A low temperature phase transition in NaOD near 150 K |
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Authors: | DT Amm TJ Bestow K Jeffrey RD Heyding SL Segel |
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Institution: | 1. Northern Telecom, P.O. Box 3511, Station C, Ottawa, K1Y 4H7 Canada;2. CSIRO Div. of Chem. Physics, Clayton 3168, Australia;3. Physics Dept., University of Guelph, Guelph, Ontario, Canada;4. Chem. Dept., Queen''s University, Kingston, Ontario, Canada, K7L 3N6;5. Physics Dept., Queen''s University, Kingston, Ontario, Canada, K7L 3N6 |
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Abstract: | A phase transition in NaOD has been observed calorimetrically near 150 K. The estimated enthalpy of the transition is 200(75) . This phase transition has no corresponding analog in the protonated material, NaOH, down to 10 K. Other physical techniques also reveal the phase transition but give slightly varying values for the transition temperature. These techniques include 23Na nuclear quadrupole resonance, 23Na nuclear magnetic resonance and 2D magnetic resonance. The resonance experiments indicate that the phase transition is a continuous one and that in the lower temperature phase there is one sodium and deuterium crystal Iographic site per cell. X-ray powder diffraction of the low temperature phase indicates that it is probably monoclinic with am = 3.388(1)A, bm = 11.34(1)A, cm = 3.418(1)A,β = 90.52° and V = 131 .4Å3. The volume of the unit cell is greater at the lower temperature than at the higher temperature. The 23Na pure quadrupole resonance frequency at 77 K is 1.784(2) MHz with an asymmetry parameter of 0.82(5). |
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