Dielectric and Mössbauer Studies of High-Permittivity BaFe_1/2Nb_1/2O₃Ceramics with Cubic and Monoclinic Perovskite Structures

Variation of Dielectric and Electrical Properties of Zr-Substituted Lead Calcium Iron Niobate with Temperature and Frequency

“…However, the ferroelectric phase transitions for the synthesized samples have been reported well below room temperature. 1,8,9 Very similar frequency-dependent e r (T) maxima, was reported by Raevski et al 24 for non-ferroelectric Ba(Fe 1/2 Nb 1/2 )O 3 ceramics being attributed to the relaxation due to oxygen vacancies. Additionally, the relative permittivity values at room temperature are smaller than 100, which is not typical of relaxor ferroelectrics or ferroelectrics with diffused phase transition.…”

“…Additionally, the relative permittivity values at room temperature are smaller than 100, which is not typical of relaxor ferroelectrics or ferroelectrics with diffused phase transition. 24 The observed anomalies of relative permittivity seems to be due to the partial reduction of the iron valance state from Fe 3+ to Fe 2+ at high temperature, thereby generating oxygen vacancies. [23][24][25] To confirm these results, ferroelectric loop measurements of (Pb 0.45 Ca 0.55 )(Fe 0.5 Nb 0.5 ) 1Ày Zr y O 3 , 0.00 £ y £ 0.15 solid solutions were carried out at room temperature as shown in Fig.…”

Giant low frequency dielectric tunability in high-k Ba(Fe1/2Nb1/2)O3 ceramics at room temperature

“…1,2 Similar to the high permittivity observed in CaCu 3 Ti 4 O 12 ͑CCTO͒, 3 these AFN oxides were reported to have a giant dielectric constant ͑Ͼ10 4 ͒ and show weak temperature dependence over a wide temperature range of 100-400 K. [4][5][6][7][8][9][10][11][12][13] It has been clarified that unlike Pb͑Fe 1/2 B 1/2 ͒O 3 ͑B = Nb, Ta͒, AFN shows no ferroelectricity. However, there are two typical dielectric relaxations in AFN ceramics, a Debye-type relaxation at low temperatures ͑50-300 K͒ and a relaxorlike relaxation with strong frequency dispersion at relatively high temperatures ͑400-700 K͒.…”

“…[4][5][6] The former relaxation can be explained by a polaronlike model and the latter can be attributed to the oxygen defect induced dielectric anomaly. 4,9 Ba͑Fe 1/2 Nb 1/2 ͒O 3 ͑BFN͒ is antiferromagnetic with a weak ferromagnetic behavior at 5 K. 1,2 Sinha et al 10,11 attributed the giant dielectric response to a ferroelectric relaxor nature in BFN. However, first-principles calculations show that BFN is not a ferroelectric.…”

“…12 Instead, BFN is a cubic ͑a = 0.4045 nm, space group Pm3m͒ or a monoclinic perovskite depending on the sintering conditions. [4][5][6][7][8][9][10][11][12] Compared to the intensively investigated CCTO, which has similar dielectric properties, BFN is much less investigated, especially on its microstructure.…”