Silica Additions and the Performance of PTC Thermistors

Abstract:

A series of PTC thermistors, based on BaTiO3, doped with Ca, Mn and Y, were prepared with additions of SiO2 at levels of 0, 1, 2 and 3 at. %. The effect of the SiO2 additions and cooling rate on microstructural development and bulk performance were characterised using a combination of SEM, EBSD, and R-T experiments. It was found that the addition of SiO2 increased grain size marginally, and decreased sample density by reducing the amount of grain-grain contact. The addition of SiO2 also modified the distribution of grain boundary types by systematically decreasing the proportion of low-Σ grain boundaries within the microstructure. Electrical behaviour was modified by adding SiO2 or increasing the sample cooling rates; in both cases there was an increase in ρ25 and a decrease in ρmax, with ρmax also being displaced to higher temperatures.

• Periodical: Advances in Science and Technology (Volume 45)
• Pages: 2362-2370
• DOI: https://doi.org/10.4028/www.scientific.net/AST.45.2362
• Online since: October 2006
• Authors: Colin Leach, M. Zubair, Robert Freer
• Keywords: Barium Titanate (BT), Local Properties, PTC Thermistors, Silica

References

[1] Goodman, G., Electrical Conduction Anomaly in Samarium-Doped Barium Titanate, J. Am. Ceram. Soc., 46, 1963, pp.48-54.

DOI: 10.1111/j.1151-2916.1963.tb13770.x

[2] Heywang, W., Resistivity anomaly in Doped Barium Titanate, J. Am. Ceram. Soc., 47, 1964, pp.484-490.

DOI: 10.1111/j.1151-2916.1964.tb13795.x

[3] Voltzke, D., Abicht, H.P., Pippel, E., Woltersdorf, J., Ca-containing additives in PTCBaTiO3 ceramics: effects on the microstructural evolution, J. Eur. Ceram. Soc., 20, 2000, pp.1663-1669.

DOI: 10.1016/s0955-2219(00)00061-3

[4] Jonker, G.H., Grain boundary phenomena in Electronic Ceramics, in Adv. In Ceramics, 1, Amer. Ceram. Soc., 1981, p.155.

[5] Gerthsen, P., Hoffmann, B., Current-voltage characteristics and capacitance of single grain boundaries in semiconducting BaTiO3 ceramics, Sol. Stat. Elec., 16, 1973, pp.617-622.

DOI: 10.1016/0038-1101(73)90161-5

[6] Nemoto, H., Oda, I., Direct Examinations of PTC Action of Single grain, J. Am. Ceram. Soc., 63, 1980, pp.398-401.

DOI: 10.1111/j.1151-2916.1980.tb10199.x

[7] Miki, T., Fujimoto, A., Jida, S., An evidence of trap activation for PTCR in BaTiO3 ceramics with substitutional Nb and Mn as impurities, J. Appl. Phys., 83, 1998, pp.1592-1603.

DOI: 10.1063/1.366870

[8] Gerthsen, P., Hoffmann, B., Current-voltage characteristics and capacitance of single grain boundaries in semiconducting BaTiO3 ceramics, Sol. Stat. Elec., 16, 1973, pp.617-622.

DOI: 10.1016/0038-1101(73)90161-5

[9] Nemoto, H., Oda, I., Direct Examinations of PTC Action of Single grain, J. Am. Ceram. Soc., 63, 1980, pp.398-401.

DOI: 10.1111/j.1151-2916.1980.tb10199.x

[10] Kuwabara, M., Morimo, K., Matsunaga, T., Single-grain boundaries in PTC resistors, J. Am. Ceram. Soc., 79, 1996, pp.997-1001.

DOI: 10.1111/j.1151-2916.1996.tb08538.x

[11] Leach, C., Russell, J.D.; Wood, G.I., Direct observation of resistive barriers in a BaTiO3 based thermistor, J. Mater. Sci., 32, 1997, pp.4641-4643.

[12] Desu, S.B., Payne, D.A., Interfacial segregation in Perovskites: IV, Internal boundary layer devices, J. Am. Ceram. Soc., 73, 1990, pp.3416-3421.

DOI: 10.1111/j.1151-2916.1990.tb06469.x

[13] Blamey, J.M., Parry, T.V., The effect of processing variables on the mechanical and electrical properties of barium titanate PTCR ceramics (Part 1), J. Mater. Sci, 28, 1993, pp.4311-4316.

DOI: 10.1007/bf01154937

[14] Ogawa, H., Demua, M., Yamamoto, T., Sakuma, T., Estimation of the PTCR effect in single grain boundary of Nb-doped BaTiO3, J. Mat. Sci. Lett, 14, 1995, pp.537-538.

DOI: 10.1007/bf00275424

[15] Hayashi, K., Yamamoto, T., Sakuma, T., Grain orientation dependence of the PTCR effect in niobium-doped Barium Titanate, J. Am. Ceram. Soc., 79, 1996, pp.1669-1672.

DOI: 10.1111/j.1151-2916.1996.tb08780.x

[16] Hayashi, K., Yamamoto, T., Ikuhara, Y., Sakuma, T., Grain boundary electrical barriers in PTC thermistors, J. Appl. Phys, 86, 1999, pp.2909-2913.

DOI: 10.1063/1.371140

[17] H M Al-Allak, G J Russell and Wood., The effect of annealing on the characteristics of the semiconducting BaTiO3 positive temperature coefficient of resistance devices, J. Phys. D: Appl. Phys. 20 (1987) 1645-1651, IOP Publishing Ltd.

DOI: 10.1088/0022-3727/20/12/016

[18] J Illingsworth, H M Al-Allak and A W Brinkman., Dependence of grain boundary potential barrier height of BaTiO3 ceramics on donor dopant comcentration, J. Phys. Appl. Phys. 23 (1990) 971-975, IOP Publishing Ltd.

DOI: 10.1088/0022-3727/23/7/036

[19] H. Ihring and Puschert., A systematic experimental and theoretical investigation of the grain boundary resistivities of n-doped BaTiO3 caramics, Journal of Applied Physics, Vol. 48, No. 7, July 1977. PACS number: 85. 20. Ea, 85. 30. Hi, 85. 50. Ly, 73. 40. Ty.

DOI: 10.1063/1.324078

[20] G.H. Jonker, Some aspects of semiconducting Barium Titanate, Solid State Electron., 7, 895 (1964).

DOI: 10.1016/0038-1101(64)90068-1

[21] H M Al-Allak, A. W. Brinkman G J Russell and J. Wood., The effect of Mn on the positive temperature coefficient of resistance characteristics of donor doped BaTiO3 ceramics, J. Appl. Phys., 63 (9), pp.4530-4535 (1988).

DOI: 10.1063/1.340150