Absence of ferroelectricity in BiMnO3 ceramics

TL;DR

This study uses phonon analysis and dielectric measurements to demonstrate that BiMnO3 ceramics are centrosymmetric and lack ferroelectricity, supporting the view that it is not multiferroic but antipolar ferromagnet.

Contribution

The paper provides experimental evidence confirming the centrosymmetric structure of BiMnO3 and its non-ferroelectric nature, aligning with recent theoretical predictions.

Findings

BiMnO3 has a centrosymmetric C2/c structure across 10-550 K.

Dielectric relaxation and anomalies suggest lattice anharmonicity and disorder.

No ferroelectric or antiferroelectric hysteresis observed in low-temperature studies.

Abstract

We performed factor-group analysis of all phonons in possible monoclinic C2/c and C2 structures of BiMnO3 and compared it with our experimental infrared and Raman spectra. We conclude that the crystal structure is centrosymmetric C2/c in the whole investigated temperature range from 10 to 550 K, therefore BiMnO3 cannot be ferroelectric. We revealed a dielectric relaxation in THz spectra above the structural phase transition taking place at T_C1=475 K giving evidence in strong lattice anharmonicity and a large dynamical disorder of Bi cations above T_C1. Step-like dielectric anomaly observed at T_C1 in THz permittivity reminds antiferroelectric phase transition. Nevertheless, the low-temperature dielectric studies did not reveal any antiferroelectric or ferroelectric hysteresis loop. Our experimental results support theoretical paper of P. Baettig et al. (J. Am. Chem. Soc. 129, 9854 (2007)) claiming that BiMnO3 is not multiferroic, but only antipolar ferromagnet.