Gateway toward efficient and miniaturized A 2 B 2 O 7 -type fluorite structure-based energy storage devices.

Defect fluorite structure with A 2 B 2 O 7 composition exhibits an intense potential for utilization in modern smart electrical devices. Efficient energy storage with low loss factors like leakage current makes them a prominent candidate for energy storage applications. Here we report a series of the form Nd 2-2 x La 2 x Ce 2 O 7 with x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0, synthesized via a sol-gel auto-combustion route. The fluorite structure of Nd 2 Ce 2 O 7 is slightly expanded with the incorporation of La without any phase transformation. A gradual replacement of Nd with La causes a decrease in grain size, which increases the surface energy and thus leads to grain agglomeration. The formation of exact composition without any impurity element is confirmed by energy-dispersive X-ray spectra. The polarization versus electric field loops, energy storage efficiency, leakage current, switching charge density, and normalized capacitance, which are considered key features of any ferroelectric material, are comprehensively examined. The highest energy storage efficiency, low leakage current, small switching charge density, and large value of normalized capacitance are observed for pure Nd 2 Ce 2 O 7 . This reveals the enormous potential of the fluorite family for efficient energy storage devices. The temperature-dependent magnetic analysis exhibited very low transition temperatures throughout the series.