Synthesis and Characterization of the High-Pressure Nickel Borate γ‑NiB4O7

γ-NiB4O7 was synthesized in a high-pressure/high-temperature experiment at 5 GPa and 900 °C. The single-crystal structure analysis yielded the following results: space group P6522 (No. 179), a = 425.6(2), c = 3490.5(2) pm, V = 0.5475(2) nm3, Z = 6, and Flack parameter x = −0.010(5). Second harmonic generation measurements confirmed the acentric crystal structure. Furthermore, γ-NiB4O7 was characterized via vibrational as well as single-crystal electronic absorption spectroscopy, magnetic measurements, high-temperature X-ray diffraction, differential scanning calorimetry, and thermogravimetry. Density functional theory-based calculations were performed to facilitate band assignments to vibrational modes and to evaluate the elastic properties and phase stability of γ-NiB4O7.γ-NiB₄O₇于5 GPa与900 ℃的高压高温实验条件下合成。单晶结构分析得到如下结果：空间群P6522（编号179），晶胞参数a=425.6(2) pm、c=3490.5(2) pm，晶胞体积V=0.5475(2) nm³，Z=6，弗拉克参数（Flack parameter）x=-0.010(5)。二次谐波产生（Second harmonic generation）测试证实了该晶体的非中心对称结构。此外，通过振动光谱、单晶电子吸收光谱、磁学测试、高温X射线衍射、差示扫描量热法（differential scanning calorimetry）以及热重分析法对γ-NiB₄O₇进行了表征。本研究开展了基于密度泛函理论（Density functional theory）的计算，以实现振动模式的谱带归属，并评估γ-NiB₄O₇的弹性性质与相稳定性。