970(17)
8.887(2)
a (1)
b (1)
g (1)
76.843(4)
79.933(4)
75.688(4)
427.40(17)
3
˚
Volume (A )
Temperature (K)
293.0(2)
4.726
rcalc (g cmꢀ3
)
m (mmꢀ1
Crystal color
)
12.902
Colorless
Crystal habit
Crystal size
Block
0.10 ꢁ 0.10 ꢁ 0.12
Reflections collected
Independent reflections
R(int)
2611
1834
0.0261
0.225, 0.267
Tmin, Tmax
No. of parameters
Goodness-of-fit on F2
128
1.212
˚
X-ray radiation (l, A)
MoKa (0.71073)
2.37–27.98
y range (1)
Limiting indices
Refinement method
ꢀ8php8, ꢀ9pkp9, ꢀ11plp7
Full-matrix least-squares on F2
[SHELXL-97]
Final Ra,b indices [I42sðIÞ]
R indices (all data)
˚
Largest diff. peak and hole (e A
RðFÞ ¼ 0:0230, RwðF2oÞ ¼ 0:0624
RðFÞ ¼ 0:0242, RwðF2oÞ ¼ 0:0629
0.848 and ꢀ0.809
ꢀ3
)
aRðFÞ ¼ SjjFojFjFcjj=SjFoj.
2.2. Crystallographic determination
b
2
2
1=2
RwðF2oÞ ¼ ½SwðFo2FFc2Þ =SwðFo2Þ ꢂ
.
The structure of Ba2TeO(PO4)2 was determined by
standard crystallographic methods. A colorless block
crystal (0.10 ꢁ 0.10 ꢁ 0.12 mm3) was used for single-crystal
XRD. Room temperature intensity data were collected on
a Siemens SMART diffractometer equipped with a 1 K
CCD area detector using graphite monochromated MoKa
radiation. A hemisphere of data was collected using a
narrow-frame method with scan widths of 0.301 in omega,
and an exposure time of 30 s frameꢀ1. The first 50 frames
were remeasured at the end of the data collection to
monitor instrument and crystal stability. The maximum
correction applied to the intensities was o1%. The data
were integrated using the Siemens SAINT program [32],
with the intensities corrected for Lorentz, polarization, air
absorption, and absorption attributable to the variation in
the path length through the detector faceplate. C-scan was
used for the absorption correction on the hemisphere of
data. The data were solved and refined using SHELXS-97
and SHELXL-97, respectively [33,34]. All of the atoms
were refined with anisotropic displacement parameters and
converged for I42sðIÞ. All calculations were performed
using the WinGX-98 crystallographic software package
[35]. Crystallographic data, atomic coordinates and dis-
placement parameters, and selected bond distances and
angles for Ba2TeO(PO4)2 are given in Tables 1–3. The
Table 2
Atomic coordinates for Ba2TeO(PO4)2
a
Ueq (A )
2
˚
Atom
x
y
z
Ba(1)
Ba(2)
Te(1)
P(1)
0.3691(1)
0.1056(1)
0.3525(1)
0.1351(2)
0.3755(2)
0.5512(6)
0.2726(6)
0.6200(6)
0.4647(6)
0.8049(1)
0.3830(1)
0.8881(1)
1.1218(2)
0.5215(2)
0.3504(6)
1.1107(6)
0.9284(6)
0.7041(6)
0.4162(1)
0.2434(1)
0.9547(1)
0.6483(2)
0.8164(2)
0.8568(5)
0.7801(5)
0.8986(5)
0.8018(5)
0.9400(5)
0.6554(4)
0.6776(5)
0.4967(5)
0.6520(5)
0.013(1)
0.013(1)
0.010(1)
0.011(1)
0.011(1)
0.014(1)
0.016(1)
0.014(1)
0.015(1)
0.015(1)
0.015(1)
0.020(1)
0.016(1)
0.020(1)
P(2)
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
O(9)
0. 1972(6) 0.5292(6)
0.3285(6)
0.0652(7)
0.2786(6)
0.5215(6)
0.9354(6)
1.1481(6)
1.2917(6)
ꢀ0.0395(6)
aUeq is defined as one third of the trace of the orthogonalized Uij tensor.
X-ray powder diffraction data were collected on a Scintag
XDS2000 diffractometer at room temperature (CuKa
radiation, yꢀy mode, flat plate geometry) equipped with

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1347
Table 3
Selected bond distances (A) and angles (1) for Ba2TeO(PO4)2
polycrystalline Ba2TeO(PO4)2 sample was contained within
a platinum crucible and heated at a rate of 10 1C minꢀ1
from room temperature to 900 1C in static air.
˚
Bond distances
Bond valence
Te(1)ꢀO(1)
2.198(4)
2.028(4)
1.917(4)
2.144(4)
2.062(4)
0.5431
0.8294
1.0948
0.6197
0.7610
3.8480
3. Results and discussion
Te(1)ꢀO(2)
Te(1)ꢀO(3)
3.1. Structure
Te(1)ꢀO(3)
Te(1)ꢀO(4)
Ba2TeO(PO4)2 is a new one-dimensional tellurite phos-
phate compound containing chains that run parallel to the
b-axis. The chains are composed of PO4 and TeO5 units
Bond valence sum of Te(1)
P(1)ꢀO(2)
1.612(4)
1.526(4)
1.534(4)
1.517(4)
1.0183
1.2417
1.2184
1.2656
4.7440
P(1)ꢀO(7)
connected by PꢀOꢀTe and TeꢀOꢀTe bonds (see Fig. 1).
P(1)ꢀO(8)
2ꢀ
ꢀ
P(1)ꢀO(9)
As can be seꢀen in Fig. 1, the two [P(1)O1/2O3/1
]
]
and
poly-
Bond valence sum of P(1)
[P(2)O2/2O2/1
]
anionic tetrahedra and a [TeO5/2
hedron link to form one-dimensional chains. The two
[TeO5/2]ꢀ polyhedra share edges through O(3) and produce
Te2O8 dimers (see Fig. 2). Thꢀese dimers are further
P(2)ꢀO(1)
1.550(4)
1.591(4)
1.504(4)
1.522(4)
1.1742
1.0696
1.3048
1.2531
4.8017
P(2)ꢀO(4)
P(2)ꢀO(5)
P(2)ꢀO(6)
connected by the [P(2)O2/2O2/1
]
anions through O(1)
Bond valence sum of P(2)
and O(4) to form a chain along [010] direction. An intra-
chain coꢀnnection is made, between the [P(1)O1/2O3/1
2ꢀ and
Bond angles
]
polyhedra through O(2) (see Fig. 1). The lone
O(3)ꢀTe(1)ꢀO(2)
O(3)ꢀTe(1)ꢀO(4)
O(2)ꢀTe(1)ꢀO(4)
O(3)ꢀTe(1)ꢀO(3)
O(2)ꢀTe(1)ꢀO(3)
O(4)ꢀTe(1)ꢀO(3)
O(3)ꢀTe(1)ꢀO(1)
O(2)ꢀTe(1)ꢀO(1)
O(4)ꢀTe(1)ꢀO(1)
O(3)ꢀTe(1)ꢀO(1)
87.02(17)
79.72(16)
92.33(16)
74.62(17)
92.26(16)
153.65(15)
91.06(16)
178.04(15)
87.75(15)
86.81(15)
[TeO5/2
]
pairs on the Te4+ point in the [100] and [ꢀ100] direction
which interact with the Ba2+ cations.
There are two crystallographically unique P5+ cations in
the Ba2TeO(PO4)2 structure. Both P5+ cations are in
tetrahedral environments connected to four oxygen atoms.
The PꢀO bond distances for each PO4 tetrahedron range
˚
from 1.504(4) to 1.612(4) A. The OꢀPꢀO bond angles
range from 103.1(2) to 114.3(2)1. The Te4+ cation is in an
asymmetric coordination environment attributable to its
stereoactive lone pair. The Te4+ cation is in distorted
square pyramidal environment bonded to five oxygen
atoms resulting in TeO5 polyhedra (see Fig. 2). The TeꢀO
Peltier germanium solid-state detector in the 2y range
5–601 with a step size of 0.021, and a step time of 1 s.
˚
bond distances range from 1.917(4) to 2.198(4) A. The
2.3. Spectroscopic characterizations
OꢀTeꢀO bond angles range from 74.62(17) to 178.04(15)1.
The two unique Ba2+ cations are in eight- and ten-fold
coordination environments with BaꢀO contacts ranging
Infrared data were recorded on a Matteson FTIR 5000
spectrometer in the 400–4000 cmꢀ1 range, with the sample
pressed between two KBr pellets. The Raman spectrum
was recorded at room temperature on a Digilab FTS 7000
spectrometer equipped with a germanium detector with the
powder sample placed in separate capillary tubes. Excita-
tion was provided by a Nd:YAG laser at a wavelength of
1064 nm, and the output laser power was 544 mW. The
spectral resolution was about 4 cmꢀ1, and 200 scans were
collected. UV–Vis diffuse reflectance data for Ba2TeO
(PO4)2 were collected with a Varian Cary 500 scan
UV–Vis–NIR spectrophotometer over the spectral range
200ꢀ1500 nm at room temperature. Polytetrafluoroethy-
lene was used as a reference material. Reflectance spectrum
was converted to absorbance with the Kubelka–Munk
values [36].
˚
from 2.655(4) to 3.282(4) A. In connectivity terms, Ba2
ꢀ
TeO(PO4)2 can be formulated as consisting of {[TeO5/2
2ꢀ
]
[P(1)O1/2O3/1
]
[P(2)O2/2O2/1]ꢀ}4ꢀ anionic chains, with
charge balance maintained by the two Ba2+ cations. Bond
valence calculations [37,38] resulted in values range
2.04ꢀ2.16, 4.74ꢀ4.80, and 3.85 for Ba2+, P5+, and
Te4+, respectively.
3.2. Infrared and Raman spectroscopy
The infrared and Raman spectra of Ba2TeO(PO4)2
revealed TeꢀO, PꢀO, and TeꢀOꢀP vibrations. TeꢀO
vibrations are observed in both the IR and Raman and
found around 650ꢀ880 and 430 cmꢀ1. PꢀO vibrations are
also observed in both the IR and Raman and occur at
about 950ꢀ1150 and 450ꢀ570 cmꢀ1. A band, occurring
around 600 cmꢀ1, is attributable to TeꢀOꢀP vibration.
The infrared and Raman vibrations and assignments for
Ba2TeO(PO4)2 are listed in Table 4. The assignments are
consistent with those previously reported [31,39,40].
2.4. Thermogravimetric analysis
Thermogravimetric analysis was performed on a TGA
2950 Thermogravimetric Analyzer (TA Instruments). The

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1348
Fig. 1. Ball-and-stick diagram showing one-dimensional structure of Ba2TeO(PO4)2 in the bc-plane. Note the chains run along the b-axis.
Table 4
Infrared and Raman vibrations for Ba2TeO(PO4)2
PꢀO
TeꢀO
PꢀOꢀTe
IR (cmꢀ1
1149
1103
1081
1047
983
)
887
831
656
430
619
603
964
576
557
538
453
Raman (cmꢀ1
1161
1095
1060
972
)
860
837
659
432
613
952
574
Fig. 2. ORTEP (50% probability ellipsoids) drawing for Ba2TeO(PO4)2.
The Ba2+ cations are removed for clarity. Note 4-coordinate tetrahedral
and 5-coordinate distorted pyramidal environments for P5+ and Te4+
cations, respectively.
555
536
505
459
3.3. UV–Vis diffuse reflectance spectroscopy
Ba2TeO(PO4)2 is white and the spectrum shows that it is
transparent. Absorption (K/S) data were calculated from
the following Kubelka–Munk function:
where R represents the reflectance, K the absorption, and S
the scattering. In a K/S vs. E (eV) plot, extrapolating the
linear part of the rising curve to zero provides the onset of
absorption at 3.6 eV for Ba2TeO(PO4)2. The overall band
gap for the material may be attributable to the degree of
the distortions arising from TeO5 and PO4 polyhedra. The
2
ð1 ꢀ RÞ
2R
K
S
FðRÞ ¼
¼
,

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1349
UV–Vis diffuse reflectance spectrum for Ba2TeO(PO4)2 is
deposited in the Supporting Information.
Table 5
Calculation of dipole moments for TeO5 polyhedra
Compound
TeO5
Dipole moment (D)
3.4. Thermogravimetric analysis
a
Ba2TeO(PO4)2
BaTe2O6 [48]
Bi2Te2O8 [49]
Te(1)O5
Te(2)O5
Te(2)O5
Te(1)O5
Te(2)O5
Te(2)O5
Te(1)O5
Te(5)O5
Te(1)O5
Te(2)O5
Te(1)O5
Te(2)O5
Te(1)O5
Te(1)O5
Te(2)O5
Te(1)O5
Te(1)O5
Te(3)O5
7.14
7.75
7.19
8.40
8.58
10.08
7.46
8.41
7.96
7.79
7.64
7.13
8.64
10.82
9.64
7.89
8.90
7.78
The thermal behavior of Ba2TeO(PO4)2 was investigated
using thermogravimetric analysis. Ba2TeO(PO4)2 is not
stable at high temperature. A single-step decomposition
occurs at 730 1C attributable to the condensation of
phosphate groups with simultaneous volatilization of
TeO2 at higher temperature. Powder XRD measurement
on the calcined material revealed Ba2TeO(PO4)2 decom-
posed to Ba2P2O7 [41]. The decomposition is consistent
with the following reaction:
Ca(TeO)2(TeO6) [50]
Cs2Te4O9 [51]
In2Te3O9 [52]
K2Te4O9 [19]
K2Te(Te3O12) [53]
Na2Te4O9 [54]
NiTe2O5 [55]
Te2Se2O8 [56]
Te3SeO8 [57]
Te8O10(PO4)4 [29]
Ba2TeOðPO4Þ2 ꢀ! Ba2P2O7 þ TeO2:
D
TeSeO4 [58]
Tl2Te2O5 [59]
(Ag0.4Na1.6)Te5O14
[60]
The thermogravimetric analysis diagram for Ba2TeO
(PO4)2 and powder XRD pattern for calcined material,
Ba2P2O7 are deposited in the Supporting Information.
Te(4)O5
Te(2)O5
Te(1)O5
Te(1)O5
Te(1)O5
Te(1)O5
Te(2)O5
Te(2)O5
Te(1)O5
Te(2)O5
Te(1)O5
Te(1)O5
5.43
8.22
4.31
7.71
9.74
9.72
7.89
7.73
10.80
10.23
9.02
8.64
Bi4Te2O9Br2 [61]
Bi10Te2O17I4 [46]
3.5. Dipole moment calculations
Ca2Te2O4(CO3)2 [62]
GdTe2O5Cl [63]
InTeO3Cl [64]
Na2MoTe4O12 [65]
Na2WTe4O12 [65]
NaGaTe2O6 [66]
NdTe2O5Br [67]
NdTe2O5Cl [63]
NH4TeTeO5(OH)
[68]
Although Ba2TeO(PO4)2 crystallizes in centrosymmetric
space group, the material contains a cation in an
asymmetric coordination environment, i.e., Te4+. One of
our motivations for investigating materials containing
asymmetric lone pair cations is to better understand these
coordination environments. The direction and magnitude
of the distortions in the TeO5 polyhedra may be quantified
by determining the local dipole moments. This approach
has been described earlier [42–44]. The method uses a
bond-valence approach to calculate the direction and
magnitude of the local dipole moments. With the lone
pair polyhedra, the lone pair is given a charge of ꢀ2 and
the localized Te4+-lone pair distance is estimated to be
Average
TeO5
8.33 (71.33)
D ¼ Debyes.
aThis work.
˚
1.25 A [45]. Using this methodology, the dipole moment for
are available (PDF). Further details of the crystal structure
investigation can be obtained from the Fachinformations-
zentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen,
Germany, (fax: (49) 7247-808-666; e-mail: crysdata@fiz.
karlsruhe.de) on quoting the depository number CSD-
416032.
the TeO5 polyhedra is approximately 7.14 Debyes (D). In
fact, an examination of 30 examples of TeO5 polyhedra
reveals that the dipole moments range from 4.31 to 10.82 D
and average value of 8.3371.33 D (see Table 5). With
Bi10Te2O17I4 [46], a relatively small dipole moment of
4.31 D is estimated, which may be attributable to the
disorder between Bi(3)3+ and Te(1)4+ cations. The TeO5
polyhedron contains shorter bond distances than BiO5
group. In addition, Te4+ lone pair is more ‘‘directional’’
than that of Bi3+ based on the coordination environment.
We are in the process of examining all Te4+ oxides that
contain TeO3, TeO4, or TeO5 groups in order to better
understand the asymmetric polar environment [47].
Acknowledgments
We thank the Robert A. Welch Foundation for support.
This work was also supported by the NSF-Career Program
through DMR-0092054, and by the NSF-Chemical Bond-
ing Center. P.S.H. is a Beckman Young Investigator. We
also acknowledge Yushin Park and Prof. Rigoberto
Advincula for assistance in obtaining the Raman spectra.
4. Supporting information available
Powder XRD (calculated and experimental), UV–Vis
diffuse reflectance spectrum, IR and Raman spectra,
thermogravimetric analysis diagram for Ba2TeO(PO4)2,
and powder XRD pattern for calcined material, Ba2P2O7
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