Li2B3O4F3, a new lithium-rich fluorooxoborate

Article abstract of DOI:10.1016/j.jssc.2011.11.053

The new lithium fluorooxoborate, Li₂B₃O ₄F₃, is obtained by a solid state reaction from LiBO ₂ and LiBF₄ at 553 K and crystallizes in the acentric orthorhombic space group P2₁2₁2₁ (no. 19) with the cell parameters a=4.8915(9), b=8.734(2), and c=12.301(2) A. Chains of fluorinated boroxine rings along the b axis consists of BO₃ triangles and BO₂F₂ as well as BO₃F tetrahedra. Mobile lithium ions are compensating the negative charge of the anionic chain, in which the fourfold coordinated boron atoms bear a negative formal charge. Annealing Li₂B₃O₄F₃ at temperatures above 573 K leads to conversion into Li₂B₆O₉F ₂. The title compound is an ionic conductor with the highest ion conductivity among the hitherto know lithium fluorooxoborates, with conductivities of 1.6×10^-9 and 1.8×10^-8 S cm^-1 at 473 and 523 K, respectively.

Full text of DOI:10.1016/j.jssc.2011.11.053

Journal of Solid State Chemistry 186 (2012) 104–108
Contents lists available at SciVerse ScienceDirect
Journal of Solid State Chemistry
journal homepage: www.elsevier.com/locate/jssc
Li2B3O4F3, a new lithium-rich fluorooxoborate
Thomas Pilz, Hanne Nuss, Martin Jansen n
Max Planck Institute for Solid State Research, Heisenbergstraße 1, 70569 Stuttgart, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
The new lithium fluorooxoborate, Li2B3O4F3, is obtained by a solid state reaction from LiBO2 and LiBF4
Received 18 October 2011
Accepted 30 November 2011
Available online 8 December 2011
at 553 K and crystallizes in the acentric orthorhombic space group P212121 (no. 19) with the cell
˚
parameters a¼4.8915(9), b¼8.734(2), and c¼12.301(2) A. Chains of fluorinated boroxine rings along
the b axis consists of BO3 triangles and BO2F2 as well as BO3F tetrahedra. Mobile lithium ions are
compensating the negative charge of the anionic chain, in which the fourfold coordinated boron atoms
bear a negative formal charge. Annealing Li2B3O4F3 at temperatures above 573 K leads to conversion
into Li2B6O9F2. The title compound is an ionic conductor with the highest ion conductivity among the
hitherto know lithium fluorooxoborates, with conductivities of 1.6 ꢀ 10ꢁ9 and 1.8 ꢀ 10ꢁ8 S cmꢁ1 at
473 and 523 K, respectively.
Keywords:
Lithium fluorooxoborate
Lithium ion conductivity
Acentric borate
& 2011 Elsevier Inc. All rights reserved.
1. Introduction
warranting any application. Since the commonly used approach to
increase the charge carrier concentration in ionic conductors by
Many oxoborates feature pronouncedly anisotropic oligomeric
or polymeric anions, and show a certain inclination to assume
non-centrosymmetric space group symmetries. The set of special
physical properties related to acentric structures have nourished
significant interest in this class of compounds, which includes top
performing SHG materials, among others LiB3O5 (LBO) [1] and
CsLiB6O10 (CLBO) [2].
Recently, we have started investigating alkali fluorooxobo-
rates, with a twofold motivation. (1) Adding a fluoride ion to
boron in a threefold planar coordination would shift negative
charge to the central boron atom, now in fourfold coordination,
thus reducing partial negative charge at the respective terminal
oxygen and/or fluorine atoms, which commonly act as pinning
sites for the cations. By this measure we aim at enhancing e.g.
lithium ion mobility in lithium borates. (2) Including electrone-
gative fluorine would increase the anisotropy of charge distribu-
tion within the borate anions, which might improve the SHG,
piezoelectric or pyroelectric performance, in general.
By the examples of LiB6O9F [3] and Li2B6O9F2 [4] we have
demonstrated that lithium fluorooxoborates are accessible by an
acid–base reaction in the solid state, where boron oxide or
oxoborates with boron in threefold coordination may serve as
acids, and LiF or LiBF4 as fluoride bases.
Indeed, all lithium fluorooxoborates discovered are acentric, and
show non-linear optical properties, LiB6O9F even with an efficiency
comparable to KDP [5], they furthermore are pure lithium ion
conductors. However, the conductivities found are too low for
aliovalent doping has failed for lithium fluorooxoborates, so far, we
have moved on by synthesizing species with higher stoichiometric
Li contents. Here we present the new Li2B3O4F3.
2. Experimental
2.1. Synthesis
All reactions were carried out in purified argon atmosphere
using standard Schlenk techniques. LiBO2 (lithium metaborate,
anhydrous, Fischer Scientific, reagent grade) was dried at 673 K
under vacuum for 4 days. Tetrahydrofurane (Merck, 499%) was
dried with sodium and freshly distilled prior to use.
LiBO2 and LiBF4 (Sigma Aldrich, anhydrous, ultra dry 99.998%)
were mixed in a ratio of 2:1 and thoroughly ground. The mixture
was placed in closed silver crucibles, sealed in glass ampoules
and heated from room temperature to 553 K at a heating rate of
100 K/h. After holding the reaction mixture at 553 K for 500 h, it was
finally cooled to room temperature at a rate of 1 K/h. The reaction
product contained LiF and Li2B3O4F3 in the ratio of 1:2. In order to
remove the byproduct, LiF is transformed into LiBF4 by stirring the
reaction products in a solution of boron trifluoride tetrahydrofuran
complex (50%, Acros Organics) in absolute tetrahydrofurane at
room temperature for 3 days. By subsequent filtering, the pure
fluorooxoborate was obtained as an insoluble residue.
2.2. Characterization
n Corresponding author. Fax: þ49 711 689 1502.
E-mail address: M.Jansen@fkf.mpg.de (M. Jansen).
Powder X-ray diffraction patterns were recorded at room
temperature on
a high resolution X-ray diffractometer (D8
0022-4596/$ - see front matter & 2011 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2011.11.053

T. Pilz et al. / Journal of Solid State Chemistry 186 (2012) 104–108
105
ADVANCE, Bruker AXS, Karlsruhe, Germany) using Cu–K
tion (Ge(1 1 1)—monochromator). The samples were sealed under
argon in a glass capillary with a diameter of 0.5 mm. Diffraction
a
radia-
Table 2
Atomic coordinates (104) and equivalent isotropic displacement parameters
2
(A ꢂ 103) for Li2B3O4F3. U(eq) is defined as one third of the trace of the
˚
orthogonalized Uij tensor.
patterns were collected between 51 and 951 2
y
for 14 h. The lattice
˚
constants, a¼4.8915(9), b¼8.734(2), c¼12.301(2) A, were deter-
Atom
x
y
z
U(eq)
mined from a Le Bail fit [6] using TOPAS [7].
Li(1)
Li(2)
B(1)
B(2)
B(3)
O(1)
O(2)
O(3)
O(4)
F(1)
F(2)
F(3)
4142(9)
6452(4)
2063(5)
3182(3)
5316(3)
5792(3)
3734(2)
6339(2)
4266(2)
6742(2)
5798(2)
5505(2)
2879(2)
3966(3)
5718(3)
6600(2)
5385(2)
7303(2)
5595(1)
6289(1)
7483(1)
8176(1)
4477(1)
5033(1)
6448(1)
23(1)
27(1)
16(1)
18(1)
17(1)
20(1)
22(1)
18(1)
20(1)
29(1)
27(1)
31(1)
For structure determination, a colorless crystal, suitable for
single-crystal X-ray diffraction, was placed on top of a glass fiber
and sealed within a glass capillary in a glove box.
16,593(9)
10,814(5)
9080(6)
Intensity data were collected at 298 K on a SMART-APEX CCD
10,214(5)
9647(3)
X-ray diffractometer (Bruker AXS Inc., Karlsruhe, Germany) with
˚
9582(4)
Mo–Ka radiation (l¼0.71073 A) and a graphite monochromator.
10,596(3)
10,526(3)
10,710(3)
6352(3)
A
semi-empirical absorption correction was applied using
SADABS [8]. The structure was solved with direct methods and
refined using the program package SHELXTL [9]. Further details of
the crystal structure investigation are available from the Fachin-
formationszentrum Karlsruhe, D-76344 Eggenstein-Leopoldsha-
fen (Germany), on quoting the depository number CSD-423661,
the name of the authors, and citation of the paper.
13673(3)
Details of single crystal measurement, atom coordinates and
displacement parameters are given in Tables 1–3.
The cavity calculations have been performed using the pro-
gram ATOMSV6.3 [10].
Table 3
Anisotropic displacement parameters (A ꢂ 103) for Li2B3O4F3. The anisotropic
2
˚
displacement factor exponent takes the form: ꢁ2
p
2[h2 an2U11þ?þ2 h k an bn
U
12].
Infrared spectra were recorded between 400 and 4000 cmꢁ1
using the FT-IR spectrometer IFS 113v (Bruker Optic, Karlsruhe).
Sample pellets were prepared by pressing a thoroughly ground
mixture of 300 mg dry KBr and 1 mg sample.
Ionic conductivity was measured from a compact pressed
powder pellet (diameter 6 mm; thickness 0.65 mm), placed
between two silver electrodes in a quartz tube, floated with argon.
The Novocontrol Alpha A 4.2 Analyzer was used with the ZG-4
interface in an 2-wire arrangement. Spectra were recorded from
1 Hz up to 5 MHz during continuous heating at a rate of 0.5 K/min,
controlled by WinDeta program [11]. All parameters including
Atom
U11
U22
U33
U23
U13
U12
Li(1)
Li(2)
B(1)
B(2)
B(3)
O(1)
O(2)
O(3)
O(4)
F(1)
F(2)
F(3)
31(3)
26(2)
18(1)
19(2)
16(1)
32(1)
33(1)
29(1)
28(1)
33(1)
23(1)
21(1)
19(2)
31(2)
14(1)
16(1)
15(1)
14(1)
11(1)
12(1)
12(1)
33(1)
30(1)
36(1)
19(2)
23(2)
15(1)
17(1)
19(1)
14(1)
20(1)
15(1)
18(1)
22(1)
29(1)
36(1)
1(2)
1(2)
1(2)
1(2)
ꢁ5(2)
ꢁ1(1)
1(1)
ꢁ3(2)
ꢁ1(1)
ꢁ2(1)
2(1)
ꢁ1(1)
ꢁ1(1)
0(1)
1(1)
ꢁ1(1)
0(1)
ꢁ4(1)
ꢁ6(1)
ꢁ2(1)
ꢁ5(1)
6(1)
2(1)
3(1)
ꢁ1(1)
ꢁ1(1)
7(1)
2(1)
3(1)
ꢁ6(1)
4(1)
1(1)
ꢁ6(1)
2(1)
ꢁ8(1)
5(1)
sbulk, Q and n were calculated using the WinFit program [12].
3. Results and discussion
Table 1
Crystal data and structure refinement for Li2B3O4F3.
3.1. Synthesis
Empirical formula
Li2B3O4F3
Li2B3O4F3 was synthesized from LiBO2 and LiBF4 at 553 K
(Eq. (1)). Pure phase material was obtained after the extraction
of the byproduct LiF with dilute THF ꢂ BF3.
Formula weight
Temperature
Wavelength
167.31
298(2) K
˚
0.71073 A
Crystal system
Space group
orthorhombic
2LiBO2þLiBF4-Li2B3O4F3þLiF
(1)
P212121 (no. 19)
Unit cell dimensions
˚
a¼4.8915(9) A
b¼8.734(2) A
c¼12.301(2) A
525.5(2) A
˚
Annealing of the fluorooxoborate at temperatures higher than
573 K leads to the formation of Li2B6O9F2, which decomposes at
753 K [4]. Solid state reaction of the starting materials LiBO2 and
LiBF4, in an appropriate ratio at 623–673 K will directly result in
Li2B6O9F2 [4].
˚
3
Volume
˚
Z
4
Density (calculated)
Absorption coefficient
F(0 0 0)
2.115 g cmꢁ3
0.235 mmꢁ1
320
Crystal size
0.20 ꢀ 0.18 ꢀ 0.10 mm3
2.86–27.491
3.2. Crystal structure
Theta range for data collection
Index ranges
ꢁ6rhr6, ꢁ11rkr11, ꢁ15rlr15
5480
Li2B3O4F3 crystallizes in the orthorhombic space group P212121
(no. 19) with two formula units per unit cell. The structure is built of
Reflections collected
Independent reflections
Completeness to theta¼27.491
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I42sigma(I)]
R indices (all data)
1216 [R(int)¼0.0485]
100.0%
1
N[B3O4F3]2ꢁ chains running along b and two crystallographically
0.9769 and 0.9545
Full-matrix least-squares on F2
1216/0/109
independent, fourfold coordinated Liþ cations (Fig. 1a). In Fig. 1b, a
cutout of the structure shows fluorinated boroxine rings, [B3O4F3]2ꢁ
,
0.961
bonded to each other via a bridging oxygen atom. Thereby, always a
threefold boron atom of one ring (B3) is connected to a fourfold
coordinated boron (B1) of another, bearing three O atoms (two ring
atoms and one terminal O) and one F atom as nearest neighbors. The
third ring-B-atom (B2), not involved in the setup of the chains, is
R1¼0.0347, wR2¼0.0664
R1¼0.0568, wR2¼0.0726
ꢁ0.2(10)
Absolute structure parameter
Largest diff. peak and hole
ꢁ3
˚
0.233 and ꢁ0.232 eA

106
T. Pilz et al. / Journal of Solid State Chemistry 186 (2012) 104–108
Fig. 1. (a) Projection of the orthorhombic cell in the bc plane: chains of the anionic matrix are along the b axis. (b) The fundamental building block consists of one trigonal
planar BO3 unit, one tetrahedral BO2F2 as well as a tetrahedral BO3F unit.
Table 4
Table 5
Coordination geometry around lithium (symmetry codes as given in Table 1).
˚
Selected bond lengths/A and angles/deg. of the boroxine backbone. Symmetry
codes: (I) ꢁxþ2, yꢁ1/2, ꢁzþ3/2; (II) xꢁ1, y, z; (III) ꢁxþ3/2,ꢁyþ1, zþ3/2;
(IV) xꢁ1/2, ꢁyþ3/2, ꢁzþ1; (V) xꢁ3/2, ꢁyþ1/2, ꢁzþ1; (VI) ꢁxþ3, yꢁ1/2,
ꢁzþ3/2; (VII) xþ1/2, ꢁyþ1/2, ꢁzþ1; (VIII) xþ3/2, ꢁyþ1/2, ꢁzþ1.
Atom contact
Distance
Atom contact
Angle
Li1–F1II
Li1–F2
1.881(4)
1.891(4)
1.966(4)
1.933(4)
F1II–Li1–F2
98.4(2)
F1II–Li1–O3III
F2–Li1–O3III
F1II–Li1–O2IV
F2–Li1–O2IV
O3III–Li1–O2IV
F3–Li2–O4VI
F3–Li2–O1VII
O4VI–Li2–O1VI
F3–Li2–O1II
106.0(2)
118.4(2)
116.7(2)
118.5(2)
99.2(2)
Atom contact
Distance
Atom contact
Angle
Li1–O2IV
Li1–O3III
B1–F3
B1–O1
B1–O3
B1–O4I
1.436(3)
1.444(3)
1.444(3)
1.445(3)
F3–B1–O1
F3–B1–O3
F3–B1–O4I
O1–B1–O3
O1–B1–O4I
O3–B1–O4I
109.6(2)
106.9(2)
107.9(2)
113.3(2)
105.6(2)
113.2(2)
Li1yLi2V
Li2–F3
Li2–O1VII
Li2–O1II
Li2–O4VI
3.336(6)
1.832(4)
2.000(4)
2.094(4)
1.979(4)
105.8(2)
99.2(2)
147.7(2)
108.7(2)
68.9(1)
B2–F1
B2–F2
B2–O1
B2–O2
1.435(3)
1.412(3)
1.433(3)
1.448(3)
O4VI–Li2–O1II
O1VII–Li2–O1II
F1–B2–O1
F1–B2–O2
F2–B2–O1
F2–B2–O2
F1–B2–F2
O1–B2–O2
O2–B3–O3
O2–B3–O4
O3–B3–O4
108.4(2)
108.8(2)
110.5(2)
108.9(2)
104.6(2)
115.0(2)
121.3(2)
121.9(2)
116.8(2)
Li2yLi1VIII
Li2yLi2VII
3.335(6)
3.112(5)
121.6(2)
B3–O2
B3–O3
B3–O4
1.371(3)
1.364(3)
1.365(3)
of the BO3 triangle is 120.01, whereby the largest deviation of 3.21 is
observed for the bridging oxygen atom O4 (O3–B3–O4).
In contrast to the two other fluorooxoborates mentioned above,
the title compound exhibits an additional structural feature, a
BO2F2 tetrahedron incorporated into the ring (Fig. 1b). The O–B–O,
O–B–F and F–B–F angles of this building block lie in the expected
range, with the F–B–F angle of 104.6(2)1 exhibiting the smallest
value. For significant deviation from the ideal tetrahedral angle
one can discuss several reasons, as e.g. the reduced mutual
repulsion of the terminal, strongly electronegative fluorine atoms
or an evasive movement due to embedding into a ring-like
arrangement. In case of Li2B3O4F3 we attribute the angular distor-
tion mainly to the latter, since the F–B–F angles of BO2F2 tetra-
hedra not included in boroxine rings, as found in Li2B6O9F2 [4] and
(C2H10N2)(BPO4F2) [20], have close to ideal tetrahedral angles.
The B–O and B–F bond lengths are comparable to those in the
BO3F tetrahedron, whereby one of the B–F bonds, d(B2–F2)¼
bonded to two ring-O atoms and two terminal F atoms. Table 4
summarizes selected bond lengths and angles. The mean d(B–O)
distance of the ring-B–O bonds within the [B3O4F3]2ꢁ units is 1.417 A,
˚
with the B–O bonds involving threefold coordinated boron being
significantly shorter (average: 1.368 A) than those including fourfold
bonded B (av.: 1.442 A). All distances are in good agreement with
reported data for borates [13–17] tetrafluoroborates [18,19] and
lithium fluorooxoborates [3,4]. The boroxine ring exhibits a twisted-
boat conformation with the maximum dihedral angle B3–O3–B1–
O1¼20.961, as expected by insertion of tetrahedrally coordinated B
and in accordance with the fluorinated boroxine ring found in
LiB6O9F [3] and the interconnected boroxine rings of Li2B6O9F2 [4].
The geometry of the BO3F unit resembles the similar building
block found in LiB6O9F [3]. Compared to the latter, the mean O–B–O
angle¼110.81 and the mean O–B–F angle¼108.11 approaching
more closely that of the ideal tetrahedron and no significant
difference in B–O and B–F bond lengths within experimental
standard deviations is observed (Table 4). The mean O–B–O angle
˚
˚
˚
1.412(3) A, is significantly shorter than the other B–F contacts
˚
within the structure. The value of about 1.41 A resembles to the
B–F bonds found for BO2F2 tetrahedra in the recently reported
new acentric fluorooxoborate Li2B6O9F2 [4]. In this compound,
however, the BO2F2 unit is not part of the boroxine ring, but
˚
isolated, showing B–F distances of 1.407(2) A.

T. Pilz et al. / Journal of Solid State Chemistry 186 (2012) 104–108
107
Besides the boroxine backbone, the unit cell contains two
523 K: Cbulk = 9.4 pF
-0.4
-0.3
-0.2
-0.1
0.0
crystallographically independent lithium cations, interconnecting
the chains. Table 5 summarizes the coordination geometry around
lithium, indicating a distorted tetrahedral coordination of Liþ
.
As can be seen from Fig. 2, the lithium cations are surrounded by
two F and two O (Li1), and three O and one F atom (Li2),
semicircle 1
1
respectively, in both cases connecting three adjacent N[B3O4F3]2ꢁ
chains. Looking at the space-filling model of Li2B3O4F3 on the left in
Fig. 3, it is obvious that the structure is not densely packed, and is
displaying channels along b. The small white spots, in this, indicate
the Liþ positions within the structure at room temperature. The
lithium cations occupy pockets along the chains that exhibit the best
coordination with respect to the donor atoms O and F. However, the
distances to the channel centers are small, and at elevated tem-
peratures a diffusion along the channels might become possible.
In Fig. 3 right, cavities within the unit cell are shown, which are
0.0
0.5
1.0
1.5
473 K: Cbulk = 8.9 pF
-4
-2
0
accessible by particles with a radius of about 0.7 A (0.65rr(Liþ)r
˚
˚
0.76 A, depending on the coordination number). Since these cavities
semicircle 1
0
2
4
6
8
10
12
14
16
18
-70
-60
-50
-40
-30
-20
-10
0
423 K: Cbulk = 8.4 pF
semicircle 1
0
50
100
150
200
Z(real) [MΩ]
Fig. 4. Nyquist plots for 423, 473 and 523 K obtained from impedance measur-
Fig. 2. Tetrahedrally coordinated lithium atoms.
emnt of Li2B3O4F3.
Fig. 3. Left: space-filling representation of the structure using van-der-Waals radii for all non-metal atoms; little white spots indicate the Liþ positions; right: cavities big
˚
enough for particles with a radius of 0.7 A, calculated with ATOMSV6.3 [10].

108
T. Pilz et al. / Journal of Solid State Chemistry 186 (2012) 104–108
416 and 1435 cmꢁ1, thus presence of hydroxyl group can be
convincingly excluded. Strong vibration bands originate from
asymmetric stretching modes ( as) of terahedrally surrounded,
and from symmetric stretching modes ( s) of trigonally sur-
T / °C
250
400 350 300
200
150
-6.5
-6.5
-7.0
n
-7.0
n
rounded boron [24]. The assignment was performed in agreement
to literature values of tetrafluoroborates [25], lithiumtriborate
[26] and other borates [24]. IR(KBr, cmꢁ1): 1435, 1336 (m)
-7.5
-7.5
Li B O F : E = 101 kJ/mol
2
3
4
3
a
-8.0
-8.0
-8.5
-8.5
(
n
asB(3)–O); 1226 (m) (
n
(ring)); 1047, 1035 (s) (
nasB(4)–O,F);
-9.0
-9.0
941 (s) ( sB(3)–O) , 827, 798 (w) (
n
n
sB(4)–O,F); 727, 698, 675 (w)
-9.5
-9.5
(bending (B(3)–O) out of plane ; 567, 546, 442, 416 (w–m) (further
-10.0
-10.5
-11.0
-11.5
-12.0
-10.0
-10.5
-11.0
-11.5
-12.0
deformation bands).
Li B O F : E = 89 kJ/mol
2
6
9
2
a
LiB O F: E = 160 kJ/mol
6
9
a
4. Conclusion
1.4
1.6
1.8
2.0
2.2
2.4
Li2B3O4F3 is the third member among the new family of
lithium fluorooxoborates. It consists of one BO3F and one BO2F2
tetrahedron as well as one trigonal planar BO3 group as a primary
building unit. We have attributed the improved Li ion conductiv-
ity of Li2B6O9F2 compared to LiB6O9F to the higher amount of
lithium [4]: this view receives support by the results obtained in
the recent work.
1000/T / 1/K
Fig. 5. Arrhenuis plots of lithium fluorooxoborates: obviously the ionic conduc-
tivity increases from LiB6O9F [3] to Li2B6O9F2 [4] to Li2B3O4F3 (this work).
form continuous channels, they provide possible pathways for ion
conduction. The closest intermolecular LiþyLiþ distance within
this structure is 3.112(5) A between Li2 and Li2VII, which is the
˚
closest LiyLi distance found within fluorooxoborates by now.
References
Hydroxoborates with analogous composition N[B3O4X3]2ꢁ
1
(X¼OH) are colemanite CaB3O4(OH)3 ꢂ H2O [21,22] and hydrobor-
acite CaMg[B3O4(OH)3]2 ꢂ 3H2O [23]. The anionic repetition units
are identical with the fluorooxborate, and can be mutually
transformed by replacing fluorine with the hydroxo-group and
vice versa.
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3.3. Ionic conductivity
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The ionic conductivity, bulk capacitance and activation energy
for ionic conduction of Li2B3O4F3 was determined by impedance
spectroscopy. Data were recorded by heating a pressed pellet of
the powdered sample up to 553 K at a rate of 0.5 K/min.
Fig. 4 represents the imaginary part of the impedance plotted
versus the real part (so called Nyquist plot) for different tem-
peratures. The semicircle I can be described as an ohmic resistor
in parallel to a constant phase element Q, where the latter
represents the capacitance C and the ‘‘roughness’’ of the pressed
powder, n, according to C¼Q1/n ꢂ R(1/n)ꢁ1 (ideal capacitor: n¼1,
C¼Q). In the hole temperature range the values for n are
approximately 0.7.
Compared to our previous reported lithium fluorooxoborates
LiB6O9F and Li2B6O9F2, Li2B3O4F3 exhibits the highest lithium ion
conductivity (Fig. 5).
We attribute this to the increased volumetric density of
lithium ions of latter compared to the former.
3.4. IR spectroscopy
For Li2B3O4F3 the spectrum was recorded from 400 to
4000 cmꢁ1, with vibration bands exclusively appearing between
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