Abstract The constituent phases of a Nd14.2Fe79.4B6.3Cu0.1 sintered magnet and their crystal structures at ambient and elevated temperatures have been determined by synchrotron X-ray diffraction. At room temperature, dhcp-Nd, NdOx, hcp-Nd2O3, and Nd5Fe18B18 (Nd1.1Fe4B4) secondary phases have been identified in addition to the Nd2Fe14B main phase. The dhcp-Nd phase melts around 600 °C, corresponding to the eutectic temperature for the ternary Nd2Fe14B, Nd and Nd5Fe18B18 system. Below 600 °C, the variation of the lattice constants of the dhcp-Nd phase with temperature is strongly influenced by an internal stress from the spontaneous magnetostriction of the Nd2Fe14B phase. The difference of the lattice constants of the dhcp-Nd phase compared to those of pristine Nd metal is also significant, which is possibly associated with the inclusion of interstitial oxygen atoms at the 4f Wyckoff positions in the dhcp-Nd crystal. The validity of this scenario is confirmed by first-principles calculations of the equilibrium lattice constants of three-, four-, and nine-unit-cell supercells, in which different numbers of oxygen atoms quasi-randomly occupy some of the unoccupied 4f-sites.

中文翻译：

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Nd-Fe-B烧结磁体中二次相的晶体结构和相分数的温度依赖性

摘要 通过同步辐射 X 射线衍射确定了 Nd14.2Fe79.4B6.3Cu0.1 烧结磁体的组成相及其在室温和高温下的晶体结构。在室温下，除了 Nd2Fe14B 主相之外，还确定了 dhcp-Nd、NdOx、hcp-Nd2O3 和 Nd5Fe18B18 (Nd1.1Fe4B4) 次生相。dhcp-Nd 相在 600 °C 左右熔化，对应于三元 Nd2Fe14B、Nd 和 Nd5Fe18B18 系统的共晶温度。在 600 °C 以下，dhcp-Nd 相的晶格常数随温度的变化受到 Nd2Fe14B 相自发磁致伸缩的内应力的强烈影响。dhcp-Nd 相的晶格常数与原始 Nd 金属的晶格常数差异也很显着，这可能与在 dhcp-Nd 晶体的 4f Wyckoff 位置包含间隙氧原子有关。该方案的有效性通过三、四和九单元超胞的平衡晶格常数的第一性原理计算得到证实，其中不同数量的氧原子准随机地占据一些未占据的 4f 位点.