Temperature-dependent electrical transport behavior and structural evolution in hollandite-type titanium-based oxide

Electrical transport behavior and structural characteristics directly determine the use of functional ceramic materials in electronic information storage, catalytic conversion, and energy field applications. However, these properties are poorly understood because most of the relevant experiments were performed in a rather narrow temperature range. Herein, we used hollandite-type K_xTi₈O₁₆ as an example to systematically study the temperature-dependent structure and electrical transport properties in a wide temperature range from 25 to 900°C. The electrical transport involves both potassium ionic conduction and electronic conduction. With increasing temperature, the ionic conductivity increases below 800°C and decreases above 800°C. The electronic conductivity displays two maxima at 0.15 S/cm at 400°C and 5.2 × 10⁻⁴ S/cm at 800°C. These interesting variations in the conductivities are related to the presence of Ti³⁺ and the structural transformation from hollandite to a mixture of rutile and jeppeite. The findings reported herein support the potential application of titanium-based hollandites and provide an understanding of the electrical transport properties of functional ceramic materials.