A discrete tetrahedral indium cage, {[In 12 (μ 3 -OH) 4 (HCO 2 ) 24 (tcma) 4 ]} (In 12 -GL), was synthesized solvothermally by the reaction of indium nitrate with the tripodal tricarboxylic acid ligand N,N,N-tris{(2′-carboxy[1,1′-biphenyl]-4yl)methyl}methylammonium chloride ([H 3 tcma] + Cl). This cage consists of four trimeric units [In 3 (μ 3 -OH)(μ 2 -CO 2 ) 3 (μ 2 -HCO 2 ) 3 ] and four [tcma] 2− ligands, which all perform as 3-connection nodes to bridge each other, resulting in a tetrahedral cage structure. The trimeric unit [In 3 (μ 3 -OH)(μ 2 -CO 2 ) 3 (μ 2 -HCO 2 ) 3 ] is observed for the first time in the family of In-based metal−organic structures and can be considered as an evolution of a 6-connected [In 3 (μ 3 -O)(μ 2 -CO 2 ) 6 ] unit. Each In 3+ is terminally coordinated by a μ 1 -HCO 2 group. This cage contains potential Lewis acidic/basic active sites endowed by In 3+ ions as Lewis acidic sites and the uncoordinated oxygen atoms of μ 1 -HCO 2 moieties as Lewis basic sites and was explored as an effective heterogeneous catalyst in the cycloaddition of CO 2 with epoxides and the Strecker reaction for amino nitriles. These catalytic reactions were deduced to happen on the surface of the In 12 -GL cage.

The importance of electroceramics is well-recognized in applications of high energy storage density of dielectric ceramic capacitors. Despite the excellent properties, lead-free alternatives are highly desirous owing to their environmental friendliness for energy storage applications. Herein, we provide a facile synthesis of lead-free ferroelectric ceramic perovskite material demonstrating enhanced energy storage density. The ceramic material with a series of composition (1-z) (0.94Na0.5Bi0.5TiO3-0.06BaTiO3)-zNd0.33NbO3, denoted as NBT-BT-zNN, where, z = 0.00, 0.02, 0.04, 0.06, and 0.08 are synthesized by the conventional solid-state mix oxide route. Microphases, microstructures, and energy storage characteristics of the as-synthesized ceramic compositions were determined by advanced ceramic techniques. Powder X-ray diffraction analysis reveals pure single perovskite phases for z = 0 and 0.02, and secondary phases of Bi2Ti2O7 appeared for z = 0.04 and 0.08. Furthermore, scanning electron microscopy analysis demonstrates packed-shaped microstructures with a reduced grain size for these ceramic compositions. The coercive field (Ec) and remnant polarization (Pr) deduced from polarization vs. electric field hysteresis loops determined using an LCR meter demonstrate decreasing trends with the increasing z content for each composition. Consequently, the maximum energy storage density of 3.2 J/cm3, the recoverable stored energy of 2.01 J/cm3, and the efficiency of 62.5% were obtained for the z content of 2 mol% at an applied electric field of 250 kV/cm. This work demonstrates important development in ceramic perovskite for high power energy storage density and efficiency in dielectric capacitors in high-temperature environments. The aforementioned method makes it feasible to modify a binary ceramic composition into a ternary system with highly enhanced energy storage characteristics by incorporating rare earth metals with transition metal oxides in appropriate proportions.

Lead-based electro-ceramic compositions are excellent energy storage materials used for high-energy storage density applications in dielectric ceramic capacitors. However, these materials have lead contents in their compositions, making them toxic, with a negative impact on human health and the environment. For this reason, we synthesized a lead-free bismuth-based electro-ceramic perovskite, 0.80(0.92Bi1/5Na1/5TiO3-0.08BaTiO3)-0.20(Na0.73Bi0.09NbO3−xTa2O5), abbreviated (BNT-BT-NBN1−xTx), from mixed oxides with doping of tantalum (Ta) at different concentrations, using a conventional solid-state reaction method. The effects of Ta doping on the phase evolution, microstructure development, and energy storage applications were investigated. Detailed powder X-ray diffraction analysis revealed a pure perovskite phase with Ta doping at ≤0.05. Furthermore, it was observed that excessive addition of Ta has been resulted in secondary phase generation. Scanning electron microscopy validated the development of dense microstructures with a reduced grain size for the Ta concentration of ≤0.01. Electrochemical analysis revealed a maximum polarization (Pm) of ~22 µC/cm2 and a recoverable energy density of 1.57 J/cm3 with 80% efficiency for Ta doping at 0.05 with an applied field of 175 kV/cm. These results demonstrate the development of enhanced ferroelectric characteristics in an as-synthesized electro-ceramic perovskite for high-energy storage density applications in electro-ceramic capacitors.