Impact of BiBO₃, NaF and BiF₃ Substitution on the Thermoelectric Properties of Bi₂Ca₂Co₂O_y Ceramics

In this work, we studied the impact of (i) partial substitution of bismuth oxide (Bi2O3) by bismuth borate (BiBO3), (ii) dual-substitution of Bi2O3 by BiBO3 and sodium fluoride (NaF), and (iii) dual-substitution of Bi2O3 by BiBO3 and bismuth fluoride (BiF3) on the thermoelectric characteristics of Bi2Ca2Co2Oy layered cobaltite.Thermoelectric cobaltites were synthesized using the sol-gel method.The phase composition of prepared materials was examined by the X-ray diffraction (XRD) analysis.The values of power factor (PF) and figure of merit (ZT) were calculated through measurements of electrical resistivity (), Seebeck coefficient (S), and thermal conductivity (k).The XRD analysis confirms that all the samples consist of a nearly pure Bi2Ca2Co2Oy phase.When compared to the reference (pristine) sample, the dual NaF/BiBO3 substitution leads to a sharp decrease in due to the partial substitution of NaF for Bi2O3, which increases the concentration of charge carriers (holes).At the same time, partial substitution of BiF3 for Bi2O3 led to a decrease in hole concentration and, hence, an increase in .Seebeck coefficients were positive for all the samples, indicating p-type conductivity.The maximum PF and ZT values achieved in the NaF/BiBO3 co-substituted composition are 18% and 13% higher, respectively, than the reference Bi2Ca2Co2Oy.