Temperature--Composition Mapping and Growth-History Dependence of rBN-Related Raman Responses in BN Grown on Fe--B under Flowing N${}_2$

BN products formed on Fe–B sources under flowing N${}_2$ were investigated primarily at 1250–1400~${}^{\circ }$C over nominal B contents of 1–10~wt% to determine how rBN-related Raman character depends on growth condition and history. Spatially resolved Raman mapping across 44 growth conditions identified a restricted temperature–composition region in which the integrated rBN-related low-frequency response over 750–835~cm${}^{-1}$, $A_{750-835}$, is strongly developed together with the integrated total response of the main $\sim$1367~cm${}^{-1}$ BN band, $A_{1367}^{\mathrm{t}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l}}$. In addition, the asymmetric high-wavenumber extension of the $\sim$1367~cm${}^{-1}$ band was quantified by subtracting a symmetric fitted core and integrating the far high-wavenumber residual, $T_{\mathrm{h}\mathrm{i}\mathrm{g}\mathrm{h}}^{\mathrm{f}\mathrm{a}\mathrm{r}}$. The independently defined $A_{750-835}$ and $T_{\mathrm{h}\mathrm{i}\mathrm{g}\mathrm{h}}^{\mathrm{f}\mathrm{a}\mathrm{r}}$ responses exhibit a strong correspondence across the full dataset, supporting their use as complementary rBN-related Raman observables. In contrast, $A_{750-835}\mathrm{/}{A}_{1367}^{\mathrm{t}\mathrm{o}\mathrm{t}\mathrm{a}\mathrm{l}}$ varies systematically among growth conditions, indicating that the relative prominence of the low-frequency response changes with temperature and composition rather than tracking the overall BN response through a fixed proportionality. Growth-duration experiments at 1350~${}^{\circ }$C further show that this ratio also depends on high-temperature N${}_2$ dwell time, establishing growth history as an additional kinetic variable. Powder X-ray diffraction on selected products independently confirms the presence of rBN-related stacking, while second-harmonic generation provides complementary symmetry-sensitive evidence. These results define a processing window favorable for strong rBN-related Raman response and introduce a quantitative framework for tracking both the low-frequency and band-asymmetry signatures associated with rBN-related BN structure.