PhD Thesis Colloquium: Mr. Getaw Abebe Tina (29/05/26)
Thesis title:
Effects of oxygen deficient chemical modifications on the structure and properties of BaTiO3 and Na1/2Bi1/2TiO3-based lead-free Piezoceramics
Faculty advisor(s):
Prof. Rajeev Ranjan
When?
29th May, 2026 (Friday), 04:00 PM (India Standard Time)
Where
KPA Auditorium, Department of Materials Engineering
Abstract
Perovskite (ABO3) piezoelectric ceramics are widely studied for applications in actuators, sensors, transducers, ferroelectric memories and energy storage devices. Although Pb(Zr, Ti)O3 (PZT) remains the benchmark due to its superior piezoelectric performance and wide operating temperature range, environmental concerns over lead toxicity have driven research into lead-free alternatives such as K1/2Na1/2NbO3 (KNN), BiFeO3 (BFO), Na1/2Bi1/2TiO3 (NBT) and BaTiO3 (BT) piezoceramics. Among these, BT and NBT have certain benefits such as ease of reproducibility of properties, which are lacking in BFO and KNN-based systems. BaTiO3, the first perovskite ferroelectric ceramic, has been studied since World War II and exhibits moderate piezoelectric performance (d33) and a Curie temperature (Tc), but its properties remain inferior to PZT-based ceramics. Most attempts at improving the d33 of BT by inducing inter-ferroelectric instability and coexistence of ferroelectric phase at room temperature via chemical modifications significantly reduces the Tc. Beyond this, a 6.5 mol% tetragonal BT solid solution with rhombohedral NBT forms a morphotropic phase boundary, NBT-6.5BT, providing another way to enhance NBT’s properties. However, widely reported results show that chemically modified BT and NBT-based piezoceramics exhibit a common trend: an enhancement of d33 and/or electrostrain, accompanied by a significant reduction in the Curie temperature and depolarization temperature (Td) to near room temperature, limiting their practical applications. In this thesis, we have studied the effect of the oxygen-deficient BaAlO2.5 modification and sintering temperature on the structure-property correlations in BT and NBT-based systems. Structural, microstructural, and electrical properties analyses were carried out to comprehensively understand this phenomenon. Furthermore, field-dependent in situ x-ray diffraction, x-ray photoelectron spectroscopy, and thickness-dependent electrostrain measurements were employed to investigate the role of oxygen vacancies in stabilizing domain switching and regulating electrostrain behavior. An important finding of this work is to show that it is possible to increased both the Curie point and the piezoelectric response by a controlled modulation of oxygen deficiency.