(K_0.5(1+x)Bi_0.5)Bi₄Ti₄O₁₅ [KBT-10000x, 10000x = (−200)–7] were prepared by the conventional ceramic fabrication process using the KHCO₃ powder as the starting material. KBT-0 ceramic indicated high density ratio of higher than 95% and high resistivity of approximately 10¹² Ω·cm. A remanent polarization P_r, and coercive field E_c, are 10.4 µC/cm² and 70.8 kV/cm, respectively. Additionally, a high relative density ratio and resistivity exceeding 97% and approximately 10¹⁴ Ω·cm were obtained in K-poor KBT-(−100) ceramics derived from KHCO₃. This ceramic also indicated good ferroelectric and piezoelectric properties such as P_r of 12.6 µC/cm², piezoelectric constant d₃₃ of 16.0 pC/N and the mechanical quality factor Q_m of 2366, respectively.