Nanoporous crystalline material CsLiB6O10

Article abstract of DOI:10.1023/A:1021327622149

CsLiB₆O₁₀ crystals up to 60 × 40 × 20 mm in dimensions were prepared by top-seeded solution growth, and their interaction with water was studied. The crystals were found to be subject to hydration followed by hydrolysis, during which

Full text of DOI:10.1023/A:1021327622149

Inorganic Materials, Vol. 38, No. 12, 2002, pp. 1264–1269. Translated from Neorganicheskie Materialy, Vol. 38, No. 12, 2002, pp. 1485–1490.
Original Russian Text Copyright © 2002 by Kononova, Kokh, Fedorov, Ferapontova, Zakalyukin, Tkachenko.
Nanoporous Crystalline Material CsLiB6O10
N. G. Kononova*, A. E. Kokh*, P. P. Fedorov**, M. S. Ferapontova**,
R. M. Zakalyukin**, and E. A. Tkachenko**
* Institute of Mineralogy and Petrography, Siberian Division, Russian Academy of Sciences,
pr. Akademika Koptyuga 3, Novosibirsk, 630090 Russia
** Shubnikov Institute of Crystallography, Russian Academy of Sciences,
Leninskii pr. 59, Moscow, 117333 Russia
e-mail: ppf@newmail.ru
Received February 28, 2002
Abstract—CsLiB6O10 crystals up to 60 × 40 × 20 mm in dimensions were prepared by top-seeded solution
growth, and their interaction with water was studied. The crystals were found to be subject to hydration fol-
lowed by hydrolysis, during which water leaches Cs from the structural channels to yield Cs2B10O16 · 8H2O as
the final product. The channel dimensions are not large enough to incorporate ethanol or acetone molecules.
INTRODUCTION
Li2CO3–Cs2CO3–B2O3–MoO3 system using platinum
crucibles [6, 8].
The crystal growth, structure, and nonlinear optical
properties of cesium lithium borate, CsLiB6O10
(CLBO), a new noncentrosymmetric crystal (tetragonal
Thermal analysis (DTA + TG) was carried out in air
with a MOM Q-1500 system at a heating rate of 10 or
20°C/min, using 300- to 500-mg samples placed in
platinum crucibles. The thermocouples were calibrated
against the melting points of ground NaCl (800°C) and
LiF (845°C) crystals.
system, sp. gr. I4 2d), were first reported in 1995 [1–3].
CLBO finds rather wide application in nonlinear optics
for frequency conversion—in particular, for conversion
of visible light to UV radiation—through second and
higher (up to fourth or fifth) harmonic generation [1–
11]. Moreover, CLBO crystals have a laser damage
threshold as high as 26 GW/cm2, which is several times
higher than that of β-BaB2O4 (BBO), a widely used
nonlinear optical material. Accordingly, in going from
BBO to CLBO, the mean incident UV power can be
raised by an order of magnitude. In addition, CLBO is
superior to BBO in that less stringent requirements are
imposed on phase mismatch, which allows one to
employ CLBO crystals for efficient higher harmonic
generation using industrial multimode lasers with a
beam divergence of up to 3–5 mrad/cm [12].
X-ray diffraction (XRD) studies were performed on
HZG-4 and AFV-202E diffractometers (CuKα radia-
tion, external silicon standard). In data processing, we
used the Profit and Powder 2 application programs.
RESULTS AND DISCUSSION
Our XRD data for CLBO (Fig. 1) were similar to
those presented in [13] (tetragonal structure with a =
10.48 Å and c = 8.92 Å).
The thermal analysis results are displayed in Fig. 2.
During the first heating, the endothermic peak due to
melting occurred at 852 ± 5°C. During subsequent
cooling to 400°C and a second heating to 1000°C, ther-
mal effects were missing. Therefore, the melt solidified
without crystallization. After cooling, the sample
appeared as transparent glass. The crucible was washed
with water.
However, a serious problem arises because CLBO
crystals are subject to embrittlement in the course of
postgrowth storage and may collapse into powder as a
result of mechanical processing. The purpose of this
work was to establish the reason for the degradation of
CLBO crystals during storage.
The melting point of CLBO determined in this study
agrees well with those reported earlier: 848°C in [1]
and 859 ± 2°C in [9].
EXPERIMENTAL
One possible reason for the cracking of CLBO crys-
tals as a result of mechanical processing is the stress-
induced low-temperature polymorphism of this com-
As starting materials, we used extrapure-grade
Li2CO3, Cs2CO3, B2O3 and MoO3.
CLBO crystals up to 60 × 40 × 20 mm in dimensions pound (“tin pest” effect). To check this assumption, we
were prepared by top-seeded solution growth in the took XRD patterns from a crystal which was ground for
0020-1685/02/3812-1264$27.00 © 2002 MAIK “Nauka/Interperiodica”

NANOPOROUS CRYSTALLINE MATERIAL CsLiB6O10
1265
(a)
(b)
10
20
30
40
50
2θ, deg
Fig. 1. Powder XRD patterns of CsLiB O after (a) dry grinding and (b) grinding with ethanol for many days.
6
10
TG
852
DTG
t, °ë
DTA
Fig. 2. Thermal analysis of CsLiB O (sample weight of 0.268 g).
6
10
several hours in a jasper mortar fitted with a mechanical CLBO sample was placed over a water surface in a
drive. Long-term grinding of CLBO, dry or with etha-
nol and acetone, caused no changes in the XRD pattern
(Fig. 1), indicating that our assumption was wrong.
closed vessel, in which the room-temperature (20–25°C)
humidity of air was close to 100%, and its XRD pat-
terns were taken at regular intervals. The results are
presented in Fig. 3. The XRD pattern of moist CLBO
contained peaks from an additional phase. The XRD
According to earlier studies [5, 8], CLBO is
hydrated at high humidity. We studied the interaction of
CLBO with atmospheric moisture by XRD. A powdered pattern from the surface layer of CLBO powder pressed
INORGANIC MATERIALS Vol. 38 No. 12 2002

1266
KONONOVA et al.
(a)
(b)
(c)
(d)
10
20
30
40
50
2θ, deg
Fig. 3. XRD patterns of hydrolyzed CLBO samples: (a) after storage in air at ambient humidity for many days, (b, c) after storage
at 100% humidity for 3 and 7 days, respectively, (d) final hydrolysis product.
into a holder and stored in humid air showed no peaks begins at about 85°C and terminates around 130°C. The
from CLBO. The additional peaks could be assigned to second step begins at Ӎ176°C and terminates at
Cs2B10O16 · 8H2O [14], in line with previous results [5]. Ӎ210°C.
Thermal analysis of hydrated CLBO is illustrated in
We also studied the interaction of CLBO with ace-
Fig. 4. The weight loss occurs in two steps: the first tone and ethanol by exposing CLBO powder to vapors
INORGANIC MATERIALS Vol. 38 No. 12 2002

NANOPOROUS CRYSTALLINE MATERIAL CsLiB6O10
1267
of these compounds for many days. No interaction was
TG
detected by XRD.
Water sorption by CLBO is closely related to its
crystal structure. Figure 5 shows different projections
of the CLBO structure (Diamand program) [3]. The
structure contains three-membered rings, each built
from two BO3 triangles (sp2-hybridized boron) and one
DTG
BO4 tetrahedron (sp3 hybridization). These rings (also
present in LBO crystals) are responsible for the nonlin-
ear optical properties of the crystals [15]. Each tetrahe-
dron shares a corner (bridging oxygen) with one of the
triangles of the neighboring ring so as to form infinite
zigzag chains (Fig. 5d) which run along the body diag-
onals of the unit cell. In Fig. 5c, some of the chains are
viewed from the side, and some from the front.
t, °ë
DTA
The structure contains spacious pores occupied by
Cs. The pores (channels) are best seen in the c-axis pro-
jection (Fig. 5a), where the channels have an ellipsoidal
cross section with minor and major axes of 4.16 and
6.4 Å (center-to-center distance between the projec-
tions of oxygen atoms). Note that the actual dimensions
of the channels are larger since they are tilted. There-
fore, the Cs ions would be expected to have a high
mobility.
210
176
131
85
Fig. 4. Thermal analysis of hydrated CLBO.
There are also channels running along the c axis
(Fig. 5b) and having an approximately square cross sec-
tion about 3.55 Å in size (center-to-center distance
between the projections of oxygen atoms). These chan-
nels are also rather spacious; however, along this direc-
tion, the Cs ions alternate with Li ions, which seem to
be rather strongly bonded to the boron–oxygen chains.
Therefore, the cation mobility in this direction must be
lower.
The initial steps of this process can be described by the
equations
CsLiB6O10 + xH2O
CsLiB6O10 + 2H2O
CsLiB6O10 + 3H2O
CsLiB6O10 xH2O, (2)
Li(H3O)B6O10 + CsOH, (3)
Li(H5O2)B6O10 + CsOH. (4)
Equation (2) describes water sorption (hydration), and
Eqs. (3) and (4) describe substitution of oxonium and
hydroxonium ions for Cs. The compounds resulting
from reactions (3) and (4) are polymeric acids.
Note that the hydration process must be anisotropic
and must take place, for the most part, in directions per-
pendicular to the c axis.
To avoid water sorption, CLBO crystals should be
stored in a dry atmosphere. According to DTA data, the
first step of dehydration reaches completion at 130°C.
Consequently, another way to prevent hydration fol-
lowed by hydrolysis is to store CLBO above this tem-
perature [7]. Accordingly, devices in which CLBO
crystals are used must operate in a dry atmosphere or
contain a thermostat.
CLBO crystals can be thought of as nanoporous,
zeolite-like materials [16]. They would be expected to
have a high ionic conductivity and good ion-exchange,
sorptive, and catalytic properties. In particular, CLBO
crystals should have a high cesium ion conductivity in
directions perpendicular to the c axis. Since the size of
the water molecule is close to the cross-sectional size of
Proceeding from structural data, one can easily
understand the mechanism of the interaction between
CLBO crystals and water: the latter penetrates into the
porous structure of CLBO and leaches Cs ions (hydra-
tion followed by hydrolysis).
Our results on the influence of moisture on CLBO
crystals agree well with earlier findings [6]. According
to IR spectroscopic data [11], there are four inequiva-
lent positions of protons in the CLBO structure:
adsorbed H2O, H2O in inclusions, H3O+ and H5O2+ ions
on the Cs site, and H2O molecules in the form of H–O–H
bridges between borate chains normal to the c axis.
The present and earlier reported data indicate that
CLBO reacts with water according to the following
overall equation:
2CsLiB6O16 + 12H2O
2LiOH
(1)
+ Cs2B10O16 8H2O + 2H3BO3.
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KONONOVA et al.
(a)
(b)
a
b
a
c
(c)
(d)
Fig. 5. Crystal structure of CLBO: (a) b-axis projection, (b) c-axis projection, (c) projection along the body diagonal, (d) character-
istic structural component; large circles represent Cs atoms, and small circles represent Li and B atoms.
the channels in the structure of CLBO, water is easy to
incorporate into the channels. The acetone and ethanol
molecules are substantially larger and cannot be
inserted into the channels. CLBO would be expected to
react with ammonia.
This work was supported by the Presidium of the
Siberian Division of the Russian Academy of Sciences
(resolution no. 118, April 9, 2002) through the inte-
grated program New Principles and Methods of Pro-
ducing Materials with Controlled Properties (project
Investigation of Phase Diagrams, Search for Solvents,
and Growth of Nonlinear Optical Crystals in Thermal
Fields of Various Symmetries; coordinator, Academi-
cian N.T. Kuznetsov).
ACKNOWLEDGMENTS
We are grateful toA.M.Yurkin andYu.V. Pisarevskii
for support of this research.
INORGANIC MATERIALS Vol. 38 No. 12 2002

NANOPOROUS CRYSTALLINE MATERIAL CsLiB6O10
1269
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INORGANIC MATERIALS Vol. 38 No. 12 2002