Temperature and field-dependent electrical property and energy density correlations studies in KNN-modified NBT–KBT solid solution ceramics

Ceramics of solid solutions of (1 − x − y )(Na 0.5 Bi 0.5 )TiO 3 − x (K 0.5 Bi 0.5 )TiO 3 − y (K 0.5 Na 0.5 )NbO 3 ( x = 0.20, y = 0.00, 0.05, 0.10) were successfully prepared using a conventional solid-state reaction method. Preliminary investigations of the structural, dielectric, ferroelectric, and field-dependent energy density properties were performed for all synthesized samples. The crystal structure of the undoped NBT–KBT compound was stabilized in the dual phase of both rhombohedral and tetragonal (MPB) regions at RT. With a higher substitution concentration (K 0.5 Na 0.5 )NbO 3 composition was examined as tetragonal with P4bm structure at room temperature. All solid solutions stabilize the tetragonal phase and broaden the temperature range of the large tetragonal phase over wide intervals. In temperature-dependent dielectric property investigation, observation of two abnormal peaks corresponding to depolarization temperature ( T_d ) and Curie temperature ( T_m ) at the range of 75–90 °C and 295–320 °C. The shift of T_d towards low temperature and T_m towards high temperature was noted with the substitution of (K 0.5 Na 0.5 )NbO 3 concentration in the NBT–KBT host lattice. A slim symmetric loop character with reasonable saturation ( P_s ) and remnant ( P_r ) polarization values was observed for all measured samples and was enhanced with substituent compounds. The dielectric phase transitions (i.e., Para-Ferro) with a correlation of electrical property study by impedance and conductivity spectroscopy was performed over a wide frequency range at various temperatures using Nyquist diagram. Temperature-dependent impedance spectroscopy studies showed grain boundary dominance by substituting KNN in the NBT–KBT ceramics. In addition, a typical conversion of the positive temperature coefficient to the negative temperature coefficient of resistance (NTCR) behavior was observed in the impedance studies i.e., insulating to semiconductor behavior for all measured samples.