Variability sources of DC voltage–current measurements in the study of TiO 2 -based varistors M.A.A. Santana a,b , F.S.N. dos Santos c , V.C. Sousa d , Q.S.H. Chui a, * a USF Universidade São Francisco – PPG ECM, Programa de Pós-Graduac ßão em Engenharia e Ciências dos Materiais, Rua Alexandre R. Barbosa, 45, Itatiba, SP – CEP:13251-900, Brazil b INPE/CPTEC/LIM – Instituto Nacional de Pesquisas Espaciais/Centro de Previsão do Tempo e Estudos Climáticos/Laboratório de Instrumentac ßão Meteorológica Ambiental, Brazil c USF Universidade São Francisco, UAACET, Bolsista Iniciac ßão Científica CNPq, Brazil d UFRGS/DEMAT/LABIOMAT and Advanced Ceramics - Universidade Federal do Rio Grande do Sul, Brazil article info Article history: Received 25 March 2006 Received in revised form 22 November 2007 Accepted 11 March 2008 Available online 27 March 2008 Keywords: TiO 2 Low voltage varistors Electronic ceramics Metrology Traceability abstract TiO 2 -based ceramic varistors have called attention due to their low voltage characteristics. Metallic ions with +5 valence have been used as additives for the sintering of TiO 2 as they allow the increase of the electric conductivity of titanium dioxide. In this work, an exper- iment was carried out to study the influence of Ta 2 O 5 and Cr 2 O 3 addition on the electrical properties of TiO 2 varistors and identify the various sources of uncertainties associated with the measurement results of current and voltage. The EA-4/02 standard (Expression of the Uncertainty of Measurement in Calibration) was used and it was demonstrated the traceability chain of the variables: pressure, temperature, humidity, voltage, current and electric resistance. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Circuits and electronic components need protection de- vices against overvoltage. Ceramic varistors are the most efficient devices for the protection of circuits and compo- nents by means of the restriction of transitory overvoltag- es. This capacity of overvoltage protection originates from the non-linear current–voltage characteristics of the varis- tors. This is one of the most important properties of varis- tors and it is noticed in voltages, for which the electric current can increase several orders of magnitude due to a small increase in the voltage. The non-linear behavior is empirically expressed by the expression, I = KV a , in which K is a constant related to the electric resistivity of the material and ‘‘a” is the non-linear coefficient, an important varistor parameter. The higher the value of this coefficient the better is the device. Several types of varistors were developed, and the first type was based on SiC. They were substituted by the ZnO- based varistors [1]. In order to assist to the need of new de- vices, other types of varistors have been developed. These new types are based on other oxides, such as SnO 2 , WO 3 , TiO 2 . The need of low voltage varistors led to the research for new varistor types, among them the TiO 2 -based. Several works were developed varying the type and proportion of dopants used, the sintering temperature and atmosphere [2–9]. The best non-linear coefficients were achieved upon using Cr 2 O 3 and Nb 2 O 5 (a = 12) [2], and also using BaO, Bi 2 O 3 and Nb 2 O 5 (a = 17) [3]. The current concern of the measurement science is rep- resented by the subject of the calculation of the uncertain- ties associated with the results experimentally obtained. To permit the comparability of the measurement results 0263-2241/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.measurement.2008.03.006 * Corresponding author. E-mail address: queenie.hang@saofrancisco.edu.br (Q.S.H. Chui). Measurement 41 (2008) 1105–1112 Contents lists available at ScienceDirect Measurement journal homepage: www.elsevier.com/locate/measurement