Study of Co-Doped K 2 Ti 6 O 13 Lead-Free Ceramic for Positive Temperature Coefficient Thermistor Applications.

Cobalt-doped potassium hexa-titanate (Co_x:K₂Ti₆O₁₃ (x = 0.05, 0.10, 0.15 mole%)) ceramics were synthesized by the solid-state reaction method. The XRD patterns confirmed single-phase development in a monoclinic symmetry of various samples, and they were used for different structural calculations of Co_x:K₂Ti₆O₁₃ ceramics. The dielectric constant, tanδ, electrical modulus, and ac conductivity of Co-doped K₂Ti₆O₁₃ were studied in the temperature range of 100–500 °C. Anomalies were observed in graphs of the dielectric constant versus temperature, showing the transition phase in the studied samples. Dielectric peaks at transition temperature decreased with an increasing frequency, and the peaks shifted toward higher temperatures, illustrating the relaxation of the dielectric materials. The composition with x = 0.10 showed low dielectric loss and a higher dielectric constant and can be utilized for high-temperature dielectric material. Small doping of cobalt improved the ac conductivity of K₂Ti₆O₁₃ ceramics due to the increase in the spin–phonon interaction and dominant electron hopping conduction; however, the conductivity diminished with substantial doping because of the contraction of the tunnel space and ambushing of conduction electrons. The uniqueness of this study is in the high dielectric optimization of lead-free ceramic Co_x:K₂Ti₆O₁₃ and the discovery of positive temperature coefficients of the resistivity of these ceramic samples. [ABSTRACT FROM AUTHOR]