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The use of hydrothermal procedures to synthesize NASICON and some comments on the stoichiometry of NASICON phases
895
Solid State Ionics 9 & 10 (1983) 895-902 North-Hoard ~bli~jng Company
THE USE OF HYDROTHERMAL
PROCEDURES TO SYNTHESIZE NASICON
AND SOME COMMENTS ON THE STOICHIOMETRY
OF NASICON PHASES
Abraham Clearfield, M. A, Subramanian, W. Wang, * P. Jerus
Department of Chemistry, Texas A&M University, College Station, Texas 77843, U.S.A. *Visiting Scholar, Fuzhou University, People's Republic of China NASICON was prepared by a two step process. and Na4Si04 are treated hydrothermally approximate composition an orthorhombic
at 300°C.
In the first step zirconium phosphate This produced a hydrated phase with
Na4Zr2Si2 25P1 80 15 'H2 0 which could be indexed on the basis of
cell with a = 8.743(l); b = 10.317(4), c = 7.317(l)&
this orthorhombic
phase to llOO"C, P205 splits out to yield monoclinic
Upon heating NASICON of com-
This formula reflects both a deficiency of ZrO2
;;;i;;;; Na3.3Zr1.65Si1.9P~.1011.5compensated by Na for charge balance,over that required by Nal+xZr2SixP3_xO12. It is proposed that both a NASICON series of the latter type and the defect type described in this paper exist,with the stoichiometric
one being unstable and degrading to
the defect structure upon heating. 1.
INTRODUCTION
NaZr2(P04)3 and Na4ZrSi30,D and not Na4Zr2Si3-
Interest in ceramic solid-state electrolytes for use in battery applications
has led to
a widespread search for new ionically conducting materials
[l].
@,2 as Hong proposed for NAS~CON.
Thus, an
extended study to reconcile these differences was initiated.
Until recently B-alumina and
Our work with zirconium phosphate [9] led
~~-alumina were the premier materials with the
us to new preparations of NaZr~(PO4)3
requisite high conductivity and favorable cera-
high temperature reactions [lO,ll] and by hy-
mic properties.
drothermal methods
More recent discoveries of NA-
SICON [2] and Na5M(III)Si40,2
type compounds [3]
indicate that fast ion conduction materials may be more widespread thought.
in ceramic than originally
Intensive investigation of these ma-
terials is warranted
both fromthepoint
of practical applications
of view
formed NAS~CON, could also thermally.
this synthesis and a comparison of the products
EXPERIMENTAL
2.1 Materials
that a complete solid solution of the type
A highly crystalline a-zirconium
existed over a range of x =
l+xZrZSixP3-x012 o-3. Maximum conductivity was reported for x = Subseouently,
be prepared hydro-
In this paper we present details of
with high temperature solid state preparations.
2.
In the case of NASICON, it was reported [4]
2-2.3.
It was also shown
[ll] thata precursor phase, which on heating
and the structure-con-
duction mechanism relationships.
Na
[13].
both by
other workers [5-71 re-
phosphate
(hereafter referred to as a-ZrP) was prepared by refluxing the gel in 12M H3PO4 for 36 hours [12].
It was characterized
by X-ray diffraction
ported that excess Zr02 was always present in
and TGA which showed it to be a-Zr(HP04)2'H20,
their preparations.
while electron microprobe analysis showed less
In fact, Von Alpen et al.
CS] stated that pure NASICON cannot be prepared
than 50 ppm total impurities.
by Hong's method [4].
phosphate (ZrP207) was prepared from d-ZrP by
They proposed instead
a new series of the type Na,+xZr2_x,3SixP3 '12-2/3x'
x-
The end members of this series are
0 167-2738/83/0000-0000/$03.00 0 1983 North-Holland
Zirconium pyro-
heating in a platinum crucible at 1OOO'C for several hours.
Zr02 (99.9975%) and Si02
~99.999~~) were Puratronic grade (Johnson Matthey).
Na4SiO4 and Na2Si03 were Fisher cer-
was determined as Mg2P207.
The details of the
analytical procedures were given elsewhere
tified and Na2C03 (99.999%) was from Aldrich.
[12].
The starting materials were dried at 200°C and
by electron microprobe and X-ray fluorescence
stored in a desiccator before weighing.
techniques
2.2 Hydrothermal Hydrothermal
In addition, the samples were analysed (Micron, Inc., Wilmington,
Delaware).
Synthesis
The standards for the above analyses were pre-
reactions were carried out in
pared from highly pure starting materials
by
teflon lined Parr bombs of 300ml capacity. The
solid state reactions in sealed Pt tubes (4mm
procedure is given in the form of a flowchart
dia.) to avoid evaporation of P and Na.
in Figure
and Si were also determined by an ICPA method.
1 and outlined in our earlier paper
[131. 2.3 Compositional Analysis Quantitative
Thermogravimetric
The Na
analysis was carried out with
a Columbia Scientific Industries model TGA=3A
elemental analyses were per-
formed by wet chemical and instrumental methods.
unit at heating rate of lO"/min. 2.4 X-ray Methods
In wet chemical analysis, the sample was
X-ray powder diffraction patterns were ta-
brought into solution in HF and zirconium was
ken with a PAD11 (Scintag) computer automated
determined by precipitating
diffractometer
as Zr-Cupferron
complex and igniting to Zr02.
The phosphorous
i ).
using CuK(l radiation
(I = 1.5418
The patterns were run by step scanning the
samples at O.O3"/5sec and the position of each peak was determined by PEAK SEARCH programs (locally modified)
supplied with the PADII.
Guinier patterns were obtained with a camera (Enraf-Nonius) with quartz monochromator, In all the cases, silicon 1 powder NBS-SR 640 with a = 5.43088A, was used r(CuK;b = 1.54056i).
as an internal standard.
lattice parameters
were obtained by least-squares fitting of accuTRANSFER TEFLON LINED BOMBSAND STIR 60% FILLING I 3OOOC HYDROTHERMAL. -120ATM.
20HRS.
rately determined d-spacings using program LSUCRE (141. 2.5 Ionic Conductivity Measurements Ionic conductivities
were measured by an
impedance technique on sintered discs (13 lnm dia. and 3-4 mm thick) from room temperature to 300°C using Hewlett Packard impedance meters (models 4800A and 4815A) in the frequency range
HEATED
1200°C
5Hz to 108MHz.
The discs were prepared by
pressing the powders in an evacuable die at 20 tons/sq. in. for 15-20 hr.
They were sintered at 1150-12OC"C The hydrothermally
prepared
NASICONS gave pellets of density 92 - 95:, of Figure
1
:
The discs were polished
Block diagram of the hydrothermal
theoretical values.
synthesis of NASICON.
with 400 grit emery paper and the faces were coated with conductive silver paint (E-Kote 3027, Acme Industries Co.) and dried at 200°C for 6 hours.
The sample was sandwiched between
A. Clearfield et al. / The use of hydrothermal procedures
891
two platinum plates which were spring loaded to
Na4Si04 in varying proportions at 300°C and 120
ensure good electrode/electrolyte
Atm. pressures are given in Table 1.
contact.
The
Among the
entire cell assembly was placed in a tubular
various new phases formed, the most interesting
furnace whose temperature could be controlled
compound for the present purpose is one desig-
to +2"C using a Barber-Coleman
nated as the 6.06 phase [the number designates
524D).
controller
(model
The furnace and the cell assembly were
grounded to avoid stray A. C. fields.
the first interplanar spacing (i) in the X-ray
For a
diffraction pattern].
particular solid sample, at a constant tempe-
This phase could be iso-
lated in pure form when the ratio of a-ZrP to
rature, the values of Z'(/Zlsine) and -Z"(iZl-
Na4Si04 were 1:1.4 to 1:1.7. The X-ray diffrac-
cos8) were calculated and plotted.
tion patterns looked similar (but with a slight
The elec-
trolyte resistance was obtained by extrapola-
shift in d-spacings) and were hydrates with one
ting the electrode characteristics
mole of H20.
3.
to -Z" = 0.
Wet chemical and microprobe ana-
RESULTS
lysis showed the phase to be a sodium zirconium
The results of a number of hydrothermal
silicophosphate monohydrate.
reactions obtained by heating u-ZrP with
TABLE 1:
RESULTS OF HYDROTHERMAL
Expt. No.
Reactant Ratio a-ZrP:Na4Si04
NPJ 17A
1.O:l.O
The chemical for-
mula as derived from the analytical data for
SYNTHESIS - Zr(HP04)2 H20 (c+ZrP) + Na4Si04 AT 3OO'C
Time
20
Hydrothermally Phases
Formed
High Temperature (1200°C) Phases Formed
6.06(10) + 6.3(5) + 6.5(5) + F(80)
NPJ 17B
1.O:l.O
98
6.06(40) + 6.5(5) + F(5)
*R-N(75)
+
I(25)
**
+ 9.2(50) MSW 15
l.O:l.O(2NaCl)
20
6.06(80) + F(20)
R-N(90)
+
U(10)
MSW 24
l.O:l.l(:2NaOH)
20
6.06(40) + 6.47(20)
M-N(88)
+
Zr02(12)
R-N(83)
+
I(17)
+
I(4)
+
Zr02(20)
+ 7.90(20) f 11.1(20) MSW 16
1.0:1.2
20
6.06(70) + 11.5A(20) + F(10)
MSW
9
1.0:1.3
20
6.06(95) + 12.9(5)
M-N(96)
MSW 10
1.0:1.4
20
6.06(100)
M-N(lOO)
MSW
7
1.0:1.5
20
6.06(100)
M-N(lOO)
MSW 11
1.0:1.6
20
6.06(100)
M-N(lOO)
MSW 12
1.0:1.7
20
6.06(100)
M-N(lOO)
MSW 13
1.0:1.8
20
6.06(60) + 6.5(40)
M-N(80)
MSW 14
1.0:2.0
20
6.06(50) + 6.5(50)
MSW 20
1.0:3.0
20
6.5(100)
*R-N = Rhombohedral NASICON, M-N = Monoclinic NASICON; for other phases see Text ** Numbers in parenthesis are approximate
percentages
A. Clewfield et al. / The use of‘ hydrothermal procedures
898
the 6.06 pears
phase
obtained
from a 1:1.5
sample
to be Na4Zr2Si2.25P1.8015*H20.
analytical
data
are
ap-
The
6.06
(wt%)
Found:
Na, 13.93;
Zr, 27.6;
Si, 9.85;
P, 8.56
Calc:
Na, 14.1;
Zr, 28.0;
Si, 9.7;
P, 8.5
X-ray
diffraction
samples
showed
on heating, phase
dexed
broadened
these
change
patterns
patterns
and gave
(Figure
crease sized
The
in Table
phases
around
sion was much more fraction phases solid
patterns
were
Thermogravimetric phase
from
the unit cell unit cell increase
data
the Na4Si04
TABLE
2:
parameters
heated
loss
. 9'1 . 1'11 . 5
Found:
Na, 14.8;
Zr, 29.8;
Si, 10.8;
P, 7.1
Calc.:
Na, 15.1;
Zr, 30.1;
Si,
P, 6.9
The TGA pattern There
is a weight is attributed
from
the 6.06 phase
there
is observed continuous
6.06
phase.
in
temperatures
weight
amounting
loss
in a
to about
experiment,
from a sample
It was only
by the bands
4;:.
to the loss of P205 from
decomposition
contained
absorption
a further
In a separate
component
perature
is confirmed
At higher
manner
is attributed
latile
which
spectrum.
This
3.
to the split out of water
of the water
infrared
10.7;
in Figure
loss of ?,2.85 up to 150°C.
This
disappearance
is shown
of the high
of the 6.06
soluble
phosphorus
phase
in water,
tem-
was
acidic
as analysed
the
the vo-
and
by plasma
arc technique.
(A)
HYDROTHERMAL
(6)
NASICON
(6.06)
PHASE
with
3.
The
but small, due
of the sample
in the reactant
as
PHASE
I
ratio.
fluorescence
CELL PARAMETERS OF HYDROTHERMALLY PREPARED PHASES (6.06)
aZrP: Na4Si04
a(A)
I
I
35
30
0
b(%
c(A)
25
I
I
20
15
28
MSWW7
1:1.5
8.743
10.317
7.317
MSWW12
1:1.7
a.777
10.611
7.354
Variation
Na3.3Zrl.65Sil data are (wtX)
(1:1.4
possibly
0
Sample
The analytical
to,
from
in Table
parameters
X-ray
is close
the NASICONS
a systematic,
and
which
the
28).
a weight
were monoclinic
in Si content
microprobe
from
from
gave a formula
collected.
(Figure
All
given
indicate
increased
UNIT
dif-
but were
preparations
Na4Si04)
in the lattice
to an increase
Electron
of 6.7% when
hydrothermal
:
[4,6]
showed
to 1100°C.
n-ZrP
X-ray
obtained
impurities
analysis
temperature
to 1:1.7;
at 1200°C.
obtained
(tr-ZrP:NaSiO4 = 1:1.5)
slow,
but the conver-
by others
free of Zr02 and other
obtained
was
the 6.06
a slow conver-
to NASICONS
reactions
for the 6.06
in-
sample
phase
the
of the high temperature
similar
state
the in-
to a-ZrP
compounds,
rapid
cell and
phases
Heating
indicated
type
in-
it is hypothe-
of Na4Si04
1OOO'C
sion to NASICON
diffraction
From
in these
1.4 to 1.7.
but
of the NASICON
precursor
without
data were
2.
parameters,
as the ratio from
X-ray
X-ray
that the Si content
increased
peaks,
dehydrated
of an orthorhombic
are given
in lattice
creased
room
diffraction
sharper
2).
on the basis
the results
of the air dried
compounds
analyses
due to Si content
& heating
treatment
Figure
2
:
Comparison
of X-ray
powder
terns
of the hydrothermally
pared
6.06 phase
heated
- (A) and to 1200°C
patpre-
to 600°C
- (B)
899
A. Clearfield et pl. 1 The use of hydrothermal procedures
In another experiment,
the 6.06 phase was
a small amount of impurities so the conductivity
treated with 6M HCl at 300°C in a sealed teflon lined Parr bomb.
data was not obtained.
The product was a rhombdhedral
proton form of NASICON.
Some interesting facts emerge from consider-
The filtrate contained
Nat and PO:- (phosphomolybdate
test).
ation
of the mixed products which arise from
the hydrothermal study.
Thus, it
The starting material,
appears that the 6.06 phase has a framework
aZrP, is an ion exchanger with a layered struc-
structure which is robust and stable to water
ture [16] which forms a half-exchanged
loss but converts to NASICON phases when enough
ion phase and a fully exchanged one, Zr(NaP04)2-
P205 is removed, either by acid extraction, or
3H20, referred to as phase II [lo].
by evolution at high temperatures.
On heating
phase D to lOO'C, it forms a monohydrate
In order to confirm the stoichiometry of the hydrothermally
sodium
E) and at 200°C an anhydrous phase F.
prepared NASICON a solid
(phase
The ma-
jor product obtained in the hydrothermal exper-
state reaction, using a mixture of Na3P04, Zr02,
iment NPJ#17A (Table 1) was this phase F.
SiO2 and ZrP207 in the correct ratio was carried
er heating times (NPJ#17B) produces more of the
out at 1200°C for 20 hr in sealed platinum
6.06 phase together with a new compound labelled
tubes.
This reaction yielded a pure phase
9.2.
Long-
Heating this mixture to 1100°C produces
whose X-ray pattern matched that shown in
rhombohedral NASICON and phase I.
Figure 28.
phase was reported earlier [ll] as resulting
Ionic conductivity data on all the hydro-
from the decomposition
This latter
of Zr(NaP04)2 at 1100°C.
thermally prepared NASICONS, in the form of sin-
In a subsequent paper it will be shown that
tered disks, are given in Table 3 and Figure 3.
phase I belongs to a solid solution series of
The data show that all the NASICONS behave like
the type Nal+4xZr2_x (P04)3 where x = 0.85-1.0
superionic conductors with the highest conduc-1 -1 tivity of 0.17 ohm cm at 300°C for the sample
[13,15].
the NASICON phase and observation of a rhombo-
prepared from the reactant ratio of 1:1.7.
hedral NASICON indicates that insufficient Si
The
Thus, most of the silicon resides in
conductivity at room temperature and 300°C
is incoporated into the hydrothermal phases
showed a slight increase as the Na4Si04 content
when the ratio of reactants is 1:l.
increased in the hydrothermal reaction.
of this hydrothermal experiment
The
sample obtained from the ratio 1:1.3 contained
TABLE 3:
aZrP: Na4Si04
a(i)
MSWW9A
1:1.3
MSWWlOB
in the presence
of excess NaCl (MSW#15) increased the yield of
UNIT CELL PARAMETERS AND ELECTRICAL DATA OF HYDROTHERMALLY
SAMPLE
Repetition
'RT
PREPARED NASICONS
a300"c -1
Ea(<200) ev
Ea(>200) ev
b(i)
c(i)
B(O)
15.591
8.992
9.215
123.75
1:1.4
15.603
9.013
9.214
123.62
6.6x10-4
0.11
0.38
0.21
MSWW7A
1:1.5
15.609
9.023
9.214
123.60
2.5~10-~
0.15
0.39
0.20
MSWWllA
1:1.6
15.623
9.020
9.215
123.2d
3.1x10-4
0.17
0.41
0.20
MSWW12A
1:1.7
15.627
9.018
91223
123.23
3.3x1o-4
0.17
0.40
0.21
a, b, c values are ?O.OOli; B values are ?O.Ol"
ohm-'cm-'
ohm-'cm
900
A. Clewfield
e[ al. / The use of’hydrothermal
TEMP
Figure
3
Weight
:
loss as a function
Heating
6.06 phase
which
hedral
NASICON
latter
phase
on heating
together
ceeded
state
of Na4Si04
1.7 a new phase, This
(MSW#20) similar
phase
and gave
4.
and
study
has shown
NASICON-like
route.
This
result
in which
hydrothermally materials
requires licate
its
pattern
CON,
of NASICON
In this formulation NASICON
solid
it is possible
were
prepared
relative et al.
both end members
solution,
to
out of our earlier
by Hong,
NaZr2(P04)3
twelve
solutions
the anions
are present.
and
that Zr02
anionic
0.50 moles
groups
of oxygen
also
Thus,
contain
are either
ortho-
Loss of oxygen
condensed
by assuming
oxygens.
phosphate
This
then
or si-
loss can be
-that the ortho-system orecipitates behind. and
leaving
In our NASI-
therefore
0.25
of Zr are thus eliminated ilydrothermally. c+ is missing and In addition, 0.1 mole of 7r
via a hydrothermal
some comment
phase.
moles
The stoichiometry
[ll].
groups
condensed
[13] and
and
that either
is unstable
some-
solid
or orthosilicate.
rationalized
in a pure
We original-
Nai'r2(P04)3 phases
requires
formulation
arose
oxygens
ex-
NASICON
that
phases
twelve
to w-ZrP
6.5, made
contain
the intermediate
phosphate
DISCUSSION This
(TGA) for the 6.06
and Na4Zr2Si30,2,
This
it at a later date.
prepare
work
U.
[15].
an X-ray
it as a hydrated
rhombo-
Na5Zr(P04)3
to that of NASICON.
upon
of temperature
I series
labelled
ly labelled report
gave
was obtained
will
("Cl
5"/minute.
some phase
of the phase
the ratio
appearance.
what
again
has the composition
is the end member When
with
rate
procedures
of our to the [2,4].
of the and
the charge Thus
deficiency
the formula
can
is corpcnsated be represented
by Na+. as
Nal+z+4vZr2_x_vSizP3_z012_0.,. Tr ?'?e formula iA for our hydrothermal p;‘er;arat'on, x =
given
0.25, y = 0.1, and z = 1.9. Von Alpen stoichiometric cate groups their
series
et al. phases
[8,17].
have also based The
is Na4ZrSi30
obtained
on condensed
silicate
nonsili-
end member
of
,. and they succeeded
A. Clearfield et al. / The use
in preparing this compound and showing that it is a fair conductor
[18].
However, their com-
positions do not fit the proposed solid solu-
of hydrothermal procedures
901
or employment of special gel methods of synthesis [4,19,20].
A similar ciaim is made for
Na3Hf2Si2P012 and As and Ge substituted composiIn fact, Weunsch et al. [20] have
tion formula of Nal+xZr2_,,3xSixP3_x0,2_2,3x,
tions [Zl].
nor do they fit our general formula.
carried out a neutron diffraction
Since no
study on
details of their analytical methods were given,
Nal+xZr2SixP3_x072
it is not possible to assess the limits of er-
They confirmed the structure proposed by Hong
ror in these formulas.
and were able to explain the volume changes
They did not observe a
change in slope in the curve of conductivity,as
with x = 7, 1.6, 2.0 and 2.5.
with increasing values of x.
Thus, we believe
a function of temperature, for Na3 lZr, 55 -
that Hong's series does exist, but the phases
Si2.3Po 7011 as is observed for our prepara-
are quite unstable when x = 1.5-2.5.
tions. 'Thus the von Alpen phases may in fact
Gordon et al. [7] found that Zr02 precipitates
be quite different in structure from NASICON.
from such compositions
*
.
In fact,
if they are heated above
On the other hand, our unit cell dimensions
1200°C.
and conductivity
to obtain singie phase NASICON until they re-
data are very close to those
reported earlier for Nal+xZr2SixP3_xO12
[4,61.
The question arises as to what the correct formulation for NASICON really is.
Several
moved 0.5 moles of Zr02.
Thus, their composi-
tion is close to Na3Zr, SSi2PO,, and must then contain condensed silicate groups. In an earlier study [13] we showed that
groups have reported a single phase NASICON, achieved either by thorough mixing of reagents
Boilot et al. [6] likewise were unable
stoichiometric
NaZr2(PO4)3 does not exist, or
is very difficult to prepare.
Rather, a solid
solution of the type Nal+4xZr2_x (PO4)3 with x = 0.02-0.06 was synthesized.
Although it is
difficult to see why the defect structure would be preferred (except perhaps to fill some of the empty type II cavities for added stability) the 4xNa+ could account for the conductivity of the triphosphate.
We are checking this point.
However, we make the point that our hydrother4+ ma1 preparation shows both the ZrO2 and Zr deficiency for maximum stability and the more stoichiometric
phases may degrade to the defect
type on heating by precjpitation of fro;. 5.
ACKNOWLEDGMENT This work was supported by NSF grant number
DMR 80-25184 for which grateful acknowledgment is made, 6. 2
I
3
4
1000/T,(K)
Figure
4
:
Conductivity as a function of l/T for the hydrothermal samples. ZrP:Na4SiO4
=
1.5,
ZrP:NaSiO4
=
1.7,
0
0.
,
REFERENCES
[ 11 P. Hagenmuller and W. von Gool, eds., Solid Electrolytes (Academic Press, New York, 1978). ['2] J. B. Goodenough, H.Y.-P. Hong and J.. A. Kafalas, Mat. Res. Bull. 11 (1976) 203. [ 33 R. D. Shannon, H. Y. Chen and T. Berzins, Mat. Res. Bull. 12 (1977) 969. [ 41 yi3Y.-P. Hong, Mat. Res. Bull. 11 (1976) [ S] M. i. Bayard and G. G. Barna, 3. Electroanal. Chem. 91 (1978) 201.
902
A. Clearfield et al. / The use of hydrothermal procedures
[ 61 J. P. Boilot, J. P. Salanie, G. Desplanches and D. LePotier, Mat. Res. Bull. 14 (1979) 1469. [ 71 R. S. Gordon, G. R. Miller, B. J. McEntire, E. 0. Beck and J. R. Rasmussen, Solid State Ionics 3/4 (1981) 243. [ 81 U. Von Alpen, M. .F. Bell and H. H. Hofer, Solid State Ionics 3/4 (1981) 215. [ 91 A. Clearfield, in: Inorganic Ion Exchange Materials, ed.A. Clearfield (CRC Press, Boca Raton, Florida, 1982) ch. 1. [lo] A. Clearfield, W, L. Duax, A. S. Medina, G. D. Smith and J. R. Thomas, J. Phys. Chem. 73 (1969) 3424. [ll] A. Clearfield, P. Jirustithipong, R. N. Cotman and S. P. Pack, Mat. Res. Bull. 15 (1980) 1603. [12] A. Clearfield and J. A. Stynes, J. Inorg. Nucl. Chem. 26 (1964) 117. [13] A. Clearfield, P. Jerus and R. N. Cotman, Solid State Ionics 5 (1981) 301.
[14] LSUCRE, Least Squares Unit Cell Refinement, Univ. Freiburg i. Br., West Germany (1972). [15] A. Clearfield, R. Guerra, A. Oskarsson, M. A. Subramanian and W. Wang, Mat. Res. Bull., submitted for publication. [16] A. Clearfield and G. D. Smith, Inorg. Chem. 8 (1969) 431. [17] U. Von Alpen and M. F. Bell, Extended Abstracts, Spring Meeting, The Electrochem. sot., Montreal, No. 732 (1982) 1170. [18] U. Von Alpen, M. F. Bell and H. H. Hofer, Solid State Ionics 7 (1982) 345. [19] D. H. H. &on, T. A. Wheat and W. Nesbitt, Mat. Res. Bull. 15 (1980) 1533. [20] B. J. Wuensch, L. J. Shioler and E. Prince, Abst. Amer. Cryst. Assoc. Winter Meeting, Univ. of Missouri, Columbia, MO., March 1983. [21] R. J. Cava, E. M. Vogel and D. Johnson, Jr., Amer. Ceram. Sot. Comm. C-157 (1982).
Solid State Ionics 9 & 10 (1983) 895-902 North-Hoard ~bli~jng Company
THE USE OF HYDROTHERMAL
PROCEDURES TO SYNTHESIZE NASICON
AND SOME COMMENTS ON THE STOICHIOMETRY
OF NASICON PHASES
Abraham Clearfield, M. A, Subramanian, W. Wang, * P. Jerus
Department of Chemistry, Texas A&M University, College Station, Texas 77843, U.S.A. *Visiting Scholar, Fuzhou University, People's Republic of China NASICON was prepared by a two step process. and Na4Si04 are treated hydrothermally approximate composition an orthorhombic
at 300°C.
In the first step zirconium phosphate This produced a hydrated phase with
Na4Zr2Si2 25P1 80 15 'H2 0 which could be indexed on the basis of
cell with a = 8.743(l); b = 10.317(4), c = 7.317(l)&
this orthorhombic
phase to llOO"C, P205 splits out to yield monoclinic
Upon heating NASICON of com-
This formula reflects both a deficiency of ZrO2
;;;i;;;; Na3.3Zr1.65Si1.9P~.1011.5compensated by Na for charge balance,over that required by Nal+xZr2SixP3_xO12. It is proposed that both a NASICON series of the latter type and the defect type described in this paper exist,with the stoichiometric
one being unstable and degrading to
the defect structure upon heating. 1.
INTRODUCTION
NaZr2(P04)3 and Na4ZrSi30,D and not Na4Zr2Si3-
Interest in ceramic solid-state electrolytes for use in battery applications
has led to
a widespread search for new ionically conducting materials
[l].
@,2 as Hong proposed for NAS~CON.
Thus, an
extended study to reconcile these differences was initiated.
Until recently B-alumina and
Our work with zirconium phosphate [9] led
~~-alumina were the premier materials with the
us to new preparations of NaZr~(PO4)3
requisite high conductivity and favorable cera-
high temperature reactions [lO,ll] and by hy-
mic properties.
drothermal methods
More recent discoveries of NA-
SICON [2] and Na5M(III)Si40,2
type compounds [3]
indicate that fast ion conduction materials may be more widespread thought.
in ceramic than originally
Intensive investigation of these ma-
terials is warranted
both fromthepoint
of practical applications
of view
formed NAS~CON, could also thermally.
this synthesis and a comparison of the products
EXPERIMENTAL
2.1 Materials
that a complete solid solution of the type
A highly crystalline a-zirconium
existed over a range of x =
l+xZrZSixP3-x012 o-3. Maximum conductivity was reported for x = Subseouently,
be prepared hydro-
In this paper we present details of
with high temperature solid state preparations.
2.
In the case of NASICON, it was reported [4]
2-2.3.
It was also shown
[ll] thata precursor phase, which on heating
and the structure-con-
duction mechanism relationships.
Na
[13].
both by
other workers [5-71 re-
phosphate
(hereafter referred to as a-ZrP) was prepared by refluxing the gel in 12M H3PO4 for 36 hours [12].
It was characterized
by X-ray diffraction
ported that excess Zr02 was always present in
and TGA which showed it to be a-Zr(HP04)2'H20,
their preparations.
while electron microprobe analysis showed less
In fact, Von Alpen et al.
CS] stated that pure NASICON cannot be prepared
than 50 ppm total impurities.
by Hong's method [4].
phosphate (ZrP207) was prepared from d-ZrP by
They proposed instead
a new series of the type Na,+xZr2_x,3SixP3 '12-2/3x'
x-
The end members of this series are
0 167-2738/83/0000-0000/$03.00 0 1983 North-Holland
Zirconium pyro-
heating in a platinum crucible at 1OOO'C for several hours.
Zr02 (99.9975%) and Si02
~99.999~~) were Puratronic grade (Johnson Matthey).
Na4SiO4 and Na2Si03 were Fisher cer-
was determined as Mg2P207.
The details of the
analytical procedures were given elsewhere
tified and Na2C03 (99.999%) was from Aldrich.
[12].
The starting materials were dried at 200°C and
by electron microprobe and X-ray fluorescence
stored in a desiccator before weighing.
techniques
2.2 Hydrothermal Hydrothermal
In addition, the samples were analysed (Micron, Inc., Wilmington,
Delaware).
Synthesis
The standards for the above analyses were pre-
reactions were carried out in
pared from highly pure starting materials
by
teflon lined Parr bombs of 300ml capacity. The
solid state reactions in sealed Pt tubes (4mm
procedure is given in the form of a flowchart
dia.) to avoid evaporation of P and Na.
in Figure
and Si were also determined by an ICPA method.
1 and outlined in our earlier paper
[131. 2.3 Compositional Analysis Quantitative
Thermogravimetric
The Na
analysis was carried out with
a Columbia Scientific Industries model TGA=3A
elemental analyses were per-
formed by wet chemical and instrumental methods.
unit at heating rate of lO"/min. 2.4 X-ray Methods
In wet chemical analysis, the sample was
X-ray powder diffraction patterns were ta-
brought into solution in HF and zirconium was
ken with a PAD11 (Scintag) computer automated
determined by precipitating
diffractometer
as Zr-Cupferron
complex and igniting to Zr02.
The phosphorous
i ).
using CuK(l radiation
(I = 1.5418
The patterns were run by step scanning the
samples at O.O3"/5sec and the position of each peak was determined by PEAK SEARCH programs (locally modified)
supplied with the PADII.
Guinier patterns were obtained with a camera (Enraf-Nonius) with quartz monochromator, In all the cases, silicon 1 powder NBS-SR 640 with a = 5.43088A, was used r(CuK;b = 1.54056i).
as an internal standard.
lattice parameters
were obtained by least-squares fitting of accuTRANSFER TEFLON LINED BOMBSAND STIR 60% FILLING I 3OOOC HYDROTHERMAL. -120ATM.
20HRS.
rately determined d-spacings using program LSUCRE (141. 2.5 Ionic Conductivity Measurements Ionic conductivities
were measured by an
impedance technique on sintered discs (13 lnm dia. and 3-4 mm thick) from room temperature to 300°C using Hewlett Packard impedance meters (models 4800A and 4815A) in the frequency range
HEATED
1200°C
5Hz to 108MHz.
The discs were prepared by
pressing the powders in an evacuable die at 20 tons/sq. in. for 15-20 hr.
They were sintered at 1150-12OC"C The hydrothermally
prepared
NASICONS gave pellets of density 92 - 95:, of Figure
1
:
The discs were polished
Block diagram of the hydrothermal
theoretical values.
synthesis of NASICON.
with 400 grit emery paper and the faces were coated with conductive silver paint (E-Kote 3027, Acme Industries Co.) and dried at 200°C for 6 hours.
The sample was sandwiched between
A. Clearfield et al. / The use of hydrothermal procedures
891
two platinum plates which were spring loaded to
Na4Si04 in varying proportions at 300°C and 120
ensure good electrode/electrolyte
Atm. pressures are given in Table 1.
contact.
The
Among the
entire cell assembly was placed in a tubular
various new phases formed, the most interesting
furnace whose temperature could be controlled
compound for the present purpose is one desig-
to +2"C using a Barber-Coleman
nated as the 6.06 phase [the number designates
524D).
controller
(model
The furnace and the cell assembly were
grounded to avoid stray A. C. fields.
the first interplanar spacing (i) in the X-ray
For a
diffraction pattern].
particular solid sample, at a constant tempe-
This phase could be iso-
lated in pure form when the ratio of a-ZrP to
rature, the values of Z'(/Zlsine) and -Z"(iZl-
Na4Si04 were 1:1.4 to 1:1.7. The X-ray diffrac-
cos8) were calculated and plotted.
tion patterns looked similar (but with a slight
The elec-
trolyte resistance was obtained by extrapola-
shift in d-spacings) and were hydrates with one
ting the electrode characteristics
mole of H20.
3.
to -Z" = 0.
Wet chemical and microprobe ana-
RESULTS
lysis showed the phase to be a sodium zirconium
The results of a number of hydrothermal
silicophosphate monohydrate.
reactions obtained by heating u-ZrP with
TABLE 1:
RESULTS OF HYDROTHERMAL
Expt. No.
Reactant Ratio a-ZrP:Na4Si04
NPJ 17A
1.O:l.O
The chemical for-
mula as derived from the analytical data for
SYNTHESIS - Zr(HP04)2 H20 (c+ZrP) + Na4Si04 AT 3OO'C
Time
20
Hydrothermally Phases
Formed
High Temperature (1200°C) Phases Formed
6.06(10) + 6.3(5) + 6.5(5) + F(80)
NPJ 17B
1.O:l.O
98
6.06(40) + 6.5(5) + F(5)
*R-N(75)
+
I(25)
**
+ 9.2(50) MSW 15
l.O:l.O(2NaCl)
20
6.06(80) + F(20)
R-N(90)
+
U(10)
MSW 24
l.O:l.l(:2NaOH)
20
6.06(40) + 6.47(20)
M-N(88)
+
Zr02(12)
R-N(83)
+
I(17)
+
I(4)
+
Zr02(20)
+ 7.90(20) f 11.1(20) MSW 16
1.0:1.2
20
6.06(70) + 11.5A(20) + F(10)
MSW
9
1.0:1.3
20
6.06(95) + 12.9(5)
M-N(96)
MSW 10
1.0:1.4
20
6.06(100)
M-N(lOO)
MSW
7
1.0:1.5
20
6.06(100)
M-N(lOO)
MSW 11
1.0:1.6
20
6.06(100)
M-N(lOO)
MSW 12
1.0:1.7
20
6.06(100)
M-N(lOO)
MSW 13
1.0:1.8
20
6.06(60) + 6.5(40)
M-N(80)
MSW 14
1.0:2.0
20
6.06(50) + 6.5(50)
MSW 20
1.0:3.0
20
6.5(100)
*R-N = Rhombohedral NASICON, M-N = Monoclinic NASICON; for other phases see Text ** Numbers in parenthesis are approximate
percentages
A. Clewfield et al. / The use of‘ hydrothermal procedures
898
the 6.06 pears
phase
obtained
from a 1:1.5
sample
to be Na4Zr2Si2.25P1.8015*H20.
analytical
data
are
ap-
The
6.06
(wt%)
Found:
Na, 13.93;
Zr, 27.6;
Si, 9.85;
P, 8.56
Calc:
Na, 14.1;
Zr, 28.0;
Si, 9.7;
P, 8.5
X-ray
diffraction
samples
showed
on heating, phase
dexed
broadened
these
change
patterns
patterns
and gave
(Figure
crease sized
The
in Table
phases
around
sion was much more fraction phases solid
patterns
were
Thermogravimetric phase
from
the unit cell unit cell increase
data
the Na4Si04
TABLE
2:
parameters
heated
loss
. 9'1 . 1'11 . 5
Found:
Na, 14.8;
Zr, 29.8;
Si, 10.8;
P, 7.1
Calc.:
Na, 15.1;
Zr, 30.1;
Si,
P, 6.9
The TGA pattern There
is a weight is attributed
from
the 6.06 phase
there
is observed continuous
6.06
phase.
in
temperatures
weight
amounting
loss
in a
to about
experiment,
from a sample
It was only
by the bands
4;:.
to the loss of P205 from
decomposition
contained
absorption
a further
In a separate
component
perature
is confirmed
At higher
manner
is attributed
latile
which
spectrum.
This
3.
to the split out of water
of the water
infrared
10.7;
in Figure
loss of ?,2.85 up to 150°C.
This
disappearance
is shown
of the high
of the 6.06
soluble
phosphorus
phase
in water,
tem-
was
acidic
as analysed
the
the vo-
and
by plasma
arc technique.
(A)
HYDROTHERMAL
(6)
NASICON
(6.06)
PHASE
with
3.
The
but small, due
of the sample
in the reactant
as
PHASE
I
ratio.
fluorescence
CELL PARAMETERS OF HYDROTHERMALLY PREPARED PHASES (6.06)
aZrP: Na4Si04
a(A)
I
I
35
30
0
b(%
c(A)
25
I
I
20
15
28
MSWW7
1:1.5
8.743
10.317
7.317
MSWW12
1:1.7
a.777
10.611
7.354
Variation
Na3.3Zrl.65Sil data are (wtX)
(1:1.4
possibly
0
Sample
The analytical
to,
from
in Table
parameters
X-ray
is close
the NASICONS
a systematic,
and
which
the
28).
a weight
were monoclinic
in Si content
microprobe
from
from
gave a formula
collected.
(Figure
All
given
indicate
increased
UNIT
dif-
but were
preparations
Na4Si04)
in the lattice
to an increase
Electron
of 6.7% when
hydrothermal
:
[4,6]
showed
to 1100°C.
n-ZrP
X-ray
obtained
impurities
analysis
temperature
to 1:1.7;
at 1200°C.
obtained
(tr-ZrP:NaSiO4 = 1:1.5)
slow,
but the conver-
by others
free of Zr02 and other
obtained
was
the 6.06
a slow conver-
to NASICONS
reactions
for the 6.06
in-
sample
phase
the
of the high temperature
similar
state
the in-
to a-ZrP
compounds,
rapid
cell and
phases
Heating
indicated
type
in-
it is hypothe-
of Na4Si04
1OOO'C
sion to NASICON
diffraction
From
in these
1.4 to 1.7.
but
of the NASICON
precursor
without
data were
2.
parameters,
as the ratio from
X-ray
X-ray
that the Si content
increased
peaks,
dehydrated
of an orthorhombic
are given
in lattice
creased
room
diffraction
sharper
2).
on the basis
the results
of the air dried
compounds
analyses
due to Si content
& heating
treatment
Figure
2
:
Comparison
of X-ray
powder
terns
of the hydrothermally
pared
6.06 phase
heated
- (A) and to 1200°C
patpre-
to 600°C
- (B)
899
A. Clearfield et pl. 1 The use of hydrothermal procedures
In another experiment,
the 6.06 phase was
a small amount of impurities so the conductivity
treated with 6M HCl at 300°C in a sealed teflon lined Parr bomb.
data was not obtained.
The product was a rhombdhedral
proton form of NASICON.
Some interesting facts emerge from consider-
The filtrate contained
Nat and PO:- (phosphomolybdate
test).
ation
of the mixed products which arise from
the hydrothermal study.
Thus, it
The starting material,
appears that the 6.06 phase has a framework
aZrP, is an ion exchanger with a layered struc-
structure which is robust and stable to water
ture [16] which forms a half-exchanged
loss but converts to NASICON phases when enough
ion phase and a fully exchanged one, Zr(NaP04)2-
P205 is removed, either by acid extraction, or
3H20, referred to as phase II [lo].
by evolution at high temperatures.
On heating
phase D to lOO'C, it forms a monohydrate
In order to confirm the stoichiometry of the hydrothermally
sodium
E) and at 200°C an anhydrous phase F.
prepared NASICON a solid
(phase
The ma-
jor product obtained in the hydrothermal exper-
state reaction, using a mixture of Na3P04, Zr02,
iment NPJ#17A (Table 1) was this phase F.
SiO2 and ZrP207 in the correct ratio was carried
er heating times (NPJ#17B) produces more of the
out at 1200°C for 20 hr in sealed platinum
6.06 phase together with a new compound labelled
tubes.
This reaction yielded a pure phase
9.2.
Long-
Heating this mixture to 1100°C produces
whose X-ray pattern matched that shown in
rhombohedral NASICON and phase I.
Figure 28.
phase was reported earlier [ll] as resulting
Ionic conductivity data on all the hydro-
from the decomposition
This latter
of Zr(NaP04)2 at 1100°C.
thermally prepared NASICONS, in the form of sin-
In a subsequent paper it will be shown that
tered disks, are given in Table 3 and Figure 3.
phase I belongs to a solid solution series of
The data show that all the NASICONS behave like
the type Nal+4xZr2_x (P04)3 where x = 0.85-1.0
superionic conductors with the highest conduc-1 -1 tivity of 0.17 ohm cm at 300°C for the sample
[13,15].
the NASICON phase and observation of a rhombo-
prepared from the reactant ratio of 1:1.7.
hedral NASICON indicates that insufficient Si
The
Thus, most of the silicon resides in
conductivity at room temperature and 300°C
is incoporated into the hydrothermal phases
showed a slight increase as the Na4Si04 content
when the ratio of reactants is 1:l.
increased in the hydrothermal reaction.
of this hydrothermal experiment
The
sample obtained from the ratio 1:1.3 contained
TABLE 3:
aZrP: Na4Si04
a(i)
MSWW9A
1:1.3
MSWWlOB
in the presence
of excess NaCl (MSW#15) increased the yield of
UNIT CELL PARAMETERS AND ELECTRICAL DATA OF HYDROTHERMALLY
SAMPLE
Repetition
'RT
PREPARED NASICONS
a300"c -1
Ea(<200) ev
Ea(>200) ev
b(i)
c(i)
B(O)
15.591
8.992
9.215
123.75
1:1.4
15.603
9.013
9.214
123.62
6.6x10-4
0.11
0.38
0.21
MSWW7A
1:1.5
15.609
9.023
9.214
123.60
2.5~10-~
0.15
0.39
0.20
MSWWllA
1:1.6
15.623
9.020
9.215
123.2d
3.1x10-4
0.17
0.41
0.20
MSWW12A
1:1.7
15.627
9.018
91223
123.23
3.3x1o-4
0.17
0.40
0.21
a, b, c values are ?O.OOli; B values are ?O.Ol"
ohm-'cm-'
ohm-'cm
900
A. Clewfield
e[ al. / The use of’hydrothermal
TEMP
Figure
3
Weight
:
loss as a function
Heating
6.06 phase
which
hedral
NASICON
latter
phase
on heating
together
ceeded
state
of Na4Si04
1.7 a new phase, This
(MSW#20) similar
phase
and gave
4.
and
study
has shown
NASICON-like
route.
This
result
in which
hydrothermally materials
requires licate
its
pattern
CON,
of NASICON
In this formulation NASICON
solid
it is possible
were
prepared
relative et al.
both end members
solution,
to
out of our earlier
by Hong,
NaZr2(P04)3
twelve
solutions
the anions
are present.
and
that Zr02
anionic
0.50 moles
groups
of oxygen
also
Thus,
contain
are either
ortho-
Loss of oxygen
condensed
by assuming
oxygens.
phosphate
This
then
or si-
loss can be
-that the ortho-system orecipitates behind. and
leaving
In our NASI-
therefore
0.25
of Zr are thus eliminated ilydrothermally. c+ is missing and In addition, 0.1 mole of 7r
via a hydrothermal
some comment
phase.
moles
The stoichiometry
[ll].
groups
condensed
[13] and
and
that either
is unstable
some-
solid
or orthosilicate.
rationalized
in a pure
We original-
Nai'r2(P04)3 phases
requires
formulation
arose
oxygens
ex-
NASICON
that
phases
twelve
to w-ZrP
6.5, made
contain
the intermediate
phosphate
DISCUSSION This
(TGA) for the 6.06
and Na4Zr2Si30,2,
This
it at a later date.
prepare
work
U.
[15].
an X-ray
it as a hydrated
rhombo-
Na5Zr(P04)3
to that of NASICON.
upon
of temperature
I series
labelled
ly labelled report
gave
was obtained
will
("Cl
5"/minute.
some phase
of the phase
the ratio
appearance.
what
again
has the composition
is the end member When
with
rate
procedures
of our to the [2,4].
of the and
the charge Thus
deficiency
the formula
can
is corpcnsated be represented
by Na+. as
Nal+z+4vZr2_x_vSizP3_z012_0.,. Tr ?'?e formula iA for our hydrothermal p;‘er;arat'on, x =
given
0.25, y = 0.1, and z = 1.9. Von Alpen stoichiometric cate groups their
series
et al. phases
[8,17].
have also based The
is Na4ZrSi30
obtained
on condensed
silicate
nonsili-
end member
of
,. and they succeeded
A. Clearfield et al. / The use
in preparing this compound and showing that it is a fair conductor
[18].
However, their com-
positions do not fit the proposed solid solu-
of hydrothermal procedures
901
or employment of special gel methods of synthesis [4,19,20].
A similar ciaim is made for
Na3Hf2Si2P012 and As and Ge substituted composiIn fact, Weunsch et al. [20] have
tion formula of Nal+xZr2_,,3xSixP3_x0,2_2,3x,
tions [Zl].
nor do they fit our general formula.
carried out a neutron diffraction
Since no
study on
details of their analytical methods were given,
Nal+xZr2SixP3_x072
it is not possible to assess the limits of er-
They confirmed the structure proposed by Hong
ror in these formulas.
and were able to explain the volume changes
They did not observe a
change in slope in the curve of conductivity,as
with x = 7, 1.6, 2.0 and 2.5.
with increasing values of x.
Thus, we believe
a function of temperature, for Na3 lZr, 55 -
that Hong's series does exist, but the phases
Si2.3Po 7011 as is observed for our prepara-
are quite unstable when x = 1.5-2.5.
tions. 'Thus the von Alpen phases may in fact
Gordon et al. [7] found that Zr02 precipitates
be quite different in structure from NASICON.
from such compositions
*
.
In fact,
if they are heated above
On the other hand, our unit cell dimensions
1200°C.
and conductivity
to obtain singie phase NASICON until they re-
data are very close to those
reported earlier for Nal+xZr2SixP3_xO12
[4,61.
The question arises as to what the correct formulation for NASICON really is.
Several
moved 0.5 moles of Zr02.
Thus, their composi-
tion is close to Na3Zr, SSi2PO,, and must then contain condensed silicate groups. In an earlier study [13] we showed that
groups have reported a single phase NASICON, achieved either by thorough mixing of reagents
Boilot et al. [6] likewise were unable
stoichiometric
NaZr2(PO4)3 does not exist, or
is very difficult to prepare.
Rather, a solid
solution of the type Nal+4xZr2_x (PO4)3 with x = 0.02-0.06 was synthesized.
Although it is
difficult to see why the defect structure would be preferred (except perhaps to fill some of the empty type II cavities for added stability) the 4xNa+ could account for the conductivity of the triphosphate.
We are checking this point.
However, we make the point that our hydrother4+ ma1 preparation shows both the ZrO2 and Zr deficiency for maximum stability and the more stoichiometric
phases may degrade to the defect
type on heating by precjpitation of fro;. 5.
ACKNOWLEDGMENT This work was supported by NSF grant number
DMR 80-25184 for which grateful acknowledgment is made, 6. 2
I
3
4
1000/T,(K)
Figure
4
:
Conductivity as a function of l/T for the hydrothermal samples. ZrP:Na4SiO4
=
1.5,
ZrP:NaSiO4
=
1.7,
0
0.
,
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