Thermometers for low temperature Magic Angle Spinning NMR

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Kemp, Thomas F. ; Balakrishnan, Geetha ; Pike, Kevin J. ; Smith, Mark E. ; Dupree, Ray (2010)

The measurement of temperature in a Magic Angle Spinning NMR probe in the temperature range 85-300 K is discussed. It is shown that the shift of the Sn-119 resonance of Sm2Sn2O7 makes a good thermometer with shift being given by delta = 223 - 9.54 x 10(4)/T ppm and a potential precision of better than 0.5 K over the entire temperature range. The sensitivity is such (e.g. 4.2 ppm/K at 150 K) that small temperature gradients across the sample can readily be measured. Furthermore, since the spin-lattice relaxation time is very short, measurements can be made in similar to 1 s enabling relatively rapid temperature changes to be followed. Values for the chemical shift of Pb-207 in Pb(NO3)(2) down to similar to 85 K are also presented. Although the Pb-207 shift variation is approximately linear near room temperature (we find a slope 0.725 +/- 0.002 ppm/K over the range 293-153 K), it clearly deviates from linearity below similar to 130 K.
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