THE DIAMOND C-13 C-12 ISOTOPE RAMAN PRESSURE SENSOR SYSTEM FOR HIGH-TEMPERATURE/PRESSURE DIAMOND-ANVIL CELLS WITH REACTIVE SAMPLES/

By using a thin C-13 diamond chip together with a C-12 diamond chip as sensors, the diamond Raman spectra provide the means to measure press ure precisely (+/- 0.3 GPa) at any temperature (10-1200 K) and simulta neous hydrostatic (or quasihydrostatic) pressure (0-25 GPa) for any, s ample compatible with an externally heated diamond-anvil cell. Minimum interference between the Raman spectrum from the diamond anvils and t hose of the pressure sensors is obtained by measuring pressures with t he Raman signal from the C-13 diamond chip up to 13 GPa, and that from the C-12 chip above 10 GPa. The best crystallographic orientation of the diamond anvils is with the [100] direction along the direction of applied force, in order to further minimize the interference. At 298 K , the pressure dependence of the C-13 diamond first-order Raman line i s given by v(P) v(RT) +aP for 91 at.% C-13 diamond, where v(RT)(C-13) = 1287.79 +/- 0.28 cm(-1) and a(C-13) = 2.83 +/- 0.05 cm(-1)/GPa. Anal ysis of values from the literature shows that the pressure dependence of the Raman line of C-12 diamond is best described by the parameters v(RT)(C-12) = 1332.5 cm(-1) and a(C-12) = 2.90 +/- 0.05 cm(-1)/GPa. Th e temperature dependence of the diamond Raman line is best described b y v(T) - v(RT) = b(0) for T less than or equal to 200K, and v(T) - v(R T) = b(0) + b(1.5)T(k)(1.5) for 200K less than or equal to T less than or equal to 1500K, where T-k = T - 200K. For 91 at.% C-13 diamond, th e parameters are b(0) = 0.450 +/- 0.025 cm(-1) b(1.5) = -(7.36 +/- 0.0 9) X 10(-4) cm(-1) K-1.5; and for C-12 diamond, the parameters are b(0 ) = 0.467 +/- 0.033 cm(-1), b(1.)5 = -(7.56 +/- 0.10) X 10(-4) cm(-1) K-1.5. Although no quantitative theoretical models are available for c alculating the Raman shift as a function of temperature, the excellent fits to the data suggest that the T-k(1.5) dependence above has a phy sical basis. (C) 1997 American Institute of Physics.