RESUMEN
Copper tellurides have garnered substantial interest for their applicability as an electrocatalyst for water splitting, battery anodes and photodetectors, etc. Moreover, synthesis of phase pure metal tellurides using the multi-source precursor method is challenging. Therefore, a facile synthesis protocol for copper tellurides is anticipated. The current study involves a simplistic single source molecular precursor pathway for the synthesis of orthorhombic-Cu2.86Te2 nano blocks and -Cu31Te24 faceted nanocrystals employing the [Cu{TeC5H3(Me-5)N}]4 cluster in thermolysis and pyrolysis, respectively. The pristine nanostructures were carefully characterized by powder X-ray diffraction, energy-dispersive X-ray spectroscopy, electron microscopic techniques (scanning electron microscopy and transmission electron microscopy), and diffuse reflectance spectroscopy to know the crystal structure, phase purity, elemental composition, distribution of elements, morphology, and optical band gap. These measurements suggests that the reaction conditions fetch nanostructures of different sizes, crystal structures, morphologies, and band gaps. As prepared nanostructures were evaluated for lithium-ion batteries (LIBs) anode material. The cells fabricated with orthorhombic Cu2.86Te2 and orthorhombic Cu31Te24 nanostructures deliver capacities of 68 and 118 mA h/g after 100 cycles. The LIB anode made up of Cu31Te24 faceted nanocrystals exhibited good cyclability and mechanical stability.
RESUMEN
The orthorhombic polymorph of Ca2Zr5Ti2O16 (space group Pbca) has been studied by powder X-ray diffraction under high pressures up to 30 GPa using synchrotron radiation. We have found evidence of a structural phase transition at 12-13 GPa. The phase transition causes an enhancement of the crystal symmetry. The high-pressure phase is tetragonal, being described by space group I41/acd. The space groups of the high- and low-pressure phases have a group/subgroup relationship. However, the phase transition is accompanied by a discontinuous change in the unit-cell volume, indicating that the phase transition can be classified as first order. We have also performed density functional theory calculations. These simulations support the occurrence of the orthorhombic-to-tetragonal transition. The pressure-volume equation of state and axial compressibilities have been determined for both polymorphs. The results are compared with previous studies in related oxides.
RESUMEN
Gd2Zr2O7 is being contemplated as a futuristic matrix for the incorporation of high-level radioactive nuclear waste. This compound has the unique ability to incorporate several fission products and heavy metal ions like uranium and thorium into its lattice sites without undergoing structural changes. X-ray diffraction analyses of Gd2-xUxZr2O7+δ samples indicate that the parent compound can incorporate a substantial amount of uranium, both under oxidizing and reducing conditions. The oxidation state of these samples was investigated by X-ray photoelectron spectroscopy. The thermodynamic stability of uranium-substituted Gd2Zr2O7 is an important parameter that will govern the long-term storage of uranium and minor actinides in this matrix. High-temperature calorimetry has been used to investigate the stability of the Gd2-xUxZr2O7+δ (0.00 ≤ x ≤ 0.15) compositions. The standard molar free energy of the formation of Gd2-xUxZr2O7+δ (0.00 ≤ x ≤ 0.15) compositions has been estimated. From the free energy of formation data, the sample corresponding to x = 0.15 was found to be most stable in the Gd2-xUxZr2O7+δ (0.00 ≤ x ≤ 0.15) series. The relative stabilities of U(4+) and U(6+) substituted gadolinium zirconate have been discussed on the basis of the charge on the uranium ion and the incorporation of corresponding extra oxygen atoms into the lattice for charge compensation.
