Calculation of the Raman frequencies using volume data close to the tricritical and second order phase transitions in NH4Cl

Yurtseven, H.; Kavruk, D.

doi:10.1016/j.molstruc.2008.10.069

Cited by 5 publications

(2 citation statements)

References 18 publications

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“…A change in the transition type under pressure is uncommon but not unique. A rather well-known example is the II-III transition in NH 4 Cl, which goes the opposite way, from being first order at atmospheric pressure to becoming second order [45][46][47] above about 0.2 GPa.…”

Section: I4mm-pmn2 1 Transitionmentioning

confidence: 99%

Phase coexistence and hysteresis effects in the pressure-temperature phase diagram of NH3BH3

Andersson

Filinchuk

Dmitriev³

et al. 2011

Phys. Rev. B

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The potential hydrogen storage compound NH 3 BH 3 has three known structural phases in the temperature and pressure ranges 110-300 K and 0-1.5 GPa, respectively. We report here the boundaries between, and the ranges of stability of, these phases. The phase boundaries were located by in situ measurements of the thermal conductivity, while the actual structures in selected areas were identified by in situ Raman spectroscopy and x-ray diffraction. Below 0.6 GPa, reversible transitions involving only small hysteresis effects occur between the room-temperature tetragonal plastic crystal I4mm phase and the low-temperature orthorhombic Pmn2 1 phase. Transformations of the I4mm phase into the high-pressure orthorhombic Cmc2 1 phase, occurring above 0.8 GPa, are associated with very large hysteresis effects, such that the reverse transition may occur at up to 0.5 GPa lower pressures. Below 230 K, a fraction of the Cmc2 1 phase is metastable to atmospheric pressure, suggesting the possibility that dense structural phases of NH 3 BH 3 , stable at room temperature, could possibly be created and stabilized by alloying or by other methods. Mixed orthorhombic Pmn2 1 /Cmc2 1 phases were observed in an intermediate pressure-temperature range, but a fourth structural phase predicted by Filinchuk et al. [Phys. Rev. B 79, 214111 (2009)] was not observed in the pressure-temperature ranges of this experiment. The thermal conductivity of the plastic crystal I4mm phase is about 0.6 W m −1 K −1 and only weakly dependent on temperature, while the ordered orthorhombic phases have higher thermal conductivities limited by phonon-phonon scattering.

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Section: I4mm-pmn2 1 Transitionmentioning

confidence: 99%

Phase coexistence and hysteresis effects in the pressure-temperature phase diagram of NH3BH3

Andersson

Filinchuk

Dmitriev³

et al. 2011

Phys. Rev. B

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“…The existence of various solid phases of the organic ammonium salts has long been established, but mainly alkyl ammonium halides appear to have been studied in any details [8][9][10][11][12][13]. It is found that in such ionic compounds hydrogen bonding helps in undergoing a series of phase transitions.…”

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confidence: 99%

Temperature‐dependent Raman spectroscopy of anilinium chloride near phase transition

Vishwakarma

Ghalsasi

2011

Physica Status Solidi (b)

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The existence of various solid phases of organic ammonium halides, due to the presence of hydrogen bonding, has long been established but is limited to alkyl ammonium halides. On the other hand, the presence of such phase transitions was eluded in case of anilinium chloride. In the present work, we have undertaken a systematic temperature dependent Raman spectroscopic study on anilinium chloride, in the range 300–100–350 K. Spectral variation in the low frequency (100–400 cm−1) and high frequency (2500–3700 cm−1) regions around 350 and 260 K shows the signature of the phase transitions in this compound. These phase transitions were reversible in nature. The latter transition is in agreement with DSC measurements.magnified image

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Calculation of the Raman frequencies as a function of pressure in the solid phases II and III (III’) of benzene

Yurtseven

Tarı

2013

J Mol Model

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We calculate here the Raman frequencies of the lattice modes A(Ag), B(B₂g) and C(B₁gB₃g) as a function of pressure at room temperature for the solid phases (II, III and III') of benzene. This calculation is performed using volume data through the mode Grüneisen parameter. It is found that our calculated frequencies of those lattice modes increase with increasing pressure, as expected. Calculated frequencies are in good agreement with the measurements of the three lattice modes for the solid phases studied in benzene.

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Calculation of the Raman frequencies using volume data close to the tricritical and second order phase transitions in NH4Cl

Cited by 5 publications

References 18 publications

Phase coexistence and hysteresis effects in the pressure-temperature phase diagram of NH3BH3

Phase coexistence and hysteresis effects in the pressure-temperature phase diagram of NH3BH3

Temperature‐dependent Raman spectroscopy of anilinium chloride near phase transition

Calculation of the Raman frequencies as a function of pressure in the solid phases II and III (III’) of benzene

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