Why is there no low-temperature phase transition in NaOH?

Abstract

Articles you may be interested inDeuteration effect on tricritical phase transition of triglycine selenate: Calorimetric and dielectric measurements analyzed in the framework of Landau theory Although NaOH and NaOD exhibit parallel polymorphism at high temperatures, NaOD exhibits a low-temperature phase transition to a hydrogen-bonded antiferroelectric phase and no comparable transition has been found in NaOH. Measurements of NaOH by dielectric relaxation and adiabatic calorimetry were undertaken to determine if proton disorder becomes frozen in NaOH at low temperatures. No evidence for relaxation in NaOH was found from calorimetry or dielectric measurements. A comparison of the low-temperature heat capacities of NaOH and NaOD showed that NaOH has excess heat capacity, likely due to the existence of tunneling levels, and this was satisfactorily fit to a two-level Schottky anomaly. Thus, hydrogen-atom ordering in NaOH appears to take place through a more gradual process at low temperatures, rather than a low-temperature phase transition as in NaOD. The difference in the behaviour of NaOH and NaOD likely is associated with oxygen-oxygen distances that are slightly longer in NaOH than in NaOD, owing to the different nature of higher-temperature dynamical disorder ͑classical double-well potential for OD Ϫ and tunneling for OH Ϫ ͒.

Exceptional Deshielding of59Co Caused by Deuteration of the Hydrogen Bonds in Cobaloximes

“…[10] A large positive p D is characteristic of a double-well potential with a low central barrier and high anharmonicity. [13] The magnitude of p D leads to an estimated secondary geometric effect of about 1 ± 2 pm [14] (note that 3 pm is the maximum secondary geometric effect reported so far [15] ). [8] A double minimum is consistent with the r(O´´´O) values found in cobaloximes, which cluster about 2.49 , [12] provided the O-H-O angle is less than 1808, as was previously proposed on the basis of IR data for [Ni(Hdmg) 2 ].…”

Dynamics of anions and cations in cesium hydrogensulfide (CsHS, CsDS): Neutron and x-ray diffraction, calorimetry and proton NMR investigations

“…͑It is only possible to do the calorimetric experiments in the heating mode, so they do not give information about hysteresis.͒ The similarities in transition temperature and entropy change indicate that most likely both CsHS and CsDS have very similar origins for the LTM MTM and the MTM HTM transition, in contrast with, for example, sodium hydroxide in which deuteration adds an additional phase transition. 38 The shapes of the calorimetric curves for CsHS and CsDS indicate that the higher-temperature transition is first order, and the lower-temperature transition is of higher order. These results are in agreement with the present diffraction data.…”

Lithium hydroxide, LiOH, at elevated densities

“…7-10, 15-17, 34 A peculiar case is NaOH, which does not exhibit such a phase transition, while its deuterated analogue, NaOD, does; it has been argued that tunnelling of the protons in NaOH prevent the phase transition. 7,35 In LiOH the P4/nmm phase is stable down to at least 10 K. 36 It is designated as LiOH-II, while a high-temperature phase of unknown structure is designated as LiOH-I. 36,37 The absence of hydrogen bonds in room temperature alkali hydroxides (and LiOH at all temperatures) is curious.…”