Phase transitions and thermal expansion in pyroelectric energy conversion

This paper elucidates dynamic effects of phase transitions and thermal expansion on pyroelectric energy conversion. The Olsen cycle was performed on [001]-oriented 0:72PbMg1=3Nb2=3O30:28PbTiO3 (PMN-28PT) single crystals at different frequencies with electric field cycled between 0.2 and 0.75 MV/m and temperature between 22 and 140 C. The measured energy density more than doubled as frequency increased from 0.0173 to 0.0211 Hz. This was attributed to secondary pyroelectric effect caused by thermal expansion. At 0.0211 Hz, the samples transitioned from pseudocubic to highly polarized tetragonal phase during cooling. At lower frequency, it underwent additional phase transition from tetragonal to less polarized monoclinic phase. VC 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4776668]