Chin. Phys. Lett.  2021, Vol. 38 Issue (4): 047701    DOI: 10.1088/0256-307X/38/4/047701
 CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES |
Polarization Mechanism in Filled Tungsten Bronze Ba$_{4}$Eu$_{2}$Ti$_{4}$Nb$_{6}$O$_{30}$ with Pinched $P$–$E$ Hysteresis Loops
Lang Zhu , Xiao-Li Zhu*, Xiao-Qiang Liu , and Xiang-Ming Chen
School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
 Abstract Pinched $P$–$E$ hysteresis loops have been observed in filled tungsten bronze Ba$_{4}$Eu$_{2}$Ti$_{4}$Nb$_{6}$O$_{30}$, indicating the presence of novel polarization mechanisms. We investigate the evolution of polar order in filled tungsten bronze Ba$_{4}$Eu$_{2}$Ti$_{4}$Nb$_{6}$O$_{30}$, together with its dielectric properties over a wide temperature range, from 50 K to 773 K. The temperature dependences of the dielectric properties exhibit two low-temperature dielectric relaxations, at around 300 K (P1), and 100 K (P2), and a high temperature peak at 588 K with no frequency dispersion, indicating the ferroelectric transition temperature $T_{\rm c}$. Pinched $P$–$E$ loops are observed in the temperature range between the low temperature relaxation at P1, and the ferroelectric transition. On cooling, the pinched $P$–$E$ hysteresis loops open gradually, with increasing remnant polarization ($P_{\rm r}$). Two pairs of reversal electric fields indicate two types of polar reversal mechanisms, with an activated energy of 1.41 eV ($E_{1}$), and 0.94 eV ($E_{2}$), respectively. One corresponds to the field-induced transition from a nonpolar to a polar state, which dominates at a high temperature close to $T_{\rm c}$, while the other relates to the reversal of ferroelectric domains which stabilize gradually on cooling. At temperatures below 300 K, the polarization exhibits an evident decrease, probably related to the disruption of the polar order due to the dielectric relaxation at P1. Received: 20 November 2020      Published: 06 April 2021 Fund: Supported by the National Natural Science Foundation of China (Grant Nos. 51790493 and 51961145105).