Outstanding comprehensive energy storage performance in lead-free BiFeO3-based relaxor ferroelectric ceramics by multiple optimization design

Significantly Enhanced Energy Storage Performance of Lead-Free BiFeO3-Based Ceramics via Synergic Optimization Strategy

“…[1][2][3]12,13 (2) The introduction of NaTaO 3 helps to improve the relaxor behavior, leading to a slender P−E curve with remarkably reduced P r (Figure 1). (3) To optimize the E b of BiFeO 3 -based ceramics, the chemical doping [rare earth ion (such as La 3+ , Nd 3+ , Sm 3+ ) 14−16 and/or alkaline earth metal ion (Na + , Ba 2+ , Sr 2+ ) 11,17,18 substitution in Bi-site and transition-metal ions (such as Nb 5+ , Co 2+/3+ , Mn 2+ ) 19,20 substitution in Fe-site] is widely adopted to improve the sintering behavior, suppress leakage current, promote electrical homogeneity, and increase intrinsic band gap (E g ) and/or activation energy (E a ). 11,12,14 −17,19 The electrical homogeneity means the uniform distribution of conductivity and dielectric constant, which is conducive to delay the formation of a conductive pathway at a high field, resulting in higher E b .…”

“…Herein, the perovskite oxide NaTaO 3 is introduced into the 0.67BiFeO 3 –0.33BaTiO 3 matrix to form ternary ceramic (0.67 – x )­BiFeO 3 –0.33BaTiO 3 – x NaTaO 3 [expressed as (0.67 – x )­BF–0.33BT– x NT] based on the following considerations: (1) as a result of hybridization of electron orbitals between Bi 3+ and O 2– , BiFeO 3 -based ferroelectric ceramics generally exhibit very large P max (>40 μC/cm 3 for BiFeO 3 –BaTiO 3 ceramics), which outperforms other lead-free compositions. ,, In addition, the composition of 0.67BiFeO 3 –0.33BaTiO 3 ceramic is famous for its morphotropic phase boundary with high P max . − ,, (2) The introduction of NaTaO 3 helps to improve the relaxor behavior, leading to a slender P – E curve with remarkably reduced P r (Figure ). (3) To optimize the E b of BiFeO 3 -based ceramics, the chemical doping [rare earth ion (such as La 3+ , Nd 3+ , Sm 3+ ) − and/or alkaline earth metal ion (Na + , Ba 2+ , Sr 2+ ) ,, substitution in Bi-site and transition-metal ions (such as Nb 5+ , Co 2+/3+ , Mn 2+ ) , substitution in Fe-site] is widely adopted to improve the sintering behavior, suppress leakage current, promote electrical homogeneity, and increase intrinsic band gap ( E g ) and/or activation energy ( E a ). ,,− , The electrical homogeneity means the uniform distribution of conductivity and dielectric constant, which is conducive to delay the formation of a conductive pathway at a high field, resulting in higher E b . In addition, the microstructural modification is also widely reported to improve E b .…”

Improved Electric Breakdown Strength and Energy Storage Performances in La(Mg2/3Nb1/3)O3 and MnO2-Modified BiFeO3–SrTiO3 Ceramics

“…All the samples exhibit classic relaxation properties, proved by the frequency-dependent dielectric constant (ε r ) and a wide dielectric peak. With the increasing content of LMN, the dielectric peak becomes more dispersive and the value of ε r decreases monotonically, suggesting the improved relaxation degree, which is further confirmed by the modified Curie–Weiss law (insets in Figure a–c) , 1 ε normalr − 1 ε normalr , max = false( T − T normalm false) γ C where T m , γ, and C are the temperature corresponding to ε r,max , diffusion factor, and constant. It is well-known that the normal ferroelectrics and ideal relaxor ferroelectrics show the γ values of 1 and 2, respectively .…”

“…Among various dielectric materials, BiFeO 3 (BF)-based ceramics normally show large polarization due to the strong hybridization between the outermost electrons of Bi 3+ and O 2– . ,− For instance, Lu et al found that the 0.6BF-0.4ST ceramics with mixed rhombohedral and pseudocubic phases exhibited an enormous P max of 52.7 μC/cm 2 under 150 kV/cm . The relaxor strategy through introducing other perovskite end-members is demonstrated to be an effective approach to reduce the P r of ferroelectric ceramics. − For instance, Zhu et al prepared the Sr 0.7 Bi 0.2 TiO 3 (SBT)-modified 0.6BF-0.4ST ceramics and observed the significantly decreased P r owing to the construction of polar nanoregions (PNRs). Accordingly, a noteworthy W rec of 5.61 J/cm 3 and a high η of 86.76% were obtained under 440 kV/cm .…”

“…The high polarization of 0.6BF-0.4ST is expected to maintain the relatively large P max after doping. (3) The substitution of rare ions in the Bi-site and/or transition metal ions in the Fe-site is broadly reported to suppress the conductivity of BF ceramics. , In addition, MnO 2 , a well-known sintering aid, favors to optimize the sintering behavior and decrease the concentration of oxygen vacancies to suppress the conductivity of BF ceramics. , The above process can be described via defect equations 2 normalB normali normalB normali × + 3 normalO normalO × → 2 normalV normalB normali ‴ + 3 normalV normalO • • + normalB normali 2 normalO 3 4 normalF normale normalF normale × + 2 normalO normalO × → 4 normalF normale normalF normale ′ + 2 normalV normalO • • + normalO 2 4 normalM normaln normalF normale ′ + 2 normalV normalO • • + normalO 2 → 4 normalM normaln …”