Journal of the European Ceramic Society 26 (2006) 2777–2783 A mechanism for low-temperature sintering Matjaz Valant a,∗ , Danilo Suvorov a , Robert C. Pullar b , Kumaravinothan Sarma b , Neil McN. Alford b a Advanced Materials Department, Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia b Centre for Physical Electronics and Materials, Faculty of Engineering, Science and the Built Environment (FESBE), London South Bank University, 103 Borough Road, London SE1 0AA, UK Received 20 April 2005; received in revised form 30 May 2005; accepted 4 June 2005 Available online 22 August 2005 Abstract We explain the basic mechanism of the low-temperature sintering called reactive liquid-phase sintering. The mechanism involves the presence of a low-temperature liquid phase that must be able to directly or indirectly accelerate a reaction with the matrix phase. The mechanism is explained in details for the case of the low-temperature sintering of BaTiO 3 , which was sintered to more than 95% of relative density in 15 min at 820 ◦ C. We have applied reactive liquid-phase sintering to a number of different compounds with very different crystal-chemistry characteristics, and managed to sinter them as much as 400 ◦ C below their original sintering temperatures. A thorough understanding of this sintering mechanism makes it possible to closely control the sintering behavior. © 2005 Elsevier Ltd. All rights reserved. Keywords: Sintering; Perovskites; BaTiO 3 and titanates; Capacitors; LTCC 1. Introduction Until recently, the rapid developments in semiconduc- tor technology have not been matched by the progress in passive components. This situation was especially critical for the telecommunications industry, where the miniatur- ization of handset devices plays a key role. An important breakthrough came with the introduction of low-temperature cofired ceramic (LTCC) technology, which has enabled miniaturization, the integration of passive functions and a reduction in costs, and has led to the production, for example, of the well-known Bluetooth module. LTCC mod- ules are produced by co-firing ceramic layers with a three- dimensional Ag-microstrip circuitry. To avoid melting of the Ag-microstrips the firing temperature must be around 900 ◦ C, which is extremely low for a ceramic material and repre- sents the major problem with this technology. For a variety of different reasons lowering the sintering temperature is also ∗ Corresponding author. Tel.: +386 1 477 3547; fax: +386 1 477 3875. E-mail address: matjaz.valant@ijs.si (M. Valant). important for many other technologies, which means it rep- resents the same challenge for other functional materials, e.g. capacitor materials (the production of a base-metal electrode capacitor), piezo-materials (the reduction of Pb losses), etc. A number of material-research laboratories have focused their research on reducing the sintering temperatures of func- tional materials. However, because of the lack of fundamen- tal knowledge about low-temperature sintering mechanisms researchers are forced to apply specific empirical principles for each particular material. Only a few attempts to explain the basic mechanisms of low-temperature sintering have been published so far, 1–4 and no general principles have been described. Many researchers have already investigated the low- temperature sintering of BaTiO 3 -based ceramics, however, they did not so far clearly explain all the reaction and sinter- ing mechanisms involved in the process. 1,2,5–7 As a rule, the investigators used lithium-fluorite salts as a sintering aid and agreed about the mechanism of incorporating the lithium into the titanium sites of BaTiO 3 . They assigned an important role in the reduction of the sintering temperature to fluorine ions, 0955-2219/$ – see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2005.06.026