Order-disorder phase transition in NH4AlF4

In this study we calculate the specific heat C-VI for NH4AlF4 due to the nearest-neighbor interactions between the NH4+ tetrahedra using an Ising model superimposed on an Einstein and/or Debye model. The specific beat C-VI calculated using a power-law formula is in good agreement with the observed C-P for the NH4AlF4 system. This is an indication that NH4AlF4 undergoes a weak first-order or a nearly second-order phase transition as predicted by our model.


Critical Behaviour of the Heat Capacity Near the alpha-beta Phase Transition in Quartz
Yurtseven, Hasan Hamit (Walter de Gruyter GmbH, 2013-04-01)
The alpha-beta transition ( T-Q = 578 degrees C) is studied in quartz by analyzing the experimental heat capacity C-p data taken from the literature, using a power-law formula. Values of the critical exponent alpha for C-p are extracted below and above T-Q, which describe the alpha-beta transition as a second order transition in quartz. The alpha values obtained here are compared with the predictions of the theoretical models.
Calculation of the Raman Linewidths of Lattice Modes Close to the alpha-beta Transition in Quartz
Lider, Mustafa Cem; Yurtseven, Hasan Hamit (Walter de Gruyter GmbH, 2012-12-01)
The Raman frequencies of the lattice modes (147 cm(-1) and 207 cm(-1)) are analyzed for the alpha-beta transition in quartz according to a power-law formula with the critical exponent by using the experimental data. The temperature dependence of the Raman frequency is associated with the order parameter (polarization P) for this transition in the quartz crystal.
Calculation of the specific heat from the Raman frequency shifts close to the tricritical and second order phase transitions in NH4Cl
Kaya, D.; Yurtseven, Hasan Hamit (Elsevier BV, 2007-05-01)
This study gives our calculation for the specific heat using our Raman frequency shifts of the v(5) (174 cm(-1)) mode close to the tricritical (P = 1.6 kbar) and second order (P = 2.8 kbar) phase transitions in NH4Cl. For this calculation we use as the values of the critical exponent for the specific heat, a = 0.11 (T < T-c and T > T-c) for the tricritical (T-c = 257.17 K), and a = 0.18 (T < T-c), a = 0.64 (T > T-c) for the second order (T-c = 268 K) phase transitions, which we deduce from our analysis of t...
JELINEK, R; Özkar, Saim; OZIN, GA (American Chemical Society (ACS), 1992-07-01)
Na-23 double-rotation NMR (DOR) provides details on site specific adsorption and anchoring interactions in intrazeolite hexacarbonylmetal(0) complexes, M{M(CO)6}-Na56Y, where M = Mo and W, and their molecular photooxidation products, n{MO3-x}-Na56Y, over the full composition range 0 < m less-than-or-equal-to 16, 0 < n less-than-or-equal-to 32 and 0 less-than-or-equal-to x less-than-or-equal-to 1. The shifts, intensities, and line shapes of the Na-23 DOR resonances carry information on the environments of th...
Calculation of the specific heat for the first order, tricritical and second order phase transitions in NH4Cl
Yurtseven, Hasan Hamit; Sherman, WF (Informa UK Limited, 1998-01-01)
This work presents our calculation for the specific heat Cv under an Ising model that uses our Raman frequencies of the nu(7)TA (93 cm(-1)) and nu(5)TO (144 cm(-1)) modes for NH4Cl. The specific heat calculation has been performed for first-order (P = 0 kbar), tricritical (P = 1.6 kbar) and second-order (P = 2.8 kbar) phase transitions in the NH4Cl crystal. Our calculated Cv values are in good agreement with the experimentally observed Cp data from the literature for NH4Cl. This indicates that the NH4Cl cry...
Citation Formats
H. H. Yurtseven, “Order-disorder phase transition in NH4AlF4,” JOURNAL OF PHASE EQUILIBRIA, pp. 502–505, 2002, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/52220.