Journal of the European Ceramic Society 37 (2017) 2011–2020 Contents lists available at www.sciencedirect.com Journal of the European Ceramic Society jo ur nal home p ag e: www. elsevier.com/locate/jeurceramsoc Electrical and thermal response of silicon oxycarbide materials obtained by spark plasma sintering M. Alejandra Mazo a,∗ , Aitana Tamayo a , Amador C. Caballero b , Juan Rubio a a Departamento de Química-Física de Superficies y Procesos, Instituto de Cerámica y Vidrio (CSIC), C/Kelsen 5, 28049, Madrid, Spain b Departamento de Electrocerámica, Instituto de Cerámica y Vidrio (CSIC), C/Kelsen 5, 28049, Madrid, Spain a r t i c l e i n f o Article history: Received 17 October 2016 Received in revised form 27 December 2016 Accepted 3 January 2017 Available online 17 January 2017 Keywords: Silicon oxycarbide material Spark plasma sintering HRTEM Electrical conductivity Thermal conductivity a b s t r a c t In order to obtain dense silicon oxycarbide (SiOC) materials that maintain the properties of glass, non- conventional spark plasma sintering was used to sinter SiOC powders from 1300 to 1700 ◦ C and with 40 MPa of pressure. The concurrence of electrical current, high pressure and low vacuum while the mate- rial is being heating produces a dense SiOC-derived material composed of a SiO 2 glassy matrix reinforced with SiC nanowires grown in situ, graphene-like carbon and turbostratic graphite. SiOC materials with high electrical and thermal response are obtained as a result of this new processing technique. Electrical resistivity undergoes an extraordinary decrease of five orders of magnitude from 1300 (1.0 × 10 5  m) to 1700 ◦ C (0.78  m), ranging from insulate to semiconductor material; and thermal conductivity increases by 30%, for these sintering temperatures. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction It is well known that silicon oxycarbide materials (SiOC) are composed of a metastable Si O C glassy matrix and graphite-like carbon (C free ) which is homogenously dispersed and embedded inside the matrix. At temperatures above 1200 ◦ C, this matrix decomposes into more thermodynamically stable species (i.e. SiO 2 and SiC) and the material is then formed by a new glassy matrix (mainly SiO 2 although some Si O C species are still present), a- SiC (a = amorphous) and highly disordered graphite-like carbon. As the temperature increases, both a-SiC and graphite-like carbon undergo incipient crystallization, while the SiO 2 matrix remains amorphous [1]. At higher temperatures the carbothermal reduction of silica with carbon also occurs in accordance with reaction (1). Several authors state that this reaction must be rewritten into reactions (2) and (3) [2,3], as gaseous SiO and CO have been found to be important intermediates of reaction (1) SiO 2 (s) + 3C(s) → SiC(s) + 2CO(g) (1) SiO 2 (s) + C(s) → SiO(g) + CO(g) (2) ∗ Corresponding author. E-mail address: sandra@icv.csic.es (M.A. Mazo). SiO(g) + 2C(s) → SiC(s) + CO(g) (3) The degree of conversion of SiO 2 into SiC is determined by a wide variety of factors of which the most important is the amount of C free in the material. An insufficient amount of C free favours the formation of SiO (g) (2), preventing the total conversion of SiO 2 into SiC [4]. Other factors which influence this conversion are the microstructure of the material [5,6], the temperature [7] and the pressure reached during the treatment [8]. Zhang et al. [9] found the formation of SiC nanowires inside the SiOC matrix during high-temperature annealing, via a Vapor-Solid (V-S) growth mechanism according to the following reactions: SiO 2 (s) + CO(g) → SiO(g) + CO 2 (g) (4) SiO(g) + CO(g) → SiC(s) + CO 2 (g) (5) As a consequence of the thermal decomposition of the SiOC matrix, SiC nanodots precipitate and can nucleate the growth of SiC nanowires within the SiOC matrix [9] without any additive. This may be very useful for developing SiOC matrix composites rein- forced with SiC nanowires grown in situ [9]. In another recent study, Pereira et al. [10] also grew SiC nanowires via a Vapor–Liquid–Solid (V–L–S) mechanism with the aid of a cobalt catalyst and polyethy- lene (PE) as a pore former in PE-containing Co-doped SiOC-derived materials. Metallic cobalt reacts with the silicon matrix to form a CoSi-derived alloy which acts as an active deposition site for the SiO http://dx.doi.org/10.1016/j.jeurceramsoc.2017.01.003 0955-2219/© 2017 Elsevier Ltd. All rights reserved.