Forming thermodynamics, structure, and electrical conductivity of TiCxOy compounds fabricated through the carbothermal reduction process

Abstract

In this study, TiCxOy was fabricated using TiO2 as a Ti source through a carbothermic reduction process in an Ar atmosphere. Six reaction types were considered during the fabrication process. Based on thermodynamic analysis, the reduction of TiO2 to TiCxOy could only be realized through the first or second reaction type, involving the direct carbothermal reduction and simultaneous CO production. The third and fourth reaction types, which also involved the direct carbothermal reduction with simultaneous CO2 release, could only reduce TiO2 to TinO2n−1 (n≥2), not to TiCxOy. The fifth and sixth reaction types could not occur. The C content in the raw material and the sintering temperature had significant effects on the structures and electrical conductivities of the samples. The TiCxOy phase began to form in the samples sintered at 1673 K with a C/TiO2 mole ratio of 2 and transformed into a single TiCxOy phase completely at 1823 K according to X-ray diffraction results. The TiCxOy samples crystallized with a layered formation structure had a coral shape, and Ti, C, and O were distributed evenly in the samples according to scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy analyses. High-resolution X-ray photoelectron spectroscopy results showed that Ti existed in the samples with II, III, and IV valence states. The electrical resistivity decreased with the increase in the C content and sintering temperature. The mean resistivity and conductivity of the fabricated samples with a single TiCxOy phase were determined to be 5.04×10−5 Ω m and 1.99×104 S m−1, respectively, through four-probe measurements. Theoretically, TiCxOy proved to be a good electrical conductor through the analysis of the band structure and the density of states based on density functional theory calculations, which agreed with the experimental results.