First-order Raman spectrum of diamond at high temperatures

Measurements of the first-order Raman spectrum in natural type-IIa diamond for the temperature range of 293 to 1850 K are presented. Both the Stokes and anti-Stokes components are analyzed for their intensity, Raman shift, and width variation with temperature. Optical pyrometry was used to make the temperature measurements, the results of which were independently confirmed by the Stokes–to–anti-Stokes intensity ratios. The shift and width variations with temperature are in general agreement with the molecular-dynamics simulations of C. Z. Wang, C. T. Chan, and K. M. Ho [Phys. Rev. B 42, 11 276 (1990)]. Heating of the samples to temperatures as high as 1850 K in vacuo could be performed without any evidence of polymorphic conversion to graphite, also in agreement with previous investigations. Our experimental first-order Raman shifts, using units of ${\mathrm{cm}}^{\mathrm{-}1}$ and absolute temperature, are conveniently expressed as Δν=${\mathit{a}}_1$ ${\mathit{T}}^2$+${\mathit{a}}_2$T+${\mathit{a}}_3$ with the coefficients found to be -1.075×${10}^{\mathrm{-}5}$ ${\mathrm{cm}}^{\mathrm{-}1}$ ${\mathrm{K}}^{\mathrm{-}2}$, -0.007 77 ${\mathrm{cm}}^{\mathrm{-}1}$ ${\mathrm{K}}^{\mathrm{-}1}$, and 1334.5 ${\mathrm{cm}}^{\mathrm{-}1}$, respectively.