Characterization of Highly‐Oriented Carbon and Graphite Fibers by High‐Temperature Raman Spectroscopy

In this study, carbon and graphite fibers (GFs) using confocal Raman microscopy at 405 and 532 nm wavelengths are analyzed and explored the influence of incident laser power and sample temperature on the Raman spectra. At room temperature, the G‐ and D‐band shifts of turbostratic fibers show a slight reduction with increased laser power, indicating potential surface heating under an inert atmosphere. In contrast, the graphitic fibers display consistent G‐ and G′‐band positions across varying the laser power, with a noticeable decrease in D‐band values at higher wavelengths. The I D / I G′ ratio for GFs is calculated with different excitation powers and wavelengths and indicates a constant value of 1.91 ± 0.12, suggesting that the fibers have fewer on‐site ( sp 3 hybridization) defects compared to defect‐free graphite, which has a higher I D / I G′ ratio of ≈3.5. The high‐temperature Raman spectroscopy demonstrates linear correlations between Raman shifts and temperature for both types. For GFs, the G‐band thermal coefficient ( χ G ) is −0.0239 ± 2 × 10 −3 cm −1 K −1 , and that of D‐band ( χ D ) is −0.0177 ± 1×10 −3 cm −1 K −1 . For turbostratic fibers, the G‐band thermal coefficient ( χ G ) is −0.0358 ± 0.004 cm −1 K −1 , significantly higher than that of GFs, likely due to the higher lattice disorder.