Structural correlation to magnetodielectricity and coercivity at room temperature in multiferroic Bi0.7Ba0.3−xPbxFeO3

Structural correlation to spontaneous electric and magnetic order in multiferroic LiCr0.99Fe0.01O2

“…Multiferroicity usually involves breaking of inversion symmetry during ferro(antiferro)electric order and is usually associated with first order structural change. Thus elastic coupling is intimately correlated to spontaneous electric and/or magnetic ordering of multiferroic materials [5][6][7][8][9] .…”

Tuning Ferroelectric, Dielectric, and Magnetic Properties of BiFeO3 Ceramics by Ca and Pb Co‐Doping

“…The increase of the dielectric constants with increasing Ca/Pb concentration in the higher frequency ranges may be attributed to the reduction of defects (V O 2+ and V Bi 3− ) during heat treatment, which may promote the formation of intrinsic 6s 2 lone electrons of the Bi ions . In addition, the contraction of unit cell volume with the increase in doping content x leads to an increase in the packing fraction as described by Böttcher's formula, which may be correlated with the increase of the dielectric constants . Meanwhile, as revealed in Figure a–d, the densification of the BFO ceramics after Ca/Pb co‐doping is one direct evidence of the increased packing fraction for the increased dielectric constants.…”

“…The Fe–O–Fe bond angles increase as the structural transition from rhombohedral to cubic induced by Ca/Pb co‐doping, eventually alters tilting of FeO 6 octahedra and enhances the double exchange Fe 2+ –O–Fe 3+ interaction. The changes of tilting of FeO 6 octahedra affect the spin canting, releasing the potential ferromagnetic component which is manifested by the increased coercivity in Figure a . Therefore, the obviously enhanced magnetization with Ca/Pb content increasing may originate from the double exchange Fe 2+ –O–Fe 3+ interaction and spin canting manipulated by Fe–O–Fe bond angles during the structural transition in Bi 1−x (Ca 1/2 Pb 1/2 ) x FeO 3 ceramics.…”

“…The shrinkages of the lattice constant and unit cell volume are caused by the decrease of A‐site average ionic radius, indicating that Pb ions are introduced into BFO ceramics as Pb 4+ (0.775 Å) ions rather than Pb 2+ (1.19 Å) ones under the existence of Ca 2+ ions, due to that only the average ionic radius of Ca 2+ (1.00 Å) and Pb 4+ ions is less than that of Bi 3+ ions (1.03 Å). It is worth to notice that the normalized unit cell volume decreases from 62.10 to 61.03 Å 3 when it is scaled by Z value, besides the crystal structure changing from a rhombohedral to a cubic one, indicating the average Fe–O bond length decrease and Fe–O–Fe bond angle increase, leading to changes of FeO 6 octahedra tilt and modifying the magnetic properties of BFO . Besides, the possible formation of tetragonal distortion within the cubic structure induced by Ca doping may also contribute to the ferroelectric polarization …”

“…When x ≥ 0.2, tan δ follows a similar trend like that of ϵ r . The reduction of ϵ r at low frequency can be attributed to the Maxwell–Wagner type space charge polarization and grain boundary effect, which cannot be neglected . At low frequencies, the space charges in the samples, including the conversion of Fe 3+ to Fe 2+ as well as the distribution of the lone electron pair of Bi 3+ ions, are rapid enough to follow the frequencies of the applied field and lead to a large dielectric constant.…”