Materials Sciences and Applicatio ns, 2011, 2, 1219-1224
doi:10.4236/msa.2011.29165 Published Online September 2011 (http://www.SciRP.org/journal/msa)
1219
Cadmium Stannates Synthesis via Thermal
Treatment of Coprecipitated Salts
Andrey V. Sidorak, Viktor V. Ivanov, Alexander A. Shubin
Siberian Federal University, Svobodniy, Russia.
Received March 21st, 2011; revised April 29th, 2011; accepted June 2nd, 2011.
ABSTRACT
Cadmium meta- and orthostannate were synthesized by thermal treatment using the coprecipitation method. Tin (IV)
chloride, cadmium acetate were used as the initia l compon ents, the ammonium carbonate was a precipitant. The copre-
cipitated compounds and the thermolysis products were analyzed by TGA/DSC methods, the thermal treatment samp les
were studied by XRD and SEM. The formation of proper products in soft thermal treatment conditions was confirmed.
The stannates formation in terms of submicron sized particles was observed by microscopial investigation.
Keywords: Cadmium Metastannate, Cadmium Orthostannate, Chemica l Precipitation, Powders, Thermolysis, Synthesis
1. Introduction
CdSnO3 и Cd2SnO4 cadmium stannates are interesting
due to their optical and electrical properties. These com-
pounds, related to so-called optically limpid conductive
oxides, are used as thin films which are transparent in
visible spectrum part [1], in semiconductor technology
[2], as sensitive elements of chemical sensors [3-5] etc.
Different ways of stannates obtaining are used de-
pending on a purpose. Thin films are prepared by means
of aerosol of cadmium and tin compounds solutions
composition pyrolysis [6], substrate covering with meta-
lorganic compounds followed their thermolysis [7], so-
dium stannate and water-soluble cadmium salt ion-ex-
changing reaction [8], etc. For stoichiometric products
powders obtaining the conventional method of solid-
phase synthesis from prepared powder oxides [5,9,10] is
used. The method is simple but rather time-consumimg
because of the necessity to perform some intermediate
mechanical grinds and also requires high temperatures
and long time of synthesis. Such product is not optimal
e.g. for electroconductive composite materials technolo-
gies because they require high dispersibility and statistic-
cally homogeneous stannate phase distribution [11].
Stannate synthesis of fine-grained form with soft tem-
perature conditions and of short duration is desirable for
electroconductive composite materials technologies.
Evidently there is no data for kinetics of cadmium
stannates synthesis. We can meet with some descriptions
of syntheses e.g. in [9,12,13]: they are carried out in the
open air under 1073 - 1273 K temperature range using
long stepped anneals for volatile cadmium oxide loss
reduction. On the other hand it is well known that high
dispersibility of initial powder components substantially
accelerates kinetics and decreases the temperature of
efficient solid-phase synthesis. It also concerns the ex-
amined compounds [14].
Thus, the work is devoted to study the potential of
cadmium meta- and orthostannate powder forms synthe-
sis under low temperatures by means of thermal treat-
ment of tin and cadmium thermally unstable salts copre-
cipitated composition.
2. Experimental Part
The decomposition of thermally unstable salts-precursors
to obtain CdSnO3 and Cd2SnO4 was used. The powder
precursors with Cd:Sn molar ratios 1:1 and 1:2 were pre-
pared by a chemical coprecipitation. Analytically pure
reagents of SnCl45H2O, Cd(CH3COO)22H2O and
(NH4)2CO3 were used as starting materials. Solutions
with 0.1 mol/L tin and cadmium salts, in stoichiometric
ratios 1:1 and 2:1, for CdSnO3 and Cd2SnO4, accordingly,
were mixed and then a 0.2 mol/L solution (NH4)2CO3
was added. White fine-grained precipitates, dried for 10
h at temperature 383 K. Further products were calcinated
in the open air at 783, 873, 973, 1073, 1173, 1223 K for
an hour.
Thermal, XRD, elemental and microscopic analyses of
obtained samples were carried out at different stages.

Cadmium Stannates Synthesis via Thermal Treatment of Coprecipitated Salts
1220
Elemental analysis was performed by means of XRF
using the ARL Advant`X (Thermo) spectrometer (Joint
Use Center SFU) with an Rh anode X-ray tube. Quantita-
tive elements content was evaluated by fundamental pa-
rameter method using the UniQuant 5. Thermal decom-
position processes of precipitates were studied by ther-
mogravimetry (TG) and differential scanning calorimetry
(DSC) methods using the synchronous thermal analysis
STA Jupiter 449C (Netzsch) device (heating rate 10
K/min in flowing Ar atmosphere and a corundum cruci-
ble).
Thermal treatment products were studied by an
X’Pert-Pro (PANalytical) X-ray diffractometer (XRD)
with monochromatized Cu Kα radiation (λ1 = 0.15406).
The angular 2θ range of registration was from 5˚ to 80˚
with the step of 0.026˚. Micrographs were obtained using
a JEOL JSM-7001F scanning electron microscope (Joint
Use Center SFU).
3. Results and Discussion
3.1. Thermal Analysis of Precipitated Salt Mixtures
The thermal behavior of Precipitated salts was inves-
tigated to obtain typical temperature intervals of the
thermolysis. The TG and DSC curves for mixtures of
CdSnO3 and Cd2SnO4 proper compositions are presented
in Figure 1. TG-curves are substantially different:
CdSnO3 mixture has two defined stages of weight loss
and Cd2SnO4 mixture has only one. The first stage begins
at the temperature of about 375 K and finishes at ~650 K
for both systems. We can notice the overlapping of some
thermal effects within this temperature range. First of all
the crystal water loss and cadmium carbonate decompo-
sition are possible during the process:
3
CdCOCdO CO
2
(1)
The authors [15] recorded the intensive peak of
precipitated cadmium carbonate decomposition at the
temperature of 623 K. Our data are in accordance with
their values.
For CdSnO3 precursors the second stage of weight loss
is observed in the range 780 K to 950 K. It is probably
caused by tin (IV) compounds decomposition. It is well
known that during the tin (IV) precipitation from water
solutions the α-stannic acid SnO2nН2О is formed (n is
closed to 1.8) [16]. Makeup precipitated α-SnO2nН2О is
an X-ray amorphous phase but ageing and heating lead to
water loss. Thus α-SnO2nН2О turns into β-SnO2nН2О
(n < 0.4), which then detaches the rest of water step-by-
step and crystallizes in SnO2 form. This process finishes
at 870 K [17]. Our results of weight loss value and tem-
perature range correlate to the mentioned above. The
absence of significant weight loss for Cd2SnO4 precursors
(a)
(b)
Figure 1. TG (dotted line) and DSC (solid line) curves of
precipitated salt mixtures for CdSnO3 (a) and Cd2SnO4 (b)
compositions.
in the range of 780 - 950 K (Figure 1(b)) is con- nected
with powder sample keeping for a week before the ex-
periment. It led to natural ageing of α-SnO2nН2О in the
sample and its turning into β-SnO2nН2О. Gradual weight
decrease at the temperature above 1150 K in both cases
is caused by cadmium oxide sublimation. And also crys-
tallization thermal effects can be observed under the
same conditions.
The results of X-ray fluorescence analysis for samples
at different stages treatment are presented in Table 1. As
you can see, low-temperature samples correspond to the
specific composition. Thermal treatment temperatures
higher than ~1000 K lead to substantial cadmium oxide
evaporation and Cd: Sn molar ratio decreasing.
3.2. X-Ray Phase Analysis of the Products
Both Figure 2 and Table 2 show the XRD results for
powder mixtures with a specific compositions which
were annealed at different temperatures. The initial dried
mixture consists of only crystal phase of cadmium car-
bonate. X-ray amorphous phase corresponding to tin (IV)
oxide is present at the sample which was annealed at

Cadmium Stannates Synthesis via Thermal Treatment of Coprecipitated Salts
1221
Table 1. Elemental composition (XRFA) of thermally treated
powder mixtures.
873 K. These results confirm the data of thermal analysis.
The CdO phase formation comes to an end up to 670 K
according to TGA data. It is also confirmed by XRF
analysis. The Quantitative phase contribution is condi-
tional with the X-ray amorphous phase presence in the
sample. Such values are marked with “*” in Table 2.
molar fraction of the element
Annealing temperature, K Cd Sn Cd:Sn ratio
CdSnO3 proper composition
Initial mixture 0.49 0.51 0.97
783 K 0.49 0.51 0.97
873 K 0.49 0.51 0.97
973 K 0.48 0.52 0.94
1073 K 0.47 0.53 0.88
1173 K 0.46 0.54 0.86
1223 K 0.46 0.54 0.86
Cd2SnO4 proper composition
Initial mixture 0.66 0.34 1.96
783 K 0.66 0.34 1.96
873 K 0.66 0.34 1.96
973 K 0.66 0.34 1.96
1073 K 0.65 0.35 1.87
1173 K 0.64 0.36 1.77
1223 K 0.65 0.35 1.87
XRF analysis results of specific composition Cd2SnO4
mixtures are presented in both Figure 2(b) and Table 2.
The phase of tin dioxide is possible to be registered in
Cd2SnO4 system in contrast to CdSnO3 system. Starting
from 873 K the samples contain both CdSnO3 and
Cd2SnO4 cadmium stannates. As the temperature in-
creases the comparative amount of metastannate slightly
increases too. It seems to be connected with the increas-
ing of volatile CdO velocity elimination. Orthostannate is
presented by two modifications: they are cubic modifica-
tion and orthorhombic one. However the content of or-
thorhombic modification exceeds 5% at the temperature
over 973 K only.
(a) (b)
Figure 2. X-ray diffraction patterns of CdSnO3 (а) and Cd2SnO4 (b) proper composition powder mixtures annealed at given
temperatures: О – Cd2SnO4 (cubic), О1 – Cd2SnO4 (orthorhombic), М – CdSnO3, K – CdO, C – CdCO3, S – SnO2.

Cadmium Stannates Synthesis via Thermal Treatment of Coprecipitated Salts
1222
Table 2.Thermally treated powder mixtures composition (XRD).
mass fraction
Annealing temperature
CdCO3 CdO SnO2 CdSnO3 Cd2SnO4
(cubic)
Cd2SnO4
(orthorhombic)
CdSnO3 proper system
without annealing 1* - - - - -
773 K - 1* - - - -
873 K - 0.15 - 0.77 - 0.08
973 K - - - 0.91 - 0.09
1073 K - - - 0.99 - 0.01
1173 K - - 0.06 0.94 - -
1223 K - - 0.05 0.91 0.04 -
Cd2SnO4 proper system
without annealing 1* - - - - -
773 K - 0.76* 0.24* - - -
873 K - 0.19 - 0.11 0.65 0.05
973 K - 0.07 - 0.11 0.73 0.09
1073 K - 0.08 - 0.13 0.71 0.08
1173 K - - - 0.17 0.66 0.17
1223 K - - - 0.16 0.66 0.18
Shortage of cadmium oxide, comparatively to assigned
stoichiometry of CdSnO3 and Cd2SnO4 compositions, is
recorded in both involved systems in the samples at 1073
K and above what is caused by CdO sublimation. CdO
loss in Cd2SnO4 system leads to phase composition
change (Table 2) at the expense of CdSnO3 metastannate
formation.
Thus specific compositions synthesis completes during
an hour at 873 K. In both cases the samples of the mix-
ture contain some amount of CdO and improper stannate
(Table 2).
The authors [9] studied of a cadmium stannates syn-
thesis from prefabricated powders had evaluated phase
ratios of CdO-SnO2 and 2CdO-SnO2 mixtures after six-
hours-long annealing at the range 970 to 1420 K above.
Cd2SnO4 appears in an equimolar mixture at about 970 K.
At 1170 K orthostannate is absolutely synthesized and
CdO is used up. Metastannate forms at 1170 K above:
24 2
Cd SnOSnO2CdSnO 3 (2)
This process finishes at about 1340К and then CdSnO3
decomposes into CdO and SnO2. Cd2SnO4 synthesis in
2CdO-SnO2 mixture comes to an end at about 1320 K. At
1320 K above Cd2SnO4 decomposes into CdSnO3 and
CdO.
Thus long time and temperature of about 1300 K is
necessary to synthesize both stannates from prefabricated
powder components. Though the processes laws of stan-
nates synthesis from coprecipitated salts confirm the ob-
servations given in the work [9], they require lower tem-
peratures and shorter time for thermal treatment.
Cd2SnO4 and CdSnO3 obtaining in terms of individual
phases requires the adjustment of firing regimes and
formation of conditions preventing cadmium oxide vola-
tilization. However practical application of such process
of synthesis that gives the powder mixture with pre-
dominant content of proper cadmium stannates is possi-
ble e.g. in metalloxide electrocontact composites produc-
tion when silver(copper)/oxide powder pressings sinter-
ing is combined with oxide phase synthesis. It provides
high dispersion ability and statistical homogeneity of
phase inclusions and also it does the production less
power-consuming.
3.3. Microscopy of Powder Products
SEM-micropictures of CdSnO3 and Cd2SnO4 powders
thermally treated at 1223 K are presented in Figure 3.
We can see the likeness of microstructure and the mor-
phology of particles when comparing. The powders are
rather massive, loose, weakly bonded agglomerates,
formed from crystal particles in the submicron range of
dispersibility (from ~50 - 100 nm to 1 μm).
4. Conclusions
The synthesis of CdSnO3 and Cd2SnO4 by thermal treat-
ment of thermally unstable tin and cadmium composi-
tions were carried out. It allows to obtain fine-grained
products in the form of submicron sized powders with
predominant content of proper stannates for short period
of time under soft temperature conditions. Decomposi-
tion of salt mixture components carries in wide tempera-
ture range but cadmium meta- and orthostannates forma-
tion generally completes at 873 K already. In spite of
powder products complicated structure which includes
both of stannates and tin and cadmium oxides, the given
powder synthesis method can be used for metalloxide
composite materials “in-situ” synthesis in practice. With

Cadmium Stannates Synthesis via Thermal Treatment of Coprecipitated Salts 1223
(a) (b)
(c) (d)
Figure 3. SEM-micropictures of CdSnO3 (a, b) and Cd2SnO4 (c, d) proper composition powders (zoomed 500 and 10000).
all this the technology is simplified substantially and
time and energy charges for the production are reduced.
5. Acknowledgements
We would like to thank to Sergey D. Kirik and Galina M.
Zeer for XRF and SEM measurements carrying out.
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