119Sn Mossbauer spectroscopic study of nanometric

tin dioxide powders prepared by pyrolysis

of organotin oxides

A.G. Pereiraa, A.O. Portoa, G.M. de Limaa,*, H.G.L. Siebalda, J.D. Ardissonb

aDepartamento de Quimica, ICEx, Universidade Federal de Minas Gerais, Avenida Antonio Carlos 6627, Belo Horizonte,

MG CEP-31270-901, BrazilbLaboratorio de Fısica Aplicada, CDTN/CNEN, Belo Horizonte, MG 31270-010, Brazil

Received 11 November 2002; received in revised form 23 April 2003; accepted 30 April 2003 by H. Akai

Abstract

This paper reports the results of 119Sn Mossbauer Spectroscopy of residues from the pyrolysis of Sn3O3Bu6 (1) and Sn4O6Bu4

(2) (Bu ¼ n-butyl) in air, O2, and N2. The isomer shift and quadrupole splitting parameters of the samples allowed the

identification of the tin oxidation states, as well as the number of non-equivalent coordinated tin sites. The result of the 119Sn

Mossbauer study correlates perfectly with those of X-ray electron probe microanalysis, scanning electron microscopy and

X-ray powder diffraction for the formation of pure SnO2 from the decomposition of (1) and (2) in air or O2. However, in N2,

evidences suggest the formation of a mixture of SnO2 and SnO.

q 2003 Elsevier Science Ltd. All rights reserved.

PACS: 28.52.Fa; 33.45+X

Keywords: A. Tin (IV) oxide; E. 119Sn Mossbauer spectroscopy; C. Pyrolysis

1. Introduction

A broad range of analytical techniques, such as UV, IR,

mass spectrometry and XPS can be employed to study tin

derivatives. Spectroscopic techniques such as 119Sn Moss-

bauer and 119Sn MAS-NMR are very important to under-

stand the structural and electronic properties of nanometric

tin composites [1]. Materials containing tin (IV) oxide

exhibit among other important properties, optical transpar-

ency and electrical conductivity, which allow their use in the

preparation of light transmitting electrodes for optical

electronic devices [2].

In the last two years, our research team has investigated

the preparation of tin calchogenides by pyrolysis of single

source precursors in order to improve the yield and the

quality of tin-based materials. In the previous work, we

reported the preparation of pure nanometric SnS [3] and

SnO2 [4] through the pyrolysis of Sn3R6M3 and Sn4R4M6

(M ¼ O or S, and R ¼ Methyl, n-Butyl or Phenyl). In the

case of SnO2, thermal analysis (TG) and X-ray diffraction

(XRD), the data point to the formation of pure SnO2 in the

pyrolysis of both precursors in air, and O2. However, the

formation of a mixture of tin (II) and tin (IV) oxides in N2

could not be clearly identified by XRD measurements due to

the low intensity of the diffraction lines. This could be

indicative of a low concentration of tin (II) oxides in the

mixture.

The main goal of this report is to show how Mossbauer

spectroscopy, in association with other techniques, can be an

important tool to elucidate structural features, therefore

playing an important role in materials science. Herein, we

discuss the results of 119Sn Mossbauer spectroscopy of

0038-1098/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.

doi:10.1016/S0038-1098(03)00375-2

Solid State Communications 127 (2003) 223–227

www.elsevier.com/locate/ssc

* Corresponding author. Tel.: þ55-313-499-5744; fax: þ55-313-

499-5720.

E-mail address: gmlima@dedalus.lcc.ufmg.br (G.M. de Lima).

pyrolysis residues of Sn3R6O3 and Sn4R4O6 (R ¼ n-butyl)

in the light of the previous XRD data [4].

2. Experimental

The synthesis and characterisation of the precursors as

well as the preparation of tin oxides can be found in earlier

work by our group [4]. The chemical structures of the

precursors, Sn3R6O3 (1) and Sn4R4O6 (2) (R ¼ n-Butyl), are

shown in Fig. 1.

The 119Sn Mossbauer experiments were performed

employing a conventional apparatus with the sample in liquid

N2 and a CaSnO3 source at room temperature. All spectra were

computer-fitted assuming Lorentzian single lines.

3. Results and discussion

119Sn Mossbauer data demonstrate that the residues

obtained by the pyrolysis of (1) and (2) in air, and O2

consisted of only tin (IV), as shown in Figs. 2 and 3,

respectively. The isomer shifts (IS), Table 1, are somewhat

higher than those for pure SnO2 (0.03 mm s21) recorded as

standard, which suggests a small variation in the Sn–O

bonding scheme in nanometric SnO2. The IS values are

quite different from those of the starting materials,

1.00 mm s21 for Sn3Bu6O3 and 0.86 mm s21 for

Sn4Bu6O4, which indicates the complete decomposition of

the precursors into SnO2. They correlate with other

literature parameters [5] very well. Two tin (IV) sites

were evident for all residues, except (2) decomposed in air.

In the case of N2, the two small values and the large ones

at 2.65 and 2.69 mm s21 are related to tin (IV), and tin (II)

(1) and (2), respectively.

The non-zero quadrupole splitting (QS), indicative of a

symmetry break in the tin center possibly due to the

existence of oxygen vacancies, can also explain the

deviation in the IS parameters in comparison to the standard

ones. QS values confirm the results obtained by other

techniques [4] that suggest the formation of a mixture of tin

oxides in the pyrolysis of (1) and (2) in N2.

Table 1119Sn Mossbauer parameters, isomer shift (IS), quadrupole splitting (QS), area and width obtained at liquid nitrogen temperature for the

pyrolysis residue of Sn3O3Bu6 (1) and Sn4O6Bu4 (2) in air, O2, and N2, and the pure precursors (1), and (2)

Material Atmosphere Sn oxidation state IS (mm s21) QS (mm s21) Area (%) Width (mm s21)

Residue of (1)

Air Sn(IV) 0.06 0.39 100 0.90

0.07 1.09 0.90

O2 Sn(IV) 0.06 0.50 100 0.90

0.08 1.50 0.90

N2 Sn(IV) 0.04 0.49 50 0.90

0.00 1.99 0.90

Sn(II) 2.65 1.86 50 1.15

Residue of (2)

Air Sn(IV) 0.04 0.59 100 0.90

O2 Sn(IV) 0.04 0.52 100 0.90

0.00 1.72 0.90

N2 Sn(IV) 0.00 0.58 43 0.90

0.05 1.68 0.90

Sn(II) 2.69 1.60 57 1.15

Pure SnO2 Sn(IV) 0.03 0 100 0.90

Sn3O3Bu6a Sn(IV) 1.00 2.05 100 0.95

Sn4O6Bu4a Sn(IV) 0.86 1.75 100 0.90

The experimental errors associated to IS, QS, and Width are 0.04, 0.05, and 0.05, respectively. The 119Sn Mossbauer parameters in this work

refer to the quadrupole distribution maximum.a Refs. [7] and [8].

Fig. 1. Chemical structures of Sn3O3Bu6 (1) (a) and Sn4O6Bu4 (2)

(b).

A.G. Pereira et al. / Solid State Communications 127 (2003) 223–227224

The results of quadrupole distribution accomplished to

explain the broad line widths and also to allow a greater

certainty in the calculation of the Mossbauer parameters

suggest that not only a mixture of tin (IV) and tin (II), but

also different types of tin (IV) oxides are formed.

Unfortunately, for this very reason, it was not possible to

make signal assignments for each of the oxides. In the

pyrolysis of (2) in air, only one type of tin (IV) oxide, with

tetragonal (rutile-type structure), was obtained. However, in

O2 two different forms of SnO2 were produced during the

pyrolysis of (2). The product obtained in N2 is probably a

mixture of SnO2 and SnO, or Sn3O4 [6]. For products

originated from (1), the quadrupole distribution displayed a

much more complicated pattern. In air, the product presents

at least three tin (IV) centers. No sign of metallic tin was

obtained in the Mossbauer experiments.

Fig. 2. 119Sn Mossbauer spectra (1), and the respective quadrupole distribution (2) for the Sn3O3Bu6 residue obtained in air (a), Oxygen (b), and

Nitrogen (c).

A.G. Pereira et al. / Solid State Communications 127 (2003) 223–227 225

4. Conclusions

119Sn Mossbauer spectroscopy has shown a good corre-

lation to the other methods [4], and consequently, it is a useful

tool to understand the chemical aspects of nanometric

materials. Our data strongly suggest that it is possible to

prepare nanometric SnO2 by the pyrolysis of Sn3O3Bu6 (1) and

Sn4O6Bu4 (2). According to 119Sn Mossbauer parameters,

only tin (IV) oxide was obtained when compounds (1) and (2)

were decomposed either in air or O2. In contrast, a discrete

mixture of SnO2, and SnO or Sn2(II)Sn(IV)O4 resulted from their

pyrolysis in N2.

Fig. 3. 119Sn Mossbauer spectra (1), and the respective quadrupole distribution (2) for the Sn4O6Bu4 residue obtained in air (a), Oxygen (b), and

Nitrogen (c).

A.G. Pereira et al. / Solid State Communications 127 (2003) 223–227226

Acknowledgements

We would like to thank TWAS—Third World Academy

of Science (Research Grant Agreement 00-229

RG/CHE/LA) and CNPq-Brazil for the financial support.

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