The effect of Cr concentration and preparation method on the microstructure and electrical characterization of SnO2-based ceramics

Daniela Russo Leite,Jose Arana Varela,Mario Cilense,Maria Aparecida Zaghete,Wanda Cecilia Las

doi:10.1590/s1516-14392003000400005

Abstract

This paper reports a study of the influence of Cr concentration and preparation method in the electrical conductivity and microstructure of SnO2-based powders doped with Mn and Nb, prepared by an organic route (Pechini method) and a mixture of oxides. All the samples were compacted into discs and sintered at 1300 °C for 3h, resulting in ceramics with relative density varying between 81 and 99%. The powders were morphologically characterized by X-ray diffraction and their specific surface area was determined by N2 adsorption/desorption isotherms. Electrical conductivity characterization indicated that the conductivity decreases as Cr concentration increases, probably due to Cr segregation at grain boundaries, which reduces grain size, increasing the number of resistive boundaries, thus limiting the passage of current.

Highlights

Tin dioxide (SnO2) is a n-type semiconductor whose tetragonal crystalline structure is similar to the rutile one[1]
The X-ray diffraction patterns of the compositions studied are shown in Fig. 1 for powders prepared by Pechini method and in Fig. 2 for mixture of oxides
The Effect of Cr Concentration and Preparation Method on the Microstructure and Electrical Characterization of SnO -Based Ceramics 459 2 method showed to be finer and more reactive than those prepared by the mixing oxide method and that milling reduces the particle size of powders prepared by Pechini method

Summary

Introduction

Tin dioxide (SnO2) is a n-type semiconductor whose tetragonal crystalline structure is similar to the rutile one[1]. The use of tin dioxide ceramics is limited due to poor densification during sintering caused by the dominance of non-densifying mechanisms for mass transport such as surface diffusion or evaporation condensation[5]. These mechanisms promote grain coarsening of SnO2 leading to poor densification of this ceramics[6]. The addition of Cr2O3 in SnO2-based ceramics leads to a high non-linearity coefficient of α = 41 due the introduction of defects in the crystal lattice that are responsible for the formation of Schottky type potential barriers at the grain boundaries, enabling its use in varistors[11]. Due to the large influence of Cr+3 in the electrical properties of SnO2-based ceramics, the effect of this ion on electrical conductivity in Sn-Mn-Nb systems, prepared by Pechini method and mixture of oxides, and its correlation with microstructural results were investigated in this work

Experimental Procedure

Results and Discussion

Pechini Method Mixture of Oxides

Conclusion