Synthesis and Electrical Properties of Ammonium Fluorostannates(II)

Article abstract of DOI:10.1023/A:1025685625331

With the aim of developing new fluorine-conducting solid electrolytes, the compound NH₄SnF₃ was synthesized and its electrical conductivity and thermal behavior were studied.

Full text of DOI:10.1023/A:1025685625331

Russian Journal of Applied Chemistry, Vol. 76, No. 3, 2003, pp. 497 499. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 3,
2003, pp. 512 514.
Original Russian Text Copyright
2003 by Sorokin, Rakov, Fedorov, Zakalyukin.
BRIEF
COMMUNICATIONS
Synthesis and Electrical Properties
of Ammonium Fluorostannates(II)
N. I. Sorokin, E. G. Rakov, P. P. Fedorov, and R. M. Zakalyukin
Shubnikov Institute of Crystallography, Russian Academy of Sciences, Moscow, Russia
Mendeleev Russian University of Chemical Engineering, Moscow, Russia
Received December 5, 2001; in final form, July 2002
Abstract With the aim of developing new fluorine-conducting solid electrolytes, the compound NH4SnF3
was synthesized and its electrical conductivity and thermal behavior were studied.
Tin(II) fluoride SnF forms compounds MSnF
1%. The content of fluoride ions was not determined.
2
4
(M is Pb, Ba, or Sr) and MSn F (M is NH , Na, K,
2 5
4
Found, mol %: NH3 9.5; Sn(II) 59.5.
NH4SnF3. Calculated, mol %: NH3 9.31; Sn(II) 61.34.
Rb, Cs, or Tl), which have high unipolar electrical
conductivity with respect to fluoride ions [1, 2]. In-
creased interest in solid electrolytes derived from
The product yield with respect to tin(II) was
92.4%. According to the X-ray phase analysis (HZG-4
diffractometer, CuK radiation), the samples studied
are single-phase, and their structure (trigonal crystal
system, a = 6.841(1) and c = 15.930(4) , Fig. 1a)
corresponds that of NH SnF [4]. The values available
SnF is stimulated by prospects of their application in
2
all-solid-state power sources, sensors, and other elec-
trochemical apparatus. At the same time, successful
application of solid electrolytes in practice requires
reliable synthesis procedures to obtain materials with
well reproducible chararacteristics.
4
3
from Powder Diffraction File, Data Cards, JCPDS,
no. 33 0081, are a = 6.842 and c = 15.92
In this work, ammonium trifluorostannate(II)
NH SnF was prepared and its electrical conductivity
.
4
3
Electrophysical properties were studied by im-
pedance spectroscopy with a VM-507 impedansom-
eter (frequency range 5 Hz 500 kHz, resistance range
was studied.
EXPERIMENTAL
1
10 M ) in a vacuum ( 0.1 Pa). The electrodes
were made from DAG-580 graphite paste (the Nether-
lands). The electrical conductivity was measured on
pellets 5 mm diameter and 2 4 mm thick, obtained
Ammonium trifluorostannate(II) was synthesized
from tin(II) oxide, which, in turn, was prepared from
SnCl solution by adding a solution of NH H O to
2
3
2
pH 9.5, separating the precipitate, repeatedly washing
(b)
with distilled water, and heating the Sn(OH) suspen-
2
sion for 4 5 h. The SnO and NH HF weighed por-
4
2
tions in a molar ratio of 1 : 1.5 were dissolved in
distilled water at 60 70 C, and the solution was
evaporated on a water bath until a precipitate formed,
which was filtered off after cooling the solution and
dried at room temperature.
(a)
Chemical analysis was performed as follows. Ap-
proximately 0.2-g portion was dissolved in hydro-
chloric acid, and tin(II) was determined by direct titra-
tion with an iodine solution in the presence of starch.
The relative eror of the determination was less than
2%. The ammonia content was determined according
to [3]. The relative determination error was less than
2 , deg
Fig. 1. X-ray diffraction patterns of ammonium fluorostan-
nates(II). Sample: (a) initial (NH SnF ) and (b) subjected
to temperature measurements (NH SnF + NH Sn F ).
4
3
4
3
4
2 5
(2 ) Bragg angle.
1070-4272/03/7603-0497$25.00 2003 MAIK Nauka/Interperiodica

498
SOROKIN et al.
a = 12.4(3), b = 10.12(9), and c = 7.911(6) ] ap-
log( T) [S cm 1 K]
peared in the diffraction pattern (Fig. 1b). The values
available from Powder Diffraction File, Data Cards,
JCPDS, no. 16-0795, are a = 12.86, b = 10.05, and
c = 7.91
.
Heating to 100 C is accompanied by weight loss
(1.4 wt %). On cooling to 80 C, a clear endothermic
peak, lacking in the heating curve, was recorded. This
peak can be assigned to decomposition:
2NH4SnF3
NH4Sn2F5 + NH3 + HF .
This reaction is complete at a weight loss of
9.6 wt %, i.e., in the course of taking DTA curves
15% of the initial NH SnF decomposed.
4
3
1
103/T, K
Thus, the samples were NH SnF after the first
4
3
Fig. 2. log( T) T plot. ( ) Conductivity of ammonium
fluorostannates(II). Sample 1: (1) heating 1, (2) cooling 1,
(3) heating 2, and (4) cooling 2; sample 2: (5) heating 1 and
(6) cooling 1.
heating to 90 C and an NH SnF + NH Sn F mix-
4
3
4
2 5
ture after cooling and the second heating cooling
cycle. Apparently, a comparatively high electrical con-
ductivity observed in this case in the samples studied
(NH SnF + NH Sn F ) is completely determined
from thoroughly ground NH SnF powder under
a pressure of 4 5 MPa. The error in measuring was
less than 5%. The activation energy E of the elec-
trical conductivity was found from the formula
4
3
4
2 5
4
3
by the formation of ammonium pentafluorostan-
nate(II). The obtained data on the phase transition
agree with the results of [2, 5, 6], according to which
the phase transition in NH Sn F occurs at 75 C [2,
a
4
2 5
5] or 70 84 C [6]. A small thermal effect accompany-
ing this transition shows that the NH Sn F polymor-
T = A exp( Ea /kT),
4
2 5
phous modifications being formed have similar struc-
where A is the preexponential factor.
6
1
tures. The conductivity value
= 3 10 S cm
In measurements, the temperature was increased
and decreased in steps, during each measurement it
was kept constant.
at 20 C is close to the published value ( = 1
6
1
10 S cm at 27 C [7]), and the activation energy
E = 0.52 eV (20 75 C) reasonably agrees with the
a
The conductivity of the NH SnF samples heated
4
3
published values for NH Sn F (E = 0.5 [2, 5] and
4
2 5
a
for the first time to 90 C remained lower than the sen-
0.65 eV [7]).
sitivity of the device (the total resistance exceeded
7
The phase transition in NH Sn F is accompanied
4
2 5
10
). The low values of the NH SnF conductivity
4 3
by an approximately twofold increase in the activa-
tion energy of the ionic transfer and increase in the
electrical conductivity by an order of magnitude. The
in this temperature range are close to
of alkali
metal trifluorostannates at room temperature {
9
1
10 S cm [1]}. Above 90 C, dramatically grows
(Fig. 2). On cooling and secondary heating, the com-
pound showed a complex behavior indicative of
hysteresis and phase transition. The transition region
is recorded at 84 5 on heating and at 74 5 C on
cooling. The temperature of the onset of the transition,
as determined from both cooling and heating curves,
is 78 2 C.
3
1
ionic conductivity reaches 10 S cm at 100 C. The
high conductivity of NH Sn F above 80 C was also
4
2 5
observed in [5 7]. The obtained value of the activa-
tion energy for the high-temperature modification
(E = 0.3 eV) is close to the published value (E =
a
a
0.34 eV at T>84 C [6]).
The measurement of the transferrence numbers for
electrons (t ) in MSn F shows that the contribution
To interpret the results, we measured the diffrac-
tion patterns of the sample after measurements of at
various temperatures and performed thermogravimetric
e
2 5
of electronic transfer to the total electrical conductiv-
5
ity is insignificant: for RbSn F t
2 10 at 122
2 5 e
1
168 C [7]. The structural elements of NH Sn F are
ammonium ions [NH ] and complex anions [Sn F ] .
Therefore, it was important to reveal their role in
analysis (Pt crucible, heating/cooling rate 10 deg min ,
4
2 5
+
heating to 115 C). In addition to the NH SnF lines,
4
2 5
4
3
the lines due to NH Sn F [rhombic crystal system,
4
2 5
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 3 2003

SYNTHESIS AND ELECTRICAL PROPERTIES OF AMMONIUM FLUOROSTANNATES(II)
499
the ionic transfer. NMR studies [1, 8] showed that
ACKNOWLEDGMENTS
+
reorientation of [NH ] ions is the main relaxation
4
The authors are grateful to V.V. Kireev for par-
ticipation in the experiment.
process in NH Sn F at low temperatures, and diffu-
4
2 5
sion of fluoride ions, above 20 C. In addition, ac-
19
cording to the F NMR data, fluoride ions occupy
REFERENCES
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equivalence disappears after the phase transition. All
this shows that the transfer of fluoride ions is respons-
ible for the observed temperature dependence of the
electrical conductivity in NH Sn F .
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Nauk, 1984, no. 2, pp. 53 61.
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4
2 5
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CONCLUSIONS
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7. Murin, I.V., and Chernov, S.V., Vestn. Leningr. Gos.
Univ., 1982, no. 10, issue 2, pp. 105 107.
A study of the electrophysical properties of ammo-
nium fluorostannate(II) shows that the NH SnF con-
4
3
6
1
ductivity is low ( < 10 S cm below 90 C). Ap-
parently, comparatively low values of in NH SnF
4
3
and alkali metal trifluorostannates(II) are due to a long
distance between the [SnF ] complex anions in the
3
crystal lattice. It was confirmed that at 74 84 C
NH Sn F undergoes the phase transition into the
4
2 5
3
1
state with a high ionic conductivity (
at 114 C).
10 S cm
8. Battut, J.P., Dupuis, J., Robert, H., and Granier, W.,
Solid State Ionics, 1983, vol. 8, pp. 77 81.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 3 2003