Influence of Temperature and Pressure on the Densification, Microstructure, and Electrical Properties of the Dual-Phase System Y₂O₃-Doped ZrO₂ and RuO₂

Abstract

Dual-phase nanocomposite powders of 3Y-TZP (tetragonal-ZrO 2 doped with 3 mol % Y 2 O 3 ) and RuO 2 have been prepared and densified into compacts. The electrical conductivity of the densified compacts was correlated with the microstructure. Variations in the synthesis method and powder composition influenced the densification and resulting microstructure of the composites. Densification of the composites was sensitive to changes in experimental temperature/pressure conditions. Sinterforging the material in the range 1150-1250 °C and 50-100 MPa pressure resulted in dense (>95%) composites. The microstructure of the sinterforged materials revealed that macroscopic phase separation had occurred as a result of the aerial oxidation of RuO 2 species above ≈700 °C. Because of the volatilization of RuO 2 , the pores in the pressed powder compact became filled with large ruthenia grains during densification. The microstructure thus reflected the agglomerate structure of the starting powder. The "inhomogeneous" microstructure led to high electrical conductivity in the material. The electrical conductivity of the dense composites was measured by the fourpoint technique and conductivity values on the order of 1-6 × 10 3 S cm -1 were obtained. High electrical conductivity (4.4 × 10 3 S cm -1 ) could be obtained, even at relatively low RuO 2 contents of 15 mol %.

Dynamic shock compaction of a ZrO2–RuO2 electronic nanocomposite: toward functionally graded materials

“…Full densification (>98%) of this compact can readily be achieved under pressureless sintering (1450 °C) or sinterforging (1150 °C, 50 MPa) conditions, as we previously demonstrated [9]. In those cases, however, irreversible inhomogeneous microstructural changes were evident, caused by evaporation and condensation sequences of gaseous RuO 4 (formed from aerial oxidation of RuO 2 ) whereby the initial nano-sized powder grains were destroyed through rigorous aggregation and eventually replaced by growth of numerous micro-sized (1-5 µm) grains.…”

“…In those cases, however, irreversible inhomogeneous microstructural changes were evident, caused by evaporation and condensation sequences of gaseous RuO 4 (formed from aerial oxidation of RuO 2 ) whereby the initial nano-sized powder grains were destroyed through rigorous aggregation and eventually replaced by growth of numerous micro-sized (1-5 µm) grains. A sideeffect of this micro-sized grain microstructure was that it allowed for good electronic percolation pathways and showed metallic-like conduction, namely σ = 4.4 × 10 3 and 2.1 × 10 3 S cm -1 at 15 mol% [9] and 10 mol% RuO 2 [this work], respectively. These results are summarized in Table 1.…”

Preparations of CaRuO<SUB>3</SUB> Body by Plasma Sintering and Its Thermoelectric Properties

“…This might be caused by the second phase of RuO 2 because of its high conductivity (1:4 Â 10 6 Sm À1 at 293 K). Raming et al 15) reported that YSZ (Y 2 O 3 -stabilized ZrO 2 )-RuO 2 composite had high electrical conductivity due to agglomerated RuO 2 . However, the second phase of CaO in CRO at R Ru/Ca < 1:0 may result in the decrease in because CaO is an insulating material (<10 À8 Sm À1 at 293 K).…”

Rutile-type dense ceramics fabricated by pressureless sintering of Ti1−xRuxO2 powders prepared by sol–gel

“…It places restrictions on their possible applications. Raming et al 22 prepared dual-phase nanocomposite powders of tetragonal-ZrO 2 doped with 3 mol% Y 2 O 3 and RuO 2 and densified them into compacts by hot-pressing. However, the sinterforging or hot-pressing method is an expensive sintering method and is not always available in the laboratory.…”