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The crystal structure, cryogenic magnetic properties, and magnetocaloric performance of double perovskite Eu2NiMnO6 (ENMO), Gd2NiMnO6 (GNMO), and Tb2NiMnO6 (TNMO) ceramic powder samples synthesized by solid-state method have been investigated. X-ray diffraction structural investigation reveal that all compounds crystallize in the monoclinic structure with a P21/n space group. A ferromagnetic to paramagnetic (FM-PM) second-order phase transition occurred in ENMO, GNMO, and TNMO at 143, 130, and 112 K, respectively. Maximum magnetic entropy changes and relative cooling power with a 5 T applied magnetic field are determined to be 3.2, 3.8, 3.5 J/kgK and 150, 182, 176 J/kg for the investigated samples, respectively. The change in structural, magnetic, and magnetocaloric effect attributed to the superexchange mechanism of Ni2+–O–Mn3+ and Ni2+–O–Mn4+. The various atomic sizes of Eu, Gd, and Tb affect the ratio of Mn4+/Mn3+, which is responsible for the considerable change in properties of double perovskite.

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TiNb2O7 represents a promising anode material for lithium‐ion batteries (LIBs), but its practical applications are currently hampered by the non‐negligible volumetric expansion and contraction during the charge/discharge process and the sluggish ion/electron kinetics. A combination technique is reported by systematically optimizing the porous and spherical morphology, crystal structure, and surface decoration of mesoporous Cu2+‐doped TiNb2O7 microspheres to enhance the electrochemical Li+ storage performance and stability simultaneously. The Cu2+ dopants preferentially replace Ti4+ in crystal lattices, which decreases the Li+ diffusion barrier and increases the electronic conductivity, as confirmed by density functional theory (DFT) calculation and demonstrated by diverse electrochemical characterizations. The successful Cu2+ doping significantly reduces the lattice expansion coefficient from 7.26% to 4.61% after Li+ insertion along the b‐axis of TiNb2O7, as visualized from in situ and ex situ XRD analysis. The optimal 5% Cu2+‐doped TiNb2O7 with surface coating of N‐doped carbon exhibits significantly enhanced specific capacity and rate and cyclic performances in both half‐ and full‐cell configurations, demonstrating an excellent electrochemical behavior for fast‐charging LIB applications.

Electron-doped superconducting cuprate of Eu 2– x Ce x CuO 4+α–δ has been studied in the whole doping regime from x = 0.10–0.20 with reducing oxygen content to investigate the relation between the crystal structure and the hopping conduction in the normal state. Parameter of the crystal structure has been extracted from the X-ray diffraction (XRD) measurement while hopping conduction parameters have been obtained from resistivity measurements. The Eu–O bond length decreases with the increasing doping concentration, indicating the successful doping by the partial replacing of Eu 3+ with Ce 4+ . The resistivity increases with decreasing temperature in all measured samples. This is an indication of bad metal-like behavior in the whole regime in the normal state of electron-doped superconducting cuprate of Eu 2– x Ce x CuO 4+α–δ . The temperature dependence of resistivity was analyzed by the Arrhenius law and the variable range hopping model. It is found that the hopping conduction mechanism more likely follows the variable range hopping rather than the Arrhenius law, indicating that the hopping mechanism occurs in three dimensions. The Cu–O bond length probably plays an important role in decreasing the activation energy. The decreasing value of the activation energy correlates with the increase in the localization radius.