Narrow Results

Novel three-dimensional (3D) branched nanotubes of sodium niobate (NaNbO₃) were produced by a multi-step reaction, which involves the synthesis of Nb₂O₅ branched nanowires and subsequently treating these precursors in alkali solution. XRD and SEM have been used to analyze current products. All the obtained nanobranches exhibited tubular structure, which was induced by nanoscale Kirkendall effect and surface diffusion. This work demonstrates a simple and efficient pathway to design hierarchical and complex hollow nanostructures, which are expected to have important applications, such as sensors and photocatalysts.

Niobates with tungsten bronze crystal structures are regarded as prospective Li${}^{+}$-storage anode candidates due to the rich chemistry of niobium and structural openness. However, the exploration of this type of materials is still insufficient. Here, BiNb${}_{5.4}$O${}_{15}$ with a tetragonal tungsten bronze crystal structure (Cmmm space group) is explored. Abundant large-sized tunnels and a large interlayer spacing of $\sim$3.97 Å are found in this open structure, enabling fast Li${}^{+}$ diffusivity (3.25 × 10${}^{-11}$/1.68 × 10${}^{-10}$ cm² ⋅ s${}^{-1}$ during lithiation/delithiation). Additionally, this structure is very stable after the first lithiation process, resulting in excellent cyclability (95.4%/$\sim$100% capacity retention after 100/1000 cycles at 1C/10C). BiNb${}_{5.4}$O${}_{15}$ further exhibits a safe Li${}^{+}$-storage potential ($\sim$1.55 V) and a large reversible capacity (309.7 mAh ⋅ g${}^{-1}$@ 0.1C). Therefore, BiNb${}_{5.4}$O${}_{15}$ can be a practical Li${}^{+}$-stora ge anode compound for large-scale energy-storage applications.

Phase diagram of $(1-x)$Na${}_{0.5}$K${}_{0.5}$NbO₃–x(Bi${}_{0.5}$Na${}_{0.5})$ZrO₃ solid solution has been established from dielectric constant measurements and structure analyses. It is found that with increasing x, the C–T phase transition temperature $T_{\text{C}-\text{T}}$ and the T–O phase transition temperature $T_{\text{T}-\text{O}}$ decrease, while the $O-R$ phase transition temperature $T_{\text{O}-\text{R}}$ increases. $T_{\text{T}-\text{O}}$ of NKN–xBNZ is much different from that of NKN–xBZ solid solution. The result could be mainly elucidated by the hybridization between the A-site ion and oxygen.