X-ray photoelectron spectroscopy characterization of barium titanate ceramics prepared by the citric route. Residual car
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X-ray photoelectron spectroscopy characterization of barium titanate ceramics prepared by the citric route. Residual carbon study C. Miot CRPHT, CNRS UPR 4212, 45071 Orl´eans cedex 2, France
E. Husson and C. Proust CRPHT, CNRS UPR 4212, 45071 Orl´eans cedex 2, and ESEM, Universit´e d’Orl´eans, 45072 Orl´eans cedex 2, France
R. Erre CRMD, CNRS et Universit´e d’Orl´eans, 45071 Orl´eans cedex 2, France
J. P. Coutures CRPHT, CNRS UPR 4212, 45071 Orl´eans cedex 2, France (Received 31 May 1996; accepted 25 April 1997)
Powder and ceramics of barium titanate prepared by the citric process were studied by x-ray photoelectron spectroscopy (XPS). Spectra of C1s , O1s , Ti2p , Ba3d , and Ba4d levels are analyzed in powder and ceramics immediately after the sintering step and after several months of exposure in the air. Ar-ion etching allowed one to characterize the material intrinsic carbon. The results are discussed in comparison with works previously published on oxide single crystals.
I. INTRODUCTION
The use of organic precursors in elaboration of homogeneous and fine powders to obtain materials of good quality is extensively developed. This type of process may induce the presence of residual carbon in powders and even in ceramics after the sintering step. Very little was published on the subject.1 In the 80s, Freund and his co-workers2–5 studied residual carbon present in several single crystals of natural or synthetic oxides such as magnesium oxide, olivine, or forsterite. They used essentially the sd, pd nuclear method; only one work3 reports on an x-ray photoelectron spectroscopy (XPS) analysis. No study was found on ceramic oxides in the literature. In the present work, we studied powder and ceramics of BaTiO3 obtained by a citric process. The residual carbon content was expected to be low; thus techniques very sensitive to the presence of light elements in very low content were needed. The nuclear reaction 12 Csd, pd13 C and XPS spectroscopy were therefore chosen. The 12 Csd, pd13 C method gave carbon contents in surface layers of about 0.5 mm depth.6,7 The XPS spectroscopy gave information on the chemical form of carbon in surface ˚ depth.3 By Ar-ion etching, it was layers of 10 –15 A possible to analyze successive layers of materials. In this paper we present the XPS characterization of BaTiO3 powder and ceramics. The state of knowledge about the surface of such ceramics being still limited,8 the 2388
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J. Mater. Res., Vol. 12, No. 9, Sep 1997
Downloaded: 24 Feb 2015
chemical states of Ba, Ti, and O as well as those of C are analyzed. II. EXPERIMENTAL PROCEDURE A. Sample preparation
BaTiO3 powders were obtained from a citric resin method described in previous papers.9–11 The mixed citrate BaTi(C6 H6 O7 )3 , 6H2 O was first prepared, then dissolved in a citric acid, ethylene glycol, and water mixture so that the R (BaTiO3 mass)y(solution mass) ratio was 1%. This mixture was calcined at 700 ±C in static air and white BaTiO3 powders w
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