Lead-free pyroelectric materials for environmentally friendly solid-state cooling systems

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Pooladvand, Hojat (2018). Lead-free pyroelectric materials for environmentally friendly solid-state cooling systems. University of Birmingham. Ph.D.

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Abstract

Due to some environmental problems for using the common cooling system which works based on the compressor air and cooling gas (Freon), researchers have focused on another type of it. One of the newest methods is using electrocaloric materials to make a cooling system. Electrocaloric effect (ECE) is the reverse of the pyroelectricity which means that the ability of the dielectric materials to change their temperature under electric field. Two ferroelectric materials were selected for this project: BCZT (Ba0.85Ca0.15Ti0.9Zr0.1O3) as a normal ferroelectric and BNT – BT (94 mol% Bi0.5Na0.5TiO3 – 6 mol% BaTiO3) as a relaxor ferroelectric.

The results for BCZT shows the best properties with a relative density of 96.1%, the grain size of 32µm, d33 of 410 pC/N and kp of 46% for sintered sample at 1450℃. The highest ECE (∆T= 0.97) was achieved for BCZT sintered at 1450℃ (∆T= 0.97). The best properties were founded at BNT-BT sintered at 1125℃ with a relative density of 97%, the grain size of 3.2µm, d33 of 165 pC/N and kp of 47%. BNT-BT shows high ECE ∆T= -2.91 and -2.1℃ for sintered sample at 1125 and 1150℃ respectively under 50 kV/cm which due to two step calcination process is higher than previous researchers.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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