In this work, we have focused on the influence of Gd 3+ substitution in structural, magnetic and electrical properties of cobalt ferrite synthesized by using sol-gel auto combustion method. The powder x-ray diffraction analysis reveals that the Gd-substituted cobalt ferrites crystallize in single phase spinel structure for lower concentrations of Gd 3+ , while a trace of GdFeO 3 appears as a minor phase for higher concentrations. Raman and Fourier transform infrared spectra confirm the formation of spinel structure. Furthermore, Raman analysis shows that the inversion degree of cobalt ferrite decreases with Gd 3+ doping. The field emission scanning electron microscopy images show that the substitution of small amount of Gd 3+ causes considerable reduction of grain size. Studies on magnetic properties reveal that the coercivity of Gdsubstituted cobalt ferrites enhances from 1265 Oe to 1635 Oe and the saturation magnetization decreases monotonically from 80 emu/g to 53.8 emu/g and the magnetocrystalline anisotropy constant increases from 5.8x10 5 erg/cm 3 to 2.23 x10 6 erg/cm 3 at 300 K. The electrical properties show that the Gd 3+ doped samples exhibit the high values of dielectric constant (616 at 100 Hz) and ac conductivity (4.83x10 -5 S/cm at 100 Hz) at room temperature. The activation energy is found to decrease from 0.408 to 0.347 eV in for the rise of Gd 3+ content. The impedance study 2 brings out role of bulk grain and grain-boundary towards the electrical resistance and capacitance of cobalt ferrite. Gd-substitution and nano size of cobalt ferrite enhance the electrical and magnetic properties which could ensure a higher memory storage capability. IntroductionSpinel ferrites with the general formula MFe 2 O 4 (M-Co, Ni, Mn and Zn etc.) are the most interesting magnetic oxides due to their superior electrical, magnetic and optical properties 1-8 .Among the spinel ferrites, cobalt ferrite is an attractive candidate due to its significant properties such as high coercivity, high electrical resistivity, moderate saturation magnetization, large magnetocrystalline anisotropy (~4x10 6 ergs/cm 3 ), good chemical stability and high Curie temperature (793 K) 9-16 . It is of significant technological interests due to its potential applications in targeted drug delivery systems 17, 18 , microwave devices 19, 20 , sensors 21 , catalysis 22, 23 and magnetic recording applications 9, 24 etc. Recently, the doping of small amount of trivalent rare earth cations in spinel ferrite has emerged as a promising strategy to improve the magnetic and electrical properties. Moreover, these properties are governed by the antiferromagnetic super exchange interaction between Fe 3+ -Fe 3+ ions; introducing small amount of trivalent rare earth (RE) ions into the spinel ferrite lattices will also induce RE 3+ -Fe 3+ interactions 25-30 . It is well known that the intrinsic properties of the spinel ferrite nanoparticles depend on the chemical composition and preparative methods 31, 32 . Spinel ferrites are prepared using several methods s...

to battery driven (electric) mobility. While a multibillion-dollar industry has come up catering various needs, the manifold consumption of Li-based resources has led to steep price rise and concerns over future geo-political tension due to its nonuniform geographic distribution. To combat this imminent issue, various alternative battery chemistries (termed as "Beyond Li-ion batteries") are widely pursued, particularly to replace Li-ion batteries in applications unrestricted by gravimetric and/or volumetric energy density. In this case, sodium-ion batteries (NIBs) are touted as the emerging futuristic battery chemistry owing to the widespread availability of sodium-based resources and well-understood electrochemical operation involving the Na + charge carriers. [1][2][3][4][5] In the quest to build robust sodiumion batteries, various 2D layered transition metal oxides and 3D polyanionic framework materials have been unraveled. While the oxide cathodes can deliver high theoretical (and reversible) capacity, they suffer from lower redox potential owing to strong covalence nature. [6] It is more so acute in case of Na-ion batteries considering the higher potential of Na/Na + (−2.71 V vs normal hydrogen electrode (NHE)) vis-à-vis Li/Li + (−3.03 V vs NHE). This issue can be circumvented by implementing polyanionic cathode materials with tunable crystal structure, robust framework providing safe operation and higher redox potential due to inductive effect. [7,8] Following the inductive effect principle, plethora of cathodes with polyanionic units [(XO 4 ) m n− : X = B, P, Si, S, W, Mo, As, Ti, V, etc.] have been discovered both for Li-ion and Na-ion batteries. [9,10] Moving a step further with polyanionic chemistry, off late, materials discovery has been realized by using different types of polyanion units. These subclass of materials are known as "mixed polyanionic" cathode materials, which can be designed by simultaneously having i) polyanionic units [(XO 4 ) m n− , X = P, S, V, etc.] along with other single anions [Y − = F − /OH − /O 2− /N 3− ], ii) different structural units of same polyanion units [(XO m ) (X 2 O m ), e.g., PO 4 -P 2 O 7 , BO 3 -B 2 O 5 , SO 4 -S 2 O 3 , etc.], and iii) two different oxyanionic [(XO 4 ) m n− ] units (e.g., PO 4 -SO 4 , PO 4 -NO 3 , PO 4 -CO 3 , etc.) as illustrated in Figure 1. These polyanionic combinations can lead to rich structural diversity and multi ple electron redox activity leading to robust electrochemical "Building better batteries" remains an ongoing process to cater diverse energy demands starting from small-scale consumer electronics to large-scale automobiles and grid storage. While Li-ion batteries have carried this burden over the last three decades, the ever-growing and highly diverse applications (based on size, energy-density, and stationary vs mobile usages) have led to an era of "beyond lithium-ion batteries." In this postlithium-battery era, sodium-ion batteries (NIBs) have emerged as a pragmatic option particularly for large-scale applications. They attract...

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Water‐splitting systems are essential for clean energy production. The oxygen reduction reaction (ORR) is a key reaction involved in water splitting, which requires a catalyst. The current work explores the possible application of sodium and potassium iron phosphates (AFePO4, A=Na and K) as electrocatalysts for ORR activity. These earth‐abundant iron phosphates were synthesized by the solution combustion synthesis (SCS) technique by using ascorbic acid both as fuel and reducing agent for Fe. The crystal structure was analyzed by Rietveld refinement. The formation of carbon coating was identified by thermogravimetric analysis and Raman spectroscopy. Electrocatalytic properties of AFePO4 were investigated in alkali electrolytes for the first time by using linear sweep voltammetry with a rotating disk electrode (RDE). The ORR activities of these alkali iron phosphates are comparable to that of the Pt/C system. The Tafel slope and electron transfer number of the alkali iron phosphates were calculated. The ORR activity of NaFePO4 was found to be better than KFePO4 and FePO4. This work demonstrates alkali iron phosphates as alternate cost‐effective, novel electrocatalysts for productive ORR activity in alkaline solution.