Effects of morphotropic phase boundary transitions and structural transformations on Olsen cycle assisted thermo-electrical energy conversion: A case study on Bi_0.5Na_0.5TiO₃-xBaTiO₃ system

Abstract

This article reports the peculiarity in the thermo-electrical energy conversion (by Olsen cycle) capability of Bi_0.5Na_0.5TiO₃-xBaTiO₃ (BNT-BT) system caused by the coupled effect of structural transformations and phase transitions in vicinity of the morphotropic phase boundary (MPB). The calculated maximum energy density estimated for nearly identical ambient conditions for MPB (x = 0.06) lies in the range of 40–110 J/L (40–110 kJ/m³) while moving away from the MPB the same elevates dramatically on both the ends. The utmost energy density found in system is 1000 J/L (1000 kJ/m³) for BNT-0.3BT (temperature range: 42.6–108.7°C; applied electric field: 0–6.5 MV/m). This energy density is significantly higher than the reported thermo-electrical energy generation (680 kJ/m³) using negative electrocaloric effect in BNT-xBT systems. It is found that ferroelectric to antiferroelectric transition as well as transformation suppresses harvested energy density at MPB. Contemporary, rhombohedral to tetrahedral transitions contributes towards enhancement in the energy harnessing capability of the system. Consequently, it is revealed that in contrast to the rombohedral phase (a = b = c) the non-centro symmetric disturbances caused by thermal fluctuations in tetrahedral phase (a≠c) are higher and facilitate the domain wall switching leading to magnification of energy density.

KEYWORDS:

• MPB; energy harvesting; modified Olsen cycle; peculiar loop shift; BNT-BT