Thermoelectric transport properties of BaFe₂Fe₁₆O₂₇ hexaferrites

Exploring new materials with earth-abundant and low-toxicity elements has been a long-standing goal in thermoelectrics. Hexaferrites, a family of environmentally friendly oxides, exhibit complex and tunable structures and excellent magnetic properties, but receive limited attention as potential thermoelectric materials. Here in this study, we systematically investigated the thermoelectric transport properties of W-type hexaferrites BaFe₂Fe₁₆O₂₇ and the cobalt-substituted derivatives prepared by sintering in the nitrogen atmosphere. These materials exhibit an n-type conduction behavior and cobalt substitution can tune the electrical transport properties effectively. Low-temperature specific heat capacity analysis unravels the existence of low-energy optical phonons that contribute to damping the heat transport. Low room temperature thermal conductivity of 1.27 W m^-1 K^-1 is obtained, and the role of cobalt substitution on the thermal conductivity reduction is rationalized by the Debye-Callaway model. This study ‌enlightens the investigation of the thermoelectric transport properties of W-type hexaferrites BaFe2Fe₁6O₂₇ and extends the scope of new thermoelectric compounds.