Influence of powder characteristics on the electrical resistivity of SiC ceramics

Abstract

Four types of commercially available SiC powders were hot-pressed with 1 wt % Dy 2 O 3 AlN additives in a 3:2 molar ratio. Three submicron-sized SiC powders could be densified so as to have a relative density higher than 98%, whereas a micron-sized SiC powder showed limited densification up to 93.5%. SiC ceramics fabricated from ¢-SiC powders exhibited electrical resistivities (³10 ¹1 ³·cm) that were lower than those from ¡-SiC powders (³10 1 ³·cm). The lower electrical resistivity of the SiC ceramics fabricated from ¢-SiC powders could be attributed to a higher carrier density and enhanced charge mobility when compared to the SiC ceramics from ¡-SiC powders.©2012 The Ceramic Society of Japan. All rights reserved.Key-words : SiC, Sintering, Electrical resistivity [Received January 5, 2012; Accepted February 28, 2012] Silicon carbide (SiC) is considered to be a suitable material for various structural applications such as mechanical seals, bearings, cylinder liners, armor plates, and mirror materials for astronomical telescopes due to its superior properties of high hardness, high temperature strength, and excellent resistance to wear and corrosion.1)6) In addition, SiC ceramics with or without a small amount of additives have attracted considerable attention for use in semiconductor processing, nuclear fusion reactors, and high temperature thermomechanical applications because of their excellent chemical and thermal stability and good mechanical properties.7)11) In the mid 1970s, Lange 12) first reported on the successful densification of SiC by liquid-phase sintering with the addition of Al 2 O 3 as a sintering additive. Since this innovative work, interest in liquid-phase sintered (LPS)-SiC has grown continuously because such materials exhibit better mechanical properties than solid-state sintered SiC ceramics.2),6),13)17) Methods for the successful densification of SiC ceramics with a smaller amount of sintering additives via liquid-phase sintering include (1) the use of colloidal processing for the homogeneous distribution of sintering additives 18),19) and (2) the addition of in situsynthesized nano-sized SiC into submicron-sized SiC powders. 20) In this study, the sinterability of four different commercially available SiC powders was investigated with the addition of 1 wt % AlNDy 2 O 3 additives by hot pressing. The effect of the SiC powder characteristics on the electrical resistivity of the hot-pressed SiC ceramics was also investigated. The AlNDy 2 O 3 additive system was selected because of the success of previous research on the densification of SiC with AlN-rare earth oxide systems 4),11) and the good chemical stability of Dy 2 O 3 at high temperatures in the presence of SiC. 21)Four types of commercially available SiC powders were used as starting materials; their characteristics are shown in Table 1. The crystalline phase of powders A1 and A2 is ¡-SiC, while that of B1 and B2 is ¢-SiC. 22) The mixtures were dried, sieved (60 mesh), pressed uniaxially, and heat-treated at 200°C for 2 h in air so ...

Effects of Y2O3–RE2O3 (RE = Sm, Gd, Lu) Additives on Electrical and Thermal Properties of Silicon Carbide Ceramics

“…The electrical conductivities obtained (1.8 × 10 3 –6.7 × 10 3 (Ω·m) −1 ) for the SiC ceramics fabricated in this study (SYRE) were higher than those of both argon‐sintered [3.3 × 10 −12 –1.3 × 10 2 (Ω·m) −1 ] and vacuum‐sintered SiC ceramics [1.8 × 10 0 –2.9 × 10 1 (Ω·m) −1 ], and were comparable to those of nitrogen‐sintered SiC ceramics . Most notably, the electrical conductivity [6.7 × 10 3 (Ω·m) −1 ] of the SYLu is higher than those (3.4 × 10 1 –2.7 × 10 3 (Ω·m) −1 ] of SiC ceramics sintered with AlN–RE 2 O 3 , indicating that the Y 2 O 3 –RE 2 O 3 additive systems have a greater potential than the AlN–RE 2 O 3 additive systems to increase the electrical conductivity of LPS‐SiC ceramics. The high electrical conductivity [~10 3 (Ω·m) −1 ] of the present SYRE specimens can be attributed to the heavy doping of nitrogen in SiC lattice (1020–1280 ppm), a small amount of electrically insulating sintering additives (2 vol%), and the confinement of an electrically insulating oxide additive (RE 2 O 3 ) in the junction areas among the grains (the white phase in Fig.…”

“…The electrical conductivities of SiC ceramics sintered in a nitrogen atmosphere are as follows: 1.3 × 10 3 (Ω·m) −1 for SiC ceramics sintered with 2 vol% Y 2 O 3 ; 3.0 × 10 4 (Ω·m) −1 for SiC ceramics sintered with 19.3 wt% yttrium nitrate; 1.4 × 10 3 (Ω·m) −1 for SiC ceramics sintered with 2 wt% AlN–Y 2 O 3 ; 1.7 × 10 3 (Ω·m) −1 for SiC ceramics sintered with 0.5 wt% AlN–Nd 2 O 3 ; 3.4 × 10 1 (Ω·m) −1 for SiC ceramics sintered with 1 wt% AlN–Lu 2 O 3 ; 1.0 × 10 3 (Ω·m) −1 for SiC ceramics sintered with 1 wt% AlN–Dy 2 O 3 ; 2.7 × 10 3 (Ω·m) −1 for SiC ceramics sintered with 1 wt% AlN–Eu 2 O 3 ; and 1.3 × 10 3 (Ω·m) −1 for SiC ceramics sintered with 1 wt% AlN–Ho 2 O 3 …”

“…The electrical conductivity of polycrystalline SiC ceramics is strongly dependent on additive composition and sintering atmosphere. [14][15][16][17][18] The electrical conductivities of SiC ceramics sintered in an argon atmosphere are as follows: 5.0 9 10 À3 (ΩÁm) À1 for SiC ceramics sintered with 1 wt% B; 19 2 9 10 À2 -1.3 9 10 2 (ΩÁm) À1 for SiC ceramics sintered with 1 wt% Al; 19,20 3.3 9 10 À12 (ΩÁm) À1 for SiC ceramics sintered with 1 wt% Be; 19 1.0 9 10 À9 (ΩÁm) À1 for SiC ceramics sintered with 10 wt% Al 2 O 3 -Y 2 O 3 ; 21 1.0 9 10 0 -7.7 9 10 À9 (ΩÁm) À1 for SiC ceramics sintered with 3 vol% AlN-Y 3 Al 5 O 12 ; 17,22 2.8 9 10 À10 (ΩÁm) À1 for SiC ceramics sintered with 7 wt% Al 2 O 3 -Er 2 O 3 ; 23 5.6 9 10 À7 (ΩÁm) À1 for SiC ceramics sintered with 7 wt% Y 2 O 3 -Al 2 O 3 -CaO; 15 9.1 9 10 À4 (ΩÁm) À1 for SiC ceramics sintered with 10 wt% 15 The electrical conductivities of SiC ceramics sintered in a nitrogen atmosphere are as follows: 1.3 9 10 3 (ΩÁm) À1 for SiC ceramics sintered with 2 vol% Y 2 O 3 ; 13 3.0 9 10 4 (ΩÁm) À1 for SiC ceramics sintered with 19.3 wt% yttrium nitrate; 16 1.4 9 10 3 (ΩÁm) À1 for SiC ceramics sintered with 2 wt% AlN-Y 2 O 3 ; 24 1.7 9 10 3 (ΩÁm) À1 for SiC ceramics sintered with 0.5 wt% AlN-Nd 2 O 3 ; 25 3.4 9 10 1 (ΩÁm) À1 for SiC ceramics sintered with 1 wt% AlN-Lu 2 O 3 ; 26 1.0 9 10 3 (ΩÁm) À1 for SiC ceramics sintered with 1 wt% AlN-Dy 2 O 3 ; 27 2.7 9 10 3 (ΩÁm) À1 for SiC ceramics sintered with 1 wt% AlN-Eu 2 O 3 ; 26 and 1.3 9 10 3 (ΩÁm) À1 for SiC ceramics sintered with 1 wt% AlN-Ho 2 O 3 . 26 The electrical conductivities of SiC ceramics sintered in a vacuum are as follows: 2.9 9 10 1 (ΩÁm) À1 for SiC ceramics sintered with 1 wt% Y 2 O 3 -La 2 O 3 and 1.8 9 10 0 (ΩÁm) À1 for SiC ceramics sintered with 1 wt% Y 2 O 3 -Nd 2 O 3 .…”