Double hysteresis loops and large negative and positive electrocaloric effects in tetragonal ferroelectrics

• Published in: Physical chemistry chemical physics : PCCP Vol. 17; no. 37; pp. 23897 - 2398
• Main Authors: Wu, Hong-Hui, Zhu, Jiaming, Zhang, Tong-Yi
• Format: Journal Article
• Language: English
• Published: England 01.01.2015
• Subjects: Compressing; Crystal structure; Curie temperature; Ferroelectric materials; Hysteresis loops; Nanoparticles; Phase transformations; Polarization
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c5cp02765a

Phase field modelling and thermodynamic analysis are employed to investigate depolarization and compression induced large negative and positive electrocaloric effects (ECEs) in ferroelectric tetragonal crystalline nanoparticles. The results show that double-hysteresis loops of polarization versus electric field dominate at temperatures below the Curie temperature of the ferroelectric material, when the mechanical compression exceeds a critical value. In addition to the mechanism of pseudo-first-order phase transition (PFOPT), the double-hysteresis loops are also caused by the abrupt rise of macroscopic polarization from the abc phase to the c phase or the sudden fall of macroscopic polarization from the c phase to the abc phase when the temperature increases. This phenomenon is called the electric-field-induced-pseudo-phase transition (EFIPPT) in the present study. Similar to the two types of PFOPTs, the two types of EFIPPTs cause large negative and positive ECEs, respectively, and give the maximum absolute values of negative and positive adiabatic temperature change (ATC Δ T ). The temperature associated with the maximum absolute value of negative ATC Δ T is lower than that associated with the maximum positive ATC Δ T . Both maximum absolute values of ATC Δ T s change with the variation in the magnitude of an applied electric field and depend greatly on the compression intensity. The double polarization-electric-field hysteresis loops are signals of the coexistence of positive and negative electrocaloric effects in one tetragonal ferroelectric material. The peak temperature of adiabatic temperature change can be tuned by an external electric field and mechanical compression.