Film-forming capacity of Sn(II), Zr(IV), and Hf(IV) acetylacetonates

Article abstract of DOI:10.1023/A:1014888715163

Zr(acac)₄, Hf(acac)₄, and SnHacacCl₂·2H₂O were prepared in the solid state and in enthanol solutions. The film-forming capacity and thermal stability of these compounds were studied. Films of ZrO₂, Hf

Full text of DOI:10.1023/A:1014888715163

Russian Journal of Applied Chemistry, Vol. 74, No. 10, 2001, pp. 1636 1640. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 10, 2001,
pp. 1587 1591.
Original Russian Text Copyright
2001 by Dyukov, Kuznetsova, Borilo, Kozik.
INORGANIC SYNTHESIS
AND INDUSTRIAL INORGANIC CHEMISTRY
Film-Forming Capacity of Sn(II), Zr(IV), and Hf(IV)
Acetylacetonates
V. V. Dyukov, S. A. Kuznetsova, L. P. Borilo, and V. V. Kozik
Tomsk State University, Tomsk, Russia
Received March 12, 2001
Abstract Zr(acac)4, Hf(acac)4, and SnHacacCl2 2H2O were prepared in the solid state and in enthanol
solutions. The film-forming capacity and thermal stability of these compounds were studied. Films of ZrO2,
HfO2, and SnO2 were prepared from film-forming solutions of the corresponding acetylacetonates.
At present there is demand for thin film materials
stable in corrosive media and having good optical
properties. The functional and physicochemical prop-
erties of these films are mainly determined by their
preparation conditions and the nature and composi-
tion of the initial film-forming compound (FFC).
The promising FFCs are -diketonates [1]. Data on
the thermal stability, volatility, behavior in organic
and inorganic solvents, and film-forming capacity of
Group IV metal -diketonates are scarce and often
contradictory [2].
The qualitative and quantitative composition of
SnHacacCl2 2H2O was determined by means of X-ray
spectral microanalysis (XSMA) [4] on a Camebax
Microbeam device at accelerating voltage of 20 keV.
Metallic tin and single-crystal sodium chloride were
used as references. The presence of acetylacetone in
the complex was confirmed by qualitative reaction
with iron(III) [3].
The compositions of the complexes are presented
in Table 1. Acetylacetone in Zr(acac)4 and Hf(acac)4
complexes is in the deprotonated enol form. The tin
complex is coordination-unsaturated and contains hy-
dration water and Hacac in the undissociated enol and
keto forms, which were previously detected in an eth-
anol solution acidified with HCl [5].
In this work, we studied the film-forming capacity
of zirconium hafnium, and tin acetylaetonates. For
this purpose, we prepared these complexes in the solid
phase and in solution, studied their thermal stability
in air, and prepared ZrO2, HfO2, and SnO2 films from
ethanol solutions of these acetylacetonates.
The solubility of zirconium, hafnium, and tin ace-
tylacetonates in organic and inorganic solvents was
studied at room temperature. The solubility of anhy-
drous zirconium acetylacetonate in chloroform, aceto-
EXPERIMENTAL
Table 1. Composition of zirconium and hafnium acetyl-
acetonates and dichloro(acetylacetone)tin(II) dihydrate
Zirconium and hafnium acetylacetonates Zr(acac)4
and Hf(acac)4 were prepared from aqueous solutions
of zirconium and hafnium oxychlorides, respectively,
and acetylacetone (molar ratio 1 : 4) at pH 1.9 3.5.
The resulting mixture was heated on water bath. The
crystalline precipitate was washed with ice-cold water
and dried in air. Tin(II) acetylacetonate was prepared
from ethanol solution (96 wt % C2H5OH) of tin(II)
chloride hydrate and acetylacetone (molar ratio 1 : 2).
Composition, wt %
M
acac
Cl
Zr(acac)4:
found
calculated
Hf(acac)4:
found
calculated
SnHacacCl2 2H4O
found
18.66
18.72
80.70
81.28
31.12
31.07
66.74
68.93
The zirconium and hafnium content was determined
gravimetrically. The actylacetonate (acac ) content
was determined by absorption of the iron(III) acetyl-
35.97
36.43
26.14
27.79
calculated
acetonate complex at
= 550 nm [3].
eff
1070-4272/01/7410-1636 $25.00 2001 MAIK Nauka/Interperiodica

FILM-FORMING CAPACITY OF Sn(II), Zr(IV), AND Hf(IV) ACETYLACETONATES
1637
Fig. 1. Thermal analysis curves of (a) SnHacacCl 2H O and (b) Zr(acac) decomposition. (m) Weight loss and (T) tem-
2
2
4
perature; the same for Fig. 3.
nitrile, and acetone is 30, 15, and 4 9 wt %, respec-
tively. The solubility of hafnium acetylacetonate in
these solvents is, on the average, 3 wt % lower owing
to the more ionic character of the coordination bonds.
SnHacacCl2 2H2O is insoluble in organic solvents
and poorly soluble in concentrated mineral acids and
water ( 6 10 4 M) at room and elevated temperatures.
As determined by X-ray spectral microanalysis, the
remaining product is identical to the initial compound,
which indicates that the first effect is due to the sub-
limation of the compound
Found, wt %: Sn 36.04, Cl 26.98.
SnHacacCl2 2H2O.
Calculated, wt %: Sn 36.43, Cl 27.79.
The thermal stability of the complexes in air was
studied on a Q-1500 MOM derivatograph (Hungary)
in the temperature range 298 1273 K at a heating rate
In the second step (510 563 K) acetylacetone is
eliminated and oxidized. As determined by X-ray phase
analysis (XPA), the product is SnCl2 2H2O, in agree-
ment with the data of [6]. Weak exothermic peaks in
the third step (563 773 K) are assigned to decomposi-
tion of SnCl2 2H2O to give SnO and to oxidation of
this product by atmospheric oxygen to SnO2 (Table 2).
1
of 10 deg min .
Thermal analysis data for SnHacacCl2 2H2O are
shown in Fig. 1a. The first decomposition step is
characterized by an exothermic effect in the temper-
ature range 298 473 K and weight loss of up to 4%.
Table 2. X-Ray diffraction patterns of the final decomposition products of metal acetylacetonates and their FFSs
SnO2 (SnHacacCl2 2H2O) ZrO2 [Zr(acac)4] HfO2 [Hf(acac)4]
d,
I/ I0
d,
I/ I0
d,
I/ I0
3.35(3.34)*
2.64(2.64)
2.37(2.36)
1.76(1.75)
1.67(1.67)
1.59(1.58)
1.49(1.49)
100(100)
84(63)
23(18)
63(63)
14(10)
8(5)
3.37(3.63)
3.19(3.19)
2.85(2.85)
2.64(2.63)
2.55(2.55)
2.10(2.09)
1.82(1.81)
1.71(1.70)
1.49(1.486)
1.43(1.426)
20(24)
100(100)
78(80)
30(32)
18(16)
23(24)
44(40)
20(20)
16(16)
14(16)
5.01(5.07)
3.69(3.68)
3.61(3.61)
3.17(3.15)
2.82(2.82)
2.59(2.59)
2.53(2.52)
2.33(2.32)
2.20(2.196)
2.17(2.171)
2.00(2.006)
1.90(1.981)
18(20)
35(40)
23(30)
100(100)
95(100)
59(60)
50(50)
45(50)
60(60)
30(30)
40(40)
56(60)
10(14)
*
The data of [8] are given in parentheses.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 10 2001

1638
DYUKOV et al.
Thus, ZrO2, HfO2, and SnO2 can be prepared from
the corresponding metal acetylacetonates at 743, 773,
773 K, respectively.
It is known that oxide films can be conveniently
prepared from film-forming solutions in ethanol [8].
Since Hf(acac)4, Zr(acac)4 and SnHacacCl2 2H2O are
poorly soluble in ethanol, we studied preparation of
these complexes directly in ethanol without their iso-
lation in the solid state.
Film-forming solutions were prepared from 96%
ethanol, acetylacetone and Group IV metal salts [zir-
conium and hafnium oxychlorides, tin(II) chloride] at
Zr4+ : acacH, Hf4+ : acacH, and Sn2+ : acacH ratios of
1 : 4, 1 : 4, and 1 : 2, respectively. The experimental
results show that tin(II) acetylacetonate is stable in
ethanol solution only at hydrochloric acid concentra-
tions of no less than 0.4 M.
Fig. 2. FFS viscosity
vs. time
.
The data obtained in thermal analysis of SnHacacCl2
2H2O and XPA of its decomposition products suggest
the following scheme of its decomposition
SnHacacCl2 2H2O
SnCl2 2H2O
In practice, the stability of FFS can be estimated
by their viscosity. The viscosity was measured with
VPZh-2 and VPZh-4 viscometers at room tempera-
ture. The time dependences of the viscosity of solu-
tions of zirconium and hafnium acetylacetonates are
similar (Fig. 2, curves 1, 2, respectively). The viscos-
Hacac + O2
oxidation products
1/2O2
SnCl2 H2O
SnO
SnO2.
H2O
2HCl
Decomposition of Zr(acac)4 is also a three-step
process (Fig. 1b). In the first step (373 473 K), one
acetylacetonate ligand is liberated with an endother-
mic effect and 18.9% weight loss. The subsequent two
steps (473 673 and 673 743 K) are due to exothermic
decomposition of the complex to finally form mono-
clinic ZrO2 (Table 2).
1
ity reaches a maximum in six days (4.05 4.35 mm2 s )
and then decreases to constant value by the 15th
day. The increase in the viscosity is due to hy-
drolysis and formation of polymeric associates
M
O=C(CH3)CH=C(CH3)OM (M = Zr and Hf)
with acetylacetonate bridges [7]. These associates de-
grade (with a decrease in viscosity) to form mutually
oriented coordination-saturated zirconium and hafni-
um chelates with coordination number of eight.
Thermolysis of Hf(acac)4 is similar to that of
Zr(acac)4, with the temperature effects shifted by
30 K to higher temperatures. As determined by XPA,
the final thermolysis product is monoclinic HfO2
(Table 2).
The time dependence of the viscosity of tin(II) ace-
tylacetonate (Fig. 2, curve 3) indicates the attainment
Fig. 3. TG, DTA, and DTG curves of dried FFSs of (a) tin acetylacetonate and (b) zirconium acetylacetonate.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 10 2001

FILM-FORMING CAPACITY OF Sn(II), Zr(IV), AND Hf(IV) ACETYLACETONATES
1639
of equilibrium in the solution in four days. The vis-
cosity is constant during the following 6 days. This
indicates that equilibrium hydrolysis and complexation
of tin(II) are complete. The increase in the viscosity
after 10 days is also due to the formation of polymeric
associates. Since the viscosity of FFSs does not reach
the critical values [8], these solutions can be used
during a year after their preparation.
Table 3. Physicochemical properties of films*
Film com-
position
d,
nm
F,
kg mm
E,
eV
n
,
2
SnO2
ZrO2
HfO2
1.84 41.5
2.14 65.7
106
108
0.450
0.801
0.765
3.9
2.12 58.9 107 108
To study the mechanism of oxide film formation,
the chemical composition of FFSs dried at 333 K
was determined and thermal analysis of these prod-
ucts in the temperature range from 293 to 1073 K
was performed.
*
n, F, and E are the refractive index, adhesion, and the optical
band gap, respectively.
thermic effects in the temperature range 321 487 K
are probably due to stepwise removal of residual
ethanol and water, and to decomposition of zirco-
nium chloride complexes. The exothermic effects in
the temperature range 487 873 K are assigned to
combustion of the ligand with complete oxidative
degradation of FFS to form monoclinic zirconium(IV)
oxide (according to XPA).
The chemical composition of an FFS of
SnHacacCl2 2H2O in EtOH, dried at 333 K, was
determined by XSMA. The tin and chlorine concen-
trations in different parts of the sample indicate the
presence of SnCl2 2H2O and SnHacacCl2.
Found in FFS, wt %
Sn
Cl
The DTA curves of dried FFS containing HfOCl2,
Hacac, and C2H5OH are characterized by three endo-
thermic peaks at 403, 448, 508 K and two exothermic
peaks at 693 and 825 K, with the second of these
corresponding to two effects. Monoclinic hafnium
dioxide is formed at 873 K.
SnCl2 2H2O
SnHacacCl2
52.49
43.75
34.75
24.16
Calculated, wt %:
SnCl2 2H2O
SnHacacCl2
52.59
42.96
33.46
24.49
The results of XPA and thermal analysis of dried
FFSs indicate that monoclinic zirconium and hafnium
dioxides and tin dioxide with rutile stricture are
formed at 873 K.
A quantitative XSMA of dried FFS of tin(II) acet-
ylacetonate and SnHacacCl2 2H2O showed that, dur-
ing drying of the sample, Hacac is evaporated with
ethanol and SnHacacCl2 2H2O partially decomposing
to form SnCl2 2H2O.
Films of zirconium, hafnium, and tin dioxides were
prepared by centrifuging FFSs at 2000 5000 rpm.
These films are thermally stable, chemically inert, and
have good adhesion to silicon, quartz, glass, and
Polikor. The physicochemical properties of high-re-
sistivity semiconducting films of ZrO2, HfO2, and
SnO2 on a silicon support are summarized in Table 3.
The optical properties of the films were studied with
an LEF-3M ellipsometer; the electrical properties, on
E7-8 and E7-12 units; and adhesion was measured
with a PMT-3 microhardness gage.
The TG, DTA, and DTG curves of an SnHacacCl2
SnCl2 2H2O mixture (Fig. 3a) somewhat differ from
those of SnHacacCl2 2H2O (Fig. 1a). In the case of
dried FFS, the temperature effects are shifted to high-
er temperatures. The first step is accompanied by two
endothermic effects at 323 473 K, associated with
sublimation of the complex and desorption of ethanol
molecules. In the second step (exothermic effect at
473 593 K), Hacac is liberated from SnHacacCl2 and
then oxidized. The third step (593 873 K) involves
decomposition of SnCl2 2H2O to SnO and oxidation
of SnO by atmospheric oxygen to give SnO2 having
the rutile structure (according to XPA).
CONCLUSION
The complexes Zr(acac)4, Hf(acac)4, SnHacacCl2
2H2O were prepared in the solid phase and in an eth-
anol solution. The film-forming capacity and thermal
stability in air of these solutions were studied. High-
resistivity semiconducting films of ZrO2, HfO2, and
SnO2 with high adhesion to different supports were
Thermolysis of dried FFS consisting of ZrOCl2,
Hacac, and ethanol is a complex process (Fig. 3b).
Four endothermic peaks at 370, 388, 448, and 473 K
and two exothermic peaks at 531 and 733 K are ob-
served in the DTA curve, with the second exothermic
peak being a sum of two effects (DTG). The endo- prepared.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 10 2001

1640
DYUKOV et al.
roanaliz slozhnykh splavov (Quantitative X-ray Fluo-
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